Introduction To Wind Power

First Edition, 2011

ISBN 978-93-81157-74-9

© All rights reserved.

Published by: The English Press 4735/22 Prakashdeep Bldg, Ansari Road, Darya Ganj, Delhi - 110002 Email: [email protected] 

Table of Contents Chapter 1- Introduction Chapter 2 - History of Wind Power Chapter 3 - High Altitude Wind Power Chapter 4 - Wind Turbine Chapter 5 - Floating Wind Turbine Chapter 6 - Darrieus Wind Turbine Chapter 7 - Unconventional Wind Turbines Chapter 8 - Small Wind Turbine Chapter 9 - Vertical Axis, Savonius & Airborne Wind Turbine Chapter 10 - Wind Turbine Design Chapter 11 - Wind Turbine Aerodynamics Chapter 12 - Wind Farm Chapter 13 - Windmill Chapter 14 - Environmental Effects of Wind Power

Chapter- 1

Introduction

Wind power: worldwide installed capacity 1996-2008

Burbo Bank Offshore Wind Farm, at the entrance to the River Mersey in North West England.

A modern wind turbine in rural scenery. Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, wind mills for mechanical power, wind pumps for pumping water or drainage, or sails to propel ships. At the end of 2009, worldwide nameplate capacity of wind-powered generators was 159.2 gigawatts (GW). Energy production was 340 TWh, which is about 2% of worldwide electricity usage; and has doubled in the past three years. Several countries have achieved relatively high levels of wind power penetration (with large governmental subsidies), such as 20% of stationary electricity production in Denmark, 14% in Ireland and Portugal, 11% in Spain, and 8% in Germany in 2009. As of May 2009, 80 countries around the world are using wind power on a commercial basis. Large-scale wind farms are connected to the electric power transmission network; smaller facilities are used to provide electricity to isolated locations. Utility companies increasingly buy back surplus electricity produced by small domestic turbines. Wind energy, as an alternative to fossil fuels, is plentiful, renewable, widely distributed, clean, and produces no greenhouse gas emissions during operation. However, the construction of wind farms is not universally welcomed because of their visual impact and other effects on the environment. Wind power is non-dispatchable, meaning that for economic operation, all of the available output must be taken when it is available. Other resources, such as hydropower, and load management techniques must be used to match supply with demand. The

intermittency of wind seldom creates problems when using wind power to supply a low proportion of total demand, but as the proportion rises, problems are created such as increased costs, the need to upgrade the grid, and a lowered ability to supplant conventional production. Power management techniques such as exporting excess power to neighboring areas or reducing demand when wind production is low, can mitigate these problems.

History

Medieval depiction of a wind mill

Windmills are typically installed in favourable windy locations. In the image, wind power generators in Spain near an Osborne bull Humans have been using wind power for at least 5,500 years to propel sailboats and sailing ships. Windmills have been used for irrigation pumping and for milling grain since the 7th century AD in what is now Afghanistan, Iran and Pakistan. In the United States, the development of the "water-pumping windmill" was the major factor in allowing the farming and ranching of vast areas otherwise devoid of readily accessible water. Windpumps contributed to the expansion of rail transport systems throughout the world, by pumping water from water wells for the steam locomotives. The multi-bladed wind turbine atop a lattice tower made of wood or steel was, for many years, a fixture of the landscape throughout rural America. When fitted with generators and battery banks, small wind machines provided electricity to isolated farms. In July 1887, a Scottish academic, Professor James Blyth, undertook wind power experiments that culminated in a UK patent in 1891. In the United States, Charles F. Brush produced electricity using a wind powered machine, starting in the winter of 18871888, which powered his home and laboratory until about 1900. In the 1890s, the Danish scientist and inventor Poul la Cour constructed wind turbines to generate electricity, which was then used to produce hydrogen. These were the first of what was to become the modern form of wind turbine. Small wind turbines for lighting of isolated rural buildings were widespread in the first part of the 20th century. Larger units intended for connection to a distribution network

were tried at several locations including Balaklava USSR in 1931 and in a 1.25 megawatt (MW) experimental unit in Vermont in 1941. The modern wind power industry began in 1979 with the serial production of wind turbines by Danish manufacturers Kuriant, Vestas, Nordtank, and Bonus. These early turbines were small by today's standards, with capacities of 20–30 kW each. Since then, they have increased greatly in size, with the Enercon E-126 capable of delivering up to 7 MW, while wind turbine production has expanded to many countries.

Wind energy

Distribution of wind speed (red) and energy (blue) for all of 2002 at the Lee Ranch facility in Colorado. The histogram shows measured data, while the curve is the Rayleigh model distribution for the same average wind speed. Energy is the Betz limit through a 100 m (328 ft) diameter circle facing directly into the wind. Total energy for the year through that circle was 15.4 gigawatt-hours (GW·h). The Earth is unevenly heated by the sun, such that the poles receive less energy from the sun than the equator; along with this, dry land heats up (and cools down) more quickly than the seas do. The differential heating drives a global atmospheric convection system reaching from the Earth's surface to the stratosphere which acts as a virtual ceiling. Most of the energy stored in these wind movements can be found at high altitudes where continuous wind speeds of over 160 km/h (99 mph) occur. Eventually, the wind energy is converted through friction into diffuse heat throughout the Earth's surface and the atmosphere. The total amount of economically extractable power available from the wind is considerably more than present human power use from all sources. An estimated 72 terawatt (TW) of wind power on the Earth potentially can be commercially viable,

compared to about 15 TW average global power consumption from all sources in 2005. Not all the energy of the wind flowing past a given point can be recovered.

Distribution of wind speed The strength of wind varies, and an average value for a given location does not alone indicate the amount of energy a wind turbine could produce there. To assess the frequency of wind speeds at a particular location, a probability distribution function is often fit to the observed data. Different locations will have different wind speed distributions. The Weibull model closely mirrors the actual distribution of hourly wind speeds at many locations. The Weibull factor is often close to 2 and therefore a Rayleigh distribution can be used as a less accurate, but simpler model. Because so much power is generated by higher wind speed, much of the energy comes in short bursts. The 2002 Lee Ranch sample is telling; half of the energy available arrived in just 15% of the operating time. The consequence is that wind energy from a particular turbine or wind farm does not have as consistent an output as fuel-fired power plants; utilities that use wind power provide power from starting existing generation for times when the wind is weak thus wind power is primarily a fuel saver rather than a capacity saver. Making wind power more consistent requires that various existing technologies and methods be extended, in particular the use of stronger inter-regional transmission lines to link widely distributed wind farms. Problems of variability are addressed by grid energy storage, batteries, pumped-storage hydroelectricity and energy demand management.

Electricity generation

Typical components of a wind turbine (gearbox, rotor shaft and brake assembly) being lifted into position In a wind farm, individual turbines are interconnected with a medium voltage (often 34.5 kV), power collection system and communications network. At a substation, this medium-voltage electric current is increased in voltage with a transformer for connection to the high voltage electric power transmission system. The surplus power produced by domestic microgenerators can, in some jurisdictions, be fed into the network and sold to the utility company, producing a retail credit for the microgenerators' owners to offset their energy costs.

Grid management Induction generators, often used for wind power, require reactive power for excitation so substations used in wind-power collection systems include substantial capacitor banks for power factor correction. Different types of wind turbine generators behave differently during transmission grid disturbances, so extensive modelling of the dynamic electromechanical characteristics of a new wind farm is required by transmission system operators to ensure predictable stable behaviour during system faults (see: Low voltage ride through). In particular, induction generators cannot support the system voltage during faults, unlike steam or hydro turbine-driven synchronous generators. Doubly-fed

machines generally have more desirable properties for grid interconnection . Transmission systems operators will supply a wind farm developer with a grid code to specify the requirements for interconnection to the transmission grid. This will include power factor, constancy of frequency and dynamic behavior of the wind farm turbines during a system fault.

Capacity factor

Worldwide installed capacity 1997–2020 [MW], developments and prognosis. Since wind speed is not constant, a wind farm's annual energy production is never as much as the sum of the generator nameplate ratings multiplied by the total hours in a year. The ratio of actual productivity in a year to this theoretical maximum is called the capacity factor. Typical capacity factors are 20–40%, with values at the upper end of the range in particularly favourable sites. For example, a 1 MW turbine with a capacity factor of 35% will not produce 8,760 MW·h in a year (1 × 24 × 365), but only 1 × 0.35 × 24 × 365 = 3,066 MW·h, averaging to 0.35 MW. Online data is available for some locations and the capacity factor can be calculated from the yearly output. Unlike fueled generating plants, the capacity factor is limited by the inherent properties of wind. Capacity factors of other types of power plant are based mostly on fuel cost, with a small amount of downtime for maintenance. Nuclear plants have low incremental fuel cost, and so are run at full output and achieve a 90% capacity factor. Plants with higher fuel cost are throttled back to follow load. Gas turbine plants using natural gas as fuel may be very expensive to operate and may be run only to meet peak power demand. A gas turbine plant may have an annual capacity factor of 5–25% due to relatively high energy production cost. In a 2008 study released by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy, the capacity factor achieved by the wind turbine fleet is shown to be increasing as the technology improves. The capacity factor achieved by new wind turbines in 2004 and 2005 reached 36%.

Penetration

Kitegen Wind energy "penetration" refers to the fraction of energy produced by wind compared with the total available generation capacity. There is no generally accepted "maximum" level of wind penetration. The limit for a particular grid will depend on the existing generating plants, pricing mechanisms, capacity for storage or demand management, and other factors. An interconnected electricity grid will already include reserve generating and transmission capacity to allow for equipment failures; this reserve capacity can also serve to regulate for the varying power generation by wind plants. Studies have indicated that 20% of the total electrical energy consumption may be incorporated with minimal difficulty. These studies have been for locations with geographically dispersed wind farms, some degree of dispatchable energy, or hydropower with storage capacity, demand management, and interconnection to a large grid area export of electricity when needed. Beyond this level, there are few technical limits, but the economic implications become more significant. Electrical utilities continue to study the effects of large (20% or more) scale penetration of wind generation on system stability and economics. At present, a few grid systems have penetration of wind energy above 5%: Denmark (values over 19%), Spain and Portugal (values over 11%), Germany and the Republic of Ireland (values over 6%). But even with a modest level of penetration, there can be times where wind power provides a substantial percentage of the power on a grid. For example, in the morning hours of 8 November 2009, wind energy produced covered more than half

the electricity demand in Spain, setting a new record. This was an instance where demand was very low but wind power generation was very high.

Wildorado Wind Ranch in Oldham County in the Texas Panhandle, as photographed from U.S. Route 385

Intermittency and penetration limits Electricity generated from wind power can be highly variable at several different timescales: from hour to hour, daily, and seasonally. Annual variation also exists, but is not as significant. Related to variability is the short-term (hourly or daily) predictability of wind plant output. Like other electricity sources, wind energy must be "scheduled". Wind power forecasting methods are used, but predictability of wind plant output remains low for short-term operation. Because instantaneous electrical generation and consumption must remain in balance to maintain grid stability, this variability can present substantial challenges to incorporating large amounts of wind power into a grid system. Intermittency and the non-dispatchable nature of wind energy production can raise costs for regulation, incremental operating reserve, and (at high penetration levels) could require an increase in the already existing energy demand management, load shedding, or storage solutions or system interconnection with HVDC cables. At low levels of wind penetration, fluctuations in

load and allowance for failure of large generating units requires reserve capacity that can also regulate for variability of wind generation. Wind power can be replaced by other power stations during low wind periods. Transmission networks must already cope with outages of generation plant and daily changes in electrical demand. Systems with large wind capacity components may need more spinning reserve (plants operating at less than full load). Pumped-storage hydroelectricity or other forms of grid energy storage can store energy developed by high-wind periods and release it when needed. Stored energy increases the economic value of wind energy since it can be shifted to displace higher cost generation during peak demand periods. The potential revenue from this arbitrage can offset the cost and losses of storage; the cost of storage may add 25% to the cost of any wind energy stored, but it is not envisaged that this would apply to a large proportion of wind energy generated. The 2 GW Dinorwig pumped storage plant in Wales evens out electrical demand peaks, and allows base-load suppliers to run their plant more efficiently. Although pumped storage power systems are only about 75% efficient, and have high installation costs, their low running costs and ability to reduce the required electrical base-load can save both fuel and total electrical generation costs. In particular geographic regions, peak wind speeds may not coincide with peak demand for electrical power. In the US states of California and Texas, for example, hot days in summer may have low wind speed and high electrical demand due to air conditioning. Some utilities subsidize the purchase of geothermal heat pumps by their customers, to reduce electricity demand during the summer months by making air conditioning up to 70% more efficient; widespread adoption of this technology would better match electricity demand to wind availability in areas with hot summers and low summer winds. Another option is to interconnect widely dispersed geographic areas with an HVDC "Super grid". In the USA it is estimated that to upgrade the transmission system to take in planned or potential renewables would cost at least $60 billion. In the UK, demand for electricity is higher in winter than in summer, and so are wind speeds. Solar power tends to be complementary to wind. On daily to weekly timescales, high pressure areas tend to bring clear skies and low surface winds, whereas low pressure areas tend to be windier and cloudier. On seasonal timescales, solar energy typically peaks in summer, whereas in many areas wind energy is lower in summer and higher in winter. Thus the intermittencies of wind and solar power tend to cancel each other somewhat. A demonstration project at the Massachusetts Maritime Academy shows the effect. The Institute for Solar Energy Supply Technology of the University of Kassel pilot-tested a combined power plant linking solar, wind, biogas and hydrostorage to provide load-following power around the clock, entirely from renewable sources. A report on Denmark's wind power noted that their wind power network provided less than 1% of average demand 54 days during the year 2002. Wind power advocates argue that these periods of low wind can be dealt with by simply restarting existing power stations that have been held in readiness or interlinking with HVDC. Electrical grids with

slow-responding thermal power plants and without ties to networks with hydroelectric generation may have to limit the use of wind power. Three reports on the wind variability in the UK issued in 2009, generally agree that variability of wind needs to be taken into account, but it does not make the grid unmanageable; and the additional costs, which are modest, can be quantified. A 2006 International Energy Agency forum presented costs for managing intermittency as a function of wind-energy's share of total capacity for several countries, as shown: Increase in system operation costs, Euros per MW·h, for 10% and 20% wind share 10% 20% Germany 2.5 3.2 Denmark 0.4 0.8 Finland 0.3 1.5 Norway 0.1 0.3 Sweden 0.3 0.7

Capacity credit and fuel saving Many commentators concentrate on whether or not wind has any "capacity credit" without defining what they mean by this and its relevance. Wind does have a capacity credit, using a widely accepted and meaningful definition, equal to about 20% of its rated output (but this figure varies depending on actual circumstances). This means that reserve capacity on a system equal in MW to 20% of added wind could be retired when such wind is added without affecting system security or robustness. But the precise value is irrelevant since the main value of wind (in the UK, worth 5 times the capacity credit value ) is its fuel and CO2 savings. According to a 2007 Stanford University study published in the Journal of Applied Meteorology and Climatology, interconnecting ten or more wind farms can allow an average of 33% of the total energy produced to be used as reliable, baseload electric power, as long as minimum criteria are met for wind speed and turbine height.

Installation placement Good selection of a wind turbine site is critical to economic development of wind power. Aside from the availability of wind itself, other factors include the availability of transmission lines, value of energy to be produced, cost of land acquisition, land use considerations, and environmental impact of construction and operations. Off-shore locations may offset their higher construction cost with higher annual load factors, thereby reducing cost of energy produced. Wind farm designers use specialized wind

energy software applications to evaluate the impact of these issues on a given wind farm design. Wind power density (WPD) is a calculation of the effective power of the wind at a particular location. A map showing the distribution of wind power density is a first step in identifying possible locations for wind turbines. In the United States, the National Renewable Energy Laboratory classifies wind power density into ascending classes. The larger the WPD at a location, the higher it is rated by class. Wind power classes 3 (300– 400 W/m2 at 50 m altitude) to 7 (800–2000 W/m2 at 50 m altitude) are generally considered suitable for wind power development. There are 625,000 km2 in the contiguous United States that have class 3 or higher wind resources and which are within 10 km of electric transmission lines. If this area is fully utilized for wind power, it would produce power at the average continuous equivalent rate of 734 GWe. For comparison, in 2007 the US consumed electricity at an average rate of 474 GW, from a total generating capacity of 1,088 GW.

Wind power usage # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Installed windpower capacity (MW) Nation 2005 2006 2007 2008 40,722 48,122 56,614 65,255 European Union United States 9,149 11,603 16,819 25,170 Germany 18,428 20,622 22,247 23,903 1,266 2,599 5,912 12,210 China 10,028 11,630 15,145 16,740 Spain 4,430 6,270 7,850 9,587 India 1,718 2,123 2,726 3,537 Italy 779 1,589 2,477 3,426 France United Kingdom 1,353 1,963 2,389 3,288 1,022 1,716 2,130 2,862 Portugal 3,132 3,140 3,129 3,164 Denmark Canada 683 1,460 1,846 2,369 1,236 1,571 1,759 2,237 Netherlands 1,040 1,309 1,528 1,880 Japan Australia 579 817 817 1,494 Sweden 509 571 831 1,067 Ireland 495 746 805 1,245 573 758 873 990 Greece 819 965 982 995 Austria 20 65 207 433 Turkey Poland 83 153 276 472

2009 74,767 35,159 25,777 25,104 19,149 10,925 4,850 4,410 4,070 3,535 3,465 3,319 2,229 2,056 1,712 1,560 1,260 1,087 995 801 725

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

29 237 247 339 606 Brazil 167 194 287 384 563 Belgium Mexico 2 84 85 85 520 New Zealand 168 171 322 325 497 104 188 280 358 436 Taiwan 268 325 333 428 431 Norway 145 230 310 390 430 Egypt 119 176 192 278 348 South Korea 64 64 125 125 253 Morocco Hungary 18 61 65 127 201 30 57 116 150 192 Czech Republic Bulgaria 14 36 57 158 177 ? ? ? 20 168 Chile Finland 82 86 110 143 147 Estonia ? ? 59 78 142 Costa Rica ? ? ? 74 123 77 86 89 90 94 Ukraine Iran 32 47 67 82 91 Lithuania 7 56 50 54 91 Other Europe (non EU27) 391 494 601 1022 1385 Rest of Americas 155 159 184 210 175 Rest of Africa 52 52 51 56 91 & Middle East Rest of Asia 27 27 27 36 51 & Oceania World total (MW) 59,024 74,151 93,927 121,188 157,899

There are now many thousands of wind turbines operating, with a total nameplate capacity of 157,899 MW of which wind power in Europe accounts for 48% (2009). World wind generation capacity more than quadrupled between 2000 and 2006, doubling about every three years. 81% of wind power installations are in the US and Europe. The share of the top five countries in terms of new installations fell from 71% in 2004 to 62% in 2006, but climbed to 73% by 2008 as those countries — the United States, Germany, Spain, China, and India — have seen substantial capacity growth in the past two years. The World Wind Energy Association forecast that, by 2010, over 200 GW of capacity would have been installed worldwide, up from 73.9 GW at the end of 2006, implying an anticipated net growth rate of more than 28% per year. Wind accounts for nearly one-fifth of electricity generated in Denmark — the highest percentage of any country — and it is tenth in the world in total wind power generation.

Denmark is prominent in the manufacturing and use of wind turbines, with a commitment made in the 1970s to eventually produce half of the country's power by wind. In recent years, the US has added substantial amounts of wind power generation capacity, growing from just over 6 GW at the end of 2004 to over 35 GW at the end of 2009. The U.S. is currently the world's leader in wind power generation capacity. The country as a whole generates just 2.4% of its electrical power from wind, but several states generate substantial amounts of wind power. Texas is the state with the largest amount of generation capacity with 9,410 MW installed. This would have ranked sixth in the world, were Texas a separate country. Iowa is the state with the highest percentage of wind generation, at 14.2% in 2009. California was one of the incubators of the modern wind power industry, and led the U.S. in installed capacity for many years. As of mid-2010, fourteen U..S. states had wind power generation capacities in excess of 1000 MW. U.S. Department of Energy studies have concluded that wind from the Great Plains states of Texas, Kansas, and North Dakota could provide enough electricity to power the entire nation, and that offshore wind farms could do the same job. China had originally set a generating target of 30,000 MW by 2020 from renewable energy sources, but reached 22,500 MW by end of 2009 and could easily surpass 30,000 MW by end of 2010. Indigenous wind power could generate up to 253,000 MW. A Chinese renewable energy law was adopted in November 2004, following the World Wind Energy Conference organized by the Chinese and the World Wind Energy Association. By 2008, wind power was growing faster in China than the government had planned, and indeed faster in percentage terms than in any other large country, having more than doubled each year since 2005. Policymakers doubled their wind power prediction for 2010, after the wind industry reached the original goal of 5 GW three years ahead of schedule. Current trends suggest an actual installed capacity near 20 GW by 2010, with China shortly thereafter pursuing the United States for the world wind power lead. India ranks 5th in the world with a total wind power capacity of 10,925 MW in 2009, or 3% of all electricity produced in India. The World Wind Energy Conference in New Delhi in November 2006 has given additional impetus to the Indian wind industry. Muppandal village in Tamil Nadu state, India, has several wind turbine farms in its vicinity, and is one of the major wind energy harnessing centres in India led by majors like Suzlon, Vestas, Micon among others. Mexico recently opened La Venta II wind power project as a step toward reducing Mexico's consumption of fossil fuels. The 88 MW project is the first of its kind in Mexico, and will provide 13 percent of the electricity needs of the state of Oaxaca. By 2012 the project will have a capacity of 3,500 MW. In May 2010, Sempra Energy announced it would build a wind farm in Baja California, with a capacity of at least 1,000 MW, at a cost of $5.5 billion. Another growing market is Brazil, with a wind potential of 143 GW.

South Africa has a proposed station situated on the West Coast north of the Olifants River mouth near the town of Koekenaap, east of Vredendal in the Western Cape province. The station is proposed to have a total output of 100 MW although there are negotiations to double this capacity. The plant could be operational by 2010. France has announced a target of 12,500 MW installed by 2010, though their installation trends over the past few years suggest they'll fall well short of their goal. Canada experienced rapid growth of wind capacity between 2000 and 2006, with total installed capacity increasing from 137 MW to 1,451 MW, and showing an annual growth rate of 38%. Particularly rapid growth was seen in 2006, with total capacity doubling from the 684 MW at end-2005. This growth was fed by measures including installation targets, economic incentives and political support. For example, the Ontario government announced that it will introduce a feed-in tariff for wind power, referred to as 'Standard Offer Contracts', which may boost the wind industry across the province. In Quebec, the provincially owned electric utility plans to purchase an additional 2000 MW by 2013. By 2025, Canada will reach its capacity of 55,000 MW of wind energy, or 20% of the country's energy needs.

Power analysis Due to ever increasing sizes of turbines which hit maximum power at lower speeds energy produced has been rising faster than nameplate power capacity. Energy more than doubled between 2006 and 2008 in the table above, yet nameplate capacity (table on left) grew by 63% in the same period.

Small-scale wind power

This wind turbine charges a 12 V battery to run 12 V appliances. Small-scale wind power is the name given to wind generation systems with the capacity to produce up to 50 kW of electrical power. Isolated communities, that may otherwise rely on diesel generators may use wind turbines to displace diesel fuel consumption. Individuals may purchase these systems to reduce or eliminate their dependence on grid electricity for economic or other reasons, or to reduce their carbon footprint. Wind turbines have been used for household electricity generation in conjunction with battery storage over many decades in remote areas. Grid-connected wind turbines may use grid energy storage, displacing purchased energy with local production when available. Off-grid system users can either adapt to intermittent power or use batteries, photovoltaic or diesel systems to supplement the wind turbine. Equipment such as parking meters or wireless Internet gateways may be powered

by a wind turbine that charges a small battery, replacing the need for a connection to the power grid. In locations near or around a group of high-rise buildings, wind shear generates areas of intense turbulence, especially at street-level. The risks associated with mechanical or catastrophic failure have thus plagued urban wind development in densely populated areas, rendering the costs of insuring urban wind systems prohibitive. Moreover, quantifying the amount of wind in urban areas has been difficult, as little is known about the actual wind resources of towns and cities. A new Carbon Trust study into the potential of small-scale wind energy has found that small wind turbines could provide up to 1.5 terawatt hours (TW·h) per year of electricity (0.4% of total UK electricity consumption), saving 0.6 million tonnes of carbon dioxide (Mt CO2) emission savings. This is based on the assumption that 10% of households would install turbines at costs competitive with grid electricity, around 12 pence (US 19 cents) a kW·h. Distributed generation from renewable resources is increasing as a consequence of the increased awareness of climate change. The electronic interfaces required to connect renewable generation units with the utility system can include additional functions, such as the active filtering to enhance the power quality.

Economics and feasibility

5 kilowatt Vertical axis wind turbine

Windmill with rotating sails

Relative cost of electricity by generation source Growth and cost trends Wind power has negligible fuel costs, but a high capital cost. The estimated average cost per unit incorporates the cost of construction of the turbine and transmission facilities, borrowed funds, return to investors (including cost of risk), estimated annual production, and other components, averaged over the projected useful life of the equipment, which may be in excess of twenty years. Energy cost estimates are highly dependent on these assumptions so published cost figures can differ substantially. A British Wind Energy Association report gives an average generation cost of onshore wind power of around 3.2

pence (between US 5 and 6 cents) per kW·h (2005). Cost per unit of energy produced was estimated in 2006 to be comparable to the cost of new generating capacity in the US for coal and natural gas: wind cost was estimated at $55.80 per MW·h, coal at $53.10/MW·h and natural gas at $52.50. Other sources in various studies have estimated wind to be more expensive than other sources. A 2009 study on wind power in Spain by the Universidad Rey Juan Carlos concluded that each installed MW of wind power destroyed 4.27 jobs, by raising energy costs and driving away electricity-intensive businesses. However, the presence of wind energy, even when subsidised, can reduce costs for consumers (€5 billion/yr in Germany) by reducing the marginal price by minimising the use of expensive 'peaker plants'. In 2004, wind energy cost a fifth of what it did in the 1980s, and some expected that downward trend to continue as larger multi-megawatt turbines were mass-produced. However, installed cost averaged €1,300 a kW in 2007, compared to €1,100 a kW in 2005. Not as many facilities can produce large modern turbines and their towers and foundations, so constraints develop in the supply of turbines resulting in higher costs. Global Wind Energy Council (GWEC) figures show that 2007 recorded an increase of installed capacity of 20 GW, taking the total installed wind energy capacity to 94 GW, up from 74 GW in 2006. Despite constraints facing supply chains for wind turbines, the annual market for wind continued to increase at an estimated rate of 37%, following 32% growth in 2006. In terms of economic value, the wind energy sector has become one of the important players in the energy markets, with the total value of new generating equipment installed in 2007 reaching €25 billion, or US$36 billion. Although the wind power industry will be impacted by the global financial crisis in 2009 and 2010, a BTM Consult five year forecast up to 2013 projects substantial growth. Over the past five years the average growth in new installations has been 27.6 percent each year. In the forecast to 2013 the expected average annual growth rate is 15.7 percent. More than 200 GW of new wind power capacity could come on line before the end of 2013. Wind power market penetration is expected to reach 3.35 percent by 2013 and 8 percent by 2018. Existing generation capacity represents sunk costs, and the decision to continue production will depend on marginal costs going forward, not estimated average costs at project inception. For example, the estimated cost of new wind power capacity may be lower than that for "new coal" (estimated average costs for new generation capacity) but higher than for "old coal" (marginal cost of production for existing capacity). Therefore, the choice to increase wind capacity will depend on factors including the profile of existing generation capacity.

Theoretical potential - World

Map of available wind power for the United States. Color codes indicate wind power density class. Wind power available in the atmosphere is much greater than current world energy consumption. The most comprehensive study as of 2005 found the potential of wind power on land and near-shore to be 72 TW, equivalent to 54,000 MToE (million tons of oil equivalent) per year, or over five times the world's current energy use in all forms. The potential takes into account only locations with mean annual wind speeds ≥ 6.9 m/s at 80 m. The study assumes six 1.5 megawatt, 77 m diameter turbines per square kilometer on roughly 13% of the total global land area (though that land would also be available for other compatible uses such as farming). The authors acknowledge that many practical barriers would need to be overcome to reach this theoretical capacity. The practical limit to exploitation of wind power will be set by economic and environmental factors, since the resource available is far larger than any practical means to develop it.

Theoretical potential - UK A recent estimate gives the total potential average output for UK for various depth and distance from the coast. The maximum case considered was beyond 200 km from shore and in depths of 100 – 700 m (necessitating floating wind turbines) and this gave an

average resource of 2,000 GWe which is to be compared with the average UK demand of about 40 GWe.

Direct costs Many potential sites for wind farms are far from demand centres, requiring substantially more money to construct new transmission lines and substations. In some regions this is partly because frequent strong winds themselves have discouraged dense human settlement in especially windy areas. The wind which was historically a nuisance is now becoming a valuable resource, but it may be far from large populations which developed in areas more sheltered from wind. Since the primary cost of producing wind energy is construction and there are no fuel costs, the average cost of wind energy per unit of production depends on a few key assumptions, such as the cost of capital and years of assumed service. The marginal cost of wind energy once a plant is constructed is usually less than 1 cent per kW·h. Since the cost of capital plays a large part in projected cost, risk (as perceived by investors) will affect projected costs per unit of electricity. The commercial viability of wind power also depends on the price paid to power producers. Electricity prices are highly regulated worldwide, and in many locations may not reflect the full cost of production, let alone indirect subsidies or negative externalities. Customers may enter into long-term pricing contracts for wind to reduce the risk of future pricing changes, thereby ensuring more stable returns for projects at the development stage. These may take the form of standard offer contracts, whereby the system operator undertakes to purchase power from wind at a fixed price for a certain period (perhaps up to a limit); these prices may be different than purchase prices from other sources, and even incorporate an implicit subsidy. Where the price for electricity is based on market mechanisms, revenue for all producers per unit is higher when their production coincides with periods of higher prices. The profitability of wind farms will therefore be higher if their production schedule coincides with these periods. If wind represents a significant portion of supply, average revenue per unit of production may be lower as more expensive and less-efficient forms of generation, which typically set revenue levels, are displaced from economic dispatch. This may be of particular concern if the output of many wind plants in a market have strong temporal correlation. In economic terms, the marginal revenue of the wind sector as penetration increases may diminish.

Incentives

Some of the over 6,000 wind turbines at Altamont Pass, in California, United States. Developed during a period of tax incentives in the 1980s, this wind farm has more turbines than any other in the United States. Wind energy in many jurisdictions receives some financial or other support to encourage its development. Wind energy benefits from subsidies in many jurisdictions, either to increase its attractiveness, or to compensate for subsidies received by other forms of production which have significant negative externalities. In the United States, wind power receives a tax credit for each kW·h produced; at 1.9 cents per kW·h in 2006, the credit has a yearly inflationary adjustment. Another tax benefit is accelerated depreciation. Many American states also provide incentives, such as exemption from property tax, mandated purchases, and additional markets for "green credits". Countries such as Canada and Germany also provide incentives for wind turbine construction, such as tax credits or minimum purchase prices for wind generation, with assured grid access (sometimes referred to as feed-in tariffs). These feed-in tariffs are typically set well above average electricity prices. The Energy Improvement and Extension Act of 2008 contains extensions of credits for wind, including microturbines. Secondary market forces also provide incentives for businesses to use wind-generated power, even if there is a premium price for the electricity. For example, socially responsible manufacturers pay utility companies a premium that goes to subsidize and

build new wind power infrastructure. Companies use wind-generated power, and in return they can claim that they are making a powerful "green" effort. In the USA the organization Green-e monitors business compliance with these renewable energy credits.

Full costs and lobbying Commenting on the EU's 2020 renewable energy target, Helm (2009) is critical of how the costs of wind power are citied by lobbyists: For those with an economic interest in capturing as much of the climate-change pork barrel as possible, there are two ways of presenting the costs [of wind power] in a favourable light: first, define the cost base as narrowly as possible; and, second, assume that the costs will fall over time with R&D and large-scale deployment. And, for good measure, when considering the alternatives, go for a wider cost base (for example, focusing on the full fuel-cycle costs of nuclear and coal-mining for coal generation) and assume that these technologies are mature, and even that costs might rise (for example, invoking the peak oil hypothesis). A House of Lords Select Committee report (2008) on renewable energy in the UK says: We have a particular concern over the prospective role of wind generated and other intermittent sources of electricity in the UK, in the absence of a break-through in electricity storage technology or the integration of the UK grid with that of continental Europe. Wind generation offers the most readily available short-term enhancement in renewable electricity and its base cost is relatively cheap. Yet the evidence presented to us implies that the full costs of wind generation (allowing for intermittency, back-up conventional plant and grid connection), although declining over time, remain significantly higher than those of conventional or nuclear generation (even before allowing for support costs and the environmental impacts of wind farms). Furthermore, the evidence suggests that the capacity credit of wind power (its probable power output at the time of need) is very low; so it cannot be relied upon to meet peak demand. Thus wind generation needs to be viewed largely as additional capacity to that which will need to be provided, in any event, by more reliable means Helm (2009) says that wind's problem of intermittent supply will probably lead to another dash-for-gas or dash-for-coal in Europe, possibly with a negative impact on energy security. In the United States, the wind power industry has recently increased its lobbying efforts considerably, spending about $5 million in 2009 after years of relative obscurity in Washington.

Environmental effects

Livestock ignore wind turbines, and continue to graze as they did before wind turbines were installed. Compared to the environmental effects of traditional energy sources, the environmental effects of wind power are relatively minor. Wind power consumes no fuel, and emits no air pollution, unlike fossil fuel power sources. The energy consumed to manufacture and transport the materials used to build a wind power plant is equal to the new energy produced by the plant within a few months of operation. Garrett Gross, a scientist from UMKC in Kansas City, Missouri states, "The impact made on the environment is very little when compared to what is gained." The initial carbon dioxide emission from energy used in the installation is "paid back" within about 2.5 years of operation for offshore turbines. Danger to birds and bats has been a concern in some locations. American Bird Conservancy cites studies that indicate that about 10,000 - 40,000 birds die each year from collisions with wind turbines in the U.S. and say that number may rise substantially as wind capacity increases in the absence of mandatory guidelines. However, studies show that the number of birds killed by wind turbines is very low compared to the number of those that die as a result of certain other ways of generating electricity and especially of the environmental impacts of using non-clean power sources. Fossil fuel generation kills around twenty times as many birds per unit of energy produced than wind-farms. Bat species appear to be at risk during key movement periods. Almost

nothing is known about current populations of these species and the impact on bat numbers as a result of mortality at windpower locations. Offshore wind sites 10 km or more from shore do not interact with bat populations. While a wind farm may cover a large area of land, many land uses such as agriculture are compatible, with only small areas of turbine foundations and infrastructure made unavailable for use. Aesthetics have also been an issue. In the USA, the Massachusetts Cape Wind project was delayed for years mainly because of aesthetic concerns. In the UK, repeated opinion surveys have shown that more than 70% of people either like, or do not mind, the visual impact. According to a town councillor in Ardrossan, Scotland, the overwhelming majority of locals believe that the Ardrossan Wind Farm has enhanced the area, saying that the turbines are impressive looking and bring a calming effect to the town. Noise has also been an issue. In the United States, law suits and complaints have been filed in several states, citing noise, vibrations and resulting lost property values in homes and businesses located close to industrial wind turbines. With careful implanting of the wind turbines, along with use of noise reducing-modifications for the wind turbines however, these issues can be addressed.

Chapter- 2

History of Wind Power

Wind power has been used as long as humans have put sails into the wind. For more than two millennia wind-powered machines have ground grain and pumped water. Wind power was widely available and not confined to the banks of fast-flowing streams, or later, requiring sources of fuel. Wind-powered pumps drained the polders of the Netherlands. In arid regions such as the American mid-west or the Australian outback, wind pumps provided water for live stock and steam engines. With the development of electric power, wind power found new applications in lighting buildings remote from centrally-generated power. Throughout the 20th century parallel paths developed distributed small wind plants suitable for farms or residences, and larger utility-scale wind generators that could be connected to electricity grids for remote use of power. Today wind powered generators operate at every size between tiny plants for battery charging at isolated residences, up to multi-megawatt wind farms that provide electricity to national electrical networks.

Antiquity

Hero's wind-powered organ, the earliest machine powered by wind Sailboats and sailing ships have been using wind power for at least 5,500 years, and architects have used wind-driven natural ventilation in buildings since similarly ancient times. The use of wind to provide mechanical power came somewhat later in antiquity. The Babylonian emperor Hammurabi planned to use wind power for his ambitious irrigation project in the 17th century BC. The windwheel of the Greek engineer Heron of Alexandria in the 1st century AD is the earliest known instance of using a wind-driven wheel to power a machine. Another early example of a wind-driven wheel was the prayer wheel, which was used in ancient Tibet and China since the 4th century.

Early Middle Ages

The Persian, horizontal-axis windmill

Medieval depiction of a windmill The first practical windmills were built in Sistan, a region between Iran and Afghanistan, since at least the 9th century, or possibly earlier in the 7th century. These "Panemone" were vertical-axle windmills, which had long vertical driveshafts with rectangle shaped

blades. Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind corn and pump water, and were used in the gristmilling and sugarcane industries. Windmills were in widespread use across the Middle East and Central Asia, and later spread to China and India from there. Horizontal-axle windmills were later used extensively in Northwestern Europe to grind flour beginning in the 1180s, and many Dutch horizontal-axle windmills still exist. By 1000 AD, windmills were used to pump seawater for salt-making in China and Sicily. A wind-powered automata is known from the mid-8th century: wind-powered statues that "turned with the wind over the domes of the four gates and the palace complex of the Round City of Baghdad". The "Green Dome of the palace was surmounted by the statue of a horseman carrying a lance that was believed to point toward the enemy. This public spectacle of wind-powered statues had its private counterpart in the 'Abbasid palaces where automata of various types were predominantly displayed." Circa 3200 B.C. the ancient Egyptians invented the sail. The way a boat moves is through the wind pushing the sail. Excluding modern times, a wind powered boat has been the primary form of water transportation in all of human history. Some examples of civilizations and countries that used wind powered sails follows. Romans used passive wind power in their extensive fleets. Some ships were large enough to carry almost a thousand tons of cargo, or a great number of passengers depending on the length of the trip and the accommodations of the passengers. By 1000 A.D. the Vikings had explored and conquered the North Atlantic because of the power of the wind.

Late Middle Ages

The horizontal-axis windmills of Campo de Criptana were immortalized in chapter VIII of Don Quixote. The first windmills in Europe appear in sources dating to the twelfth century. These early European windmills were horizontal-axle sunk post mills. The earliest certain reference to such a horizontal-axle windmill dates from 1185, in Weedley, Yorkshire, although a number of earlier but less certainly dated twelfth century European sources referring to windmills have also been adduced. While it is sometimes argued that crusaders may have been inspired by windmills in the Middle East, this is unlikely since the European horizontal-axle windmills were of significantly different design than the vertical-axle windmills of Afghanistan. Lynn White Jr., a specialist in medieval European technology, asserts that the European windmill was an "independent invention;" he argues that it is unlikely that the Afghanistan-style vertical-axle windmill had spread as far west as the Levant during the Crusader period. In medieval England rights to waterpower sites were often confined to nobility and clergy, so wind power was an important resource to a new middle class. In addition, windmills, unlike water mills, were not rendered inoperable by the freezing of water in the winter. By the 14th century Dutch windmills were in use to drain areas of the Rhine River delta.

18th century

Windmills were used to pump water for salt making on the island of Bermuda, and on Cape Cod during the American revolution.

19th century

Charles Brush wind turbine 1888

Such electric generators were used on the ships by the turn of the century. Sailing ship "Chance", New Zealand, 1902. In Denmark by 1900 there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW. In the American midwest between 1850 and 1900, a large number, perhaps six million, small windmills were installed on farms to operate irrigation pumps. Firms such as Star, Eclipse, Fairbanks-Morse and Aeromotor became famed suppliers in North and South America. The first windmill for electricity production was built in Scotland in July 1887 by Prof James Blyth of Anderson's College, Glasgow (the precursor of Strathclyde University). Blyth's 33-foot (10 m) high, cloth-sailed wind turbine was installed in the garden of his holiday cottage at Marykirk in Kincardineshire and was used to charge accumulators developed by the Frenchman Camille Alphonse Faure, to power the lighting in the cottage, thus making it the first house in the world to have its electricity supplied by wind power. Blyth offered the surplus electricity to the people of Maykirk for lighting the main street, however, they turned down the offer as they thought electricity was "the work of the devil." Although he later built a wind machine to supply emergency power to the local Lunatic Asylum, Infirmary and Dispensary of Montrose the invention never really caught on as the technology was not considered to be economically viable. Across the

Atlantic, in Cleveland, Ohio a larger and heavily engineered machine was designed and constructed in 1887-1888 by Charles F. Brush, this was built by his engineering company at his home and operated from 1886 until 1900. The Brush wind turbine had a rotor 56 feet (17 m) in diameter and was mounted on a 60 foot (18 m) tower. Although large by today's standards, the machine was only rated at 12 kW; it turned relatively slowly since it had 144 blades. The connected dynamo was used either to charge a bank of batteries or to operate up to 100 incandescent light bulbs, three arc lamps, and various motors in Brush's laboratory. The machine fell into disuse after 1900 when electricity became available from Cleveland's central stations, and was abandoned in 1908. In the 1890s a Danish scientist, Poul la Cour, constructed wind turbines to generate electricity, which was then used to produce hydrogen for experiments and light and the Askov Highschool. His latest mill from 1896 later became the local powerplant of the village Askov.

20th century Development in the 20th century might be usefully divided into the periods: • •

1900-1973, when widespread use of individual wind generators competed against fossil fuel plants and centrally-generated electricity 1973-onward, when the oil price crisis spurred investigation of non-petroleum energy sources.

1900-1973

Denmark development In Denmark wind power was an important part of a decentralized electrification in the first quarter of the 20th century, partly because of Poul la Cour from his first practical development in 1891 at Askov. By 1908 there were 72 wind-driven electric generators from 5 kW to 25 kW. The largest machines were on 24 m (79 ft) towers with four-bladed 23 m (75 ft) diameter rotors. In 1957 Johannes Juul installed a 24 m diameter wind turbine at Gedser, which ran from 1957 until 1967. This was a three-bladed, horizontalaxis, upwind, stall-regulated turbine similar to those now used for commercial wind power development. Danish wind power development stressed incremental improvements in capacity and efficiency based on extensive serial production of turbines, in contrast with development models requiring extensive steps in unit size based primarily on theoretical extrapolation. A practical consequence is that all commercial wind turbines resemble the Danish model, a light-weight three-blade upwind design.

Farm power and isolated plants In 1927 the brothers Joe Jacobs and Marcellus Jacobs opened a factory, Jacobs Wind in Minneapolis to produce wind turbine generators for farm use. These would typically be

used for lighting or battery charging, on farms out of reach of central-station electricity and distribution lines. In 30 years the firm produced about 30,000 small wind turbines, some of which ran for many years in remote locations in Africa and on the Richard Evelyn Byrd expedition to Antarctica. Many other manufacturers produced small wind turbine sets for the same market, including companies called Wincharger, Miller Airlite, Universal Aeroelectric, Paris-Dunn, Airline and Winpower. In 1931 the Darrieus wind turbine was invented, with its vertical axis providing a different mix of design tradeoffs from the conventional horizontal-axis wind turbine. The vertical orientation accepts wind from any direction with no need for adjustments, and the heavy generator and gearbox equipment can rest on the ground instead of atop a tower. By the 1930s windmills were widely used to generate electricity on farms in the United States where distribution systems had not yet been installed. Used to replenish battery storage banks, these machines typically had generating capacities of a few hundred watts to several kilowatts. Beside providing farm power, they were also used for isolated applications such as electrifying bridge structures to prevent corrosion. In this period, high tensile steel was cheap, and windmills were placed atop prefabricated open steel lattice towers. The most widely-used small wind generator produced for American farms in the 1930s was a two-bladed horizontal-axis machine manufactured by the Wincharger Corporation. It had a peak output of 200 watts. Blade speed was regulated by curved air brakes near the hub that deployed at excessive rotational velocities. These machines were still being manufactured in the United States during the 1980s. In 1936, the U.S. started a rural electrification project that killed the natural market for wind-generated power, since network power distribution provided a farm with more dependable usable energy for a given amount of capital investment. In Australia, the Dunlite Corporation built hundreds of small wind generators to provide power at isolated postal service stations and farms. These machines were manufactured from 1936 until 1970.

Experimental wind turbine at Nogent-le-Roi, France, 1955.

Utility-scale turbines A forerunner of modern horizontal-axis utility-scale wind generators was the WIME-3D in service in Balaklava, near Yalta, USSR from 1931 until 1942. This was a 100 kW generator on a 30 m (100 ft) tower, connected to the local 6.3 kV distribution system. It had a three-bladed 30 metre rotor on a steel lattice tower. It was reported to have an annual load factor of 32 per cent, not much different from current wind machines.

The world's first megawatt-size wind turbine near Grandpa's Knob Summit, Castleton, Vermont. In 1941 the world's first megawatt-size wind turbine was connected to the local electrical distribution system on the mountain known as Grandpa's Knob in Castleton, Vermont, USA. It was designed by Palmer Cosslett Putnam and manufactured by the S. Morgan Smith Company. This 1.25 MW Smith-Putnam turbine operated for 1100 hours before a blade failed at a known weak point, which had not been reinforced due to war-time material shortages. No similar-sized unit was to repeat this "bold experiment" for about forty years.

Fuel-saving turbines During the Second World War, small wind generators were used on German U-boats to recharge submarine batteries as a fuel-conserving measure. In 1946 the lighthouse and residences on the island Insel Neuwerk were partly powered by an 18 kW wind turbine 15 metres in diameter, to economize on diesel fuel. This installation ran for around 20 years before being replaced by a submarine cable to the mainland.

The Station d'Etude de l'Energie du Vent at Nogent-le-Roi in France operated an experimental 800 KVA wind turbine from 1956 to 1966.

The NASA/DOE 7.5 megawatt Mod-2 three turbine cluster in Goodnoe Hills, Washington in 1981.

Comparison of NASA wind turbines

1973-2000

Utility development and oil prices From the mid 1970's through the mid 1980's the United States government worked with industry to advance the technology and enable large commercial wind turbines. This effort was led by NASA at the Lewis Research Center in Cleveland, Ohio and was an extraordinarily successful government research and development activity. With funding from the National Science Foundation and later the United States Department of Energy (DOE), a total of 13 experimental wind turbines were put into operation including four major wind turbine designs. This research and development program pioneered many of the multi-megawatt turbine technologies in use today, including: steel tube towers, variable-speed generators, composite blade materials, partial-span pitch control, as well as aerodynamic, structural, and acoustic engineering design capabilities. The large wind turbines developed under this effort set several world records for diameter and power output. The Mod-2 wind turbine cluster produced a total of 7.5 megawatt of power in 1981. In 1987, the Mod-5B was the largest single wind turbine operating in the world with a rotor diameter of nearly 100 meters and a rated power of 3.2 megawatts. It demonstrated an availability of 95 percent, an unparalleled level for a new first-unit wind turbine. The Mod-5B had the first large-scale variable speed drive train and a sectioned, two-blade rotor that enabled easy transport of the blades. Later, in the 1980s, California provided tax rebates for wind power. These rebates funded the first major use of wind power for utility electricity. These machines, gathered in large wind parks such as at Altamont Pass would be considered small and un-economic by modern wind power development standards.

Self-sufficiency and back-to-the-land In the 1970s many people began to desire a self-sufficient life-style. Solar cells were too expensive for small-scale electrical generation, so some turned to windmills. At first they built ad-hoc designs using wood and automobile parts. Most people discovered that a reliable wind generator is a moderately complex engineering project, well beyond the ability of most romantics. Some began to search for and rebuild farm wind generators from the 1930s, of which Jacobs Wind Electric Company machines were especially sought after. Hundreds of Jacobs machines were reconditioned and sold during the 1970s. All major horizontal axis turbines today rotate the same way (clockwise) to present a coherent view. However, early turbines rotated counter-clockwise like the old windmills, but a shift occurred from 1978 and on. The individualist-minded blade supplier Økær made the decision to change direction in order to be distinguished from the collective Tvind and their small wind turbines. Some of the blade customers were companies that later evolved into Vestas, Siemens, Enercon and Nordex. Public demand required that all turbines rotate the same way, and the success of these companies made clockwise the new standard. Following experience with reconditioned 1930s wind turbines, a new generation of American manufacturers started building and selling small wind turbines not only for battery-charging but also for interconnection to electricity networks. An early example would be Enertech Corporation of Norwich, Vermont, which began building 1.8 kW models in the early 1980s. In the 1990s, as aesthetics and durability became more important, turbines were placed atop tubular steel or reinforced concrete towers. Small generators are connected to the tower on the ground, then the tower is raised into position. Larger generators are hoisted into position atop the tower and there is a ladder or staircase inside the tower to allow technicians to reach and maintain the generator, while protected from the weather.

21st century As the 21st century began, fossil fuel was still relatively cheap, but rising concerns over energy security, global warming, and eventual fossil fuel depletion led to an expansion of interest in all available forms of renewable energy. The fledgling commercial wind power industry began expanding at a robust growth rate of about 30% per year, driven by the ready availability of large wind resources, and falling costs due to improved technology and wind farm management. The steady run-up in oil prices after 2003 led to increasing fears that peak oil was imminent, further increasing interest in commercial wind power. Even though wind power generates electricity rather than liquid fuels, and thus is not an immediate substitute for petroleum in most applications (especially transport), fears over petroleum shortages only added to the urgency to expand wind power. Earlier oil crisis had already caused many utility and industrial users of petroleum to shift to coal or natural gas. Natural gas began having its own supply problems, and wind power showed potential for replacing natural gas in electricity generation.

Year-by-year 2001:Enron, owner of Enron Wind Power Services (wind turbine manufacturing and wind farm operation), goes bankrupt in one of the biggest and most complex bankruptcy cases in U.S. history. General Electric buys the wind power department. (see: Enron scandal) 2006: US$10,000 home unit can generate 80% of a typical home's needs 2007: Shawn Frayne wins the 2007 Popular Mechanics Breakthrough Award for the Windbelt, a non-turbine wind power generator that claims to produce power at 1/10 the price per watt as turbines. 2008: Rock Port, Missouri becomes the first city in the United States to receive 100 percent of its power from wind in a project developed by Wind Capital Group.

Chapter- 3

High Altitude Wind Power

High altitude wind power (HAWP) has been imagined as a source of useful energy since 1833 with John Etzler's vision of capturing the power of winds high in the sky by use of tether and cable technology. An atlas of the high altitude wind power resource has been prepared for all points on earth. Various mechanisms are proposed for capturing the kinetic energy of winds such as kites, kytoons, aerostats, gliders, gliders with turbines for regenerative soaring, sailplanes with turbines, or other airfoils, including multiple-point building- or terrain-enabled holdings. Once the mechanical energy is derived from the wind's kinetic energy, then many options are available for using that mechanical energy: direct traction, conversion to electricity aloft or at ground station, conversion to laser or microwave for power beaming to other aircraft or ground receivers. Energy generated by a high-altitude system may be used aloft or sent to the ground surface by conducting cables, mechanical force through a tether, rotation of endless line loop, movement of changed chemicals, flow of high pressure gases, flow of low-pressure gases, or laser or microwave power beams.

High altitude wind for power purposes Winds at higher altitudes become steadier, more persistent, and of higher velocity. Because power available in wind increases as the cube of velocity (the velocity-cubed law), assuming other parameters remaining the same, doubling a wind's velocity gives 2x2x2=8 times the power; tripling the velocity gives 3x3x3=27 times the available power. With steadier and more predictable winds, high-altitude wind has an advantage over wind near the ground. Being able to locate HAWP to effective altitudes and using the vertical dimension of airspace for wind farming brings further advantage using high altitude winds for generating energy. High altitude wind generators can be adjusted in height and position to maximize energy return, which is impractical with fixed tower-mounted wind generators.

In each range of altitudes there are altitude-specific concerns being addressed by researchers and developers. As altitude increases, tethers increase in length, the temperature of the air changes, and vulnerability to atmospheric lightning changes. With increasing altitude, exposure to liabilities increase, costs increase, turbulence exposure changes, liklihood of having the system fly in more than one directional strata of winds increases, and the costs of operation changes. HAWP systems that are flown must climb through all intermediate altitudes up to final working altitudes—being at first a low- and then a high- altitude device.

Methods of capturing kinetic energy of high-altitude winds Energy can be captured from the wind by kites, kytoons, tethered gliders , tethered sailplanes, aerostats (spherical as well as shaped kytoons), bladed turbines, airfoils, airfoil matrices, balloons, parachutes, drogues, variable drogues, spiral airfoils, Darrieus turbines, Magnus-effect VAWT blimps, multiple-rotor complexes, fabric Jalbert-parafoil kites, uni-blade turbines, flipwings, tethers, bridles, string loops, wafting blades, undulating forms, piezoelectric materials , and more. When a scheme's purpose is to propel ships and boats , the objects tether-placed in the wind will tend to have most of the captured energy be in useful tension in the main tether. The aloft working bodies will be operated to maintain useful tension even while the ship is moving. This is the method for powerkiting sports. This sector of HAWP is the most installed method. The folklore is that Benjamin Franklin used the traction method of HAWP. George Pocock (inventor) was a leader in tugging vehicles by traction.

Controls HAWP aircraft need to be controlled. Solutions in built systems have control mechanisms variously situated. Some systems are passive, or active, or a mix. When a kite steering unit (KSU) is lofted, the KSU may be robotic and self-contained; a KSU may be operated from the ground via radio-control by a live human operator or by smart computer programs. Some systems have built sensors in the aircraft body that report parameters like position, relative position to other parts. Kite control units (KCU) have involved more than steering; tether reeling speeds and directions can be adjusted in response to tether tensions and needs of the system during a power-generating phase or return-nonpower-generating phase. Kite control parts vary widely.

Methods of converting mechanical energy to other forms of energy The mechanical energy of the device may be converted to heat, sound, electricity, light, tension, pushes, pulls, laser, microwave, chemical changes, or compression of gases. Traction is a big direct use of the mechanical energy as in tugging cargo ships and

kiteboarders. The methods of getting the mechanical energy from the wind's kinetic energy are several. Lighter-than-air (LTA) moored aerostats are employed as lifters of turbines. Heavier-than-air (HTA) tethered airfoils are being used as lifters or turbines themselves. Combinations of LTA and HTA devices in one system are being built and flown to capture HAWP. Even a family of free-flight airborne devices are represented in the literature that capture the kinetic energy of high altitude winds (beginning with a description in 1967 by Richard Miller in book Without Visible Means of Support) and a contemporary patent application by Dale C. Kramer, soaring sailplane competitor, inventor.

Electric generator position in a HAWP system Electricity generation is just one of the optional choices of using captured mechanical energy; however, this option dominates the focus of professionals aiming to supply large amounts of energy to commerce and utilities. A long array of secondary options include tugging water turbines, pumping of water, or compressing air or hydrogen. The position of the electric generator is a distinguishing feature among systems. Flying the generator aloft is done in a variety of ways. Keeping the generator at the mooring region is another large design option. The option in one system of a generator aloft and at the ground station has been used where a small generator operates electronic devices aloft while the ground generator is the big worker to make electricity for significant loads.

Aerostat-based HAWP One method of keeping working HAWP systems aloft is to use buoyant aerostats whether or not the electric generator is lifted or left on the ground. The aerostats are usually, but not always, shaped to achieve a kiting lifting effect. Recharging leaked lifting gas receives various solutions. •

W. R. Benoit US Patent 4350897 Lighter than air wind energy conversion system by William R. Benoit, filed Oct 24,1980, and issued: Sep 21, 1982.

•

The TWIND system is based on the use of a sail surface elevated by the climbing force of an aerostatic balloon connected to the ground by a cable used also for energy transmission. The wind present at high altitudes creates a horizontal push on the sail which in its movement transmits this energy to the ground via the connecting cable. At the end of its movement forward, the sail surface is reduced allowing it to move upwind with reduced energy waste.

•

The Magenn aerostat is a vertical-axis wind turbine held with its axis horizontal by bridling the axis traverse to the wind so that Magnus-effect lift obtains during autorotation; the electricity is generated with end-hub generators.

•

The LTA Windpower PowerShip uses lift from both an aerostat and wings. It operates close to neutral buoyancy and doesn't require a winch. Power is

generated by turbines with the propellers on the trailing edge of the wings. The system is designed to be able to take off and land unattended. •

Airbine proposes to lift wind turbines into the air by use of aerostats; the electricity would return to ground loads by way of conductive tether.

•

Airship power turbine by William J. Mouton, Jr., and David F. Thompson: Their system integrated the turbine within the central portion of a near-toroidal aerostat, like putting a turbine in the hole of a aerostat donut.

Non-airborne HAWP Conceptually, two adjacent mountains (natural or terrain-enabled) or artificial buildings or towers (urban or artificial) could have a wind turbine suspended between them by use of cables. When HAWP is cabled between two mountain tops across a valley, the HAWP device is not airborne, but borne up by the cable system. No such systems are known to be in use, though patents teach these methods. When non-cabled bridges are the foundation for holding wind turbines high above the ground, then these are grouped with conventional towered turbines and are outside the intent of HAWP where the tethering an airborne system is foundational.

HAWP Safety Lightning, aircraft traffic, emergency procedures, system inspections, visibility marking of system parts and its tethers, electrical safety, runaway-wing procedures, over-powering controls, appropriate mooring, and more form the safety environment for HAWP systems.

Challenges of HAWP as an emerging industry Why is the sky not filled with HAWP devices generating significant energy for people? There have been several periods of high interest in HAWP before the contemporary activity. The first period had a high focus on pulling carriages over the lands and capturing atmospheric electricity and lightning for human use. The second period was in the 1970s and 1980s when research and investment flourished; a drop in oil price resulted in no significant installations of HAWP. Return on investment (ROI) has been the key parameter; that ROI remains in focus in the current development activity while in the background is the renewable and sustainable energy movement supporting wind power of any kind; but HAWP must compete on ROI with conventional towered solutions.

Patents and applications for patents on HAWP Filed with WIPO

• • • • •

• •

•

•

WO 2007027765 Multi-rotor wind turbine supported by continuous central driveshaft by Douglas Spriggs Selsam, filed August 8, 2006. WO 2009092181 A balloon suspension high altitude wind generator apparatus and a wind turbine generator device by LI, Quandong and LI, Yuexiu of China. WO 2009092191 A lifting type high altitude wind generator apparatus and a turbine generator device by LI, Quandong. amd LI, Yuexiu of China. WO/2008/034421 Kite Power Generator by Manfred Franetzki of Germany. WO/2008/004261 Wind system for converting energy through a vertical-axis turbine actuated by means of kites and process for producing electric energy through such system by Massimo Ippolito and Franco Taddei of Italy. Italy priority date July 4, 2006. International filing date of June 13, 2007. WO/2009/143901 Kite type sail with improved line attachment. Dec. 12, 2009 B63H 9/06 PCT/EP2008/056724 SkySails GMBH & CO. KG WO/2008/101390 A method and a special equipment converting wind energy at high altitude into kinetic energy on the ground. 28.08.2008 F23D 9/00 PCT/CN2008/000255 by Fuli Li. Application language: Chinese. WO/1992020917 Free Rotor by JACK, Colin, Humphry, Bruce (one man). Colin Jack. Colin Bruce. Colin Bruce Jack. Colin B. Jack. Multi-rotors are treated. Faired tethers are recognized. Turbines integrated at tips of free rotor is instructed. Weather and water flow modifications by working free rotors is described. 1992. WO 2008/047963 Electric power generation system using hydro turbine tracted by paraglider by Jong Chul Kim. Filed: 19 October 2006.

Filed in USA • • • • • • • • • • •

US Patent 1495036 Means for creating emergency power for airplane radio generator by Carlton David Palmer, filed Dec 6, 1921. US Patent 1717552 Airship by Alpin I. Dunn, filed Jan 30, 1926. US Patent 2368630 High altitude free-flight wind turbines charged batteries by using potential energy to form wind by Stanley Biszak, filed June 3, 1943. US Patent 3227398 Balloon Tether Cable by Arthur D. Struble, Jr., filed Mar 4, 1965. Streamlined tether. US Patent 3924827 Apparatus for extracting energy from winds at significant height above the surface by Lambros Lois, filed April 25, 1975. US Patent 3987987 Self-erecting windmill by Peter R. Payne, Charles McCutchen, filed January 28, 1975. US Patent 4073516 Wind driven power plant by Alberto Kling, filed June 6, 1975. US Patent 4076190 Apparatus for extracting energy from winds at significant height above the surface by Lambros Lois, filed March 30, 1976. US Patent 4084102 Wind driven, high altitude power apparatus by Charles Max Fry, Henry W. Hise, filed March 7, 1978. (terrain enabled) US Patent 4124182 Wind drive energy system by Arnold Loeb, filed November 14, 1977. US Patent 4165468 Wind driven, high altitude power apparatus by Charles M. Fry and Henry W. Hise, filed Mar 7, 1978.

• • • • • • • • • • • • • • • • • • • • • • • • •

US Patent 4166596 Airship power turbine by William J. Mouton, Jr., and David F. Thompson, filed April 28, 1978. US Patent 4207026 Tethered lighter than air turbine by Oliver J. Kushto, filed Sep 29, 1978. US Patent 4251040 Wind driven apparatus for power generation by Miles L. Loyd, filed Dec. 11, 1978. US Patent 4285481 Multiple wind turbine tethered airfoil wind energy conversion system by Lloyd I. Biscomb, filed Dec 7, 1979. US Patent 4309006 Tethered airfoil wind energy conversion system by Lloyd I. Biscomb, filed Jun 4, 1979. US Patent 4350897 Lighter than air wind energy conversion system by William R. Benoit, filed Oct 24,1980, and issued: Sep 21, 1982. US Patent 4450364 Lighter than air wind energy conversion system utilizing a rotating envelope by William R. Benoit, filed March 24, 1982. US Patent 4470563 Airship-windmill by Gijsbert J. Engelsman, filed Mar 9, 1982. Fan-belt. US Patent 4486669 Wind generator kite system by Paul F. Pugh, filed November 9, 1981. US Patent 4491739 Airship-floated wind turbine by William K. Watson, filed Sep 27, 1982. US Patent 4572962 Apparatus for extracting energy from winds at high altitudes by David H. Shepard, filed April 28, 1982. US Patent 4659940 Power generation from high altitude winds by David H. Shepard, filed Oct 11, 1985. US Patent 4917332 Wingtip vortex turbine by James C. Patterson, Jr., filed Oct 28, 1988. US Patent 5056447 Rein-deer kite by Gaudencio A. Labrador, filed Oct 13, 1988. US Patent 5150859 Wingtip Turbine by Thomas F. Ransick, filed Oct 11, 1988. US Patent 5909859 Multi-rotor kite glider by Stephen J. Janicki, filed March 6, 1997. US Patent 6072245 Wind-driven driving apparatus employing kites by astronaut Wubbo Johannes Ockels, filed Nov 12, 1997. US Patent 6254034 Tethered aircraft system for gathering energy from wind by Howard G. Carpenter, filed Sep 20, 1999. US Patent 6327994 Scavenger energy converter system its new applications and its control systems by Gaudencio A. Labrador, filed Dec 23, 1997. US Patent 6523781 Axial-mode linear wind-turbine by Gary Dean Ragner, filed Aug 29, 2001. US Patent 6555931 Renewable energy systems using long-stroke open-channel reciprocating engines by John V. Mizzi, filed on Sep 14, 2001. US Patent 6616402 Serpentine wind turbine by Douglas Spriggs Selsam, filed June 14, 2001. US Patent 6781254 Windmill kite by Bryan William Roberts, filed Oct 17, 2002. US Patent 6914345 Power generation by John R Webster, filed June 23, 2003. US Patent 6925949 Elevated sailing apparatus by Malcolm Phillips, filed Dec 31, 2002.

• • • • • •

• • • •

US Patent 7109598 Precisely controlled flying electric generators III by Bryan William Roberts and David Hammond Shepard, filed Oct 18, 2004. US Patent 7129596 Hovering wind turbine by Aleandro Soares Macedo, filed Oct 31, 2004. US Patent 7183663 Precisely controlled flying electric generators by Bryan William Roberts and David Hammond Shepard, filed Aug 17, 2004. US Patent 7188808 Aerial wind power generation system and method by Gaylord G. Olson, filed Feb 27, 2006. US Patent 7275719 Wind drive apparatus for an aerial wind power generation system Gaylord G. Olson, filed February 9, 2007. US Patent 7287481 Launch and retrieval arrangement for an aerodynamic profile element by Stephan Wrang and Stephan Brabeck of Hamburg, Germany, filed: September 29, 2006. US Patent 7317261 Power generating apparatus by Andrew Martin Rolt, assignee: Rolls-Royce, plc; filed July 25, 2006. US Patent 7335000 Systems and methods for tethered wind turbines by Frederick D. Ferguson, filed May 3, 2005. US Patent 7504741 Wind energy plant with a steerable kite by Stephan Wrage, Stephan Brabeck, filed March 30, 2007. US Patent 7709973 Airborne stabilized wind turbines system by Moshe Meller, Sep 18, 2008.

Applications for patents in process in US • • • •

Application: Tether handling for airborne electricity generarators by Joseph A. Carroll, filed July 17, 2009. Systems and methods for tethered wind turbines by Frederick D. Ferguson, filed Sep 10, 2009. Airborne stabilized wind turbines systems by Moshe Meller, filed May 14, 2009. Apparatus and method for making optimal use of a photovoltaic array on an airborne power system by Brian J. Tillotson, filed October 14, 2008.

Timeline for HAWP Early centuries of kiting demonstrated that the kite is a rotary engine that rotates its tether part about its mooring point and causes hands and arms to move because of the energy captured from higher winds into the mechanical device. The tension in the lofted devices performs the work of lifting and pulling body parts and things. Airborne wind energy (AWE) for HAWP was birthed th ousands of years ago; naming what happened and developing the implied potentials of tethered aircraft for doing special works is what is occurring in AWE HAWP. What is "low" for some workers is "high" for others. •

1796 George Pocock (inventor) used traction mode to travel in vehicles over land roads.

•

1827 George Pocock's book ‘The Aeropleustic Art’ or 'Navigation in the Air by the Use of Kites or Buoyant Sails' was published. The book was to be republished again several times. The Charvolant or Kite Carriage was described. Importantly Pocock described use of kites for land and sea travel.

•

1833 John Adolphus Etzler saw HAWP blossoming at least for traction.

•

1864? Book's chapter Kite-Ship well describes key dynamics of HAWP used for tugging ships by kites. John Gay's: or Work for Boys. Chapter XVIII in the Summer volume.

•

1943 Stanley Biszak instructed using potential energy in free-flight for converting ambient winds impacting turbine to drive electric generator to charge batteries.

•

1967 Richard Miller, former editor of Soaring magazine, published book Without Visible Means of Support that describes the feasibility of free-flight coupled non-ground-moored kites to capture differences in wind strata to travel across continents; such HAWP is the subject of Dale C. Kramer's contemporary patent application.

•

1977 April 3, 1977, invention declared. On September 21, 1979, Douglas Selsam notarized his kite-lifted endless chain of airfoils HAWP system, generic type that would later show in Dutch astronaut Wubbo Ockels' device called LadderMill described in a patent of 1997. Douglas Selsam conceived his Auto-oriented Wind Harnessing Buoyant Aerial Tramway on April 3, 1977. On the Selsam notarized disclosure of invention was placed a date of Sept. 20, while the notary placed the final signing on Sept. 21, 1979. notes and drawings.

•

1979 Professor Bryan Roberts begins giromill gyrocopter-type HAWP wind generator development.

•

1986 Bryan Roberts' AWE HAWP rotor generates electricity and lifts itself in tethered flight.

•

1992 Free Rotor WO/1992020917 Free Rotor by JACK, Colin, Humphry, Bruce (one man). Colin Jack. Colin Bruce. Multi-rotors are treated. Faired tethers are recognized. 1992.

•

2001 Founding of SkySails company. As leader in ship traction HAWP, in 2010 they note having just less than 10 installations.

•

2002 Drachen Foundation awarded a grant to David Lang so that he would explore the use of kites to generate practical power.

•

2004 Drachen Foundation had David Lang, former NASA expert, aerospace consultant, conduct a survey-study of kite-based power generation. He published a summary of methods in his view.

•

2005 HAWP conference held at AeroVironment, Pasadena, CA; attendees: Paul MacCready, Dave Lang, Joe Hadzicki, Scott Skinner. The long meeting was videotaped; the tape is in the archives of the Drachen Foundation, open to researchers.

•

2006 on October 19: Jong Chul Kim, filed for international patent protection for "Electric power generation system using hydro turbine tracted by paraglider." His further studies has been for at-sea production of hydrogen and other chemicals using HAWP tethering kite systems.

•

2006 Kite Sailing Symposium, Seattle, Washington, September 28–30, 2006.

•

2006 Dr. Paul MacCready, American aeronautical engineer, Inventor of the Year Award in 1981, publishes an influential article In Using Kites to Tap Power of Wind.

•

2006 January 30: First International Workshop on Modelling and Optimization of Power Generating Kites KITE-OPT 07 held in Belgium featured keynote speaker astronaut Prof. Wubbo Ockels.

•

2006 September: A 40 kW prototype of high altitude wind genereator is tested in Italy by Kite Gen Research Massimo Ippolito.

•

2007 Dave Santos demonstrated lofted Portland KiteMotor at alt-energy West Coast Climate Convergence; the generation success was announced in HIPFiSH Columbia-Pacific's Alternative Monthly (Aug.-Sept./2007). KiteMotor Growing Pains

•

2008 Dave Santos demonstrates flipwings for AWE passive-control generator systems.

•

2009 January 28, University of Texas hosted Airborne Wind Energy Seminar in its Aerospace Engineering Department. Keynote presenter: Dave Santos of KiteLab.

•

2009 Dave Santos demonstrated passive control of kite-lifted working dynamic kite operating a string tripod to transfer kite-gained mechanical energy to a ground-based generator via pulley and crank; this was not a reel-method scheme.

•

2009 Towered WECS companies open departments for AWE HAWP: Two ground-hugging towered wind-turbine companies open AWE HAWP departments: SpiralAirfoil Airborne and Selsam.

•

2009 A first international industry association was founded: Airborne Wind Energy Industry Association

•

2009 August. Dr. Hong Zhang, Kyle Fitzpatrick, and other students demonstrate working generation of electricity from powerkiting in preparation for further academic HAWP studies at Rowan University, New Jersey.

•

2009 Nov. 5-6 : HAWP conferece in Chico, CA and Oroville, CA. Scores of HAWP and AWE companies and inventors attended. Systems demonstrated: KiteLab's lifted bladed turbine with generator aloft, Selsam multi-rotor torquetube hybrid with groundstationed generator, SkyMill Energy autogiro RCcontrolled reel-in-out method.

•

2009 Dec. 9 : TU Delft University holds Kite Dynamics Symposium 09 for HAWP as central focus.

•

2010 January 13. An announcement that a large investment will be made to construct a commercial utility-scale HAWP project in the city of Foshan, China.

•

2010 March 1–3: Three HAWP companies had booths at ARPA-E Technology Showcase, Gaylord Convention Center, Washington, DC. Investment and showcasing by HAWP entities: Joby Energy, Sky Windpower, Makani Power directed visitors to each other's booths.

•

2010 March 6. Eight airborne wind energy technology entity leaders in USA held a telephone conference and decided without objection to propose a modification to bill HR 3165 ; the primary line-item proposed modification entered to a congressional member was the inclusion of "airborne wind energy technology."

•

2010 April 24. Multiple chaotic systems effectively captured for useful work: Full demonstration of working mini-AWECS involving Double Pendulum and flapping kite wing-mill under lifter kite to drive clockworks system's charging lithium battery by KiteLab of Ilwaco, Washington, USA. Designer and builder: Dave Santos.

•

2010 Another international organization has been formed: Airborne Wind Energy Consortium

•

2010 May: USA's NASA firms attention on AWECS by establishing an AWT data web site: NASA Wind Energy Airborne Harvesting Stystem Study. The NASA 2010 Innovation Fund selected Airborne Wind Turbine Energy Harvesting UAV Systems; project leader is Dr. Mark D. Moore, Aeronautics Systems.

•

2010, June 16 An international partnership between Dutch and Norwegian entities provides second-round financing for classic reel-in HAWP method using

tethered powerplane system. Airborne wind energy technology firm Ampyx Power partners with Byte and Statkraft. •

16 June 2010 A unique treasure of 700+ drawings by airborne wind energy techologist Dave Santos made from 2006 and into 2009 were made available to the public. Seven-hundred pages of drawings made from 2006 into 2009 by hand and mind of Dave Santos Alternate full name: David Santos Gorena-Guinn, roboticist, artist, founder of KiteLab, master instructor for KitePilotSchool, and chief technical officer for Airborne Wind Energy Industry Association (AWEIA).

•

2010 July 9: World's First Gondola Turbine Array Demo by KiteLab.

•

2010 September 29–30 Airborne Wind Energy Conference 2010. This complements the 2009 November first major international conference.

•

2010 October: The Wayne German Prize for Contributions to Airborne Wind Energy stated its second year awardee.

•

2010 November 25: CONOPS are being drafted by KiteLab, Ilwaco, WA, USA, and also NASA AWT project leader for submission to the USA's FAA toward obtaining response for potentially having airborne wind energy conversion systems as an integral part of aviation and air space.

Chapter- 4

Wind Turbine

Offshore wind farm using 5MW turbines REpower M5 in the North Sea off Belgium

A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or pumping water, the device is called a windmill or wind pump.

History

James Blyth's electricity generating wind turbine photographed in 1891 Windmills were used in Persia (present-day Iran) as early as 200 B.C. The windwheel of Heron of Alexandria marks one of the first known instances of wind powering a machine in history. However, the first practical windmills were built in Sistan, a region between Afghanistan and Iran, from the 7th century. These "Panemone" were vertical axle windmills, which had long vertical driveshafts with rectangular blades. Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind corn or draw up water, and were used in the gristmilling and sugarcane industries. Windmills first appeared in Europe during the middle ages The first historical records for their use in England date to the 11th or 12th centuries and there are reports of German crusaders taking their windmill-making skills to Syria around 1190. By the 14th century, Dutch windmills were in use to drain areas of the Rhine delta.

The first automatically operated wind turbine, built in Cleveland in 1887 by Charles F. Brush. It was 60 feet (18 m) tall, weighed 4 tons (3.6 metric tonnes) and powered a 12kW generator. The first electricity generating wind turbine, was a battery charging machine installed in July 1887 by Scottish academic, James Blyth to light his holiday home in Marykirk, Scotland. Some months later American inventor Charles F Brush built the first automatically operated wind turbine for electricity production in Cleveland, Ohio. Although Blyth's turbine was considered uneconomical in the United Kingdom electricity generation by wind turbines was more cost effective in countries with widely scattered populations. In Denmark by 1900, there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW. The largest machines were on 24-metre (79 ft) towers with four-bladed 23-metre (75 ft)

diameter rotors. By 1908 there were 72 wind-driven electric generators operating in the US from 5 kW to 25 kW. Around the time of World War I, American windmill makers were producing 100,000 farm windmills each year, mostly for water-pumping. By the 1930s, windmills for electricity were common on farms, mostly in the United States where distribution systems had not yet been installed. In this period, high-tensile steel was cheap, and windmills were placed atop prefabricated open steel lattice towers.

Enercon E-126, highest rated capacity A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in 1931. This was a 100 kW generator on a 30-metre (98 ft) tower, connected to the local 6.3 kV distribution system. It was reported to have an annual capacity factor of 32 per cent, not much different from current wind machines. In the fall of 1941, the first megawatt-class wind turbine was synchronized to a utility grid in Vermont. The SmithPutnam wind turbine only ran for 1,100 hours before suffering a critical failure. Due to war time material shortages the unit was not repaired. The first utility grid-connected wind turbine to operate in the U.K. was built by John Brown & Company in 1951 in the Orkney Islands. It had an 18-metre (59 ft) diameter, three-bladed rotor and a rated output of 100 kW.

Resources A quantitative measure of the wind energy available at any location is called the Wind Power Density (WPD) It is a calculation of the mean annual power available per square meter of swept area of a turbine, and is tabulated for different heights above ground. Calculation of wind power density includes the effect of wind velocity and air density. Color-coded maps are prepared for a particular area described, for example, as "Mean Annual Power Density at 50 Meters." In the United States, the results of the above calculation are included in an index developed by the U.S. National Renewable Energy Lab and referred to as "NREL CLASS." The larger the WPD calculation, the higher it is rated by class. Classes range from Class 1 (200 watts/square meter or less at 50 meters altitude) to Class 7 (800 to 2000 watts/square meter). Commercial wind farms generally are sited in Class 3 or higher areas, although isolated points in an otherwise Class 1 area may be practical to exploit.

Fuhrländer Wind Turbine Laasow, world's tallest

Types Wind turbines can rotate about either a horizontal or a vertical axis, the former being both older and more common.

The three primary types:VAWT Savonius, HAWT towered; VAWT Darrieus as they appear in operation.

Horizontal axis

Components of a horizontal axis wind turbine (gearbox, rotor shaft and brake assembly) being lifted into position Horizontal-axis wind turbines (HAWT) have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator. Since a tower produces turbulence behind it, the turbine is usually positioned upwind of its supporting tower. Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted forward into the wind a small amount.

The School of Sustainability at Arizona State University

Wind turbines on the roof a building off Mount Auburn Street in Cambridge, Massachusetts

Co-operative Insurance building, Manchester, with wind turbines on roof Downwind machines have been built, despite the problem of turbulence (mast wake), because they don't need an additional mechanism for keeping them in line with the wind, and because in high winds the blades can be allowed to bend which reduces their swept area and thus their wind resistance. Since cyclical (that is repetitive) turbulence may lead to fatigue failures, most HAWTs are of upwind design. Modern wind turbines

Turbine blade convoy passing through Edenfield in the UK Turbines used in wind farms for commercial production of electric power are usually three-bladed and pointed into the wind by computer-controlled motors. These have high tip speeds of over 320 kilometres per hour (200 mph), high efficiency, and low torque ripple, which contribute to good reliability. The blades are usually colored light gray to blend in with the clouds and range in length from 20 to 40 metres (66 to 130 ft) or more. The tubular steel towers range from 60 to 90 metres (200 to 300 ft) tall. The blades rotate at 10-22 revolutions per minute. At 22 rotations per minute the tip speed exceeds 300 feet per second (91 m/s). A gear box is commonly used for stepping up the speed of the generator, although designs may also use direct drive of an annular generator. Some models operate at constant speed, but more energy can be collected by variable-speed turbines which use a solid-state power converter to interface to the transmission system. All turbines are equipped with protective features to avoid damage at high wind speeds, by feathering the blades into the wind which ceases their rotation, supplemented by brakes.

Éole, the largest vertical axis wind turbine, in Cap-Chat, Quebec

Vertical axis design Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable. With a vertical axis, the generator and gearbox can be placed near the ground, so the tower doesn't need to support it, and it is more accessible for maintenance. Drawbacks are that some designs produce pulsating torque.

It is difficult to mount vertical-axis turbines on towers , meaning they are often installed nearer to the base on which they rest, such as the ground or a building rooftop. The wind speed is slower at a lower altitude, so less wind energy is available for a given size turbine. Air flow near the ground and other objects can create turbulent flow, which can introduce issues of vibration, including noise and bearing wear which may increase the maintenance or shorten the service life. However, when a turbine is mounted on a rooftop, the building generally redirects wind over the roof and this can double the wind speed at the turbine. If the height of the rooftop mounted turbine tower is approximately 50% of the building height, this is near the optimum for maximum wind energy and minimum wind turbulence.

Subtypes

Darrieus wind turbine of 30 m in the Magdalen Islands Darrieus wind turbine

"Eggbeater" turbines, or Darrieus turbines, were named after the French inventor, Georges Darrieus. They have good efficiency, but produce large torque ripple and cyclical stress on the tower, which contributes to poor reliability. They also generally require some external power source, or an additional Savonius rotor to start turning, because the starting torque is very low. The torque ripple is reduced by using three or more blades which results in a higher solidity for the rotor. Solidity is measured by blade area divided by the rotor area. Newer Darrieus type turbines are not held up by guy-wires but have an external superstructure connected to the top bearing. Giromill A subtype of Darrieus turbine with straight, as opposed to curved, blades. The cycloturbine variety has variable pitch to reduce the torque pulsation and is selfstarting. The advantages of variable pitch are: high starting torque; a wide, relatively flat torque curve; a lower blade speed ratio; a higher coefficient of performance; more efficient operation in turbulent winds; and a lower blade speed ratio which lowers blade bending stresses. Straight, V, or curved blades may be used. Savonius wind turbine These are drag-type devices with two (or more) scoops that are used in anemometers, Flettner vents (commonly seen on bus and van roofs), and in some high-reliability low-efficiency power turbines. They are always self-starting if there are at least three scoops. They sometimes have long helical scoops to give a smooth torque.

Turbine design and construction

Components of a horizontal-axis wind turbine Wind turbines are designed to exploit the wind energy that exists at a location. Aerodynamic modeling is used to determine the optimum tower height, control systems, number of blades and blade shape. Wind turbines convert wind energy to electricity for distribution. Conventional horizontal axis turbines can be divided into three components. • •

•

The rotor component, which is approximately 20% of the wind turbine cost, includes the blades for converting wind energy to low speed rotational energy. The generator component, which is approximately 34% of the wind turbine cost, includes the electrical generator, the control electronics, and most likely a gearbox (e.g. planetary gearbox, adjustable-speed drive or continuously variable transmission) component for converting the low speed incoming rotation to high speed rotation suitable for generating electricity. The structural support component, which is approximately 15% of the wind turbine cost, includes the tower and rotor yaw mechanism.

Highest-situated wind turbine, at the Veladero mine in San Juan Province, Argentina

Unconventional wind turbines One E-66 wind turbine at Windpark Holtriem, Germany, carries an observation deck, open for visitors. Another turbine of the same type, with an observation deck, is located in Swaffham, England. Airborne wind turbines have been investigated many times but have yet to produce significant energy. Conceptually, wind turbines may also be used in conjunction with a large vertical solar updraft tower to extract the energy due to air heated by the sun. Wind turbines which utilise the Magnus effect have been developed.

Small wind turbines Small wind turbines may be as small as a fifty-watt generator for boat or caravan use. Small units often have direct drive generators, direct current output, aeroelastic blades, lifetime bearings and use a vane to point into the wind. Larger, more costly turbines generally have geared power trains, alternating current output, flaps and are actively pointed into the wind. Direct drive generators and aeroelastic blades for large wind turbines are being researched.

Record-holding turbines Largest capacity The Enercon E-126 has a rated capacity of 7.58 MW , has an overall height of 198 m (650 ft), a diameter of 126 m (413 ft), and is the world's largest-capacity wind turbine since its introduction in 2007. At least four companies are working on the development of a 10MW turbine: • • • •

American Superconductor Wind Power Ltd are developing a 10 MW VAWT, the Aerogenerator X Clipper Windpower are developing the Britannia 10 MW HAWT Sway announced the proposed development of a prototype 10 MW wind turbine with a height of 162.5 m (533 ft) and a rotor diameter of 145 m (475 ft).

Largest swept area The turbine with the largest swept area is a prototype installed by Gamesa at Jaulín, Zaragoza, Spain in 2009. The G10X – 4.5 MW has a rotor diameter of 128m.

Tallest

The tallest wind turbine is Fuhrländer Wind Turbine Laasow. Its axis is 160 meters above ground and its rotor tips can reach a height of 205 meters. It is the only wind turbine taller than 200 meters in the world.

Largest vertical-axis Le Nordais wind farm in Cap-Chat, Quebec has a vertical axis wind turbine (VAWT) named Éole, which is the world's largest at 110 m. It has a nameplate capacity of 3.8MW.

Rønland, most productive turbines, in Denmark

Most southerly The turbines currently operating closest to the South Pole are three Enercon E-33 in Antarctica, powering New Zealand's Scott Base and the United States' McMurdo Station since December 2009 although a modified HR3 turbine from Northern Power Systems operated at the Amundsen-Scott South Pole Station in 1997 and 1998. In March 2010 CITEDEF designed, built and installed a wind turbine in Argentine Marambio Base.

Most productive Four turbines at Rønland wind farm in Denmark share the record for the most productive wind turbines, with each having generated 63.2 GWh by June 2010

Highest-situated The world's highest-situated wind turbine is made by DeWind and located in the Andes, Argentina around 4,100 metres (13,500 ft) above sea level. The site uses a type D8.2 2000 kW / 50 Hz turbine. This turbine has a new drive train concept with a special torque converter (WinDrive) made by Voith and a synchronous generator. The WKA was put into operation in December 2007 and has supplied the Veladero mine of Barrick Gold with electricity since then.

Chapter- 5

Floating Wind Turbine

The world’s first full-scale floating wind turbine, Hywind, being assembled in the Åmøy Fjord near Stavanger, Norway, before deployment in the North Sea. A floating wind turbine is an offshore wind turbine mounted on a floating structure that allows the turbine to generate electricity in water depths where bottom-mounted towers are not feasible. The wind can be stronger and steadier over water due to the absence of topographic features that may disrupt wind flow. The electricity generated is sent to shore through undersea cables. The initial capital cost of floating turbines is competitive with bottom-mounted, near-shore wind turbines while the rate of energy generation is higher out in the sea as the wind flow is often more steady and unobstructed by terrain features. The relocation of wind farms into the sea can reduce visual pollution if the windmills are

sited more than 12 miles (19 km) offshore, provide better accommodation of fishing and shipping lanes, and allow siting near heavily developed coastal cities. Floating wind parks are wind farms that site several floating wind turbines closely together to take advantage of common infrastructure such as power transmission facilities.

History The concept for "large-scale offshore floating wind turbines was introduced by Professor William E. Heronemus at the University of Massachusetts in 1972. [I]t was not until the mid 1990’s, after the commercial wind industry was well established, that the topic was taken up again by the mainstream research community." As of 2003, existing offshore fixed-bottom wind turbine technology deployments had been limited to water depths of 30-meters. Worldwide deep-water wind resources are extremely abundant in subsea areas with depths up to 600 meters, which are thought to best facilitate transmission of the generated electric power to shore communities.

Operational deep-water platforms

A tension leg mooring system as used by Blue H: left-hand tower-bearing structure (grey) is free floating, the right-hand structure is pulled by the tensioned cables (red) down towards the seabed anchors (light-grey) As of 2009, there have been only two operational floating wind turbines used to farm wind energy over deep-water. Blue H deployed the first floating wind turbine 113 kilometres (70 mi) off of the coast of Italy in December, 2007. It was then decommissioned at the end of 2008 after completing a planned test year of gathering operational data. The first large-capacity, 2.3 megawatt floating wind turbine is Hywind, which became operational in the North Sea off of Norway in September, 2009 and is still operational as of October 2009.

Blue H Technologies Blue H Technologies of the Netherlands operated the first floating wind turbine, a prototype deep-water platform with an 80-kilowatt turbine off of Puglia, southeast Italy in 2008. Installed 21 km off the coast in waters 113 meters deep in order to gather test data on wind and sea conditions, the small prototype unit was decommissioned at the end of 2008. Blue H has successfully decommissioned the unit as it embarks on plans to build a 38-unit deepwater wind farm at the same location. The Blue H technology utilizes a tension-leg platform design and a two-bladed turbine. The two-bladed design can have a "much larger chord, which allows a higher tip speed than those of three-bladers. The resulting increased background noise of the two-blade rotor is not a limiting factor for offshore sites." As of 2009, Blue H is building the first full-scale commercial 2.4 MWe unit in Brindisi, Italy which it expects to deploy at the same site of the prototype in the southern Adriatic Sea in 2010. This is the first unit in the planned 90 MW Tricase offshore wind farm, located more than 20 km off the Puglia coast line.

Hywind

A single floating cylindrical spar buoy moored by catenary cables. Hywind uses a ballasted catenary layout that adds 60 tonne weights hanging from the midpoint of each anchor cable to provide additional tension. The world's first operational deep-water floating large-capacity wind turbine is the Hywind, in the North Sea off of Norway. The Hywind was towed out to sea in early June 2009. The 2.3 megawatt turbine was constructed by Siemens Wind Power and mounted on a floating tower with a 100 metre deep draft. The float tower was constructed by Technip, and Nowitech contributed to the design. Nowitech (Norwegian Research Centre for Offshore Wind Technology) is a consortium of 30 members, including SINTEF and the Norwegian University of Science and Technology at Trondheim. Statoil says that floating wind turbines are still immature and commercialization is distant. The installation is owned by Statoil and will be tested for two years. After assembly in the calmer waters of Åmøy Fjord near Stavanger, Norway, the 120-meter-tall tower with a 2.3 MW turbine was towed 10 km offshore into 220-meter-deep water, 10 km southwest of Karmøy, on 6 June 2009 for a two year test deployment." Alexandra Beck Gjorv of Statoil said, "[The experiment] should help move offshore wind farms out of sight ... The global market for such turbines is potentially enormous, depending on how low we can press costs." The unit became operational in the summer of 2009. Hywind was inaugurated on 8 September 2009. As of October 2010, after a full year of operation, the Hywind turbine is still operating and generating electricity for the Norwegian grid. The turbine cost 400 million kroner (around US$62 million) to build and deploy. The 13kilometer (8-mile) long submarine power transmission cable was installed in July, 2009 and system test including rotor blades and initial power transmission was conducted shortly thereafter. The installation is expected to generate about 9 GW·h of electricity annually. The SWATH (Small Waterplane Area Twin Hull), a new class of offshore wind turbine service boat, will be tested at Hywind.

Topologies Platform topologies can be classified into: • •

single-turbine-floater (one wind turbine mounted on a floating structure) multiple turbine floaters (multiple wind turbines mounted on a floating structure)

Engineering considerations Undersea mooring of floating wind turbines are accomplished with three principal mooring systems. Two common types of engineered design for anchoring floating structures include tension-leg and catenary loose mooring systems. Tension leg mooring systems have vertical tethers under tension providing large restoring moments in pitch and roll. Catenary mooring systems provide station keeping for an offshore structure yet

provide little stiffness at low tensions." A third form of mooring system is the ballasted catenary configuration, created by adding multiple-tonne weights hanging from the midsection of each anchor cable in order to provide additional cable tension and therefore increase stiffness of the above-water floating structure.

Economics "Technically, the [theoretical] feasibility of deepwater [floating] wind turbines is not questioned as long-term survivability of floating structures has already been successfully demonstrated by the marine and offshore oil industries over many decades. However, the economics that allowed the deployment of thousands of offshore oil rigs have yet to be demonstrated for floating wind turbine platforms. For deepwater wind turbines, a floating structure will replace pile-driven monopoles or conventional concrete bases that are commonly used as foundations for shallow water and land-based turbines. The floating structure must provide enough buoyancy to support the weight of the turbine and to restrain pitch, roll and heave motions within acceptable limits. The capital costs for the wind turbine itself will not be significantly higher than current marinized turbine costs in shallow water. Therefore, the economics of deepwater wind turbines will be determined primarily by the additional costs of the floating structure and power distribution system, which are offset by higher offshore winds and close proximity to large load centers (e.g. shorter transmission runs)." As of 2009 however, the economic feasibility of shallow-water offshore wind technologies is more completely understood. With empirical data obtained from fixedbottom installations off many countries for over a decade now, representative costs are well understood. Shallow-water turbines cost between 2.4 and 3 million United States dollars per megawatt to install, according to the World Energy Council. As of 2009, the practical feasibility and per-unit economics of deep-water, floatingturbine offshore wind is yet to be seen. Initial deployment of single full-capacity turbines in deep-water locations began only in 2009. As of October 2010, new feasibility studies are supporting that floating turbines are becoming both technically and economically viable in the UK and global energy markets. "The higher up-front costs associated with developing floating wind turbines would be offset by the fact that they would be able to access areas of deep water off the coastlne of the UK where winds are stronger and reliable." The recent Offshore Valuation study conducted in the UK has confirmed that using just one third of the UK's wind, wave and tidal resource could generate energy equivalent to 1 billion barrels of oil per year; the same as North Sea oil and gas production. Some of the primary challenges are the coordination needed to develop transmission lines.

Proposals

Floating wind farms The US State of Maine solicited proposals in September 2010 to build the world's first floating, commercial wind farm. The RFP is seeking proposals for 25 MW of deep-water offshore wind capacity to supply power for 20-year long-term contract period via gridconnected floating wind turbines in the Gulf of Maine. Successful bidders must enter into long-term power supply contracts with either Central Maine Power Company (CMP), Bangor Hydro-Electric Company (BHE), or Maine Public Service Company (MPS). Proposals are due by May 2011. Some vendors who could bid on the proposed project have expressed concerns about dealing with the United States regulatory environment. Since the proposed site is in Federal waters, developers would need a permit from the Minerals Management Service, "which took more than seven years to approve a yet-to-be-built, shallow-water wind project off Cape Cod," and is also the agency under fire in June 2010 for lax oversight of deepwater oil drilling in Federal waters. "Uncertainty over regulatory hurdles in the United States ... is 'the Achilles heel' for Maine's ambitions for deepwater wind."

Floating design concepts

WindFloat WindFloat is a patent pending floating foundation for offshore wind turbines aimed at improving dynamic stability. The WindFloat design is intended to dampen wave and turbine induced motion utilizing a tri-column triangular platform with the wind turbine positioned on only one of the three columns. The triangular platform is then "moored with 6 lines, 4 of which are connected to the column stabilizing the turbine, thus creating an asymmetric" mooring to increase stability and reduce motion. This technology could allow wind turbines to be sited in offshore areas that were previously considered inaccessible, areas having water depth exceeding 50 meters and more powerful wind resources than shallow-water offshore wind farms typically encounter. As of 2010, Principle Power and electricity provider Energias de Portugal is utilizing the WindFloat design to construct a "three-legged floating foundation designed to accommodate any 5 MW turbine." Completion of construction and installation off of Portugal is expected by the end of summer 2012. Construction cost is expected to be below $30 million.

Nautica Windpower

Nautica Windpower's AFT design features a downwind two-bladed rotor with passive wind alignment to reduce costs Nautica Windpower uses a patented technology aimed at reducing system weight, complexity and costs for deep water sites. Scale model tests in open water have been conducted and structural dynamics modeling is under development for a multi-megawatt design. Nautica Windpower's Asymmetric Floating Tower (AFT) uses a single mooring line and a downwind two-bladed rotor configuration that is deflection tolerant and aligns itself with the wind without an active yaw system. Two-bladed, downwind turbine designs that can accommodate flexibility in the blades will potentially prolong blade lifetime, diminish structural system loads and reduce offshore maintenance needs, yielding lower lifecycle costs.

OC3-Hywind The European Wind Energy Association (EWEA), under the auspices of their Offshore Code Comparison Collaboration (OC3) initiative, has completed high-level design and simulation modeling of the OC-3 Hywind system, a 5-MW wind turbine installed on a floating spar buoy, moored with catenary mooring lines, in water depth of 320 meters. The spar buoy platform would extend 120 meters below the surface and the mass of such a system, including ballast would exceed 7.4 million kg.

DeepWind Risø and 11 international partners started a 4-year program called DeepWind in October 2010 to create and test economical floating Vertical Axis Wind Turbines up to 20MW. The program is supported with €3m through EUs Seventh Framework Programme. Partners include TUDelft, SINTEF, Statoil and United States National Renewable Energy Laboratory.

Chapter- 6

Darrieus Wind Turbine

Fig. 1: A Darrieus wind turbine once used to generate electricity on the Magdalen Islands

The Darrieus wind turbine is a type of vertical axis wind turbine (VAWT) used to generate electricity from the energy carried in the wind. The turbine consists of a number of aerofoils usually--but not always--vertically mounted on a rotating shaft or framework. This design of wind turbine was patented by Georges Jean Marie Darrieus, a French aeronautical engineer in 1931. The Darrieus type is theoretically just as efficient as the propeller type if wind speed is constant, but in practice this efficiency is rarely realised due to the physical stresses and limitations imposed by a practical design and wind speed variation. There are also major difficulties in protecting the Darrieus turbine from extreme wind conditions and in making it self-starting.

Method of Operation

Fig. 2: A very large Darrieus wind turbine on the Gaspé peninsula, Quebec, Canada

Combined Darrieus-Savonius generator in Taiwan In the original versions of the Darrieus design, the aerofoils are arranged so that they are symmetrical and have zero rigging angle, that is, the angle that the aerofoils are set relative to the structure on which they are mounted. This arrangement is equally effective no matter which direction the wind is blowing -- in contrast to the conventional type, which must be rotated to face into the wind. When the Darrieus rotor is spinning, the aerofoils are moving forward through the air in a circular path. Relative to the blade, this oncoming airflow is added vectorially to the wind, so that the resultant airflow creates a varying small positive angle of attack (AoA) to the blade. This generates a net force pointing obliquely forwards along a certain 'lineof-action'. This force can be projected inwards past the turbine axis at a certain distance,

giving a positive torque to the shaft, thus helping it to rotate in the direction it is already travelling in. The aerodynamic principles which rotate the rotor are equivalent to that in autogiros, and normal helicopters in autorotation. As the aerofoil moves around the back of the apparatus, the angle of attack changes to the opposite sign, but the generated force is still obliquely in the direction of rotation, because the wings are symmetrical and the rigging angle is zero. The rotor spins at a rate unrelated to the windspeed, and usually many times faster. The energy arising from the torque and speed may be extracted and converted into useful power by using an electrical generator. The aeronautical terms lift and drag are, strictly speaking, forces across and along the approaching net relative airflow respectively, so they are not useful here. We really want to know the tangential force pulling the blade around, and the radial force acting against the bearings. When the rotor is stationary, no net rotational force arises, even if the wind speed rises quite high -- the rotor must already be spinning to generate torque. Thus the design is not normally self starting. Under rare conditions, Darrieus rotors can self-start, so some form of brake is required to hold it when stopped. One problem with the design is that the angle of attack changes as the turbine spins, so each blade generates its maximum torque at two points on its cycle (front and back of the turbine). This leads to a sinusoidal (pulsing) power cycle that complicates design. In particular, almost all Darrieus turbines have resonant modes where, at a particular rotational speed, the pulsing is at a natural frequency of the blades that can cause them to (eventually) break. For this reason, most Darrieus turbines have mechanical brakes or other speed control devices to keep the turbine from spinning at these speeds for any lengthy period of time. Another problem arises because the majority of the mass of the rotating mechanism is at the periphery rather than at the hub, as it is with a propeller. This leads to very high centrifugal stresses on the mechanism, which must be stronger and heavier than otherwise to withstand them. One common approach to minimise this is to curve the wings into an "egg-beater" shape (this is called a "troposkein" shape, derived from the Greek for "the shape of a spun rope") such that they are self supporting and do not require such heavy supports and mountings. See. Fig. 1. In this configuration, the Darrieus design is theoretically less expensive than a conventional type, as most of the stress is in the blades which torque against the generator located at the bottom of the turbine. The only forces that need to be balanced out vertically are the compression load due to the blades flexing outward (thus attempting to "squeeze" the tower), and the wind force trying to blow the whole turbine over, half of which is transmitted to the bottom and the other half of which can easily be offset with guy wires.

By contrast, a conventional design has all of the force of the wind attempting to push the tower over at the top, where the main bearing is located. Additionally, one cannot easily use guy wires to offset this load, because the propeller spins both above and below the top of the tower. Thus the conventional design requires a strong tower that grows dramatically with the size of the propeller. Modern designs can compensate most tower loads of that variable speed and variable pitch. In overall comparison, while there are some advantages in Darrieus design there are many more disadvantages, especially with bigger machines in MW class. The Darrieus design uses much more expensive material in blades while most of the blade is too near of ground to give any real power. Traditional designs assume that wing tip is at least 40m from ground at lowest point to maximize energy production and life time. So far there is no known material (not even carbon fiber) which can meet cyclic load requirements.

Giromills

Fig 3: A Giromill-type wind turbine Darrieus's 1927 patent also covered practically any possible arrangement using vertical airfoils. One of the more common types is the Giromill or H-bar design, in which the long "egg beater" blades of the common Darrieus design are replaced with straight vertical blade sections attached to the central tower with horizontal supports. The Giromill blade design is much simpler to build, but results in a more massive structure than the traditional arrangement, and requires stronger blades, for reasons outlined above.

Cycloturbines

Another variation of the Giromill is the Cycloturbine, in which each blade is mounted so that it can rotate around its own own vertical axis. This allows the blades to be "pitched" so that they always have some angle of attack relative to the wind. The main advantage to this design is that the torque generated remains almost constant over a fairly wide angle, so a Cycloturbine with three or four blades has a fairly constant torque. Over this range of angles, the torque itself is near the maximum possible, meaning that the system also generates more power. The Cycloturbine also has the advantage of being able to self start, by pitching the "downwind moving" blade flat to the wind to generate drag and start the turbine spinning at a low speed. On the downside, the blade pitching mechanism is complex and generally heavy, and some sort of wind-direction sensor needs to be added in order to pitch the blades properly.

Fig 4: Schematic of mass-stabilised pitch control system. A schematic of a self-acting pitch control system that does not require a wind-direction system is shown in Figure 4.

Helical blades The blades of a Darrieus turbine can be canted into a helix, e.g. three blades and a helical twist of 60 degrees, similar to Gorlov's water turbines. Since the wind pulls each blade around on both the windward and leeward sides of the turbine, this feature spreads the torque evenly over the entire revolution, thus preventing destructive pulsations. The skewed leading edges reduce resistance to rotation; by providing a second turbine above the first, with oppositely directed helices, the axial wind-forces cancel, thereby minimizing wear on the shaft bearings. Another advantage is that the blades generate torque well from upward-slanting airflow, such as occurs above roofs and cliffs. This design is used by the Turby and Quiet Revolution brands of wind turbine.

Chapter- 7

Unconventional Wind Turbines

As of 2010, the most common type of wind turbine is the three-bladed horizontal-axis wind turbine (HAWT).

Wattle Point Wind Farm's information centre

Modified HAWT Ducted rotor Still something of a research project, the ducted rotor consists of a turbine inside a duct which flares outwards at the back. They are also referred as Diffuser-Augmented Wind Turbines (i.e. DAWT). The main advantage of the ducted rotor is that it can operate in a wide range of winds and generate a higher power per unit of rotor area. Another advantage is that the generator operates at a high rotation rate, so it doesn't require a bulky gearbox, so the mechanical portion can be smaller and lighter. A disadvantage is that (apart from the gearbox) it is more complicated than the unducted rotor and the duct is usually quite heavy, which puts an added load on the tower. The Éolienne Bollée is an example of a DAWT.

WindShare 750 kW, direct drive, Lagerwey Wind model LW 52 wind turbine in Toronto, Ontario

Co-axial, multi-rotor horizontal-axis turbines Two or more rotors may be mounted to the same driveshaft, with their combined corotation together turning the same generator — fresh wind is brought to each rotor by sufficient spacing between rotors combined with an offset angle (alpha) from the wind direction. Wake vorticity is recovered as the top of a wake hits the bottom of the next rotor. Power has been multiplied several times using co-axial, multiple rotors in testing conducted by inventor and researcher Douglas Selsam, for the California Energy Commission in 2004. The first commercially available co-axial multi-rotor turbine is the patented dual-rotor American Twin Superturbine from Selsam Innovations in California,

with 2 propellers separated by 12 feet. It is the most powerful 7-foot-diameter (2.1 m) turbine available, due to this extra rotor.

Counter-rotating horizontal-axis turbines When a system expels or accelerates mass in one direction, the accelerated mass will cause a proportional but opposite force on that system. A single rotor wind turbine causes a significant amount of tangential or rotational air flow to be created by the spinning blades. The energy of this tangential air flow is wasted in a single-rotor propeller design. To use this wasted effort, the placement of a second rotor behind the first takes advantage of the disturbed airflow. Contra-rotation wind energy collection with two rotors, one behind the other, can gain up to 40% more energy from a given swept area as compared with a single rotor. Much work has been done recently on this in the USA. A patent application dated 1992 exists based on work done with the Trimblemill. Ability to be point suspended, thus reducing support structure overturning moments theoretical ability to be “grid linked” without electronics, thus giving the possibility of "arrays".

Vestas V29 wind turbine at Beaufort Court, Kings Langley, UK Counter-rotating turbines can be used to increase the rotation speed of the electrical generator. As of 2005, no large practical counter-rotating HAWTs are commercially sold. When the counter-rotating turbines are on the same side of the tower, the blades in front are angled forwards slightly so as to avoid hitting the rear ones. If the turbine blades are on opposite sides of the tower, it is best that the blades at the back be smaller than the blades at the front and set to stall at a higher wind speed. This allows the generator to function at a wider wind speed range than a single-turbine generator for a given tower. To reduce sympathetic vibrations, the two turbines should turn at speeds with few common multiples, for example 7:3 speed ratio. Overall, this is a more complicated design than the single-turbine wind generator, but it taps more of the wind's energy at a wider range of wind speeds.

Appa designed and demonstrated a contra-rotor wind turbine in FY 2000–2002 funded by California Energy Commission. This study showed 30 to 40% more power extraction than a comparable single-rotor system. Further, it was observed that the slower the rotor speed, the better the performance. Consequently, Megawatt machines benefit most. This also cancels the gyroscopic forces. There will be an improvement in overall efficiency.

Furling tail and twisting blades turbines In addition to variable pitch blades, furling tails and twisting blades are other improvements on wind turbines. Similar to the variable pitch blades, they may also greatly increase the efficiency of the turbine and be used in "do-it-yourself" construction

Vestas V47 wind turbine at American Wind Power Center in Lubbock, Texas

Telescopic blades The next step in making improvements to wind turbines is the use of telescopic blades. Telescopic blades can change the blade's length, thus increasing or decreasing the turbine's swept area. Telescopic blades make a turbine more productive by increasing the turbine's rotor diameter during low-wind conditions. In high-wind conditions, when the turbine is in need of reducing loads, the blades can be retracted to make the rotor smaller.

Modified VAWT Aerogenerator The Aerogenerator is a special design of vertical axis wind turbine which could allow greater energy outputs.

Savonius wind turbine The Savonius wind turbine is another special design wind turbine.

Augmented "G" model VAWT: "G" Model Wind Turbine (GMWT) The "G" Model VAWT Turbine is equipped with three self-positioning "Augmentation And Directioning Wings=AADW" placed as the outer sections of classical Darrieus blades. The GMWT can increase almost fivefold the efficiency of classical Darrieus Blades: AADWs adjust themselves to the wind direction without any external power. The resulting combination ("G" Model Wind Turbine) works with very low cut-in wind speed, has self starting ability, together with a high capacity factor.

Enercon E-70 at GreenPark Business Park, UK

"Fuller" wind turbine The "Fuller" wind turbine is a fully enclosed wind turbine which uses boundary layers instead of blades. Imagine a stack of CDs on a central shaft with a small air gap in between, the surface tension of moving air as it passes through the small gaps creates friction and using this energy causes the CDs to rotate around the shaft. The Fuller has addition vanes to help direct the air for improved performance, hence it isn't totally bladeless, as has been suggested.

Aerial

Concept for an airborne wind generator. It has been suggested that wind turbines could be flown in high-speed winds using high altitude wind power tactics, taking advantage of the steadier winds at high altitudes. A system of automatically controlled tethered kites could also be used to capture energy from high-altitude winds.

H-rotor Another type is the H-rotor

Wind belt Invented by Shawn Frayne. A belt vibrates by the passing flow of air. A magnet is mounted at one end of the belt.

Vaneless ion wind generator Piezoelectric wind turbines Another special type of wind turbines are the piezoelectric wind turbines. Turbines with diameters on the scale of 10 centimeters work by flexing piezoelectric crystals as they rotate, sufficient to power small electronic devices.

Traffic-driven wind generator A few proposals call for generating power from the otherwise wasted energy in the draft created by traffic.

Blade Tip Power System (BTPS) Designed by Imad Mahawili with Honeywell/WindTronics. This design uses many nylon blades and turns a permanent magnet generator inside out. The magnets are on the tips of the blades, and the stator is on the outside of the generator.

Wind turbine technology used to harness other power sources Wind turbines may also be used in conjunction with a solar collector to extract the energy due to air heated by the Sun and rising through a large vertical Solar updraft tower. Wind turbines are part of experimental wave powered generators where air displaced by waves drives turbines.

Wind turbines with two blades Nearly all modern wind turbines uses rotors with three blades. However, there are and were also designs with another blade count. The most common other blade count is 2. This was used at GROWIAN, some other prototypes and several wind turbine types manufactured by NedWind. A wind park only using wind turbines with 2 blades is Eemmeerdijk Wind Park. Wind turbines with 2 blades are manufactured by Nordic Wind Power (Model N 1000) and by GC China.

Wind turbines on public display

The Nordex N50 wind turbine and visitor centre of Lamma Winds in Hong Kong.

Kiosk at the base of the Lamma Winds Nordex N50/800kW wind turbine on Lamma Island with displays showing current power output and cumulative energy produced.

The NEG Micon M700 wind turbine at the Great River Energy headquarters in Maple Grove, Minnesota The great majority of wind turbines around the world belong to individuals or corporations who use them to generate electric power or to perform mechanical work. As such, wind turbines are primarily designed to be working devices. However, the large size and height above surroundings of modern industrial wind turbines, combined with their moving rotors, often makes them among the most conspicuous objects in their areas. A few localities have exploited the attention-getting nature of wind turbines by placing them on public display, either with visitor centers around their bases, or with viewing areas farther away. The wind turbines themselves are generally of conventional horizontal-axis, three-bladed design, and generate power to feed electrical grids, but they also serve the unconventional roles of technology demonstration, public relations, and education. •

•

Australia o Blayney Wind Farm, New South Wales has a viewing area and interpretive centre o Wattle Point Wind Farm, South Australia has an information centre Canada o OPG 7 commemorative turbine is a Vestas V80-1.8MW wind turbine on the site of the Pickering Nuclear Generating Station

o •

Toronto Hydro - WindShare features a Lagerwey Wind model LW 52 wind turbine at Exhibition Place

China Inner Mongolia's Huitengxile Wind Farm has 14 visitor centers to accommodate wind power tourists to the remote region o Lamma Winds in Hong Kong has a single Nordex N50/800 kW model with a rotor diameter of 50m and a nameplate capacity of 800 kW New Zealand o Brooklyn, Wellington, New Zealand has a 230 kW wind turbine United Kingdom o GreenPark Business Park has an Enercon E-70 2 MW wind turbine adjacent to the M4 motorway, billed as the UK's most visible turbine o Renewable Energy Systems has a Vestas V29 225 kW wind turbine visible from the M25 motorway at its headquarters at Beaufort Court, Kings Langley, Hertfordshire o Scroby Sands wind farm has a visitor center at Great Yarmouth open during the tourist season (May-October) o Scout Moor Wind Farm "has become a real tourist attraction" since its 2008 opening United States o Dorchester, Massachusetts - Local 103 of the International Brotherhood of Electrical Workers installed the first commercial-scale wind turbine within the City of Boston, a 100 kW unit from Fuhrlaender on a 35-meter tower with rotor diameter of 21 meters, visible from the John F. Kennedy Library o The Great Lakes Science Center in Cleveland, Ohio has a reconditioned Vestas V27 wind turbine with a nameplate capacity of 225 kW o Great River Energy's headquarters in Maple Grove, Minnesota has a NEG Micon M700 wind turbine, visible from Interstate 94 o Laurel, New York has a Northern Power Systems 100kW turbine at the Half Hollow Nursery and private tours of the operating turbine are provided by Eastern Energy Systems Inc. of Mattituck, New York. o Lubbock, Texas has a Vestas V47 at the American Wind Power Center o McKinney, Texas has a Wal-Mart store with several sustainability features, including two wind turbines manufactured by Bergey Windpower, of 1 kW and 50 kW nameplate capacity respectively o Sweetwater, Texas has a 2 MW 60Hz DeWind D8.2 prototype wind turbine for training students in the Texas State Technical College wind energy program o

• •

•

Observation deck Some wind turbines on public display go one further, with observation decks beneath their nacelles. •

Canada

Grouse Mountain Resorts in North Vancouver, British Columbia installed a Leitwind 1.5MW wind turbine with an observation deck, atop a 65m tower, at an elevation of 1,300m, opening just before the 2010 Winter Olympics. Germany o One wind turbine of the type Enercon E-66 at Windpark Holtriem, Germany carries an observation deck, open for visitors. Netherlands o The Siemens plant in Zoetermeer features a wind turbine with 40m blade length and an observation deck. United Kingdom o Another Enercon E-66 wind turbine with an observation deck belonging to Ecotricity is in the English town of Swaffham. o

•

•

•

Enercon E-66 at Swaffham's Ecotech centre, showing observation deck below nacelle

Closeup of the Enercon E-66 at Swaffham

Wind turbine with observation deck at Siemens plant in Zoetermeer

Rooftop wind-turbines Wind-turbines can be installed on the top of a roof of a building. This is not as common as may first be assumed. Some examples include Marthalen Landi-Silo in Switzerland and Council House 2 in Melbourne, Australia. Discovery Tower is an office building in Houston, Texas, scheduled for opening in 2010, that incorporates 10 wind turbines in its architecture.

Regents Quarter in Kings Cross, London

Wind turbine on tower block in Islington

Quietrevolution wind turbine on a building in Bristol The Museum of Science in Boston, Massachusetts began constructing a rooftop Wind Turbine Lab in 2009. The Lab will test nine wind turbines from five different manufacturers on the roof of the Museum. Rooftop wind turbines may suffer from turbulence, especially in cities, which reduces power output and accelerates turbine wear. The lab seeks to address the general lack of performance data for urban wind turbines. Due to the structural limitations of buildings, the limited space in urban areas, and safety considerations, wind turbines mounted on buildings are usually small (with nameplate

capacities in the low kilowatts), rather than the megawatt-class wind turbines which are most economical for wind farms. A partial exception is the Bahrain World Trade Centre with three 225 kW wind turbines mounted between twin skyscrapers.

Chapter- 8

Small Wind Turbine

Small-scale wind power in rural Indiana. Small wind turbines are wind turbines which have lower energy output than large commercial wind turbines, such as those found in wind farms. These turbines may be as small as a fifty watt generator for boat, caravan, or miniature refrigeration unit. Small units often have direct drive generators, direct current output, aeroelastic blades, lifetime bearings and use a vane to point into the wind. Larger, more costly turbines generally

have geared power trains, alternating current output, flaps and are actively pointed into the wind. Direct drive generators and aeroelastic blades for large wind turbines are being researched.

Market United States Small wind turbines added a total of 17.3 MW of generating capacity throughout the United States in 2008, according to the American Wind Energy Association (AWEA). That growth equaled a 78% increase in the domestic market for small wind turbines, which are defined as wind turbines with capacities of 100 kW or less. AWEA's "2009 Small Wind Global Market Study", published in late 2009 May, credited the increase in part to greater manufacturing volumes, as the industry was able to attract enough private investment to finance manufacturing plant expansions. It also credited rising electricity prices and greater public awareness of wind technologies for an increase in residential sale. But a poll of small wind manufacturers found that the growth in 2008 might be only a glimmer of things to come, as the companies projected a 30-fold growth in the U.S. small wind market within as little as five years, despite the global recession. The U.S. small wind industry also benefits from the global market, as it controls about half of the global market share. U.S. manufacturers garnered $77 million of the $156 million that was spent throughout the world on small wind turbine installations. A total of 38.7 MW of small wind power capacity was installed globally in 2008.

Installation Turbines should be mounted on a suitable tower to raise them above any nearby obstacles. A good rule of thumb is that turbines should be at least 30 feet (9 m) higher than anything within 500 feet (152 m). In general, an effort should be made to make sure that a small wind turbine is as far away as possible from large upwind obstacles. Measurements made in a boundary layer wind tunnel have indicated that significant detrimental effects associated with nearby obstacles can extend up to 80 times the obstacle's height downwind. However, this is an extreme case. Another approach to siting a small turbine is to use a shelter model to predict how nearby obstacles will affect local wind conditions. Models of this type are general and can be applied to any site. They are often developed based on actual wind measurements, and can estimate flow properties such as mean wind speed and turbulence levels at a potential turbine location, taking into account the size, shape, and distance to any nearby obstacles. A small wind turbine can be installed on a roof. Installation issues then include the strength of the roof, vibration, and the turbulence caused by the roof ledge. Small-scale rooftop turbines suffer from turbulence and rarely generate significant amounts of power, especially in towns and cities.

Types

Smaller scale turbines for residential scale use are available, they are usually approximately 7 to 25 feet (2.1–7.6 m) in diameter and produce electricity at a rate of 300 to 10,000 watts at their tested wind speed. Some units have been designed to be very lightweight in their construction, e.g. 16 kilograms (35 lb), allowing sensitivity to minor wind movements and a rapid response to wind gusts typically found in urban settings and easy mounting much like a television antenna. It is claimed, and a few are certified, as being inaudible even a few feet (about a metre) under the turbine. The majority of small wind turbines are traditional horizontal axis wind turbines, but Vertical axis wind turbines are a growing type of wind turbine in the small-wind market. These turbines, by being able to take wind from multiple dimensions, are more applicable for use at low heights, on rooftops, and in generally urbanized areas. Their ability to function well at low heights is particularly important when considering the cost of a high tower necessary for traditional turbines. All big companies in this industry, such as WePower, Urban Green Energy, Mariah Power, and Helix Wind, have reported sharply increasing sales over the previous years. Dynamic braking regulates the speed by dumping excess energy, so that the turbine continues to produce electricity even in high winds. The dynamic braking resistor may be installed inside the building to provide heat (during high winds when more heat is lost by the building, while more heat is also produced by the braking resistor). The location makes low voltage (around 12 volt) distribution practical.

Local use In the United States, residential wind turbines with outputs of 2–10 kW, typically cost between $12,000 and $55,000 installed ($6 per watt), although there are incentives and rebates available in 19 states that can reduce the purchase price for homeowners by up to 50 percent, to ($3 per watt). The US manufacturer "Southwest Windpower," estimates a turbine to pay for itself in energy savings in 5 to 10 years. The American Wind Energy Association has released several studies on the small wind turbine market in the U.S. and abroad, showing that the U.S. continues to dominate the Small Wind industry. According to another organization, the World Wind Energy Association, it is difficult to assess the total number or capacity of small-scaled wind turbines, but in China alone, there are roughly 300,000 small-scale wind turbines generating electricity. The dominant models on the market, especially in the United States, are horizontal-axis wind turbines (HAWT).

Parts • •

Blades Hub

• • • • •

DC generator Diode Mount Wires Tail

Tower • • •

Base Pole Guy-wires

Loopwing The Loopwing turbine is a low-noise, low-vibration and self-stabilizing device. It is specifically designed for quiet home use. It requires only a 1.6 mph (2.6 km/h) breeze to get started.

DIY and Open Source Wind Turbines Some hobbyists have built wind turbines from kits, sourced components, or from scratch. Do it yourself or DIY-wind turbine construction has been made popular by magazines such as OtherPower and Home Power, and websites such as Instructables, and by TVseries as Jericho and The Time Machine. DIY-made wind turbines are usually smaller (rooftop) turbines of ~ 1 kW or less. These small wind turbines are usually tilt-up or fixed/guyed towers. However, larger (freestanding) and more powerful windtubines are sometimes built as well. The latter can generate power of up to 10 kW. In addition, people are also showing interest in DIYconstruction of wind turbines with special designs as the Savonius, Panemone, wind turbine to boost power generation. When compared to similar sized commercial wind turbines, these DIY turbines tend to be cheaper. Through the internet, the community is now able to obtain plans to construct DIY-wind turbines. and there is a growing trend toward building them for domestic requirements. The DIY-wind turbines are now being used both in developed countries and in developing countries, to help power homes, residences and small businesses. At present, organizations as Practical Action have designed DIY wind turbines that can be easily built by communities in developing nations and are supplying concrete documents on how to do so.

Open source

To assist people in the developing countries, and hobbyists alike, several projects have been open-sourced (e.g. the Jua Kali wind turbine, Hugh Piggot's wind turbine, ForceField Wind Turbine, Chispito Wind Generator. )

Chapter- 9

Vertical Axis, Savonius & Airborne Wind Turbine

Vertical axis wind turbine

The world's tallest vertical-axis wind turbine, in Cap-Chat, Quebec

Vertical-axis wind turbines (VAWTs) are a type of wind turbine where the main rotor shaft is set vertically. Among the advantages of this arrangement are that generators and gearboxes can be placed close to the ground, and that VAWTs do not need to be pointed into the wind. Major drawbacks for the early designs (Savonius, Darrieus, giromill and cycloturbine) included the pulsatory torque that can be produced during each revolution and the huge bending moments on the blades. Later designs solved the torque issue by using the helical twist of the blades almost similar to Gorlov's water turbines. A VAWT tipped sideways, with the axis perpendicular to the wind streamlines, functions similarly. A more general term that includes this option is "transverse axis wind turbine". For example, the original Darrieus patent , includes both options. Drag-type VAWTs, such as the Savonius rotor, typically operate at lower tipspeed ratios than lift-based VAWTs such as Darrieus rotors and cycloturbines.

General aerodynamics The forces and the velocities acting in a Darrieus turbine are depicted in figure 1. The resultant velocity vector, , is the vectorial sum of the undisturbed upstream air velocity, , and the velocity vector of the advancing blade, .

Fig1: Forces and velocities acting in a Darrieus turbine for various azimuthal positions

Five-kilowatt vertical axis wind turbine Thus, the oncoming fluid velocity varies, the maximum is found for and the minimum is found for , where θ is the azimuthal or orbital blade position. The angle of attack, α, is the angle between the oncoming air speed, W, and the blade's chord. The resultant airflow creates a varying, positive angle of attack to the blade in the upstream zone of the machine, switching sign in the downstream zone of the machine. From geometrical considerations, the resultant airspeed flow and the angle of attack are calculated as follows:

where

is the tip speed ratio parameter.

The resultant aerodynamic force is decomposed either in lift (F_L) - drag (D) components or normal (N) - tangential (T) components. The forces are considered acting at 1/4 chord from the leading edge (by convention), the pitching moment is determined to resolve the aerodynamic forces. The aeronautical terms lift and drag are, strictly speaking, forces across and along the approaching net relative airflow respectively. The tangential force is acting along the blade's velocity and, thus, pulling the blade around, and the normal force is acting radially, and, thus, is acting against the bearings. The lift and the drag force are useful when dealing with the aerodynamic behaviour around each blade, i.e. dynamic stall, boundary layer, etc; while when dealing with global performance, fatigue loads, etc., it is more convenient to have a normal-tangential frame. The lift and the drag coefficients are usually normalised by the dynamic pressure of the relative airflow, while the normal and the tangential coefficients are usually normalised by the dynamic pressure of undisturbed upstream fluid velocity.

A = Surface Area The amount of power, P, that can be absorbed by a wind turbine.

Where Cp is the power coefficient, ρ is the density of the air, A is the swept area of the turbine, and ν is the wind speed.

Advantages of vertical axis wind turbines VAWTs offer a number of advantages over traditional horizontal axis wind turbines (HAWTs). They can be packed closer together in wind farms, allowing more in a given space. This is not because they are smaller, but rather due to the slowing effect on the air that HAWTs have, forcing designers to separate them by ten times their width. VAWTs are rugged, quiet, omni-directional, and they do not create as much stress on the support structure. They do not require as much wind to generate power, thus allowing them to be closer to the ground. By being closer to the ground they are easily maintained and can be installed on chimneys and similar tall structures.

Savonius wind turbine

Savonius wind turbine Savonius wind turbines are a type of vertical-axis wind turbine (VAWT), used for converting the force of the wind into torque on a rotating shaft. The turbine consists of a number of aerofoils usually--but not always--vertically mounted on a rotating shaft or framework, either ground stationed or tethered in airborne systems. They were invented by the Finnish engineer Sigurd J. Savonius in 1922. Johann Ernst Elias Bessler (born 1680) was the first to attempt to build a horizontal windmill of the Savonius type in the

town of Furstenburg in Germany in 1745. He fell to his death whilst construction was under way. It was never completed but the building still exists.

Operation

Schematic drawing of a two-scoop Savonius turbine Savonius turbines are one of the simplest turbines. Aerodynamically, they are drag-type devices, consisting of two or three scoops. Looking down on the rotor from above, a twoscoop machine would look like an "S" shape in cross section. Because of the curvature, the scoops experience less drag when moving against the wind than when moving with the wind. The differential drag causes the Savonius turbine to spin. Because they are drag-type devices, Savonius turbines extract much less of the wind's power than other similarly-sized lift-type turbines. Much of the swept area of a Savonius rotor may be near the ground, if it has a small mount without an extended post, making the overall energy extraction less effective due to the lower wind speeds found at lower heights.

Use

Combined Darrieus-Savonius generator in Taiwan Savonius turbines are used whenever cost or reliability is much more important than efficiency. For example, most anemometers are Savonius turbines, because efficiency is completely irrelevant for that application. Much larger Savonius turbines have been used to generate electric power on deep-water buoys, which need small amounts of power and get very little maintenance. Design is simplified because, unlike with Horizontal Axis Wind Turbines (HAWTs), no pointing mechanism is required to allow for shifting wind direction and the turbine is self-starting. Savonius and other vertical-axis machines are not usually connected to electric power grids. They can sometimes have long helical scoops, to give smooth torque.

The most ubiquitous application of the Savonius wind turbine is the Flettner Ventilator which is commonly seen on the roofs of vans and buses and is used as a cooling device. The ventilator was developed by the German aircraft engineer Anton Flettner in the 1920s. It uses the Savonius wind turbine to drive an extractor fan. The vents are still manufactured in the UK by Flettner Ventilator Limited. Small Savonius wind turbines are sometimes seen used as advertising signs where the rotation helps to draw attention to the item advertised. They sometimes feature a simple two-frame animation.

Tethered airborne Savonius turbines • • •

Airborne wind turbines Kite types When the Savonius rotor axis is set horizontal and tethered, then kiting results. There are scores of patents and products that use the net lift Magnus-effect that occurs in the autorotation of the Savonius rotor. The spin may be mined for some of its energy for making noise, heat, or electricity.

Gallery

Operation of a Savonius turbine

A Savonius rotor bladed WECS

Airborne wind turbine

Airborne wind generator of Savonius style An airborne wind turbine is a design concept for a wind turbine that is supported in the air without a tower. Airborne wind turbines may operate in low or high altitudes; they are part of a wider class of airborne wind energy systems (AWE) addressed by high altitude wind power. When the generator is on the ground,[] then the tethered aircraft need not carry the generator mass or have a conductive tether. When the generator is aloft, then a conductive tether would be used to transmit energy to the ground or used aloft or beamed to receivers using microwave or laser. Airborne turbine systems would have the advantage of tapping an almost constant wind, without requirements for slip rings or yaw mechanism, and without the expense of tower construction. Kites and 'helicopters' come down when there is insufficient wind; kytoons and blimps resolve the matter. Also, bad weather such as lightning or thunderstorms, could temporarily suspend use of the machines, probably requiring them to be brought back down to the ground and covered.

Some schemes require a long power cable and, if the turbine is high enough, an aircraft exclusion zone. As of 2008, no commercial airborne wind turbines are in regular operation.

Aerodynamic variety An aerodynamic airborne wind power system relies on the wind for support. Bryan Roberts, a professor of engineering at the University of Technology, in Sydney, Australia, has proposed a helicopter-like craft which flies to 15,000 feet (4,600 m) altitude and stays there, held aloft by wings that generate lift from the wind, and held in place by a cable to a ground anchor. According to its designers, while some of the energy in the wind would be 'lost' on lift, the constant and potent winds would allow it to generate constant electricity. Since the winds usually blow horizontally, the turbines would be at an angle from the horizontal, catching winds while still generating lift. Deployment could be done by feeding electricity to the turbines, which would turn them into electric motors, lifting the structure into the sky. The Dutch ex-astronaut and physicist Wubbo Ockels, working with the Delft University of Technology in the Netherlands, has designed, and demonstrated , an airborne wind turbine he calls a "Laddermill". It consists of an endless loop of kites. The kites lift one end of the endless loop, (the "ladder") up, and the released energy is used to drive an electric generator. A Sept'09 paper from Carbon Tracking Ltd., Ireland has shown the capacity factor of a kite using ground based generation to be in 52.2% which compare favorably with terrestrial wind-farm capacity factors of 30%. A team from Worcester Polytechnic Institute in the United States has developed a smaller scale kite power system with an estimated output of about 1 kW. It uses a kiteboarding kite to induce a rocking motion in a pivoting beam. The Kitegen uses a prototype vertical-axis wind turbine. It is an innovative plan (still in the construction phase) that consists of one wind farm with a vertical spin axis, and employs kites to exploit high-altitude winds. The Kite Wind Generator (KWG) or Kitegen is claimed to eliminate all the static and dynamic problems that prevent the increase of the power (in terms of dimensions) obtainable from the traditional horizontalaxis wind turbine generators. Generating equipment would remain on the ground, only the airfoils are supported by the wind. Such a wind power plant would be capable of producing the energy equivalent to a nuclear power plant, while using an area of few square kilometres, without occupying it exclusively. (The majority of this area can still be used for agriculture, or navigation in the case of an offshore installation.) KiteLab's Dave Santos of Ilwaco, Washington, has been advancing single-surface wingmills to generate useful electricity with the generator ground-based.

The Rotokite is developed from Gianni Vergnano's idea. It uses aerodynamic profiles similar to kites that have been rotated on their own axis, emulating the performance of a propeller. The use of the rotation principle simplifies the problem of checking the flight of the kites and eliminates the difficulties due to the lengths of cables, enabling the production of wind energy at low cost. The Heli Wind Power is a project of Gianni Vergnano that uses a tethered kite.

Aerostat variety An aerostat-type wind power system relies at least in part on buoyancy to support the wind-collecting elements. Aerostats vary in their designs and resulting lift-over-drag aerodynamic characteristic; the kiting effect of higher lift-over-drag shapes for the aerostat can effectively keep an airborne turbine aloft. Balloons can be added to the mix to keep systems up without wind, but balloons leak slowly and have to be resupplied with lifting gas, possibly patched as well. Very large, sun heated balloons may solve the helium or hydrogen leakage problems. An Ontario based company called Magenn Power Inc. has developed a turbine called the Magenn Air Rotor System (MARS). The 100-foot (30 m)-wide MARS system uses a horizontal rotor in a helium suspended apparatus which is tethered to a transformer on the ground. Magenn states that their technology provides high torque, low starting speeds, and superior overall efficiency thanks to its ability to deploy higher in comparison to nonaerial solutions. The first prototypes were built by TCOM in April 2008.

Concept drawing of the Twind technology. The Twind Technology concept uses a pair of captive balloons at an altitude of 800 meters. The tether cables transmit force to a rotating platform on the ground. Each balloon has a sail connected to it. The two balloons move alternately, the balloon with the sail open moves downwind and draws the other balloon upwind, and then the motion reverses. The tether cable can be used to turn the shaft of a generator to produce electrical energy or perform other works (grinding, sawing, pumping).

Estimated costs Sky Windpower estimate that their technology will be capable of producing electricity for $0.02 per KWh, while a system of raising a kite to a high altitude while turning a generator on the ground, and then changing its shape so that it can be drawn back down with less energy than it produced on the way up, has been estimated to be capable of producing electricity for $0.01 per KWh - both numbers being significantly lower than the current price of non-subsidized electricity.

Chapter- 10

Wind Turbine Design

An example of a wind turbine, this 3 bladed turbine is the classic design of modern wind turbines Wind turbine designs are utilized to create wind turbines that exploit wind energy. A wind turbine installation consists of the necessary systems needed to capture the wind's energy, point the turbine into the wind, convert mechanical rotation into electrical power, and other systems to start, stop, and control the turbine. Here we, covers the design of horizontal axis wind turbines (HAWT) since the majority of commercial turbines use this design. Contrary to popular belief, considerable attention should be given to the structural and foundation design of HAWTs. This is mainly due to

the disproportionate amount that is spent on the foundations as a percentage of the total project cost.

Design specification The design specification for a wind-turbine will contain a power curve and guaranteed availability. With the data from the wind resource assessment it is possible to calculate commercial viability. The typical operating temperature range is -20 to 40 °C (-4 to 104 °F). In areas with extreme climate (like Inner Mongolia or Rajasthan) specific cold and hot weather versions are required.

Low temperature Utility-scale wind turbine generators have minimum temperature operating limits which apply in areas that experience temperatures below –20 °C. Wind turbines must be protected from ice accumulation, which can make anemometer readings inaccurate and which can cause high structure loads and damage. Some turbine manufacturers offer lowtemperature packages at a few percent extra cost, which include internal heaters, different lubricants, and different alloys for structural elements. If the low-temperature interval is combined with a low-wind condition, the wind turbine will require an external supply of power, equivalent to a few percent of its rated power, for internal heating. For example, the St. Leon, Manitoba project has a total rating of 99 MW and is estimated to need up to 3 MW (around 3% of capacity) of station service power a few days a year for temperatures down to –30 °C. This factor affects the economics of wind turbine operation in cold climates.

Aerodynamics The aerodynamics of a horizontal-axis wind turbine are not straightforward. The air flow at the blades is not the same as the airflow far away from the turbine. The very nature of the way in which energy is extracted from the air also causes air to be deflected by the turbine. In addition the aerodynamics of a wind turbine at the rotor surface exhibit phenomena that are rarely seen in other aerodynamic fields. In 1919 the physicist Albert Betz showed that for a hypothetical ideal wind-energy extraction machine, the fundamental laws of conservation of mass and energy allowed no more than 16/27 (59.3%) of the kinetic energy of the wind to be captured. This Betz' law limit can be approached by modern turbine designs which may reach 70 to 80% of this theoretical limit.

Power control A wind turbine is designed to produce a maximum of power at wide spectrum of wind speeds. All wind turbines are designed for a maximum wind speed, called the survival speed, above which they do not survive. The survival speed of commercial wind turbines

is in the range of 40 m/s (144 km/h) to 72 m/s (259 km/h). The most common survival speed is 60 m/s (216 km/h). The wind turbines have three modes of operation: • • •

Below rated wind speed operation Around rated wind speed operation (usually at nameplate capacity) Above rated wind speed operation

If the rated wind speed is exceeded the power has to be limited. There are various ways to achieve this.

Stall

Plastic vortex generator stripes used to control stall characteristics of the blade - in this example protecting the blade from rapid fluctuations in wind speed.

Closeup look at the vortex generators (VGs) - the larger ones are closest to the root of the blade where the boundary layer is thicker(i.e., closest to the hub) Stalling works by increasing the angle at which the relative wind strikes the blades (angle of attack), and it reduces the induced drag (drag associated with lift). Stalling is simple because it can be made to happen passively (it increases automatically when the winds speed up), but it increases the cross-section of the blade face-on to the wind, and thus the ordinary drag. A fully stalled turbine blade, when stopped, has the flat side of the blade facing directly into the wind. A fixed-speed HAWT inherently increases its angle of attack at higher wind speed as the blades speed up. A natural strategy, then, is to allow the blade to stall when the wind speed increases. This technique was successfully used on many early HAWTs. However, on some of these blade sets, it was observed that the degree of blade pitch tended to increase audible noise levels. Vortex generators may be used to control the lift characteristics of the blade. The VGs are placed on the airfoil to enhance the lift if they are placed on the lower (flatter) surface or limit the maximum lift if placed on the upper (higher camber) surface.

Pitch control Furling works by decreasing the angle of attack, which reduces the induced drag from the lift of the rotor, as well as the cross-section. One major problem in designing wind

turbines is getting the blades to stall or furl quickly enough should a gust of wind cause sudden acceleration. A fully furled turbine blade, when stopped, has the edge of the blade facing into the wind. Standard modern turbines all pitch the blades in high winds. Since pitching requires acting against the torque on the blade, it requires some form of pitch angle control. Many turbines use hydraulic systems. These systems are usually spring loaded, so that if hydraulic power fails, the blades automatically furl. Other turbines use an electric servomotor for every rotor blade. They have a small battery-reserve in case of an electricgrid breakdown. Small wind turbines (under 50 kW) with variable-pitching generally use systems operated by centrifugal force, either by flyweights or geometric design, and employ no electric or hydraulic controls.

Other controls Yawing Modern large wind turbines are typically actively controlled to face the wind direction measured by a wind vane situated on the back of the nacelle. By minimizing the yaw angle (the misalignment between wind and turbine pointing direction), the power output is maximized and non-symmetrical loads minimized. However, since the wind direction varies quickly the turbine will not strictly follow the direction and will have a small yaw angle on average. The power output losses can simply be approximated to fall with cos3(yaw angle).

Electrical braking

Dynamic braking resistor for wind turbine. Braking of a small wind turbine can also be done by dumping energy from the generator into a resistor bank, converting the kinetic energy of the turbine rotation into heat. This method is useful if the kinetic load on the generator is suddenly reduced or is too small to keep the turbine speed within its allowed limit. Cyclically braking causes the blades to slow down, which increases the stalling effect, reducing the efficiency of the blades. This way, the turbine's rotation can be kept at a safe speed in faster winds while maintaining (nominal) power output. This method is usually not applied on large grid-connected wind turbines.

Mechanical braking

A mechanical drum brake or disk brake is used to hold the turbine at rest for maintenance. Such brakes are usually applied only after blade furling and electromagnetic braking have reduced the turbine speed, as the mechanical brakes would wear quickly if used to stop the turbine from full speed. There can also be a stick brake.

Turbine size

A person standing beside medium size modern turbine blades. For a given survivable wind speed, the mass of a turbine is approximately proportional to the cube of its blade-length. Wind power intercepted by the turbine is proportional to the square of its blade-length. The maximum blade-length of a turbine is limited by both the strength and stiffness of its material. Labor and maintenance costs increase only gradually with increasing turbine size, so to minimize costs, wind farm turbines are basically limited by the strength of materials, and siting requirements. Typical modern wind turbines have diameters of 40 to 90 metres (130 to 300 ft) and are rated between 500 kW and 2 MW. As of 2010 the most powerful turbine is rated at 7 MW.

Generator

10 Israeli wind turbines in the Golan Heights 600 kW each For large, commercial size horizontal-axis wind turbines, the generator is mounted in a nacelle at the top of a tower, behind the hub of the turbine rotor. Typically wind turbines generate electricity through asynchronous machines that are directly connected with the electricity grid. Usually the rotational speed of the wind turbine is slower than the equivalent rotation speed of the electrical network - typical rotation speeds for a wind generators are 5-20 rpm while a directly connected machine will have an electrical speed between 750-3600 rpm. Therefore, a gearbox is inserted between the rotor hub and the generator. This also reduces the generator cost and weight. Commercial size generators have a rotor carrying a field winding so that a rotating magnetic field is produced inside a set of windings called the stator. While the rotating field winding consumes a fraction of a percent of the generator output, adjustment of the field current allows good control over the generator output voltage. Enercon has produced gearless wind turbines with permanent magnet generators for many years, and Siemens produces a gearless "inverted generator" 3MW model while developing a 6MW model. This gives better reliability and performance than gear based systems. Gearless turbines

Parts of DIY Wind turbine Older style wind generators rotate at a constant speed, to match power line frequency, which allowed the use of less costly induction generators. Newer wind turbines often turn at whatever speed generates electricity most efficiently. This can be solved using multiple technologies such as doubly fed induction generators or full-effect converters where the variable frequency current produced is converted to DC and then back to AC, matching the line frequency and voltage. Although such alternatives require costly equipment and cause power loss, the turbine can capture a significantly larger fraction of the wind energy. In some cases, especially when turbines are sited offshore, the DC energy will be transmitted from the turbine to a central (onshore) inverter for connection to the grid.

Blades Blade design

Blades can be made from simple objects as barrels The ratio between the speed of the blade tips and the speed of the wind is called tip speed ratio. High efficiency 3-blade-turbines have tip speed/wind speed ratios of 6 to 7. Modern wind turbines are designed to spin at varying speeds. Use of aluminum and composite materials in their blades has contributed to low rotational inertia, which means that newer wind turbines can accelerate quickly if the winds pick up, keeping the tip

speed ratio more nearly constant. Operating closer to their optimal tip speed ratio during energetic gusts of wind allows wind turbines to improve energy capture from sudden gusts that are typical in urban settings. In contrast, older style wind turbines were designed with heavier steel blades, which have higher inertia, and rotated at speeds governed by the AC frequency of the power lines. The high inertia buffered the changes in rotation speed and thus made power output more stable. The speed and torque at which a wind turbine rotates must be controlled for several reasons: • • •

•

• •

To optimize the aerodynamic efficiency of the rotor in light winds. To keep the generator within its speed and torque limits. To keep the rotor and hub within their centripetal force limits. The centripetal force from the spinning rotors increases as the square of the rotation speed, which makes this structure sensitive to overspeed. To keep the rotor and tower within their strength limits. Because the power of the wind increases as the cube of the wind speed, turbines have to be built to survive much higher wind loads (such as gusts of wind) than those from which they can practically generate power. Since the blades generate more downwind force (and thus put far greater stress on the tower) when they are producing torque, most wind turbines have ways of reducing torque in high winds. To enable maintenance; because it is dangerous to have people working on a wind turbine while it is active, it is sometimes necessary to bring a turbine to a full stop. To reduce noise; As a rule of thumb, the noise from a wind turbine increases with the fifth power of the relative wind speed (as seen from the moving tip of the blades). In noise-sensitive environments, the tip speed can be limited to approximately 60 m/s (200 ft/s).

More and more engineers realized that the scale of the today's wind turbine blades is now rendering the early trial-and-error intuition-based approaches outdated. Predictive computer tools which are fundamentally founded on mechanics principles are needed to analyze the blade structure in the early design process. Recently, VABS originally developed in helicopter industry, is introduced as a rigorous, engineering-friendly approach for modeling realistic, composite rotor blades. VABS can easily save orders of magnitude computational cost without sacrificing the accuracy. An critical assessment of computer tools for calculating composite wind turbine blade properties has shown that VABS is the best tool available for modeling composite wind turbine blades among all the other tools available in the wind industry. Using composites adds a significant level of complexity into the engineering of modern wind turbines. One has to simultaneously consider the heterogeneity and anisotropy of the material in the design and analysis. Such characteristics of composites will introduce new deformation modes such as extension-twist or twist-bending couplings defying the

conventional blade analysis. VABS is the only computational tool which can rigorously capture all the deformation modes including elastic couplings due to use of composites.

Blade count

The NASA Mod-0 research wind turbine at Glenn Research Center's Plum Brook station in Ohio tested a one-bladed rotor configuration The determination of the number of blades involves design considerations of aerodynamic efficiency, component costs, system reliability, and aesthetics. Noise emissions are affected by the location of the blades upwind or downwind of the tower and the speed of the rotor. Given that the noise emissions from the blades' trailing edges and tips vary by the 5th power of blade speed, a small increase in tip speed can make a large difference. Wind turbines developed over the last 50 years have almost universally used either two or three blades. Aerodynamic efficiency increases with number of blades but with diminishing return. Increasing the number of blades from one to two yields a six percent increase in aerodynamic efficiency, whereas increasing the blade count from two to three yields only an additional three percent in efficiency. Further increasing the blade count yields minimal improvements in aerodynamic efficiency and sacrifices too much in blade stiffness as the blades become thinner.

Component costs that are affected by blade count are primarily for materials and manufacturing of the turbine rotor and drive train. Generally, the fewer the number of blades, the lower the material and manufacturing costs will be. In addition, the fewer the number of blades, the higher the rotational speed can be. This is because blade stiffness requirements to avoid interference with the tower limit how thin the blades can be manufactured, but only for upwind machines; deflection of blades in a downwind machine results in increased tower clearance. Fewer blades with higher rotational speeds reduce peak torques in the drive train, resulting in lower gearbox and generator costs.

The 98 meter diameter, two-bladed NASA/DOE Mod-5B wind turbine was the largest operating wind turbine in the world in the early 1990s

System reliability is affected by blade count primarily through the dynamic loading of the rotor into the drive train and tower systems. While aligning the wind turbine to changes in wind direction (yawing), each blade experiences a cyclic load at its root end depending on blade position. This is true of one, two, three blades or more. However, these cyclic loads when combined together at the drive train shaft are symmetrically balanced for three blades, yielding smoother operation during turbine yaw. Turbines with one or two blades can use a pivoting teetered hub to also nearly eliminate the cyclic loads into the drive shaft and system during yawing. Finally, aesthetics can be considered a factor in that some people find that the threebladed rotor is more pleasing to look at than a one- or two-bladed rotor.

Blade materials New generation wind turbine designs are pushing power generation from the single megawatt range to upwards of 10 megawatts. The common trend of these larger capacity designs are larger and larger wind turbine blades. Covering a larger area effectively increases the tip-speed ratio of a turbine at a given wind speed, thus increasing the energy extraction capability of a turbine system. Current production wind turbine blades are manufactured as large as 100 meters in diameter with prototypes in the range of 110 to 120 meters. In 2001, an estimated 50 million kilograms of fiberglass laminate were used in wind turbine blades. New materials and manufacturing methods provide the opportunity to improve wind turbine efficiency by allowing for larger, stronger blades. One of the most important goals when designing larger blade systems is to keep blade weight under control. Since blade mass scales as the cube of the turbine radius, loading due to gravity becomes a constraining design factor for systems with larger blades. Current manufacturing methods for blades in the 40 to 50 meter range involve various proven fiberglass composite fabrication techniques. Manufactures such as Nordex and GE Wind use an infusion process for blade manufacture. Other manufacturers use variations on this technique, some including carbon and wood with fiberglass in an epoxy matrix. Options also include prepreg fiberglass and vacuum-assisted resin transfer molding. Essentially each of these options are variations on the same theme: a glass-fiber reinforced polymer composite constructed through various means with differing complexity. Perhaps the largest issue with more simplistic, open-mold, wet systems are the emissions associated with the volatile organics released into the atmosphere. Preimpregnated materials and resin infusion techniques avoid the release of volatiles by containing all reaction gases. However, these contained processes have their own challenges, namely the production of thick laminates necessary for structural components becomes more difficult. As the preform resin permeability dictates the maximum laminate thickness, bleeding is required to eliminate voids and insure proper resin distribution. A unique solution to resin distribution is the use of a partially preimpregnated fiberglass. During evacuation, the dry fabric provides a path for airflow

and, once heat and pressure are applied, resin may flow into the dry region resulting in a thoroughly impregnated laminate structure. Epoxy-based composites are of greatest interest to wind turbine manufacturers because they deliver a key combination of environmental, production, and cost advantages over other resin systems. Epoxies also improve wind turbine blade composite manufacture by allowing for shorter cure cycles, increased durability, and improved surface finish. Prepreg operations further improve cost-effective operations by reducing processing cycles, and therefore manufacturing time, over wet lay-up systems. As turbine blades are approaching 60 meters and greater, infusion techniques are becoming more prevalent as the traditional resin transfer moulding injection time is too long as compared to the resin set-up time, thus limiting laminate thickness. Injection forces resin through a thicker ply stack, thus depositing the resin where in the laminate structure before gelatin occurs. Specialized epoxy resins have been developed to customize lifetimes and viscosity to tune resin performance in injection applications. Carbon fiber-reinforced load-bearing spars have recently been identified as a costeffective means for reducing weight and increasing stiffness. The use of carbon fibers in 60 meter turbine blades is estimated to result in a 38% reduction in total blade mass and a 14% decrease in cost as compared to a 100% fiberglass design. The use of carbon fibers has the added benefit of reducing the thickness of fiberglass laminate sections, further addressing the problems associated with resin wetting of thick lay-up sections. Wind turbine applications of carbon fiber may also benefit from the general trend of increasing use and decreasing cost of carbon fiber materials. Smaller blades can be made from light metals such as aluminum. Wood and canvas sails were originally used on early windmills due to their low price, availability, and ease of manufacture. These materials, however, require frequent maintenance during their lifetime. Also, wood and canvas have a relatively high drag (low aerodynamic efficiency) as compared to the force they capture. For these reasons they have been mostly replaced by solid airfoils.

Tower Typically, 2 types of towers exist: floating towers and land-based towers.

Tower height Wind velocities increase at higher altitudes due to surface aerodynamic drag (by land or water surfaces) and the viscosity of the air. The variation in velocity with altitude, called wind shear, is most dramatic near the surface.

Wind turbines generating electricity at the San Gorgonio Pass Wind Farm. Typically, in daytime the variation follows the wind profile power law, which predicts that wind speed rises proportionally to the seventh root of altitude. Doubling the altitude of a turbine, then, increases the expected wind speeds by 10% and the expected power by 34%. To avoid buckling, doubling the tower height generally requires doubling the diameter of the tower as well, increasing the amount of material by a factor of at least four. At night time, or when the atmosphere becomes stable, wind speed close to the ground usually subsides whereas at turbine hub altitude it does not decrease that much or may even increase. As a result the wind speed is higher and a turbine will produce more power than expected from the 1/7th power law: doubling the altitude may increase wind speed by 20% to 60%. A stable atmosphere is caused by radiative cooling of the surface and is common in a temperate climate: it usually occurs when there is a (partly) clear sky at night. When the (high altitude) wind is strong (a 10-meter (33 ft) wind speed higher than approximately 6 to 7 m/s (20–23 ft/s)) the stable atmosphere is disrupted because of friction turbulence and the atmosphere will turn neutral. A daytime atmosphere is either neutral (no net radiation; usually with strong winds and/or heavy clouding) or unstable (rising air because of ground heating — by the sun). Here again the 1/7th power law applies or is at least a good approximation of the wind profile. Indiana had been rated as having a wind capacity of 30,000 MW, but by raising the expected turbine height from 50

m to 70 m, the wind capacity estimate was raised to 40,000 MW, and could be double that at 100 m. For HAWTs, tower heights approximately two to three times the blade length have been found to balance material costs of the tower against better utilisation of the more expensive active components.

Foundations Wind turbines, by their nature, are very tall slender structures, this can cause a number of issues when the structural design of the foundations are considered. The foundations for a conventional engineering structure are designed mainly to transfer the vertical load (dead weight) to the ground, this generally allows for a comparatively unsophisticated arrangement to be used. However in the case of wind turbines, due to the high wind and environmental loads experienced there is a significant horizontal load that needs to be accounted for. This loading regime causes large moment loads to be applied to the foundations of a wind turbine. As a result, considerable attention needs to be given when designing the footings to ensure that the turbines are sufficiently restrained to operate efficiently. In the current Det Norske Veritas (DNV) guidelines for the design of wind turbines the angular deflection of the foundations are limited to 0.5°. Scale model tests using a 50g centrifuge are being performed at the Technical University of Denmark to test monopile foundations for offshore wind turbines at 30-50m water depth.

Chapter- 11

Wind Turbine Aerodynamics

Wind turbine blades awaiting installation in laydown yard. The wind turbine aerodynamics of a horizontal-axis wind turbine (HAWT) are not straightforward. The air flow at the blades is not the same as the airflow further away from the turbine. The very nature of the way in which energy is extracted from the air also causes air to be deflected by the turbine. In addition the aerodynamics of a wind turbine at the rotor surface exhibit phenomena that are rarely seen in other aerodynamic fields.

Axial momentum and the Betz limit

Wind turbine power coefficient

Distribution of wind speed (red) and energy generated (blue). The histogram shows measured data, while the curve is the Raleigh model distribution for the same average wind speed. Energy in fluid is contained in four different forms: gravitational potential energy, thermodynamic pressure, kinetic energy from the velocity and finally thermal energy.

Gravitational and thermal energy have a negligible effect on the energy extraction process. From a macroscopic point of view, the air flow about the wind turbine is at atmospheric pressure. If pressure is constant then only kinetic energy is extracted. However up close near the rotor itself the air velocity is constant as it passes through the rotor plane. This is because of conservation of mass. The air that passes through the rotor cannot slow down because it needs to stay out of the way of the air behind it. So at the rotor the energy is extracted by a pressure drop. The air directly behind the wind turbine is at sub-atmospheric pressure; the air in front is under greater than atmospheric pressure. It is this high pressure in front of the wind turbine that deflects some of the upstream air around the turbine. Albert Betz and Frederick W. Lanchester were the first to study this phenomenon. Betz notably determined the maximum limit to wind turbine performance. The limit is now referred to as the Betz limit. This is derived by looking at the axial momentum of the air passing through the wind turbine. As stated above some of the air is deflected away from the turbine. This causes the air passing through the rotor plane to have a smaller velocity than the free stream velocity. The ratio of this reduction to that of the air velocity far away from the wind turbine is called the axial induction factor. It is defined as below:

where: a is the axial induction factor, U1 is the wind speed far away upstream from the rotor, and U2 is the wind speed at the rotor. The first step to deriving the Betz limit is applying conservation of axial momentum. As stated above the wind loses speed after the wind turbine compared to the speed far away from the turbine. This would violate the conservation of momentum if the wind turbine was not applying a thrust force on the flow. This thrust force manifests itself through the pressure drop across the rotor. The front operates at high pressure while the back operates at low pressure. The pressure difference from the front to back causes the thrust force. The momentum lost in the turbine is balanced by the thrust force. Another equation is needed to relate the pressure difference to the velocity of the flow near the turbine. Here the Bernoulli equation is used between the field flow and the flow near the wind turbine. There is one limitation to the Bernoulli equation: the equation cannot be applied to fluid passing through the wind turbine. Instead conservation of mass is used to relate the incoming air to the outlet air. Betz used these equations and managed to solve the velocities of the flow in the far wake and near the wind turbine in terms of the far field flow and the axial induction factor. The velocities are given below as: U2 = U1(1 − a) U4 = U1(1 − 2a)

U4 is introduced here as the wind velocity in the far wake. This is important because the power extracted from the turbine is defined by the following equation. However the Betz limit is given in terms of the coefficient of power. The coefficient of power is similar to efficiency but not the same. The formula for the coefficient of power is given beneath the formula for power:

Betz was able to develop an expression for Cp in terms of the induction factors. This is done by the velocity relations being substituted into power and power is substituted into the coefficient of power definition. The relationship Betz developed is given below: Cp = 4a(1 − a)2 The Betz limit is defined by the maximum value that can be given by the above formula. This is found by taking the derivative with respect to the axial induction factor, setting it to zero and solving for the axial induction factor. Betz was able to show that the optimum axial induction factor is one third. The optimum axial induction factor was then used to find the maximum coefficient of power. This maximum coefficient is the Betz limit. Betz was able to show that the maximum coefficient of power of a wind turbine is 16/27. Airflow operating at higher thrust will cause the axial induction factor to rise above the optimum value. Higher thrust cause more air to be deflected away from the turbine. When the axial induction factor falls below the optimum value the wind turbine is not extracting all the energy it can. This reduces pressure around the turbine and allows more air to pass through the turbine, but not enough to account for lack of energy being extracted. The derivation of the Betz limit shows a simple analysis of wind turbine aerodynamics. In reality there is a lot more. A more rigorous analysis would include wake rotation, the effect of variable geometry. The effect of air foils on the flow is a major component of wind turbine aerodynamics. Within airfoils alone, the wind turbine aerodynamicist has to consider the effect of surface roughness, dynamic stall tip losses, solidity, among other problems.

Angular momentum and wake rotation The wind turbine described by Betz does not actually exist. It is merely an idealized wind turbine described as an actuator disk. It's a disk in space where fluid energy is simply extracted from the air. In the Betz turbine the energy extraction manifests itself through thrust. The equivalent turbine described by Betz would be a horizontal propeller type operating with infinite blades at infinite tip speed ratios and no losses. The tip speed ratio is ratio of the speed of the tip relative to the free stream flow. This turbine is not too far

from actual wind turbines. Actual turbines are rotating blades. They typically operate at high tip speed ratios. At high tip speed ratios three blades are sufficient to interact with all the air passing through the rotor plane. Actual turbines still produce considerable thrust forces. One key difference between actual turbines and the actuator disk, is that the energy is extracted through torque. The wind imparts a torque on the wind turbine, thrust is a necessary by-product of torque. Newtonian physics dictates that for every action there is an equal and opposite reaction. If the wind imparts a torque on the blades then the blades must be imparting a torque on the wind. This torque would then cause the flow to rotate. Thus the flow in the wake has two components, axial and tangential. This tangential flow is referred to as wake rotation. Torque is necessary for energy extraction. However wake rotation is considered a loss. Accelerating the flow in the tangential direction increases the absolute velocity. This in turn increases the amount of kinetic energy in the near wake. This rotational energy is not dissipated in any form that would allow for a greater pressure drop (Energy extraction). Thus any rotational energy in the wake is energy that is lost and unavailable. This loss is minimized by allowing the rotor to rotate very quickly. To the observer it may seem like the rotor is not moving fast; however, it is common for the tips to be moving through the air at 6 times the speed of the free stream. Newtonian mechanics defines power as torque multiplied by the rotational speed. The same amount of power can be extracted by allowing the rotor to rotate faster and produce less torque. Less torque means that there is less wake rotation. Less wake rotation means there is more energy available to extract.

Blade Element and Momentum Theory The simplest model for horizontal axis wind turbine (HAWT) aerodynamics is Blade Element Momentum (BEM) theory. The theory is based on the assumption that the flow at a given annulus does not affect the flow at adjacent annuli. This allows the rotor blade to be analyzed in sections, where the resulting forces are summed over all sections to get the overall forces of the rotor. The theory uses both axial and angular momentum balances to determine the flow and the resulting forces at the blade. The momentum equations for the far field flow dictate that the thrust and torque will induce a secondary flow in the approaching wind. This in turn affects the flow geometry at the blade. The blade itself is the source of these thrust and torque forces. The force response of the blades is governed by the geometry of the flow, or better known as the angle of attack. Refer to the Airfoil article for more information on how airfoils create lift and drag forces at various angles of attack. This interplay between the far field momentum balances and the local blade forces requires one to solve the momentum equations and the airfoil equations simultaneously. Typically computers and numerical methods are employed to solve these models.

There is a lot of variation between different version of BEM theory. First, one can consider the effect of wake rotation or not. Second, one can go further and consider the pressure drop induced in wake rotation. Third, the tangential induction factors can be solved with a momentum equation, an energy balance or orthognal geometric constraint; the latter a result of Biot-Savart law in vortex methods. These all lead to different set of equations that need to be solved. The simplest and most widely used equations are those that consider wake rotation with the momentum equation but ignore the pressure drop from wake rotation. Those equations are given below. a is the axial component of the induced flow, a' is the tangential component of the induced flow. σ is the solidity of the rotor, φ is the local inflow angle. Cn and Ct are the coefficient of normal force and the coefficient of tangential force respectively. Both these coefficients are defined with the resulting lift and drag coefficients of the airfoil:

Corrections to Blade Element Momentum theory Blade Element Momentum (BEM) theory alone fails to accurately represent the true physics of real wind turbines. Two major shortcomings are the effect of discrete number of blades and far field effects when the turbine is heavily loaded. Secondary shortcomings come from dealing with transient effects like dynamic stall, rotational effects like coriolis and centrifugal pumping, finally geometric effects that arise from coned and yawed rotors. The current state of the art in BEM uses corrections to deal with the major shortcoming. These corrections are discussed below. There is as yet no accepted treatment for the secondary shortcomings. These areas remain a highly active area of research in wind turbine aerodynamics. The effect of the discrete number of blades is dealt with by applying the Prandtl tip loss factor. The most common form of this factor is given below where B is the number of blades, R is the outer radius and r is the local radius. The definition of F is based on actuator disk models and not directly applicable to BEM. However the most common application multiplies induced velocity term by F in the momentum equations. As in the momentum equation there are many variations for applying F, some argue that the mass flow should be corrected in either the axial equation, or both axial and tangential equations. Others have suggested a second tip loss term to account for the reduced blade forces at the tip. Shown below are the above momentum equations with the most common application of 'F':

The typical momentum theory applied in BEM is only effective for axial induction factors up to 0.4 (thrust coefficient of 0.96). Beyond this point the wake collapses and turbulent mixing occurs. This state is highly transient and largely unpredictable by theoretical means. Accordingly, several empirical relations have been developed. As the usual case there are several version, however a simple one that is commonly used is a linear curve fit given below, with ac = 0.2. The turbulent wake function given excludes the tip loss function, however the tip loss is applied simply by multiplying the resulting axial induction by the tip loss function. when a > ac Please note the following: do not confuse CT and Ct, the first one is the thrust coefficient of the rotor, which is the one which should be corrected for high rotor loading (i.e. for high values of a), whilst the second one (ct) is the tangential aerodynamic coefficient of an individual blade element, which is given by the aerodynamic lift and drag coefficients.

Other Methods of Aerodynamic Modelling BEM is widely used due to its simplicity and overall accuracy, but its originating assumptions limit its use when the rotor disk is yawed, or when other non-axisymmetric effects (like the rotor wake) influence the flow. Limited success at improving predictive accuracy has been made using computational fluid dynamics (CFD) solvers based on Reynolds Averaged Navier Stokes (RANS) and other similar three-dimensional models such as free vortex methods. These are very computationally-intensive simulations to perform for several reasons. First, the solver must accurately model the far-field flow conditions, which can extend several rotor diameters up- and down-stream and include atmospheric boundary layer turbulence, while at the same time resolving the small-scale boundary-layer flow conditions at the blades' surface (necessary to capture blade stall). In addition, many CFD solvers have difficulty meshing parts that move and deform, such as the rotor blades. Finally, there are many dynamic flow phenomena that are not easily modelled by RANS, such as dynamic stall and tower shadow. Due to the computational complexity, it is not currently practical to use these advanced methods for wind turbine design, though research continues in these and other areas related to helicopter and wind turbine aerodynamics. Free vortex models (FVM) and Lagrangian particle vortex methods (LPVM) are both active areas of research that seek to increase modelling accuracy by accounting for more of the three-dimensional and unsteady flow effects than either BEM or RANS. FVM is

similar to lifting line theory in that it assumes that the wind turbine rotor is shedding either a continuous vortex filament from the blade tips (and often the root), or a continuous vortex sheet from the blades' trailing edges. LPVM can use a variety of methods to introduce vorticity into the wake. Biot-Savart summation is used to determine the induced flow field of these wake vorticies' circulations, allowing for better approximations of the local flow over the rotor blades. These methods have largely confirmed much of the applicability of BEM and shed insight into the structure of wind turbine wakes. FVM has limitations due to its origin in potential flow theory, such as not explicitly modelling model viscous behavior, though LPVM is a fully viscous method. LPVM is more computationally intensive than either FVM or RANS, and FVM still relies on blade element theory for the blade forces.

Chapter- 12

Wind Farm

Whitelee Wind Farm in Scotland.

The Meyersdale Wind Project in southern Pennsylvania A wind farm is a group of wind turbines in the same location used for production of electric power. Individual turbines are interconnected with a medium voltage (usually 34.5 kV) power collection system and communications network. At a substation, this medium-voltage electrical current is increased in voltage with a transformer for connection to the high voltage transmission system. A large wind farm may consist of a few dozen to several hundred individual wind turbines, and cover an extended area of hundreds of square miles, but the land between the turbines may be used for agricultural or other purposes. A wind farm may be located off-shore to take advantage of strong winds blowing over the surface of an ocean or lake. The world's first wind farm – consisting of 20 wind turbines rated at 30 kilowatts each – was installed on the shoulder of Crotched Mountain in southern New Hampshire in December, 1980. The Roscoe Wind Farm (780 MW) in the state of Texas, United States, is currently the world's largest wind farm. The Whitelee Wind Farm is the largest wind farm in Europe, with a total capacity of 322 MW. The Thanet Offshore Wind Project in United Kingdom is the largest offshore wind farm in the world at 300 MW.

Location planning A quantity called the Wind Power Density (WPD) is used to select locations for wind energy development. The WPD is a calculation relating to the effective force of the wind at a particular location, frequently expressed in term of the elevation above ground level over a period of time. It takes into account velocity and mass. Color-coded maps are

prepared for a particular area describing, for example, "Mean Annual Power Density, at 50 Meters." The results of the above calculation are used in an index developed by the National Renewable Energy Lab and referred to as "NREL CLASS." The larger the WPD calculation the higher it is rated by class. Wind farm siting can be highly controversial, particularly when sites are picturesque or environmentally sensitive. Related factors may include having substantial bird life, or requiring roads to be built through pristine areas. The areas where wind farms are built are generally non-residential, due to noise concerns and setback requirements. Access to the power grid is also a factor. The further from the power grid, the more transmission lines will be needed to span from the farm directly to the power grid. Alternatively, transformers will have to be built on the premises, depending upon the types of turbines being used.

Wind speed

Map of available wind power over the United States. Color codes indicate wind power density class. As a general rule, wind generators are practical if windspeed is 10 mph (16 km/h or 4.5 m/s) or greater. An ideal location would have a near constant flow of non-turbulent

wind throughout the year, with a minimum likelihood of sudden powerful bursts of wind. An important factor of turbine siting is also access to local demand or transmission capacity. Usually sites are preselected on basis of a wind atlas, and validated with wind measurements. Meteorological wind data alone is usually not sufficient for accurate siting of a large wind power project. Collection of site specific data for wind speed and direction is crucial to determining site potential. Local winds are often monitored for a year or more, and detailed wind maps constructed before wind generators are installed. To collect wind data, a meteorological tower is installed with instruments at various heights along the tower. All towers include anemometers to determine the wind speed and wind vanes to determine the direction. The towers generally vary in height from 30 to 60 meters. The towers primarily are guyed steel-pipe structures which are used for one to two years to collect data and then are disassembled and removed. Data is collected by a data-logging device, which stores and transmits data for analysis. The siting of turbines during installation (a process known as micro-siting) because a difference of 30 m can nearly double energy production. For smaller installations where such data collection is too expensive or time consuming, the normal way that developers prospect for wind-power sites is to look for trees or vegetation that are permanently "cast" or deformed by the prevailing winds. Another way is to use a wind-speed survey map, or historical data from a nearby meteorological station, although these methods are less reliable.

Altitude The wind blows faster at higher altitudes because of the reduced influence of drag. The increase in velocity with altitude is most dramatic near the surface and is affected by topography, surface roughness, and upwind obstacles such as trees or buildings. Typically, the increase of wind speeds with increasing height follows a wind profile power law, which predicts that wind speed rises proportionally to the seventh root of altitude. Doubling the altitude of a turbine, then, increases the expected wind speeds by 10% and the expected power by 34%.

Wind park effect The "wind park effect" refers to the loss of output due to mutual interference among turbines. Wind farms have many turbines, and each extracts some of the energy of the wind. Where land area is sufficient, turbines are spaced three to five rotor diameters apart perpendicular to the prevailing wind, and five to ten rotor diameters apart in the direction of the prevailing wind, to minimize efficiency loss. The loss can be as low as 2% of the combined "nameplate" rating of the turbines. In a large wind park, due to "multifractal" effects among individual rotors, the behaviour deviates significantly from Kolmogorov's turbulence scaling for individual turbines.

Environmental and aesthetic impacts

Livestock grazing near wind turbines. Compared to the environmental effects of traditional energy sources, the environmental effects of wind power upon greenhouse gases are minor; however, there are other adverse impacts of wind power including bird mortality. Wind power consumes no fuel, and emits no air pollution, unlike fossil fuel power sources. The energy consumed to manufacture and transport the materials used to build a wind power plant is equal to the new energy produced by the plant within a few months of operation. Garrett Gross, a scientist from the University of Missouri–Kansas City, states, "The impact made on the environment is very little when compared to what is gained." While a wind farm may cover a large area of land, many land uses such as agriculture are compatible. Danger to birds and bats has been a concern in many locations. Some dismiss the number of birds killed by wind turbines as negligible when compared to the number that die as a result of other human activities, and especially when considering the adverse environmental impacts of using non-clean power sources. Others strongly disagree about the placement of wind farms. New evidence suggests that the critically endangered California Condor is being killed at the Tehachapi Pass wind farm in Southern California. Bat species appear to be at risk during key movement periods. Almost nothing is known about current populations of these species and the impact on bat numbers as a result of

mortality at windpower locations. Offshore wind sites 10 km or more from shore do not interact with bat populations, but researchers are concerned if there are nearby bird colonies. Aesthetics have also been an issue in some areas. In the USA, the Massachusetts Cape Wind project was delayed for years chiefly because of nearby residents' aesthetic concerns. In the UK, repeated opinion surveys have shown that more than 70% of people either like, or do not mind, the visual impact. According to a town councillor in Ardrossan, Scotland, the overwhelming majority of locals believe that the Ardrossan Wind Farm has enhanced the area. They say the turbines are impressive looking and bring a calming effect to the town.

Effect on power grid Utility-scale wind farms must have access to transmission lines to transport energy. The wind farm developer may be obligated to install extra equipment or control systems in the wind farm to meet the technical standards set by the operator of a transmission line. The company or person that develops the wind farm can then sell the power on the grid through the transmission lines and ultimately chooses whether to hold on to the rights or sell the farm or parts of it to big business like GE, for example.

Types Onshore Onshore turbine installations in hilly or mountainous regions tend to be on ridgelines generally three kilometers or more inland from the nearest shoreline. This is done to exploit the so-called topographic acceleration as the wind accelerates over a ridge. The additional wind speeds gained in this way make a significant difference to the amount of energy that is produced. Great attention must be paid to the exact positions of the turbines (a process known as micro-siting) because a difference of 30 m can sometimes mean a doubling in output.

Offshore

Offshore wind turbines near Copenhagen. Offshore wind turbines are less obtrusive than turbines on land, as their apparent size and noise is mitigated by distance. Because water has less surface roughness than land (especially deeper water), the average wind speed is usually considerably higher over open water. Capacity factors (utilisation rates) are considerably higher than for onshore and nearshore locations. Transporting large wind turbine components (tower sections, nacelles, and blades) is much easier over water than on land, because ships and barges can handle large loads more easily than trucks/lorries or trains. On land, large goods vehicles must negotiate bends on roadways, which fixes the maximum length of a wind turbine blade that can move from point to point on the road network; no such limitation exists for transport on open water. Offshore wind turbines will probably continue to be the largest turbines in operation, since the high fixed costs of the installation are spread over more energy production, reducing the average cost. Turbine components (rotor blades, tower sections) can be transported by barge, making large parts easier to transport offshore than on land, where turn clearances and underpass clearances of available roads limit the size of turbine components that can be moved by truck. Similarly, large construction cranes are difficult to move to remote wind farms on land, but crane vessels easily move over water. Offshore wind farms can be large. The Horns Rev array has 80 turbines and as of September 2010, the Thanet Wind Farm is the world's largest off-shore installation with 100 turbines. Several European and two Asian countries have offshore wind farms, which supply local clean, renewable energy. Although land-based turbines are prevalent in the United States, there are no offshore wind farms in U.S. waters. However, projects are under development in wind-rich areas of the East Coast, Great Lakes, and Pacific coast.

Fixed-bottom, foundation-based tower technologies In areas with extended shallow continental shelves, water not deeper than 40 m (130 feet), windy but without Category 4 or higher storms, fixed-bottom turbines are now available and practical to install. As of 2009, the economic feasibility of shallow-water offshore wind technologies is well understood. With empirical data obtained from fixedbottom installations off many countries for over a decade now, representative costs are well understood. Shallow-water turbines cost between 2.4 and 3 million United States dollars per megawatt to install, according to the World Energy Council. Offshore installation monopile wind turbines are generally more expensive than onshore installations but this depends on the attributes of the site. Offshore fixed-bottom towers are generally taller than onshore towers once the submerged height is included. Offshore foundations may be more expensive to build. Power transmission from offshore turbines is through undersea cable, often using high voltage direct current operation if significant

distance is to be covered. Offshore saltwater environments also raise maintenance costs by corroding the towers, but fresh-water locations such as the Great Lakes do not. Repairs and maintenance are usually more costly than on onshore turbines, motivating operators to reduce the number of wind turbines for a given total power by installing the largest available units. An example is Belgium's Thorntonbank Wind Farm with construction underway in 2008, featuring 5 MW wind turbines from REpower, which were among the largest wind turbines in the world at the time. Offshore saltwater wind turbines are outfitted with extensive corrosion protection measures including coatings and cathodic protection, which may not be required in fresh water locations.

Examples The United Kingdom plans to use offshore wind turbines to generate enough power to light every home in the U.K. by 2020, and as of 2010 the United Kingdom has by far the largest capacity of offshore wind farms with 1.3 GW, more than the rest of the world combined. The province of Ontario in Canada is pursuing several proposed nearshore locations in the Great Lakes, including Trillium Power Wind 1 approximately 20 km from shore and over 400 MW in size. Other Canadian projects include one on the Pacific west coast.

REpower 5MW wind turbines D4 (nearest) to D1 on the Thornton Bank As of 2008, Europe leads the world in development of fixed-bottom offshore wind power, due to strong wind resources and shallow water in the North Sea and the Baltic Sea, and limitations on suitable locations on land due to dense populations and existing developments. Denmark installed the first offshore wind farms, and for years was the world leader in offshore wind power until the United Kingdom gained the lead in October, 2008, with 590 MW of nameplate capacity installed. The United Kingdom planned to build much more extensive offshore wind farms by 2020. Other large markets for wind power, including the United States and China focused first on developing their on-land wind resources where construction costs are lower (such as in the Great Plains of the U.S., and the similarly wind-swept steppes of Xinjiang and Inner Mongolia in China), but population centers along coastlines in many parts of the world are close to offshore

wind resources, which would reduce transmission costs. In 2010, China commissioned the Donghai Bridge Wind Farm. On 21 December 2007, Q7 (later renamed as Princess Amalia Wind Farm) exported first power to the Dutch grid, which was a milestone for the Dutch offshore wind industry. The 120 MW offshore wind farm with a construction budget of €383 million was the first to be financed by a nonrecourse loan (project finance). The project comprises 60 Vestas V80-2MW wind turbines. Each turbine's tower rests on a monopile foundation to a depth of between 18–23 meters at a distance of about 23 km off the Dutch coast.

Deep-water, floating turbine technologies

The world’s first full-scale floating wind turbine, Hywind, being assembled near Stavanger, Norway, before deployment in the North Sea. New deep-water, floating-turbine technologies are only recently beginning to be deployed. The first large-capacity floating wind turbine is the Hywind, a 2.3 MW turbine mounted on a 120-meter-tall tower in 220-meter-deep water in the North Sea off of Stavanger, Norway. It will be tested for two years. The unit was constructed during the summer of 2009 and became operational in September, 2009. Until 2003, existing offshore wind turbine technology deployments had been limited to water depths of 30-meters utilizing fixed-bottom technology, which necessarily limited deployments to the near-coastal sea surface.

Worldwide deep-water wind resources are extremely abundant in deep-water areas with depths up to 600 meters, which are thought to best facilitate transmission of the generated electric power to shore communities. The U.S. deep-water wind resource is second only to China. Although limited early conceptual work on deep-water floating turbine technologies was done in 1972, it was not until the mid 1990’s, after the onshore, foundation-tower, commercial wind industry was well established, that design of deepwater technologies was taken up again by the mainstream research community. Assessment the offshore wind resource is undertaken by offshore meteorological masts, computer modelling or satellite measurements e.g. WindScan

Airborne Airborne wind turbines would eliminate the cost of towers and might also be flown in high speed winds at high altitude. No such systems are in commercial operation.

Wind farm capacity

Brazos Wind Farm in the plains of West Texas

Albania 1. Vlorë Wind Farm (500 MW) - 250 turbines 2. Kryevidhi Wind Farm (150 MW) - 75 turbines

Antarctic •

A three-turbine wind farm opened in early 2010 on Ross Island, providing all the power for New Zealand's Antarctic programme as well some electricity to America's McMurdo Station.

Australia There are a number of Wind farms currently operating in Australia. Some of the largest wind farms in Australia are: • • • • • • •

Lake Bonney Wind Farm (SA) - 239.5 MW Woolnorth Wind Farm (TAS) - 140 MW Brown Hill Range Wind Farm (Hallett, SA) - 94.5 MW Wattle Point (SA) - 90.75 MW Alinta/Walkaway (WA) - 90 MW Emu Downs Wind Farm (WA) - 80 MW Mount Millar Wind Farm (SA) - 70 MW

Wind farms currently under construction are: •

Collgar Wind Farm (WA) - 206 MW

Barbados During the 1980s the country of Barbados experimented with the construction of a wind turbine at the Lamberts, St. Lucy area of Barbados. A lone tower was built for testing purposes after it was determined that this part of the island had the best potential for the usage of wind power. The Barbados Light and Power Company (BL&P) Co. met opposition due to concerns by local residents about noise concerns. Attempts have been made to replace the current abandoned wind turbine, but opposition continues to mount against the development of the 11 additional turbines for the site which could provide an estimated roughly 10 MW of energy. The Government of Barbados has also reiterated its commitment to developing wind power but has been unsuccessful to date in the last five years.

Brazil 1. 2. 3. 4. 5. 6. 7. 8.

São Gonçalo do Amarante/CE (10 Turbines) Prainha de Aquiraz-CE (20 Turbines) Mucuripe-CE (4 Turbines) Fernando de Noronha Island-PE 1&2 (2 Turbines) Olinda-PE 1&2 (2 Turbines) Morro do Camelinho-MG (4 Turbines) Palmas-PR (5 Turbines) Osório-RS (75 Turbines)

9. Rio do Fogo - RN (61 turbines)

Canada

Huron Wind farm in Tiverton, Ontario, Canada, includes five Vestas V80s installed in November 2002 The total capacity of all wind farms in Canada is 2,369 MW as of January, 2009. There are currently no operating wind farms in Nunavut (territory) or the Northwest Territories. The largest wind farms in Canada are: 1. Melancthon EcoPower Centre - Shelburne, Ontario, 199.5 MW 2. Wolfe Island Wind Project - Kingston, Ontario, 197.8 MW 3. Prince Project — Phase I & II - Sault Ste. Marie, Ontario, 189 MW 4. Enbridge Ontario Wind Farm - Bruce County, Ontario, 181 MW 5. Murdochville Project; Phase I & II & III - Murdochville, Quebec, 162 MW 6. Centennial Wind Power Facility - Swift Current, Saskatchewan, 149.4 MW 7. Carleton Wind Farm - Carleton, Quebec, 109.5 MW 8. Bear Mountain Wind Park - Dawson Creek, British Columbia, 102 MW 9. Port Alma Wind Farm - Chatham-Kent, Ontario 101 MW 10. Anse-à-Valleau Wind Farm - Gaspé, Quebec, 100.5 MW

China Having more than doubled its installed wind power capacity each year from 2005–2009, China grew its wind power faster on a percentage basis than any other large country. With wind power investment of US$600 million in 2006 and total installed capacity of 2300 MW, China was the eighth largest wind-power producer in the world. At the end of 2007, China had increased its installed capacity to just over 6000 MW to move into fifth place globally. The Chinese wind industry reached the official target of 5 GW for the

year 2010 three years early, so policymakers doubled the target to 10 GW; however, by the end of 2009 China had already reached 25 GW, having installed more new wind power generating capacity in 2009 than any other country. Chinese analysts estimate that the total potential wind power generating capacity in China exceeds 1000 GW. Large wind resources are in the northern part of the country, including Xinjiang and Inner Mongolia, with vast windswept plains constituting China's "wind belt" similar to the Great Plains of the United States and Canada. Wind power development is increasing incomes and tourism in these formerly remote regions.

European Union

A wind farm in a mountainous area in Galicia, Spain

Wind farm in Lower Saxony, Germany Germany has the second largest number of wind farms in the world after the United States. Its installed capacity was 20,622 MW as of December 2006. The second country in capacity was Spain with 11,615 MW. The third was Denmark with 3,136 MW. Italy was in the fourth position, with 2,123 MW. In May 2006, operational wind farms in the UK comprised an installed capacity of 1,693 MW, in Portugal 1188 MW, in France 918 MW and in Ireland 1255 MW as of the 1st March 2009. A 322 MW wind farm Whitelee, south of Glasgow, Scotland, is the biggest wind farm in Europe, 55 km sq.. The €350 million farm was built for Scottish Power and the 140 wind turbines were delivered by Siemens. In 2006, the British government gave planning consent for the world's largest offshore wind farm, the 'London Array'. It is to be built 12 miles off of the Kent coast and will include 341 turbines. A small farm of eight turbines has been erected at North Pickenham run by Enertrag UK Ltd with two smaller units at nearby Swaffham run by Ecotricity. An important limiting factor of wind power is variable power generated by wind farms. In most locations the wind blows only part of the time, which means that there has to be back-up capacity of conventional generating capacity to cover periods that the wind is not blowing. To address this issue it has been proposed to create a "supergrid" to connect national grids together across western Europe, ranging from Denmark across the southern North Sea to England and the Celtic Sea to Ireland, and further south to France and Spain especially in Higueruela which was considered for some time the biggest wind

farm in the world. The idea is that by the time a low pressure area has moved away from Denmark to the Baltic Sea the next low appears off the coast of Ireland. Therefore, while it is true that the wind is not blowing everywhere all of the time, it will always be blowing somewhere. Such a supergrid would therefore reduce the need for backup capacity.

India

A wind farm in Aralvaimozhy, Tamil Nadu, India At the end of October 2009, India had 11806.69 MW of wind generating capacity and is the fifth largest market in the world. Indian Wind Energy Association has estimated that with the current level of technology, the ‘on-shore’ potential for utilization of wind energy for electricity generation is of the order of 65,000 MW. There are about a dozen wind pumps of various designs providing water for agriculture, afforestation, and domestic purposes, all scattered over the country. The wind farms are predominantly present in the states of Tamil Nadu, Maharashtra, Karnataka and Gujarat. Other states like Andhra Pradesh, Rajasthan, Kerala and Madhya Pradesh have a very good potential.

Iran

Manjeel,Iran • • •

Japan

Manjil and Rudbar Wind Farm (100.8 MW - 171 turbines) Binalood wind farm (28.2 MW - 43 turbines) "Under construction" Jarandaq wind farm (60 MW - 40 turbines) "Being studied"

Wakamatsu wind farm, Kitakyushu, Japan The Wakamatsu ward Hibikinada Wind Farm in Kitakyushu is far from the scenic areas of Wakamatsu, and on windy reclaimed land. Asahi Shimbun reported on May 18, 2005, that many utilities have put limits on the amount of wind power they will allow, because of lack of confidence in their ability to deal with the variable output. A partial list of wind farms in Japan include: • • • •

Hibikinada Wind Farm (10 turbines) Aoyama Plateau Wind Farm (32 turbines) Nunobiki Plateau Wind Farm (33 turbines) Seto Wind Farm (11 turbines)

A number of smaller projects are run by the Japan Wind Development Company, LTD.

Morocco 1. 2. 3. 4.

Tarfaya Wind Farm (200 MW) "Under construction" Tangier Wind Farm (140 MW - 165 turbines) "Under construction" Amogdoul Farm (60 MW) Touahar Farm (60 MW) "Under construction"

5. Koudia Al Baida Farm (50 MW - 84 turbines)

New Zealand New Zealand is located in the northern latitudes of the 'roaring 40s' — an abundant wind energy resource. The Brooklyn Wind Turbine was installed on the top of a hill in Brooklyn, Wellington in March 1993 as part of a research project commissioned by the now defunct Electricity Corporation of New Zealand. Later in 1996, Wairarapa Electricity (became part of Genesis Energy in 1999) built the Hau Nui Wind Farm, New Zealand's first wind farm, south east of Martinborough on the coastal road to White Rock. Meridian Energy recently applied for, and obtained with conditions, resource consent to build a consignment of wind farms in the rural Makara Hill area west of Wellington. Meridian Energy have finished the Te Apiti Wind Farm on the Ruahine Ranges. It can be seen clearly at Ashhurst near Palmerston North. The Te Rere Hau Wind Farm is under construction nearby. Meridian Energy's White Hill wind farm at Mossburn in the South Island, reached full capacity in 2007. TrustPower purchased the Tararua wind farm, located on the Tararua Ranges behind Palmerston North, from Tararua Wind Power Limited. As of September 2007 this was New Zealand's largest wind farm, and the largest in the southern hemisphere, with an installed capacity of 161MW, half of the country's total installed capacity. Applications for resource consent have been submitted for several new wind farms, with a total potential capacity of 1900MW as of late 2007.

Philippines

Bangui Windfarm, Philippines

The NorthWind Bangui Bay Project, in Bangui, Ilocos Norte is the first wind farm in the Philippines. It consists of wind turbines on-shore facing the South China Sea. The project is considered to be the biggest in Southeast Asia. The project sells electricity to the Ilocos Norte Electric Cooperative (INEC) and provides 40% of the power requirements of Ilocos Norte via Transco Laoag.

South Africa The first commercial wind farm in South Africa was opened on the 23rd of May 2008, near Darling in the Western Cape. The first phase consists of four 1.3MW turbines supplied by Fuhrlander, Germany. The total power generated estimated at 5.2MW will be put into the national grid at 66kV. It has taken the developer Herman Oelsner 10 years to achieve his dream of being the first private wind farm in South Africa. There has been serious concerns regarding environmental and aviation matters some of which are still under investigation. Fuhrlaender will be responsible for the maintenance and upkeep of the wind farm until 2011 with the assistance of locally trained technicians. Additionally, Klipheuwel wind farm, the first wind farm in sub-Saharan Africa, comprises three turbines – a Vestas V66 with 1.75 MW output, a Vestas V47 with 660 kW output and a Jeumont J48 with 750 kW output, giving a total output of almost 3.2 MW.

United States The United States is the leading country in installed capacity and produced windpower in the world. After pioneering windpower in the 1980s, it surpassed Germany again in 2008. The American Wind Energy Association stated the United States had 21,000 MW of wind energy capacity at the end of that year. A total of 8,538 MW were added in 2008. At the end of March 2008, the United States wind power capacity was 18,302 MW, enough to serve 4.9 million average households. Currently, the largest wind farm in the US and the world is the Roscoe Wind Farm (780 MW) in Texas. Prior to this, the largest wind farm was Florida Power & Light's 735 MW Horse Hollow Wind Energy Center, located in Taylor County, Texas. Other larger projects have been proposed or are under development. Three large California wind "farms" developed in the 1980s at three major mountain passes are collections of dozens of individual wind farms. The California farms have many different owners and turbine types. They have been constructed, retrofitted and occasionally dismantled since they were first installed in late 1982. As of 2005, all three of these areas are seeing renewed growth. Older and smaller wind turbines are being replaced with much larger, more efficient models. Some of the workhorses of the past were only 65 kilowatts (kW) in capacity or even smaller, though some were several hundred kW. Today, a few models approach 6,000 kW (6 MW). Non-functional turbines are also being returned to service.

The majority of the San Gorgonio Pass Wind Farm as viewed from the San Jacinto Mountains to the south. (The farm continues over the hills to the north along California State Route 62 and is not visible from this vantagepoint). The layout includes a variety of large modern and older smaller turbine designs Although California has some of the earliest and largest wind farms in the U.S., the state does not have many commercially viable wind farm sites onshore. Much of the Southwest is not much better, although there are some significant exceptions. The Great Plains states have an abundance of suitable sites for wind energy development. The region has become the major supplier of U.S. wind power. Texas (located in the South) is the leading wind power state in the U.S., followed by Iowa in the Midwest. The Pacific Northwest and the Northeast have many excellent sites as well. In contrast, the Southeast generally has few wind energy resources. A recent study has found that an off-shore region of the Georgia coast may prove to be a commercially viable wind power resource. The Appalachian Mountains may also provide promising areas for wind turbine installation.

Chapter- 13

Windmill

This Dutch windmill in Amsterdam was built in 1757 and is identified as De 1100 Roe. It is a smock mill of the type called by the Dutch a grondzeiler ("ground sailer"), since the sails almost reach the ground.

A windmill is a machine which converts the energy of wind into rotational motion by means of adjustable vanes called sails. The main use is for a grinding mill powered by the wind, reducing a solid or coarse substance into pulp or minute grains, by crushing, grinding, or pressing. Windmills have also provided energy to sawmills, paper mills, hammermills, and windpumps for obtaining fresh water from underground or for drainage (especially of land below sea level).

History

A diagram of the windwheel of Heron of Alexandria, 1st century, C.E. The windwheel of the Greek engineer Heron of Alexandria in the 1st century marks one of the first known instances of wind powering a machine in history. Another early

example of a wind-driven wheel was the prayer wheel, which was used in ancient Tibet and China since the 4th century B.C..

Vertical-axis windmills

The Persian, vertical-axis windmill The first practical windmills were the vertical-axis windmills invented in eastern Persia (what is now Afghanistan), as recorded by the Persian geographer Estakhri in the 9th century. The authenticity of an earlier anecdote of a windmill involving the second caliph Umar (AD 634–644) is questioned on the grounds that it appears in a 10th-century document. Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind grain or draw up water, and were quite different from the later European horizontal-axis versions. Windmills were in widespread use across the Middle East and Central Asia, and later spread to China and India from there. Some popular treatments of the subject have speculated that, by the 9th century, the Persian-style vertical-axle mills spread to Europe through Al-Andalus (Islamic Spain). This has been denied by the specialist of medieval European technology, Lynn White Jr., who points out that there is no evidence (archaeological or documentary) that the Afghanistan-style vertical-axle windmill spread as far west as Al-Andalus, and notes that "all Iberian windmills rotated on horizontal axles until towards the middle of the fifteenth century." Another historian of technology, Michael Jonathan Taunton Lewis, suggested an alternative route of transmission for the Islamic horizontal-shaft windmill, with its diffusion to the Byzantine Empire and its subsequent transformation into the verticalshaft windmill in Europe. Late medieval vertical-axle windmills similar to the Islamic/Persian design can be found along this route, particularly in Karpathos, Greece,

and Kandia, Crete. The Crusades has also been suggested as another possible route of transmission, though in the sense of "stimulus diffusion," where the idea was diffused rather than the technology itself. However, the debate about whether the European vertical-shaft windmill evolved from the Islamic horizontal-shaft windmill or was an independent development remains unresolved.

Horizontal-axis windmills

Fixed windmills Fixed windmills, oriented to the prevailing wind were extensively used in the Cyclades islands of Greece. The economies of power and transport allowed the use of these 'offshore' mills for grinding grain transported from the mainland and flour returned. A 1/10th share of the flour was paid to the miller in return for his service. This type would mount triangular sails when in operation. A similar type of vertical-shaft windmill with rectangle blades, used for irrigation, can also be found in 13th-century China (during the Jurchen Jin Dynasty in the north), introduced by the travels of Yelü Chucai to Turkestan in 1219.

Windmills that turn to face the wind

Diagram of the smock mill at Meopham, Kent which uses a fantail and Cubitt's patent sails In northwestern Europe, the horizontal-axle or vertical windmill (so called due to the dimension of the movement of its sails) dates from the last quarter of the 12th century in the triangle of northern France, eastern England and Flanders. Lynn White Jr. claims that the first certain reference to the European horizontal-axle windmill is dated to 1185 in Weedley, Yorkshire. (This predates Joseph Needham's claim that the earliest known reference is from the 1191 chronicle of Jocelin of Brakelond, in which a Dean Herbert of East Anglia supposedly competed with the mills of the abbey of Bury St Edmunds). These earliest mills were used to grind cereals. The evidence at present is that the earliest

type was the sunk post mill, so named because of the large upright post on which the mill's main structure (the "body" or "buck") is balanced. By mounting the body this way, the mill is able to rotate to face the wind direction; an essential requirement for windmills to operate economically in North-Western Europe, where wind directions are variable. By the end of the thirteenth century the masonry tower mill, on which only the timber cap rotated rather than the whole body of the mill, had been introduced. In the Netherlands these stone towerlike mills are called "round or eight-sided stone stage mills, groundsailers (windmills with sails reaching almost down to the ground), mound mills, etc." (Dutch: ronde/achtkante stenen stelling molens, grond-zeilers, beltmolens, etc.). Dutch tower mills ("torenmolens") are always cylindrical (such as atop castle or city wall towers). Because only the cap of the tower mill needed to be turned the main structure could be made much taller, allowing the sails to be made longer, which enabled them to provide useful work even in low winds. Such mills often have a small auxiliary set of sails called a fantail at the rear of the cap and at right angles to the sails; this rotates the cap through gearing so that the sails face into the wind. Windmills were often built on top of castle towers or city walls, and were a unique part of a number of fortifications in New France, such as at Fort Senneville. The familiar lattice style of windmill sails (also called "common" sails) allowed the miller to attach sailcloths to the sails (while applying a brake). Trimming the sails allowed the windmill to turn at near the optimal speed in a large range of wind velocities. The fantail, a small windmill mounted at right angles to the main sails which automatically turns the heavy cap and main sails into the wind, was invented by Edmund Lee in 1745, in England. The smock mill is a later variation of the tower mill, constructed of timber and originally developed in the sixteenth century for land drainage. With some subsequent development mills became versatile in windy regions for all kind of industry, most notably grain grinding mills, sawmills (late 16th century), threshing, and, by applying scoop wheels, Archimedes screws, and piston pumps, pumping water either for land drainage or for water supply. In 1772, Scottish millwright, Andrew Meikle developed the spring sail made from a series of connected parallel shutters that could be opened or closed according to windspeed. To do this the sails had to be stopped, but the sails also incorporated a spring which allowed the shutters to open a little more to prevent damage if the wind suddenly strengthens. In 1789, Stephen Hooper invented the roller reefing sail, which allowed automatic adjustment of the sail whilst in motion. In 1807, William Cubitt a Norfolk engineer, invented a new type of sail, known there on as patent sails, using a chain and a rod that passed through the centre of the windshaft. These sails had the shutters of Meikle's spring sails and the automatic adjustment of Hooper's roller reefing sails. This became the basis of self-regulating sails. These avoided the constant supervision that had been required up till then. By the 19th Century there were some 10,000 corn mills operating in Britain, but with the coming of the industrial revolution, the importance of wind as primary industrial energy source was replaced by steam and internal combustion engines. The increased use of steam, and later diesel power, however, had a lesser effect on the mills of the Norfolk Broads, these being so isolated (on extensive uninhabitable marshland) that some of them

continued service (albeith for another use) until as late as 1959. More recently windmills have been preserved for their historic value, in some cases as static exhibits when the antique machinery is too fragile to put in motion, and in other cases as fully working mills. There are around 50 working mills in operation in Britain as of 2009.

Multi-sailed windmills

An eight sailed Windmill at Wisbech, Cambridgeshire, UK The majority of windmills had four sails. An increase in the number of sails meant that an increase in power could be obtained, at the expense of an increase in the weight of the sail assembly. The earliest record of a multi-sailed mill in the United Kingdom was the five sail Flint Mill, Leeds, mentioned in a report by John Smeaton in 1774. Multi-sailed

windmills were said to run smoother than four sail windmills. In Lincolnshire, more multi-sailed windmills were found than anywhere else in the United Kingdom. There were five, six and eight sail windmills. If a four sail windmill suffers a damaged sail, the one opposite can be removed and the mill will work with two sails, generating about 60% of the power that it would with all four sails. A six sail mill can run with two, three, four or six sails. An eight sail mill can run with two, four, six or eight sails, thus allowing a number of options if an accident occurs. A five sail mill can only run with all five sails. If one is damaged then the mill is stopped until it is replaced. Apart from the UK, multi-sail mills were built in Germany, Malta and the USA.

Gearing

An isometric drawing of the machinery of the Beebe Windmill. It was built in Bridgehampton, NY in 1820. In general, the gearing inside a regular windmill has as a main function to convey the power from the rotary motion of the rotor (which connects to the windblades/windmill sails) to another device (and possibly convert the rotary motion into a reciprocating motion in the process). This could be a grist mill, saw blades, hammers or other devices. The power conveying is done by means of a windshaft, which connects to the rotor. The windshaft in turn connects to the Upright shaft. Regular windmills do not contain a gearbox. Rather, if a greater or slower speed is required for a specific part, the connecting part is instead locally fitted with smaller/greater cogs (which increase/decrease the speed).

Task specific gearing/operation With wind-powered grinding mills, there is also a governor present. This device increases or decreases the space between the grinding stones as the windblades pick up more/less wind (which increases/decreases the rotation speed). As the rotation of the stones goes faster, the grinding stones have the tendency to increase the opening between them, which would (if not corrected) result in a unhulled grain. Before the governor was invented, the miller would need to correct this manually. Besides the obvious driving of the grinding stones (usually up to 3 via the windshaft),it also drives other devices as well such as the sack hoist. The upright shaft drives pretreatment devices such as those for winnowing or threshing.

Uses As wind-pumping devices • • •

•

In the Netherlands, wind-powered pumps were important for the reclamation of flooded land. The Norfolk Broads, used windmills for powering drainage pumps until as late as 1959. In New France, particularly in Canada, they also doubled as strong points in fortifications. Prior to the 1690 Battle of Québec, the strong point of the city's landward defenses was a windmill called Mont-Carmel, where a three-gun battery was in place. At Fort Senneville, a large stone windmill was built on a hill by late 1686, doubling as a watch tower. This windmill was like no other in New France, with thick walls, square loopholes for muskets, with machicolation at the top for pouring lethally hot liquids and rocks onto attackers. This helped make it the "most substantial castle-like fort" near Montreal. In the United States, the development of the water-pumping windmill was the major factor in allowing the farming and ranching of vast areas of North America, which were otherwise devoid of readily accessible water. They contributed to the expansion of rail transport systems throughout the world, by pumping water from wells to supply the needs of the steam locomotives of those early times. Two prominent brands were the Eclipse Windmill developed in 1867 (which was later bought by Fairbanks-Morse) and the Aermotor, which first appeared in 1888 and is still in production. The effectiveness of the Aermotor's automatic governor, which prevents it from flying apart in a windstorm, led to its popularity over other models. Currently, the Aermotor windmill company is the only remaining water windmill manufacturer in the United States. They continue to be used in areas of the world where a connection to electric power lines is not a realistic option.

As electricity production systems

In the early 1980s, several small companies started wind farms for commercial energy production in the San Joaquin valley region of California. The first such wind farm was created in 1981 when John Eckland, of Fayette Manufacturing Corporation placed the first windmills on land leased from Joe Jess, Sr. on the Altamont Pass. Later, as a gift to Mr. Jess for the continued use of his land, Fayette created a 'stars and stripes' themed windmill.

Interior view, Pantigo windmill, East Hampton, New York. Historic American Buildings Survey At one point in the mid-80s there were over twenty-six wind farm companies operating in this area of the United States. This eventually expanded to areas outside of Palm Springs, as seen as backdrops in several films of the era, such as Less Than Zero. However, later legislative efforts by California lawmakers eliminated the financial incentives and tax breaks that made these early alternative energy projects feasible (Fisher, 1985). Similar tax credits and incentives have brought a resurgence in interest in renewable energy sources in other areas of the country (Maloney, 2006). Windmills and related equipment are still manufactured and installed today on farms and ranches, usually in remote parts of the western United States where electric power is not readily available. The arrival of electricity in rural areas, brought by the Rural

Electrification Administration (REA) in the 1930s through 1950s, contributed to the decline in the use of windmills in the US. Today, the increases in energy prices and the expense of replacing electric pumps has led to an increase in the repair, restoration and installation of new windmills.

Other • • • • • • • • • • • • • • • • • •

Gristmills, or corn mills, grind grains into flour. These were undoubtedly the most common kind of mill. Fulling or walk mills were used for a finishing process on cloth. Sawmills cut timber into lumber. Bark Mills ground bark from trees to powder for use in tanneries. Spoke mills turned lumber into spokes for carriage wheels. Cotton mills (initially used only to spin yarn) were usually powered by a water wheel at the beginning of the industrial revolution. Bobbin Mills made wooden bobbins for the cotton and other textile industries. Carpet mills for making carpets and rugs were sometimes water-powered. Textile mills for spinning yarn or weaving cloth were sometimes water-powered. Powder mills for making gunpowder - black powder or smokeless powder were usually water-powered. Blade mills were used for sharpening newly made blades. Slitting mills were used for slitting bars of iron into rods, which were then made into nails. Rolling mills shaped metal by passing it between rollers. Lead was usually smelted in smeltmills prior to the introduction of the cupola (a reverberatory furnace). Paper mills used water not only for motive power, but also required it in large quantities in the manufacturing process. Stamp mills for crushing ore, usually from non-ferrous mines Needle mills for scouring needles during manufacture were mostly water-powered (such as Forge Mill Needle Museum) Oil mills for crushing oil seeds might be wind or water-powered

Chapter- 14

Environmental Effects of Wind Power

Livestock ignore wind turbines, and continue to graze as they did before wind turbines were installed. A European Commission report has found wind to have the lowest external costs, comprising human health impacts, building and crop damage, global warming, loss of amenities and ecological impact, when compared to coal, oil, gas, biomass, nuclear, hydro and photovoltaic electricity generation.

Energy derived from wind power consumes no fuel, and emits no air pollution. A study by Lenzen and Munksgaard of the University of Sydney and the Danish Institute for Local Governmental Studies finds that the energy consumed in manufacturing and transporting the materials used to build a wind power plant is paid back within months. Mark Diesendorf, Director of Sustainability Centre, states that wind installations in agricultural areas take very little land and are compatible with grazing and crops. There are reports of bird and bat mortality at wind turbines, as there are around other artificial structures. The scale of the ecological impact may or may not be significant, depending on the particular site. Prevention and mitigation of wildlife fatalities, and protection of peat bogs, affect the siting and operation of wind turbines. There are conflicting reports about the effects of noise on people who live very close to a wind turbine.

Carbon dioxide emissions and pollution Wind power consumes no fuel for continuing operation, and has no emissions directly related to electricity production. Wind turbines produce no carbon dioxide, sulfur dioxide, mercury, particulates, or any other type of air pollution, as do fossil fuel power sources. Wind power plants consume resources in manufacturing and construction. During manufacture of the wind turbine, steel, concrete, aluminum and other materials will have to be made and transported using energy-intensive processes, generally using fossil energy sources. The wind turbine manufacturer Vestas claims that initial carbon dioxide emissions "pay back" is within about 9 months of operation for off shore turbines. A 2006 study found the CO2 emissions of wind power to range from 14 to 33 tonnes per GWh of energy produced. Most of the CO2 emission comes from producing the concrete for wind-turbine foundations. A study by the Irish national grid stated that "Producing electricity from wind reduces the consumption of fossil fuels and therefore leads to emissions savings", and found reductions in CO2 emissions ranging from 0.33 to 0.59 tonnes of CO2 per MWh. The UKERC study of intermittency also states that wind energy can displace fossil fuelbased generation, reducing both fuel use and carbon dioxide emissions.

Net energy gain The initial carbon dioxide emission from energy used in the installation is "paid back" within about 9 months of operation for off shore turbines. Any practical large-scale energy source must replace the energy used in its construction. The energy return on investment (EROI) for wind energy is equal to the cumulative electricity generated

divided by the cumulative primary energy required to build and maintain a turbine. The EROI for wind ranges from 5 to 35, with an average of around 18, according to windenergy advocates. EROI is strongly proportional to turbine size, and larger lategeneration turbines are at the high end of this range, at or above 35. Since energy produced is several times energy consumed in construction, there is a net energy gain.

Ecology Land use

Wind farm near an open-pit coal mine in Germany. Wind farms are often built on or near land that has already been impacted by land clearing.

In the United States, landowners typically receive $3,000 to $5,000 per year in rental income from each wind turbine, while farmers continue to grow crops or graze cattle up to the foot of the turbines.

A wind turbine at Greenpark, Reading, England, producing electricity for around one thousand homes Wind farms are often built on land that has already been impacted by land clearing. The vegetation clearing and ground disturbance required for wind farms is minimal compared with coal mines and coal-fired power stations. If wind farms are decommissioned, the landscape can be returned to its previous condition. Farmers and graziers often lease land to companies building wind farms. In the U.S., farmers may receive annual lease payments of two thousand to five thousand dollars per turbine. The land can still be used for farming and cattle grazing. Livestock are unaffected by the presence of wind farms. International experience shows that livestock

will "graze right up to the base of wind turbines and often use them as rubbing posts or for shade". Wind-energy advocates contend that less than 1% of the land would be used for foundations and access roads, the other 99% could still be used for farming. Critics point out that the clearing of trees around tower bases may be necessary for installation sites on mountain ridges, such as in the northeastern U.S. Turbines are not generally installed in urban areas. Buildings interfere with wind, turbines must be sited a safe distance ("setback") from residences in case of failure, and the value of land is high. However, there are a few notable exceptions. Toronto Hydro has built a lake shore demonstration project, and Steel Winds is a 20 MW urban project south of Buffalo, New York. Both of these projects are in urban locations, but benefit from being on uninhabited lake shore property. In the UK there has also been concern about the damage caused to peat bogs, with one Scottish MEP campaigning for a moratorium on wind developments on peatlands saying that "Damaging the peat causes the release of more carbon dioxide than wind farms save". Offshore locations use no land and avoid known shipping channels.

Impact on wildlife Environmental assessments are routinely carried out for wind farm proposals, and potential impacts on the local environment (eg plants, animals, soils) are evaluated. Turbine locations and operations are often modified as part of the approval process to avoid or minimise impacts on threatened species and their habitats. Any unavoidable impacts can be offset with conservation improvements of similar ecosystems which are unaffected by the proposal. Projects such as the Black Law Wind Farm have received wide recognition for its contribution to environmental objectives, including praise from the Royal Society for the Protection of Birds, who said that the scheme was not only improving the landscape in a derelict opencast mining site, but also benefiting a range of wildlife in the area, with an extensive habitat management projects covering over 14 square kilometres.

Birds Danger to birds is often the main complaint against the installation of a wind turbine. However, a study estimates that wind farms are responsible for 0.3 to 0.4 fatalities per gigawatt-hour (GWh) of electricity while fossil-fueled power stations are responsible for about 5.2 fatalities per GWh. The author's study therefore claims that fossil fuel based electricity causes about 10 times more fatalities than wind farm based electricity, primarily due to habitat alteration from pollution and mountain-top removal. The number of birds killed by wind turbines is also negligible when compared to the number that die

as a result of other human activities such as traffic, hunting, electric power transmission and high-rise buildings, and the introduction of feral and roaming domestic cats,. For example in Denmark, where wind turbines generate 9% of electricity, wind turbines kill about 30,000 birds per year - while cars kill 1 million birds per year; thus cars kill 33 times as many birds. Moreover, in the UK, where there are several hundred turbines, about one bird is killed per turbine per year; 10 million per year are killed by cars alone. In the United States, turbines kill 70,000 birds per year, compared to 80,000 killed by aircraft, 57 million killed by cars, 97.5 million killed by collisions with plate glass, and hundreds of millions killed by cats. An article in Nature stated that each wind turbine kills an average of 4.27 birds per year. In the UK, the Royal Society for the Protection of Birds (RSPB) concluded that "The available evidence suggests that appropriately positioned wind farms do not pose a significant hazard for birds." It notes that climate change poses a much more significant threat to wildlife, and therefore supports wind farms and other forms of renewable energy. In 2009, however, the RSPB warned that "numbers of several breeding birds of high conservation concern are reduced close to wind turbines," probably because "birds may use areas close to the turbines less often than would be expected, potentially reducing the carrying capacity of an area." The National Audubon Society in the U.S. takes a similar position, broadly supporting wind power to help mitigate global warming, while cautioning against siting wind farms in areas especially important to birds and other affected wildlife. The Peñascal Wind Power Project in Texas is located in the middle of a major bird migration route, and the wind farm uses avian radar originally developed for NASA and the United States Air Force to detect birds as far as four miles away. If the system determines that the birds are in danger of running into the rotating blades, it shuts down the turbines. The system automatically restarts the turbines when the birds have passed. At the Altamont Pass Wind Farm in California, a settlement has been reached between the Audubon Society, Californians for Renewable Energy and NextEra Energy Resources (who operate some 5,000 turbines in the area). Nearly half of the smaller turbines will be replaced by newer, more bird-friendly models. The project is expected to be complete by 2015 and includes $2.5 million for raptor habitat restoration. Some paths of bird migration, particularly for birds that fly by night, are unknown. A study suggests that migrating birds may avoid the large turbines, at least in the low-wind non-twilight conditions studied. A Danish 2005 (Biology Letters 2005:336) study showed that radio tagged migrating birds traveled around offshore wind farms, with less than 1% of migrating birds passing an offshore wind farm in Rønde, Denmark, got close to collision, though the site was studied only during low-wind non-twilight conditions.

Bats

Savi's Pipistrelle killed by "Ravna 1 wind farm" on island Pag, Croatia Bats may be injured by direct impact with turbine blades, towers, or transmission lines. Recent research shows that bats may also be killed when suddenly passing through a low air pressure region surrounding the turbine blade tips. The numbers of bats killed by existing onshore and near-shore facilities has troubled bat enthusiasts. A study in 2004 estimated that over 2200 bats were killed by 63 onshore turbines in just six weeks at two sites in the eastern U.S. This study suggests some onshore and near-shore sites may be particularly hazardous to local bat populations and more research is needed. Migratory bat species appear to be particularly at risk, especially during key movement periods (spring and more importantly in fall). Lasiurines such as the hoary bat, red bat, and the silver-haired bat appear to be most vulnerable at

North American sites. Almost nothing is known about current populations of these species and the impact on bat numbers as a result of mortality at windpower locations. It has been suggested that bats are attracted to these structures in search of roosts. Offshore wind sites 10 km (6 mi) or more from shore do not interact with bat populations. Scientists at the U.S. Geological Survey have already conducted research using stable isotope analysis to track migration among terrestrial mammals. USGS scientists are currently applying this technique in their efforts to figure out the geographic origins of bats killed by wind turbines. In April 2009 the Bats and Wind Energy Cooperative released initial study results showing a 73% drop in bat fatalities when wind farm operations are stopped during low wind conditions, when bats are most active. Bats avoid radar transmitters, and placing microwave transmitters on wind turbine towers may reduce the number of bat collisions.

Climate change One study reports simulations that show detectable changes in global climate for very high wind farm usage, on the order of 10% of the world's land area. However, wind power has a negligible effect on global-mean surface temperature, and it would deliver "enormous global benefits by reducing emissions of CO2 and air pollutants". There may be micro-climate change due to turbulence in the wakes of the spinning turbine rotors. But more efficient rotors may significantly reduce this.

Impacts on people Safety Operation of any utility-scale energy conversion system presents safety hazards. Wind turbines do not consume fuel or produce pollution during normal operation, but still have hazards associated with their construction and operation. There have been at least 40 fatalities due to construction, operation, and maintenance of wind turbines, including both workers and members of the public, and other injuries and deaths attributed to the wind power life cycle. Most worker deaths involve falls or becoming caught in machinery while performing maintenance inside turbine housings. Blade failures and falling ice have also accounted for a number of deaths and injuries. Deaths to members of the public include a parachutist colliding with a turbine and small aircraft crashing into support structures. Other public fatalities have been blamed on collisions with transport vehicles and motorists distracted by the sight and shadow flicker of wind turbines along highways.

If a turbine's brake fails, the turbine can spin freely until it disintegrates or catches fire. Often turbine fires cannot be extinguished because of the height, and are left to burn themselves out. In the process, they generate toxic fumes and can scatter flaming debris over a wide area, starting secondary fires below. Several turbine-ignited fires have burned hundreds of acres of vegetation each, and one burned 800 square kilometres (200,000 acres) of Australian National Park. Electronic controllers and safety sub-systems monitor many different aspects of the turbine, generator, tower, and environment to determine if the turbine is operating in a safe manner within prescribed limits. These systems can temporarily shut down the turbine due to high wind, electrical load imbalance, vibration, and other problems. Recurring or significant problems cause a system lockout and notify an engineer for inspection and repair. In addition, most systems include multiple passive safety systems that stop operation even if the electronic controller fails. In his book Wind Energy Comes of Age, Paul Gipe estimated that the mortality rate for wind power from 1980–1994 was 0.4 deaths per terawatt-hour. Paul Gipe's estimate as of end 2000 was 0.15 deaths per TWh, a decline attributed to greater total cumulative generation.

Aesthetics Newer wind farms have larger, more widely spaced turbines, and have a less cluttered appearance than older installations. Wind farms are often built on land that has already been impacted by land clearing and they coexist easily with other land uses (eg grazing, crops). They also have a smaller footprint than other forms of energy generation such as coal and gas plants. However, wind farms may be close to scenic or otherwise undeveloped areas, and aesthetic issues are important for onshore and near-shore locations. Aesthetic issues are subjective and some people find wind farms pleasant and optimistic, or symbols of energy independence and local prosperity. While some tourism officials predict wind farms will damage tourism, some wind farms have themselves become tourist attractions, with several having visitor centers at ground level or even observation decks atop turbine towers. Residents near turbines may complain of "shadow flicker" on nearby residences caused by rotating turbine blades, when the sun passes behind the turbine. However, this can easily be avoided by locating the wind farm to avoid unacceptable shadow flicker, or by turning the turbine off for the few minutes of the day when the sun is at the angle that causes flicker. Wind towers require aircraft warning lights, which may create light pollution. Complaints about these lights have caused the FAA to consider allowing fewer lights per turbine in certain areas.

Noise Modern wind turbines produce significantly less noise than older designs. Turbine designers work to minimise noise, as noise reflects lost energy and output. Noise levels at nearby residences may be managed through the siting of turbines, the approvals process for wind farms, and operational management of the wind farm. Renewable UK, a wind energy trade organization, has said that the noise measured 350m from a wind farm is less than that from normal road traffic or in an office. However, some studies by physicians and acoustic engineers have reported problems from wind turbine noise, including sleep deprivation, headaches, dizziness, anxiety, and vertigo. Nina Pierpont, a New York pediatrician, has said that noise can be an important disadvantage of wind turbines, especially when building the wind turbines very close to urban environments. The controversy around Pierpont's work centers around her claims made in a self-published, non-peer-reviewed book that ultra-low frequency sounds affect human health. She asserts that wind turbines affect the mood of people and may cause physiological problems such as insomnia, headaches, tinnitus, vertigo and nausea. In December 2006, a Texas jury denied a noise pollution suit against FPL Energy, after the company demonstrated that noise readings were not excessive. The highest reading was 44 decibels, which was characterized as about the same level as a 10 mile/hour (16 km/h) wind. The nearest residence among the plaintiffs was 1,700 feet from one of the turbines. More recent lawsuits have been brought in Missouri , Pennsylvania, and Maine. In the Canadian Province of Ontario, the Ministry of the Environment created noise guidelines to limit wind turbine noise levels 30 metres away from a dwelling or campsite to 40 db(A). These regulations also set a minimum distance of 550 metres (1,804 feet) for a group of up to five relatively quiet [102 dB(A)] turbines within a 3-kilometre (1.86mile) radius, rising to 1,500 metres (4,921 feet) for a group of 11 to 25 noisier (106-107 db(A)) turbines. Larger facilities and noisier turbines would require a noise study. In a 2009 report about "Rural Wind Farms", a Standing Committe of the Parliament of New South Wales, Australia, recommended a minimum setback of two kilometres between wind turbines and neighbouring houses (which can be waived by the affected neighbour) as a precautionary approach. In July 2010, Australia's National Health and Medical Research Council reported that "there is no published scientific evidence to support adverse effects of wind turbines on health". A 2008 guest editorial in Environmental Health Perspectives' published by the National Institute of Environmental Health Sciences, the U.S. National Institutes of Health, stated: "Even seemingly clean sources of energy can have implications on human health. Wind energy will undoubtedly create noise, which increases stress, which in turn increases the risk of cardiovascular disease and cancer."

The Japanese Environment Ministry will begin a "major study into the influence of sounds of wind turbines on people's health" in April 2010, because "people living near wind power facilities are increasingly complaining of health problems". They plan a fouryear examination of all 1,517 wind turbines in the country. A 2007 report by the U.S. National Research Council noted that noise produced by wind turbines is generally not a major concern for humans beyond a half-mile or so. However, low-frequency vibration and its effects on humans are not well understood and sensitivity to such vibration resulting from wind-turbine noise is highly variable among humans. There are opposing views on this subject, and more research needs to be done on the effects of low-frequency noise on humans. Research by Stefan Oerlemans for the University of Twente and the Dutch National Aerospace Laboratory suggests that noise from existing wind turbines may be reducible by up to half by adding "saw teeth" to the trailing edges of the blades, although research is not complete.

2009 review A 2009 "expert panel review", described as being the most comprehensive to date, delved into the possible adverse health effects of those living close to wind turbines. Their report findings concluded that wind turbines do not directly make people ill. The 85-page study was sponsored by the Canadian Wind Energy Association and American Wind Energy Association. The academic and medical experts who conducted the study stated that they reached their conclusions independent of their sponsors. "We were not told to find anything," said panel expert David Colby, a public health officer in Chatham-Kent and a Professor of Medicine at the University of Western Ontario. "It was completely open ended." The study did allow that some people could be stressed out by the swishing sounds wind turbines produce. "A small minority of those exposed report annoyance and stress associated with noise perception..." [however] "Annoyance is not a disease." The study group pointed out that similar irritations are produced by local and highway vehicles, as well as from industrial operations and aircraft. The wind-industry report found, amongst other things, that: •

•

"Wind Turbine Syndrome" symptoms are the same as those seen in the general population due to stresses of daily life. They include headaches, insomnia, anxiety, dizziness, etc... low frequency and very low-frequency "infrasound" produced by wind turbines are the same as those produced by vehicular traffic and home appliances, even by the beating of people's hearts. Such 'infrasounds' are not special and convey no risk factors;

•

• •

Colby stated that evidence of harm was so minuscule that the wind associations were unable to initiate other independent collinear studies by government agencies. It was not surprising that their requests met with complete blanks on the need to examine the issues further; one study member noted: "You can't control the amount of cars going by and wind turbine noise is generally quieter than highway noise"; the power of suggestion, as conveyed by news media coverage of perceived 'wind-turbine sickness', might have triggered "anticipatory fear" in those close to turbine installations.

The study panel members included: Robert Dobie, a doctor and clinical professor at the University of Texas, Geoff Leventhall, a noise vibration and acoustics expert in the United Kingdom, Bo Sondergaard, with Danish Electronics Light and Acoustics, Michael Seilo, a professor of audiology at Western Washington University, and Robert McCunney, a biological engineering scientist at the Massachusetts Institute of Technology. McCunney contested claims that infrasounds from wind turbines could create vibrations causing ill health: "It doesn't really have much credence, at least based on the literature out there" he stated.

Offshore Many offshore wind farms are being built in UK waters. In January 2009, a comprehensive government environmental study of coastal waters in the United Kingdom concluded that there is scope for between 5,000 and 7,000 offshore wind turbines to be installed without an adverse impact on the marine environment. The study – which forms part of the Department of Energy and Climate Change's Offshore Energy Strategic Environmental Assessment – is based on more than a year's research. It included analysis of seabed geology, as well as surveys of sea birds and marine mammals.