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Wind Energy
The world’s approximately 74,000 megawatts (MW) of installed wind capacity meet about 1 percent of the total global electricity demand. In the United States, as of December 2007, total installed wind capacity was approximately 14,000 MW, with an additional 5.7 MW under construction. Wind power accounts for about 20 percent of Denmark’s electricity production, 9 percent of Spain’s, and 7 percent of Germany’s. According to a recent study,22 India and China alone are expected to add 36,000 MW of wind power capacity by 2015, representing over 80 percent of the Asian wind market during that period. Market growth in those countries is being driven by the growth of independent power producers (IPP) in India and by electric utilities in China. Major wind turbine manufacturers, including Vestas, GE, Suzlon, Gamesa, and Nordex, are establishing manufacturing facilities in India and China on the basis of strong market growth for their products in those countries. Suzlon, an Indian wind manufacturing company, is also active in the global wind market, including Europe and North America, as both an equipment supplier and project developer. Large wind power generating plants, often called wind farms, can be integrated into agricultural and other land uses; a wind farm in Hawaii is shown at right.23 Wind farms typically use tens to hundreds of wind turbines rated between 600 kilowatts (kW) and 5 MW and produce between 50 and hundreds of megawatts of electric power. In some countries, especially Denmark, Germany, and the United Kingdom, interest in offshore projects is increasing. In these projects, turbines are installed in the shallow waters of coastal areas, where they are exposed to the strong prevailing coastal winds and can be located close to large load centers. Medium-sized turbines, between 10 and 600 kW, are used in distributed energy applications, supplementing or replacing grid power on farms and other commercial or industrial sites. Small wind turbines, in the 100 watt (W) to 10 kW range, are suitable for household, water pumping, or village power applications. Conventional horizontal-axis wind turbines for electricity generation consist of a rotor, nacelle, tower, and foundation. The rotor consists of wind-spun blades that drive a gearbox and electric generator in the nacelle, which is located at the top of the tower. (Some turbine designs do not include a gearbox.) The tower and foundation support the nacelle and rotor at a height above the ground where winds are strong. Other wind turbine designs include vertical-axis turbines and small turbines designed for urban use.
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