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Wind Energy

Wind energy is the kinetic energy of large masses of air moving over the Earth. Because the sun heats the Earth's surface and atmosphere unevenly, thermal differences develop, which drive air masses around the planet. The Earth's rotation also contributes to powerful air currents.

A wind turbine converts this energy into mechanical energy and then into electric energy. The conversion begins as air flows over the wind turbine blade. The cross-sectional shape of the blade, called an airfoil, is specially designed for the wind. Air passes more rapidly over the longer (or leading) edge of the blade, creating lower pressure along the leading edge. The pressure difference between the leading and trailing edges of the blade results in a force known as aerodynamic lift. This lift causes the blades to rotate around the central hub and turns the shaft. The rotational energy in the shaft can operate a mechanical device, such as a water pump, or can be used by a generator to produce electricity.

Wind energy technology is versatile and adaptable. A small stand-alone wind turbine can provide enough power for a typical U.S. household, while groups of larger turbines combine to generate utility-scale electricity. These large arrays, called wind farms, deliver power to an integrated grid. This setup is very reliable: at any time, several wind turbines at a wind plant may be shut down for maintenance, but most of the turbines run.

The power in the wind is expressed by wind power classes ranging from 1 (least energetic) to 7 (most energetic). Each class is defined by a range of wind speeds and a range of power, defined as watts per square meter.

The wind energy resource in the United States is plentiful. Good wind areas, which cover 6% of the contiguous U.S. land area, could supply more than 1.5 times the 1993 electricity consumption of the entire country.

The Great Plains has a vast wind resource, reaching from Montana to Minnesota and south through Texas. North Dakota alone has enough potential energy from windy areas of class 4 and higher to supply 36% of the total 1990 electricity consumption of the lower 48 states. California now has the most turbines in the United States, but wind farms are being developed throughout the Great Plains as this abundant wind resource is beginning to be tapped. Wind energy use is rapidly increasing in Iowa, Minnesota, Texas, Wisconsin, Colorado, and Wyoming. Visit the U.S. Department of Energy's Wind Powering America for state wind resource maps.

The single most important factor for performance of wind turbine generator installations is average wind speed. The power in the wind is proportional to the cube of the wind speed. Therefore, a 16 miles per hour (mph) average site is 137% more powerful than a 12 mph site (16/123). As this example shows, relatively small errors in measuring the average wind speed will have major impacts on energy production. Another important wind characteristic is the wind speed probability distribution (how much of the time the wind blows at various speeds), which is useful for selecting the best turbine design for the particular site. Seasonal and daily wind speed variations are especially important for load matching — correlating peak power demand with peak wind energy production. Gustiness of the wind affects the power output of a given machine design. And because wind speed increases with height above the ground, using taller towers will cost more but increase power output.

From 2000 to 2004, wind energy was one of the fastest-growing energy technologies worldwide, growing at a 30% rate to a total installed capacity of more than 46,000 megawatts at the beginning of 2005. The size of the annual worldwide wind energy market is $1.5 billion. The largest share of new wind capacity — 73% — was installed in Europe. Spain, where wind power currently provides about 5% of the nation's power, promises to be one of the strongest markets in the next 10 years. Germany has now surpassed the United States, once the world leader, in installed wind energy capacity with more than 16,000 megawatts (MW).

In the United States, wind energy growth slowed during the past several years, a result of uncertainties about deregulation and competition in the electric power industry. Total U.S. installed wind capacity at the end of 2004 was around 6,700 MW, with more than 2,000 MW installed in the last two years. This is enough energy to serve more than 1.6 million average households. Much of the recent growth in the United States was fueled by new State Renewable Portfolio Standards.

Competition in the electric industry means low-cost generation is important. Wind energy, however, offers other competitive advantages: it is clean, renewable, and preferred by some consumers. And as concerns about global climate change grow, wind energy will take a more prominent place among generation technologies. The electric industry remains the largest, single stationary source of air pollution.

Markets for off-grid systems are also strong. More than 2 billion people around the world live without electricity. Small wind turbines, coupled with other technology, such as diesel generators, photovoltaics, and batteries (collectively called hybrid systems), can provide power for remote villages. According to the World Bank, several million households worldwide are able and willing to spend $150 per year for reliable energy.

Wind energy is one of the most cost-competitive renewable energy technologies. Thanks to the efforts of the wind industry and the U.S. Department of Energy's (DOE) Wind Energy Program, the cost of electricity from wind has dropped from $0.35 per kilowatt-hour (kWh) in 1980 to less than $0.05 per kWh today at good wind sites. DOE's goal is to improve the technology to further reduce costs to $0.03 per kWh for projects at low wind speed sites and $0.05 per kWh for offshore sites by 2012.

For more information on wind power, visit DOE's Wind and Hydropower Technologies Program.

The National Renewable Energy Laboratory's National Wind Technology Center is another good source of information on wind power.