Wind farms

A wind farm is a group of wind turbines in the same location used to produce electricity. A large wind farm may consist of 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 can also be located offshore.

Many of the largest operational onshore wind farms are located in China, the United States and Germany. For example, the largest wind farm in the world, Gansu Wind Farm in China has a capacity of over 6,000 MW as of 2012, with a goal of 20,000 MW by 2020. As of April 2013, the 630 MW London Array in the UK is the largest offshore wind farm in the world.

There are many large wind farms under construction, including Fosen Vind (1000 MW), Sinus Holding Wind Farm (700 MW), Lincs Wind Farm (270 MW), Lower Snake River Wind Project (343 MW), Macarthur Wind Farm (420 MW).

As a general rule, economic wind generators require windspeed of 4.5 m/s (10 mph) 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 screened on the 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 in order to finance the project. Local winds are often monitored for a year or more, and detailed wind maps constructed before wind generators are installed.

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%.

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