A portion (approximately 25,800 KW hours annually) of the total solar energy falling on the earth, is converted into motion of air. A small fraction of this energy resource is currently being harnessed. Winds only in certain speed ranges, however, may be harnessed at the current time.
The distribution of wind is not uniform
over the earth, wind resources are higher in polar and temperate zones
than in tropical zones and also higher in coastal areas than inland.
The wind energy is harnessed by installing rotating machines (typically propellers) that
are connected to electric generators.
Because of friction losses, wind power machines usually do not operate
at wind velocities much lower than 10 miles/hour, while with winds
of gale force the rotors of wind machines are usually feathered to
prevent damage.
Wind derived energy accounted for 0.04 quadrillion Btu (or 0.042x109 Giga Joules) or .043% of the total energy consumption in the U.S. in 19961.
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