About 1% of the solar energy received from the Sun is converted to atmospheric motion because the heterogenous Earth warming produces different densities, causing the lows and high pressures that produce the winds. This energy is distributed as witnesses of huricanes and tornados.

Wind energy has not been utilized extensively by industry in the United States. It seems to be most promising in the genaration of electricity at specific sites where wind velocities are high and reasonably steady. Wind energy could be used to obtain hydrogen based on the electrolisis process

In 1972, experts from NSF and NASA estimated that 105 GW of electricity could be produced in the United States, this is about 100 times the present electrical generating capacity.

The power that is contained in a moving air stream per unit area normal to the flow is proportional to the cube of the wind velocity.

P/A = 1/2 pV3

 P = Power contained in the wind A = Area normal to the wind velocity p = Density of the air (1.23kg/m3) V= Velocity of the air stream.

The fraction of the power in a wind stream that is converted to a mechanical shaft power is given by Cp. Only 16/27 or 0.5926 of the power can be extracted by a wind machine, since there must be some flow velocity downstream from the device for the air to move out of the way, this upper limit is called Betz coefficient (or Glauert's limit). A device might extract a fraction, such as 70%, of the theoretical limit. A real device might extract 16/27 * 0.70 = 41% of the power available. Assuming a 20miles/hr wind:

P/A = (5.08 * 10-3)(20)3(0.41) = 16.7W/ft2

For a 30miles/hr wind the power would be 56.2W/ft2, more than three times as much.

Wind Devices

Wind conversion devices have been proposed and built in a very wide variety of types, being the most common, the hirizontal-axis, head-on-type, typical of conventional farm windmills. The device must be turned into the wind, either by a tail vane or by a servo device. The rotational speed of any kind of devices can be controlled by feathering of the blades or by flap devices or by varying the load.