Wind

Man has been using wind power for at least 4,000 years, first to sail the seas, then in irrigation, and later in agricultural processing. The use of wind technology to generate electricity, on the other hand, is a recent development. It began in the 1970s, when the first oil crisis drove research into new sources of renewable energy.
The successes achieved in engineering and materials technology led to significant efficiency gains, such that wind power is now one of the most technologically mature sources of renewable energy and is the closest to being economically competitive with fossil fuels, which explains the success that this technology has been having in recent years. By the end of 2007, installed wind power capacity reached 93,678 MW (56,347 MW in the EU alone), 19,288 MW of which installed in 2007 alone.

In order to generate electricity from the wind, we use vertical-axis (with the rotor perpendicular to the direction of the wind) or horizontal-axis (with the rotor parallel to the direction of the wind, such as in traditional windmills) wind generators. Horizontal-axis generators require more complex control systems, but have the advantage of providing a greater aerodynamic yield. For this reason, all modern wind turbines used in generating electricity are of the horizontal-axis variety.

The operating principle of a wind turbine is seemingly simple: the force of the wind rotates the blades, and this movement is transferred to a generator, where this mechanical energy is transformed into electricity. In actual fact, modern wind turbines are highly sophisticated machines (with complex braking systems, gearing, control systems, yaw control systems and much more) and are made of composite materials able to support stresses comparable with those of an aircraft.

Sizes vary greatly depending on power output. A medium-sized wind turbine has a rotor that is positioned about 50 meters from the ground, with a blade diameter of 50-60 meters and a capacity of some 800 kW.
The 3-MW wind turbines installed at the Snyder (Texas) plant are the tallest in the United States, having 105-meter towers and rotor blades with a diameter of 90 meters, i.e. nearly the length of a football field.