Windmills convert kinetic wind energy into mechanical power. Wind provides the energy required to turn the vanes of a windmill, which can be connected to a generator to generate electricity or used as a source of mechanical power for tasks such as pumping water or grinding grain.
The earliest known use of wind power to automate manual tasks was in Persia almost 3000 years ago. The Persians developed machines to grind grain and pump water that were very similar to windmills. They bundled reeds together to create the vanes, and exterior walls were carefully placed to drive wind in the desired direction.
The earliest documentation of a windmill was written by statesman Yehlu Chhu-Tshai in China over 2000 years ago. Between the years of 1850 and 1970, over six million small windmills had been installed in the United States. Very large windmills were also used to pump water for steam railroad trains.
The large white windmills found in groups on most wind farms are known as wind turbines. As wind blows, it passes through the wind farm and moves the blades on the turbines. This spins a shaft. This shaft is usually connected to a generator, which uses the turning motion to rotate a rotor. The rotor has oppositely charged magnets and is surrounded by copper wire loops. Electromagnetic induction is created by the rotor spinning around the inside of the core, thus generating electricity.