A wind turbine is a rotary device that extracts energy from the wind. If the mechanical energy is used directly by machinery, such as for pumping water, cutting lumber or grinding stones, the machine is called a windmill. If the mechanical energy is instead converted to electricity, the machine is called a wind generator, wind turbine, wind turbine generator (WTG), wind power unit (WPU), wind energy converter (WEC), or aero generator.
A wind power turbine is a large rotating machine that is able to harness the energy of the wind and turn it into a form that can be used by people. Historically, the most common type of wind power turbine was the windmill, which changed wind energy into direct mechanical energy, which could then be used for simple tasks like grinding grain. The modern wind power turbine tends to be a wind generator or wind energy converter, and is able to turn wind energy into electricity, which can then be transported over power lines to be used by individuals far from the location of the turbines themselves.
The earliest known wind power turbine dates from the 2nd century BCE in Persia, and was a very rudimentary design. By the 7th century, something approximating the windmill had been developed, and it spread throughout the world. This type of wind power turbine was used to turn mills for grinding grains, and also to operate pumps, allowing fresh water to be drawn up from the ground. Perhaps the most iconic uses of the windmill were in the Netherlands, where they were widely adopted by the 14th century to do everything from running gristmills to transporting water.
The modern wind power turbine is not that much different from a historical windmill, although it looks much sleeker and more aerodynamic. The most common type of turbine is a three-bladed horizontal-axis turbine, facing straight into the wind. Unlike vertical-axis turbines, horizontal-axis turbines are able to generate power through their entire rotation, never moving against the wind.
Although turbines can be quite simple, most modern turbines have a number of advanced features to make them function more efficiently. For example, most can be remotely adjusted, so that entire fields of turbines can be shifted slightly to make the best use of oncoming wind. Many modern designs also make use of variable-speed turbines, allowing them to shift their resistance and speed depending on the strength of the wind, and making them more efficient. Additionally, most modern designs also have emergency shutoff features, to ensure that they are not broken in extremely high-speed winds.