A windmill is a structure or machine that converts wind into usable energy through the rotation of a wheel. Heron of Alexandria invented the wind-wheel, constituting the earliest instance of wind harnessing on land.  It was Estakhri who created the earliest known account of windmills. Windmills convert wind power to rotational motion. The first practical windmill was built during the 9th century.

Windmills can also be used to provide energy to sawmills, paper mills, hammer mills and wind pumps. In the US, the invention of the wind-pump (which pumps water from underground) was the major reason farming could be done in dry areas of North America.

A wind farm uses groups of wind turbines to produce electrical energy. One wind farm is built in Antarctica to reduce their reliance of diesel. There are about 280 000 windmills on farms across South Africa, second in number only to Australia.

Did you know?
Traditionally, windmills were used to crush, grind or press grains in a grinding mill.