Berkswell Windmill, West Midlands, England.
A windmill is a wind energy conversion system (WECS) that is used, among other purposes, to grind grain, and that typically has a high-solidity rotor; the term "windmill" is often used to refer to all types of WECS. Windmills have been used by humans since at least 200 BC for grinding grain (hence the name 'mill'). and pumping water. The idea spread to Europe in the Middle Ages. Later windmills were used to drive pumps, particularly for draining low-lying regions of the Netherlands and eastern England in the Fens and East Anglia. Their use was widespread during the early years of the Industrial Revolution, but declined with the development of the steam engine in the nineteenth century.
Some early windmills had canvas sails, developed from those used on ships. Then slatted wooden sails were developed as the illustrations shown here. The sails turned the bonnet or cap on the top of the mill so that they always faced into the wind. In a post mill the whole structure was pivoted on a central post and turned to face the wind.
By the 1900s, windmills were used on farms and ranches in the United States to pump water and, later, to produce electricity. Traditional windmills have more blades than modern wind turbines, and they rely on drag to rotate the blades.