Bunch-Hellemans, Wind power – Inventing the Windmill

Sailboats are probably the oldest form of wind power, and it is likely that the sail inspired the first builders of windmills. Wind power that provides rotary motion is a more recent invention than waterpower. Some historians believe that the first windmills appeared in the Greek islands at the beginning of the Christian era, but a firm proof of this has yet to be found. During the seventh century windmills probably appeared in areas with no flowing water, such as the western part of Afghanistan.

Early windmills consisted of a rotor turning on a vertical axis to which were attached curved sails made of fabric. The wind was admitted through funnel shaped openings facing the direction of the wind. Because no gears were required for driving the millstone, losses from friction were minimal. By the tenth century such mills were generally used throughout the Arab world. Windmills were also in use during that time in Iran and in China, where they were used for irrigation and land drainage.

In Europe the windmill appeared about 1100. These windmills had horizontal axes or windshafts that had to be placed in the direction of the wind. The first type used was the postmill: The entire mill, including the millstones, was mounted on a fixed foundation, or “post,” on which it could rotate.

A second type of mill, the tower mill, appeared at the end of the 14th century. Only the top cap, housing the windshaft, of a tower mill rotates. In some later types of tower mills, an auxiliary windshaft with blades placed parallel to the main windshaft automatically rotates the top cap into the required position.

Windmills in Europe were first used for milling grain, but soon their use widened to include many other activities; for example, sawmills and mills were used for crushing ores. In Holland, one very important application was pumping water for the reclaiming of land. The first windmill in Holland started pumping in 1414. Windmills drove both Archimedean screws and water wheels for pumping water. Those equipped with water wheels could pump water up only a few feet and therefore several windmills in succession were required to pump water to greater heights.

At one time, 7500 windmills were in use in Holland for pumping water and for industrial applications. Their success was so great that even in the 18th century John Smeaton considered increasing the use of windmills in England. In 1759 Smeaton investigated the performance of windmills by building models, but eventually concluded that they could not compete with the more powerful steam engines then in use.

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