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Title-Wind as alternative energy source
  Evolution of Windmill
  The oldest known windmills were crude, simple devices used in the 7th century by the Persians (a region now occupied by Iran). Europeans made extensive use of the windmill beginning in the 12th century, providing mechanical energy for pumping water, sawing lumber, and grinding grain. In the United States, the windmill was used to pump water on homesteads across the American frontier. In the late 20th century, windmills were developed to convert wind energy into electric power.
  Ancient Persian Windmills
    Early Persian windmills were crude devices consisting of a simple tower supporting an array of paddles made from bundled reeds. These paddles spun around a vertical axis, with a wall to protect the blades as they spun back into the direction of the wind. These early windmills were used for grinding grain.
    Traditional European Windmills
    Traditional European windmills have been used for centuries on the lowlands of northern Europe. In fact, the term windmill derives from using these machines to grind, or mill, grain. The first windmills to appear in Europe were built during the 12th century in northwestern France and southern England. Use of the windmill subsequently spread into northern Belgium, Germany, and north to Denmark during the late 12th and 13th centuries.

Only with wind energy could Jan Leegwater and the Dutch engineers that followed him drain the wetland areas of the Netherlands and make them habitable. European windmills were also used for sawing timber, shredding tobacco, manufacturing paper, pressing flaxseed for oil, and grinding stone for paint dye. The 700 windmills erected in the Zaan district north of Amsterdam formed the core of what evolved into the center of Dutch manufacturing—an area that eventually helped launch the Industrial Revolution.

Europeans, unlike their Persian counterparts, developed windmills with rotors that turned around a horizontal axis. Typical European windmills used four blades, although some used five, and occasionally even six. The earliest European windmills placed the tower holding the windmill rotor on a vertical post. This allowed the entire windmill to turn and face the wind. Many of these short postmills, as they are called, are still standing in northern Europe.

Toward the end of the 14th century, these postmills evolved into the traditional European tower windmills—some with towers up to three stories high. The rotors of these windmills are attached to a rotating tower cap, allowing the windmill operator to point the rotor blades into the wind by turning the cap. Many of these European tower windmills contain two or three interior levels where goods milled or manufactured inside the windmill—including grain, lumber, paint, and tobacco—could also be stored.

European windmill performance increased greatly over the next 500 years. The typical windmill evolved into a tower built of wood, stone, or brick that supported a rotor with four cloth-covered blades that acted like sails. This rotor, spanning a diameter of 25 meters (80 feet), was capable of delivering 25 to 30 kilowatts of mechanical power. Technical innovations to the European windmill included the multi-blade fantail protruding behind the rotor to automatically keep the rotor pointing into the wind; air brakes; automatically adjusting slats on the blades (instead of cloth); and blades with airfoil-shaped leading edges that anticipated modern aircraft wings. During the zenith of the European windmill (which ended in the late 19th century when the steam engine came into widespread use), some 1500 megawatts of power were being produced, a level not reached again until 1988.

    American Farm Windmill
    Use of windmills began subsiding in Europe during the 19th century, but across the Atlantic Ocean, the American farm windmill was being used by homesteaders to settle the American frontier. The American farm windmill, ideally suited for pumping water from deep underground, became an integral part of agricultural communities across the American West. One historian credits the farm windmill—along with the Colt 45 revolver and the barbed-wire fence—with enabling European settlement of the American Great Plains.

A series of improvements were made during the 100-year reign of the American water-pumping windmill. Early farm windmills used blades made from simple wooden slats; American engineer Thomas Perry improved on these blades in the late 1800s. Using a steam-driven model, Perry conducted scientific tests that led to his invention of stamped sheet-metal “sails” that nearly doubled the rotor’s efficiency. Based on Perry’s improved rotor design, American businessman LaVerne Noyes built the world's most successful farm windmill, the Aermotor. The Aermotor was not the first windmill to use metal blades, but its stamped sheet-metal “sails” proved so efficient that they revolutionized the farm windmill and are still in use today.

The American water-pumping windmill is legendary for its reliability and efficiency, and is indispensable for its ability to pump water from deep under the plains. However, it only produces about one-tenth the power of an equivalent-size modern wind turbine. This poor efficiency is why the multi-blade farm windmill was not successfully adapted for generating electricity. Although the American farm windmill industry peaked in the early part of the 20th century, more than 1 million of these machines are still in use worldwide.


The Modern Wind Turbine

  During the 1930s, interest in powering electric lighting and appliances on homesteads across the Great Plains led to the development of small, battery-charging wind turbines. These so-called windchargers were early forerunners of the small two- and three-bladed wind turbines used today to provide electricity for remote residences, and to provide electricity to villages in developing countries.

The oil crisis of the 1970s spurred efforts into developing wind energy as an alternative source of electrical power. Many countries launched programs to develop modern wind turbines. While many of these programs failed, Denmark was successful in developing modern wind turbines. Countries such as the United States have adopted this technology to develop wind energy resources.

The modern wind turbine is the result of design and material advances made during the 1980s and 1990s, which have enabled wind turbines to become increasingly efficient. Today, wind turbines the same size as the traditional European windmill can generate 250 to 300 kilowatts of power—a nearly tenfold increase in efficiency.


Courtesy of Enron Wind Corp. Wind Farm These turbines are part of a wind farm located near Lake Benton, Minnesota. This region is one of the most productive wind energy sites in the midwestern United States.


Source: Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. /Wind energy/Reviewed By:
Paul Gipe