History of wind power
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Wind machines were used for grinding grain in Persia as early as 200 B.C. This type of machine was introduced into the Roman Empire by 250 A.D. By the 14th century Dutch windmills were in use to drain areas of the Rhine River delta. In Denmark by 1900 there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW. The first windmill for electricity production was built in Cleveland, Ohio by Charles F. Brush in 1888[1], and in 1908 there were 72 wind-driven electric generators from 5 kW to 25 kW. The largest machines were on 24 m (79 ft) towers with four-bladed 23 m (75 ft) diameter rotors. In Denmark wind power was an important part of a decentralized electrification in the first quarter of the 20th century, partly because of the Danish wind power scientist Poul la Cour.
By the 1930s windmills were mainly used to generate electricity on farms, mostly in the United States where distribution systems had not yet been installed. In this period, high tensile steel was cheap, and windmills were placed atop prefabricated open steel lattice towers. A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in 1931. This was a 100 kW generator on a 30 m (100 ft) tower, connected to the local 6.3 kV distribution system. It was reported to have an annual load factor of 32 per cent, not much different from current wind machines.
In 1941 the world's first megawatt-size wind turbine was connected to the local electrical distribution system on Grandpa's Knob in Castleton, Vermont, USA. This 1.25 MW Smith-Putnam turbine operated for 1100 hours before a blade failed at a known weak point, which had not been reinforced due to war-time material shortages. In the 1940s, the U.S. had a rural electrification project that killed the natural market for wind-generated power, since network power distribution provided a farm with more dependable usable energy for a given amount of capital investment.
In the 1970s many people began to desire a self-sufficient life-style. Solar cells were too expensive for small-scale electrical generation, so some turned to windmills. At first they built ad-hoc designs using wood and automobile parts. Most people discovered that a reliable wind generator is a moderately complex engineering project, well beyond the ability of most romantics. Some began to search for and rebuild farm wind-generators from the 1930s, of which Jacobs wind generators were especially sought after.
From the mid 1970's through the mid 1980's the United States government worked with industry to advance the technology and enable large commercial wind turbines. This effort was led by NASA at the Lewis Research Center in Cleveland, Ohio and was an extraordinarily successful government research and development activity. With funding from the National Science Foundation and later the Department of Energy (DOE), a total of 13 experimental wind turbines were put into operation including four major wind turbine designs. This research and development program pioneered many of the multi-megawatt turbine technologies in use today, including: steel tube towers, variable-speed generators, composite blade materials, partial-span pitch control, as well as aerodynamic, structural, and acoustic engineering design capabilities. The large wind turbines developed under this effort set several world records for diameter and power output. The Mod-2 wind turbine cluster produced a total of 7.5 megawatt of power in 1981. In 1987, the Mod-5B was the largest single wind turbine operating in the world with a rotor diameter of nearly 100 meters and a rated power of 3.2 megawatts. It demonstrated an availability of 95 percent, an unparalleled level for a new first-unit wind turbine. The Mod-5B had the first large-scale variable speed drive train and a sectioned, two-blade rotor that enabled easy transport of the blades.
Later, in the 1980s, California provided tax rebates for ecologically harmless power. These rebates funded the first major use of wind power for utility electricity. These machines, gathered in large wind parks such as at Altamont Pass would be considered small and un-economic by modern wind power development standards.
In the 1990s, as aesthetics and durability became more important, turbines were placed atop steel or reinforced concrete towers. Small generators are connected to the tower on the ground, then the tower is raised into position. Larger generators are hoisted into position atop the tower and there is a ladder or staircase inside the tower to allow technicians to reach and maintain the generator.
Originally wind generators were built right next to where their power was needed. With the availability of long distance electric power transmission, wind generators are now often on wind farms in windy locations and huge ones are being built offshore, sometimes transmitting power back to land using high voltage submarine cable. Since wind turbines are a renewable means of generating electricity, they are being widely deployed, but their cost is often subsidised by taxpayers, either directly or through renewable energy credits. Much depends on the cost of alternative sources of electricity. Wind generator cost per unit power has been decreasing by about four percent per year.
