History of Wind Energy
Wind is simple air in motion. It is caused by the uneven heating of the earth’s surface by the sun. Since the earth’s surface is made of very different types of land and water, it absorbs the sun’s heat at different rates. Since ancient times, people have harnessed the winds energy.
Over 5,000 years ago, the ancient Egyptians used wind to sail ships on the Nile River. Later, people built windmills to grind wheat and other grains. The earliest known windmills were in Persia (Iran). These early windmills looked like large paddle wheels. Centuries later, the people of Holland improved the basic design of the indmill. They gave it propeller-type blades, still made with sails. Holland is famous for its windmills. During the day, the air above the land heats up more quickly than the air over water.
The warm air over the land expands and rises, and the heavier, cooler air rushes in to take its place, creating winds. At night, the winds are reversed because the air cools more rapidly over land than over water. In the same way, the large atmospheric winds that circle the earth are created because the land near the earth's equator is heated more by the sun than the land near the North and South Poles. Today, wind energy is mainly used to generate electricity. Wind is called a renewable energy ource because the wind will blow as long as the sun shines.
Wind power is the conversion of wind energy into more useful forms, usually electricity using wind turbines. At the end of 2006, worldwide capacity of wind-powered generators was 74,223 megawatts; although it currently produces less than 1% of world-wide electricity use, it accounts for approximately 18% of electricity use in Denmark, 9% in Spain, and 7% in Germany. Globally, wind power generation more than quadrupled between 2000 and 2006.
Most modern wind power is generated in the form of electricity by converting the rotation of turbine blades into electrical current by means of an electrical generator. In windmills (a much older technology) wind energy is used to turn mechanical machinery to do physical work, like crushing grain or pumping water.
Wind power is used in
large scale wind farms for national electrical grids as well as in small individual turbines for providing electricity to rural residences or grid-isolated locations. Wind energy is ample, renewable, widely distributed, clean, and mitigates the greenhouse effect if used to replace fossil-fuel-derived electricity.
Windmills
Windmills have been used for at least 3000 years, mainly for grinding grain or pumping water, while in sailing ships the wind has been an essential source of power for even longer. From as early as the thirteenth century, horizontal-axis windmills were an integral part of the rural economy and only fell into disuse with the advent of cheap fossil-fuelled engines and then the spread of rural electrification. The use of windmills (or wind turbines) to generate electricity can be traced back to the late nineteenth century with the 12 kW DC windmill generator constructed by Brush in the USA and the research undertaken by LaCour in Denmark. However, for much of the twentieth century there was little interest in using wind energy other than for battery charging for remote dwellings and these low-power systems were quickly replaced once access to the electricity grid became available. One notable exception was the 1250 kW Smith–Putnam wind turbine constructed in the USA in 1941. This remarkable machine had a steel rotor 53 m in diameter, full-span pitch control and flapping blades to reduce loads. Although a blade spar failed catastrophically in 1945, it remained the largest wind turbine constructed forsome 40 years (Putnam, 1948).
Image from http://ec.europa.eu/research/energy
Golding (1955) and hepherd and Divone in Spera (1994) provide a fascinating history of early wind turbine development. They record the 100 kW 30 m diameter Balaclava wind turbine in the then USSR in 1931 and the Andrea Enfield 100 kW 24 m diameter pneumatic design constructed in the UK in the early 1950s. In this turbine hollow blades,open at the tip, were used to draw air up through the tower where another turbine drove the generator. In Denmark the 200 kW 24 m diameter ´ Gedser machine was built in 1956 while Electricite de France tested a 1.1 MW 35 m diameter turbine in 1963.
In Germany, Professor Hutter constructed a number of innovative, lightweight turbines in the 1950s and 1960s. In spite of these technical advances and the enthusiasm, among others, of Golding at the Electrical Research Association in the UK there was little sustained interest in wind generation until the price of oil rose dramatically in 1973.
The sudden increase in the price of oil stimulated a number of substantial Government-funded programmes of research, development and demonstration. In the USA this led to the construction of a series of prototype turbines starting with the 38 m diameter 100 kW Mod-0 in 1975 and culminating in the 97.5 m diameter 2.5 MW Mod-5B in 1987. Similar programmes were pursued in the UK, Germany and Sweden. There was considerable uncertainty as to which architecture might prove most cost-effective and several innovative concepts were investigated at full scale. In Canada, a 4 MW vertical-axis Darrieus wind turbine was constructed and this concept was also investigated in the 34 m diameter Sandia Vertical Axis Test.
In the UK, an alternative vertical-axis design using straight blades to give an ‘H’ type rotor was proposed by Dr Peter Musgrove and a 500 kW prototype constructed. In 1981 an innovative horizontal-axis 3 MW wind turbine was built and tested in the USA. This used hydraulic transmission and, as an alternative to a yaw drive, the entire structure was orientated into the wind. The best choice for the number of blades remained unclear for some while and large turbines were constructed with one, two or
three blades.
Source :
http://en.wikipedia.org
http://www.eia.doe.gov
http://ec.europa.eu/research/energy
