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Wind Turbine

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Mechanical Features and Designs
Wind turbine
A wind turbine or wind generator[1] is a structure with typically two to three blades that captures wind energy and transfers it to an electrical generator shaft, thereby converting it to mechanical energy to generate electricity.[2] Wind turbines are typically classified as either being of a vertical axis or horizontal axis configuration. They have been used throughout time to grind grain, pump water, and provide electricity.

Contents

[edit] History

The first type of wind turbine ever could be considered the windmill. Windmills have been used for centuries to pump water and grind grain. The first windmills used for this purpose were used in Persia as far back as 500 to 900 A.D. and in China in 1219 A.D. Windmills in both regions were of a vertical axis design.[3]

Horizontally configured axis windmills surfaced in Europe around 1270 A.D. These windmills consisted of four blades mounted on a center post or post mill and used wood cog-and-ring gears to translate motion from a horizontal shaft into vertical movement that turned a grinding stone. Eventually, the Dutch would refine the tower mill design by affixing a post mill to the top of a multi-story tower.[4]

Windmill development continued to evolve throughout Europe with the use of sails as a type of blade. Sails provided more aerodynamic lift that resulted in overall better rotor efficiency and speed and thereby better pumping and grinding operations. It would take almost 500 years for the use of sails to be replaced with the use of modern turbine blades.[5]

Electric motors on windmills were first used in pre-industrial Europe for a broad range of applications such as water well irrigation, water drainage and pumping, grain grinding, saw mill timbering, and in the processing of commodities. However, once the steam engine was invented, the use of large tower mills fell into rapid decline.[6]

During the 19th century, the reliance on windmills grew more towards the use of smaller systems with rotors of one to several meters. The trend was perfected particularly in the U.S. as inventors came up with new types of windmill designs. These small windmill systems were used in agricultural and farm operations such as stock watering and farm home water needs. In fact, between 1850 and 1970, over six million one horsepower or less mechanical output wind machines were installed all over the U.S.[7]

[edit] Charles Brush: Pioneer of the Wind Turbine

Charles Brush has been accredited with developing the first large-scale use, automatically operated wind turbine for the generation of electricity within the United States. The Giant Brush Windmill was based in Cleveland, Ohio and developed by Brush in the winter of 1887 to 1888. His device was a post mill type windmill that featured a multiple bladed “picket fence” type rotor measuring 50 feet (17 m) in diameter and had a hinged tail that pulled the rotor out of the wind. One of the drawbacks of his wind turbine was that at 12 kilowatts it was too low-speed and not very efficient in generating the kind of power needed to produce electricity.[8] By the 1920s, both the use of fan-type and sail-type windmills had proven to be virtually insufficient in effectively generating electricity.[9]

[edit] Bulk Power Large Wind Turbines

The push to develop wind turbines that could be connected to an electrical power grid was pursued in Europe and in the U.S. Similar to the U.S., the use of large windmills to generate electricity was a concept explored in Denmark as early as 1890. A direct correlation in harnessing the wind to produce energy was often precipitated by shortages in fossil fuel. After World War II, however, as fuel prices fell, an interest in the use of large wind turbines to produce electricity waned.[10]

[edit] Wind Farms in the 1970s

Oil embargoes throughout the 1970s brought about resurgence in interest in the use of wind turbines to generate electricity. The concept of the "wind farm" or wind power plants grew throughout Europe and the United States. These wind farms consisted of groups of wind turbines that were fed directly into a utility grid for the sole purpose of generating electricity.[11] A popular application even to this day, one wind farm can produce enough electricity to power thousands of homes. The largest wind farm of this type is located in Texas and has approximately 421 turbines over 47,000 acres (19,020 ha) producing 735 megawatts of electricity.[12]

[edit] How it Works

The operation of a wind turbine is fairly simple in that the kinetic energy of wind is converted into mechanical energy. The wind works to turn two or three propeller-like blades around a rotor. The rotor, connected to a shaft, spins a generator. The higher up the wind turbine is mounted or positioned from the ground, the greater its capacity to capture wind. In most cases, a wind turbine is mounted at least 100 to 300 feet (30.5 to 91 m) above ground level.[13]

Wind turbine farm

[edit] Horizontal Axis Wind Turbines

Wind turbines are either classified as having a horizontal or vertical axis configuration. A horizontal axis wind turbine (HAWT) converts linear motion of the wind into rotational energy used to drive a generator. The same principle applies to the operation of modern water turbines—the flow of water is directly parallel to the rotational axis of the turbine blades. Most commercial models are utility wind turbines connected to an electrical power grid consisting of propeller type rotors on a horizontal axis.[14]

[edit] Vertical Axis Wind Turbines

A vertical axis wind turbine (VAWT) is very similar to a water wheel. Wind is captured perpendicular to the rotational axis of the shaft. The most commonly known type of vertical axis turbine ever commercially produced is known as a Darrieus machine, named after the French designer George Darrieus who invented and patented it in 1931. This wind turbine is rather unconventional looking with two to three C-shaped blades that resemble an eggbeater.[15]

[edit] Large vs. Small Wind Turbine Systems

Today, wind turbines are used in various applications. Large utility based wind turbines over 100 kilowatts are typically grouped together on wind farms and connected to an electrical grid to provide bulk power to many households. Smaller turbines below 100 kilowatts are used on a home per home basis to provide power. Small wind turbines can also be used to power telecommunications dishes and for pumping water. Sometimes they are also connected to diesel generators, batteries, or to a photovoltaic system. This set up is known as a hybrid wind system and is often used in off-grid, remote regions where a utility power grid is not readily available for use.[16]

[edit] References

  1. Glossary. ZMotor. 2008-09-30.
  2. Glossary. Enwin. 2008-09-30.
  3. Wind. Telosnet. 2008-09-30.
  4. Wind. Telosnet. 2008-09-30.
  5. Early Telosnet. 2008-09-30.
  6. Wind. Telosnet. 2008-09-30.
  7. Wind. Telosnet. 2008-09-30.
  8. Brush. Windpower Org. 2008-09-30.
  9. Wind. Telosnet. 2008-09-30.
  10. Wind History. Energy Gov. 2008-09-20.
  11. Wind History. Energy Gov. 2008-09-20.
  12. Farms. Canwea. 2008-09-30.
  13. Wind How. Energy Gov. 2008-09-30.
  14. Horver. Windpower Org. 2008-09-30.
  15. Horver. Windpower Org. 2008-09-30.
  16. Wind How. Energy Gov. 2008-09-20.