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Monday, 27 June 2011

High altitude wind power

High altitude wind power

From Wikipedia, the free encyclopedia
Kitegen
High altitude wind power (HAWP) has been imagined as a source of useful energy since 1833 with John Etzler's vision[1] of capturing the power of winds high in the sky by use of tether and cable technology. An atlas of the high altitude wind power resource has been prepared for all points on earth.[2]
Various mechanisms are proposed for capturing the kinetic energy of winds such as kites, kytoons, aerostats, gliders, gliders with turbines for regenerative soaring,[3] sailplanes with turbines, or other airfoils, including multiple-point building- or terrain-enabled holdings.[4] Once the mechanical energy is derived from the wind's kinetic energy, then many options are available for using that mechanical energy: direct traction,[5][6] conversion to electricity aloft or at ground station, conversion to laser or microwave for power beaming to other aircraft or ground receivers. Energy generated by a high-altitude system may be used aloft or sent to the ground surface by conducting cables, mechanical force through a tether, rotation of endless line loop, movement of changed chemicals, flow of high pressure gases, flow of low-pressure gases, or laser or microwave power beams.



Turbine design and construction

Turbine design and construction

Components of a horizontal-axis wind turbine
Wind turbines are designed to exploit the wind energy that exists at a location. Aerodynamic modeling is used to determine the optimum tower height, control systems, number of blades and blade shape.
Wind turbines convert wind energy to electricity for distribution. Conventional horizontal axis turbines can be divided into three components.
  • The rotor component, which is approximately 20% of the wind turbine cost, includes the blades for converting wind energy to low speed rotational energy.
  • The generator component, which is approximately 34% of the wind turbine cost, includes the electrical generator, the control electronics, and most likely a gearbox (e.g. planetary gearbox,[19] adjustable-speed drive [20] or continuously variable transmission[21]) component for converting the low speed incoming rotation to high speed rotation suitable for generating electricity.
  • The structural support component, which is approximately 15% of the wind turbine cost, includes the tower and rotor yaw mechanism.[22]
A 1.5 MW wind turbine of a type frequently seen in the United States has a tower 80 meters high. The rotor assembly (blades and hub) weighs 48,000 pounds (22,000 kg). The nacelle, which contains the generator component, weighs 115,000 pounds (52,000 kg). The concrete base for the tower is constructed using 58,000 pounds (26,000 kg) of reinforcing steel and contains 250 cubic yards (190 cubic meters) of concrete. The base is 50 feet (15 m) in diameter and 8 feet (2.4 m) thick near the center.[23]

History

History

James Blyth's electricity generating wind turbine photographed in 1891
Windmills were used in Persia (present-day Iran) as early as 200 B.C.[1] The windwheel of Heron of Alexandria marks one of the first known instances of wind powering a machine in history.[2][3] However, the first known practical windmills were built in Sistan, a region between Afghanistan and Iran, from the 7th century. These "Panemone" were vertical axle windmills, which had long vertical driveshafts with rectangular blades.[4] Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind grain or draw up water, and were used in the gristmilling and sugarcane industries.[5]
Windmills first appeared in Europe during the middle ages. The first historical records for their use in England date to the 11th or 12th centuries and there are reports of German crusaders taking their windmill-making skills to Syria around 1190.[6] By the 14th century, Dutch windmills were in use to drain areas of the Rhine delta.
The first automatically operated wind turbine, built in Cleveland in 1887 by Charles F. Brush. It was 60 feet (18 m) tall, weighed 4 tons (3.6 metric tonnes) and powered a 12kW generator.[7]
The first electricity generating wind turbine, was a battery charging machine installed in July 1887 by Scottish academic James Blyth to light his holiday home in Marykirk, Scotland.[8] Some months later American inventor Charles F Brush built the first automatically operated wind turbine for electricity production in Cleveland, Ohio.[8] Although Blyth's turbine was considered uneconomical in the United Kingdom[8] electricity generation by wind turbines was more cost effective in countries with widely scattered populations.[6] 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 largest machines were on 24-metre (79 ft) towers with four-bladed 23-metre (75 ft) diameter rotors. By 1908 there were 72 wind-driven electric generators operating in the US from 5 kW to 25 kW. Around the time of World War I, American windmill makers were producing 100,000 farm windmills each year, mostly for water-pumping.[9] By the 1930s, windmills for electricity were common 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-metre (98 ft) tower, connected to the local 6.3 kV distribution system. It was reported to have an annual capacity factor of 32 per cent, not much different from current wind machines.[10] In the fall of 1941, the first megawatt-class wind turbine was synchronized to a utility grid in Vermont. The Smith-Putnam wind turbine only ran for 1,100 hours before suffering a critical failure. The unit was not repaired because of shortage of materials during the war.

Types

Types

Three primary types of wind turbine in operation.
The three primary types:VAWT Savonius, HAWT towered; VAWT Darrieus as they appear in operation.
Wind turbines can rotate about either a horizontal or a vertical axis, the former being both older and more common.[13]

[edit] Horizontal axis

Components of a horizontal axis wind turbine (gearbox, rotor shaft and brake assembly) being lifted into position
Horizontal-axis wind turbines (HAWT) have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.[14]
Since a tower produces turbulence behind it, the turbine is usually positioned upwind of its supporting tower. Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted forward into the wind a small amount.

Resources

Resources

A quantitative measure of the wind energy available at any location is called the Wind Power Density (WPD) It is a calculation of the mean annual power available per square meter of swept area of a turbine, and is tabulated for different heights above ground. Calculation of wind power density includes the effect of wind velocity and air density. Color-coded maps are prepared for a particular area described, for example, as "Mean Annual Power Density at 50 Meters." In the United States, the results of the above calculation are included in an index developed by the U.S. National Renewable Energy Lab and referred to as "NREL CLASS." The larger the WPD calculation, the higher it is rated by class. Classes range from Class 1 (200 watts/square meter or less at 50 meters altitude) to Class 7 (800 to 2000 watts/square meter). Commercial wind farms generally are sited in Class 3 or higher areas, although isolated points in an otherwise Class 1 area may be practical to exploit.[12]

Wind turbine

Wind turbine

From Wikipedia, the free encyclopedia
Offshore wind farm using 5MW turbines REpower M5 in the North Sea off Belgium
This article discusses wind-powered electrical generators. See windmill for wind-powered machinery used to grind grain or pump water.
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or pumping water, the device is called a windmill or wind pump. Developed for over a millennium, today's wind turbines are manufactured in a range of vertical and horizontal axis types. The smallest turbines are used for applications such as battery charging or auxiliary power on sailing boats; while large grid-connected arrays of turbines are becoming an increasingly large source of commercial electric power.