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Wind power is the conversion of wind energy into more useful forms, usually electricity, using , 9% in Spain , and 7% in Germany . European wind companies grow in U.S. 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 Windmill s (a much older technology), wind energy is used to turn mechanical machinery to do physical work, such as 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 plentiful, Renewable , widely distributed, clean, and reduces toxic atmospheric and Greenhouse Gas Emissions if used to replace fossil-fuel-derived electricity (which hasn't ever happened due to the need for conventional backup of all wind inputs to a grid). The Intermittency of wind seldom creates problems when using wind power at low to moderate penetration levels (though such intermittency has caused problems for grid stability in Denmark and Germany, where penetration is greatest).http://www.ieawind.org/AnnexXXV/Meetings/Oklahoma/IEA%20SysOp%20GWPC2006%20paper_final.pdf IEA Wind Summary Paper, ''Design and Operation of Power Systems with Large Amounts of Wind Power'', September 2006 WIND ENERGY There is an estimated 50 to 100 times more wind energy than plant biomass energy available on Earth. Most of this wind energy can be found at high altitudes where continuous wind speeds of over 160 km/h (100 mph) occur. Eventually, the wind energy is converted through friction into diffuse heat throughout the Earth's surface and the atmosphere. The origin of wind is complex. The Earth is unevenly heated by the sun resulting in the Pole s receiving less energy from the sun than the Equator does. Also the dry land heats up (and cools down) more quickly than the seas do. The differential heating powers a global Atmospheric Convection system reaching from the Earth's surface to the Stratosphere which acts as a virtual ceiling. Wind variability and turbine power .]] The power in the wind can be extracted by allowing it to blow past moving wings that exert Torque on a rotor. The amount of Power transferred is directly proportional to the density of the air, the area swept out by the rotor, and the cube of the wind speed. The power available in the wind is given by: :, where P = power in watts, alpha = Efficiency constant, rho = mass density of air in kilograms per cubic meter, r = radius of the wind turbine in meters, and v = velocity of the air in meters per second. The Mass Flow of air that travels through the swept area of a wind turbine varies with the wind speed and air density. As an example, on a cool 15 °C (59 °F) day at sea level, air density is 1.225 kilograms per cubic metre. An 8 m/s breeze blowing through a 100 meter diameter rotor would move almost 77,000 kilograms of air per second through the swept area. The Kinetic Energy of a given mass varies with the square of its velocity. Because the mass flow increases linearly with the wind speed, the wind power available to a wind turbine increases as the cube of the wind speed. The power of the example breeze above through the example rotor would be about 2.5 megawatts. As the wind turbine extracts energy from the air flow, the air is slowed down, which causes it to spread out and diverts it around the wind turbine to some extent. Albert Betz , a German physicist, determined in 1919 (see Betz' Law ) that a wind turbine can extract at most 59% of the energy that would otherwise flow through the turbine's cross section. The Betz limit applies regardless of the design of the turbine. s.]] Windiness varies, and an average value for a given location does not alone indicate the amount of energy a wind turbine could produce there. To assess the climatology of wind speeds at a particular location, a probability distribution function is often fit to the observed data. Different locations will have different wind speed distributions. The distribution model most frequently used to model wind speed climatology is a two-parameter Weibull Distribution because it is able to conform to a wide variety of distribution shapes, from Gaussian to exponential. The Rayleigh model, an example of which is shown plotted against an actual measured dataset, is a specific form of the Weibull function in which the shape parameter equals 2, and very closely mirrors the actual distribution of hourly wind speeds at many locations. Because so much power is generated by higher windspeed, much of the average power available to a windmill comes in short bursts. The 2002 Lee Ranch sample is telling; half of the energy available arrived in just 15% of the operating time. The consequence is that wind energy does not have as consistent an output as fuel-fired power plants; additional output can only be made to compensate for load increase by utilizing advanced wind storing technologies (e.g. giant compressed air storage-tank facilities). — |
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