The strength of wind 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 frequency 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 Weibull model closely mirrors the actual distribution of hourly wind speeds at many locations. The Weibull factor is often close to 2 and therefore a Rayleigh distribution can be used as a less accurate, but simpler model.
Because so much power is generated by higher wind speed, much of the energy 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 from a particular turbine or wind farm does not have as consistent an output as fuel-fired power plants; utilities that use wind power provide power from starting existing generation for times when the wind is weak thus wind power is primarily a fuel saver rather than a capacity saver. Making wind power more consistent requires that various existing technologies and methods be extended, in particular the use of stronger inter-regional transmission to link widely distributed wind farms, since the average variability is much less; the use of hydro storage and demand-side energy management.
Wind power density (WPD) is a calculation relating to the effective force of the wind at a particular location, frequently expressed in terms of the elevation above ground level over a period of time. It further takes into account wind velocity and mass. Color coded maps are frequently prepared for a particular area, described for example as "Mean Annual Power Density at 70 Meters." The results of the above calculation are used in an index developed by the National Renewable Energy Labs and referred to as "NREL CLASS." The larger the WPD calculation, the higher it is rated by class. Even though wind power is comparable in Texas and Kansas, there are about 10 times as many wind turbines in Texas as there are in Kansas
Because so much power is generated by higher wind speed, much of the energy 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 from a particular turbine or wind farm does not have as consistent an output as fuel-fired power plants; utilities that use wind power provide power from starting existing generation for times when the wind is weak thus wind power is primarily a fuel saver rather than a capacity saver. Making wind power more consistent requires that various existing technologies and methods be extended, in particular the use of stronger inter-regional transmission to link widely distributed wind farms, since the average variability is much less; the use of hydro storage and demand-side energy management.
Wind power density (WPD) is a calculation relating to the effective force of the wind at a particular location, frequently expressed in terms of the elevation above ground level over a period of time. It further takes into account wind velocity and mass. Color coded maps are frequently prepared for a particular area, described for example as "Mean Annual Power Density at 70 Meters." The results of the above calculation are used in an index developed by the National Renewable Energy Labs and referred to as "NREL CLASS." The larger the WPD calculation, the higher it is rated by class. Even though wind power is comparable in Texas and Kansas, there are about 10 times as many wind turbines in Texas as there are in Kansas
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