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[[file:Vestas-V90-power-curve.png|thumb|Power curve (power | [[file:Vestas-V90-power-curve.png|thumb|Power curve (power generation versus wind speed) for two Vestas V90 models. They are most efficient at wind speeds of ~11–12 m/s (25–27 mph). At wind speeds of 25 m/s and above (≥56 mph), the wind turbines shut down.]] | ||
''Efficiency'' is often – incorrectly – confused with ''[[capacity factor]]''. | |||
Wind turbines | Thermal plants (e.g., nuclear and coal) are rather inefficient, with around two-thirds of the energy released from their fuel being lost to heat. But they can have a very high capacity factor, particularly if they are used to provide [[Electrical grid|base load]]. | ||
Wind turbines, on the other hand, can be quite efficient, capturing and converting most of the energy from the wind that is physically possible (the [[wikipedia:Betz%27s_law|Betz limit]]), although only at a rather narrow range of wind speed. | |||
At wind speeds slower than ideal, there is not enough wind energy to generate power at the full rate of the wind turbine’s design. | At wind speeds slower than ideal, there is not enough wind energy to generate power at the full rate of the wind turbine’s design. | ||
At faster wind speeds, the blades must be pitched | At faster wind speeds, the blades must be pitched so that their rotation rate remains constant, thus reducing efficiency. | ||
The result is that wind turbines have a rather low [[capacity factor]] of 25%–35%, and that is due to the intermittent and variable wind instead of the demands of the [[Electrical grid|grid]]. | |||
''See also:'' [[Availability]]. |