Efficiency

Power curve (power generated versus wind speed) for two Vestas V90 models. They are most efficient at a wind speed of ~11–12 m/s (25–27 mph). At wind speeds of 25 m/s and above (≥56 mph), the wind turbines shut down.

With wind energy, efficiency is often confused with capacity factor.

Wind turbines are actually quite efficient, extracting as much energy from the wind as physically possible, although 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 faster wind speeds, the blades must be pitched to be less efficient, so that their rotation rate remains constant.