Efficiency
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.