How does Betz’s law limit the power a wind turbine can extract from wind?

Betz’s law establishes a theoretical limit on the efficiency of a wind turbine, stating that no turbine can capture more than approximately 59.3 percent of the kinetic energy available in the wind.1

This limitation exists because wind must maintain a finite velocity as it passes through and exits the turbine blades; if a turbine were to extract 100 percent of the energy, the air would come to a complete stop, preventing further air from passing through the rotor. In practical application, actual wind turbines are less efficient than this theoretical maximum. For instance, modern propeller-type windmills typically achieve efficiencies of roughly 47 percent.1

The power a turbine can extract is also heavily dependent on environmental factors, specifically the cube of the wind velocity and the square of the rotor diameter. Because of these physical constraints and the requirement for consistent wind speeds, wind energy faces significant challenges in meeting the total power demands of industrialized nations.1