The Betz limit states that no wind turbine can capture more than 59.3% of the wind’s kinetic energy.
German physicist Albert Betz described the theoretical limit in 1919. A turbine must allow some air to continue moving downstream; if it removed all the air’s kinetic energy, airflow through the rotor would stop. The maximum therefore occurs when the turbine slows the wind substantially but does not bring it to a complete halt.
The limit applies to an idealized turbine in an open flow and is not a prediction that every real turbine approaches 59.3 percent. Blade friction, generator losses, turbulence, electrical losses, and site conditions reduce practical performance. The Betz limit is a wind-energy principle, not a general efficiency limit for all renewable technologies.