The theoretical maximum efficiency of a wind turbine under the Betz limit is 59.3%.
German physicist Albert Betz described this limit in 1919. His analysis showed that a turbine cannot capture all the kinetic energy in moving air, because air must continue flowing through and away from the rotor. If the rotor stopped the air completely, no new air could pass through it.
The precise limit is 16/27 of the wind's kinetic power, or about 59.3%. It applies to an idealized rotor, not to an entire wind farm or a real machine. Blade friction, generator losses, turbulence, and electrical equipment reduce practical output.
The Betz limit is often confused with a turbine's capacity factor, which measures actual generation over time compared with maximum possible generation. Capacity factor depends on wind conditions and is not an efficiency ceiling.