A Wind Turbine Efficiency Limit Higher than the Lanchester (Betz) Limit

It is shown that the upper limit on the fraction of power that can be extracted from an airstream approaching a wind turbine is about 78% rather than the historical value of 59%. This higher limit is based on the assumption that the wind turbine cannot accelerate the flow at its exit plane above the freestream velocity. The derivation of the historical limit of 59% must either violate the angular momentum equation or the continuity equation.