Wind Energy Conversion Efficiency Limit

Abstract

The momentum analysis of Sharpe [3] is considered further. It is shown that the maximum wind energy conversion efficiency limit, or the Betz limit of 59.3%, deduced from conventional actuator disc theory is the limiting stationary maximum value as wind turbine rotor speed approaches infinity and rotor outlet swirl approaches zero. Theoretically, solution of the governing equations indicates 100% conversion efficiency could be possible with suitable wind turbine design and without wake limitations for all tip-speed ratios. Analogous to the thermodynamics laws for heat engines and similar to a Pelton wheel with hydro power, the wind turbine efficiency is not limited by the laws of fluid mechanics but by physical constraints only. Low tip-speed ratio would have greater prospects in achieving higher conversion efficiency in practice. Though the set of equations derived in the present technical note has assumed uniform bound circulation along the blade span, the same approach can be used for determination of optimum conditions for other blade designs or using other assumptions.