sentences:  This article covers the design of horizontal axis wind turbines (HAWT) since the majority of commercial turbines use this design.In 1919, the physicist Albert Betz showed that for a hypothetical ideal wind-energy extraction machine, the fundamental laws of conservation of mass and energy allowed no more than 16/27 (59.3%) of the kinetic energy of the wind to be captured.This Betz' law limit can be approached by modern turbine designs which may reach 70 to 80% of this theoretical limit.