Abstract: A horizontal-shaft wind machine having improved low wind speed performance and greater overall efficiency consists of multiple rotors, wherein each successive rotor is larger in diameter than the previous rotor moving from the most windward rotor to the most leeward rotor. Each rotor may be coupled to a shroud/diffuser that is displaced axially downwind from the rotor.

Abstract: A horizontal-shaft wind machine having improved low wind speed performance and greater overall efficiency consists of multiple rotors, wherein each successive rotor is larger in diameter than the previous rotor moving from the most windward rotor to the most leeward rotor. Each rotor may be coupled to a separate concentric shaft, and all rotors may rotate in the same direction with the output shafts of each rotor coupled via an overrunning clutch to a single shaft, the output of which is used to drive the load. Winglets attached to the leading edge and tip of the rotor sails improve low wind startup torque.