Power loss by blade deflection in flexible rotor wind turbines

Abstract

Effects of deflection onto the performance of small wind turbines with flexible rotor-blades have been studied and analysed. The goal of the study has been the evaluation of the wind turbine output power loss due to angular deflection because of bending effects caused by gravity. Wind turbine blades have been deformed under constant load at the tip of the blade for periods up to 40 days. Deformation process has been accelerated using a very heavy load and the corresponding angular deflection has been obtained. Wind turbine performance has been characterized through the P-V curve for different wind speed operation conditions. Tests have been run for different deformation states to compare the evolution of the power loss with angular deflection. Results from experimental tests have shown there is a constant power loss with deformation increase. Power reduction for angular deflection of 2.3o is between 35% and 45% for blade tip wind speed from 27.6 m/s to 42 m/s. Power coefficient, C p , has also been analyzed and determined for the angular deflection of 2.3o and 4.3o; the reduction of the power coefficient value has been computed through a power loss factor, f P , that shows a reduction in the range of 25% to 50% for the 2.3o angular deflection, and between 45% and 55% for the angular deflection of 4.3o.