Improved rotor design for a small scale horizontal axis wind turbine suitable for low wind potential

Abstract

The design wind speeds of most of the existing wind turbine rotors are in the range of 6 to 15 m/s with cut-in wind speed of 3.5 m/s. The performance of such a wind turbine in Sri Lanka is not satisfactory, where the wind velocities are relatively low. This is due to low initial torque, which leads to difficulty in starting, as well as due to poor running efficiencies. This makes wind turbines less attractive for areas with low wind speeds. The main objectives of this study were to predict the performance of the existing NERDC wind turbine system and identity the main causes for its poor running performance at low wind speed and thereby design a rotor with improved performance. When improve the performance of the rotor to extract more energy from low wind-speeds, cut-in wind speed and design wind speed of wind turbine should be reduced. Low starting torque of wind rotors was identified as a main restriction against the reduction of cut-in wind speed of wind turbines. This study intends to analyse the aerodynamics of wind rotors theoretically and thereby introduces appropriate changes to the geometrical parameters of the blades. Especially, possibility of increase of solidity of the rotor, without effecting adversely on its aerodynamic efficiency was analysed. The blade elementary theory and the momentum theory were used to analyse the aerodynamic performance of rotors theoretically and these results were validated by wind tunnel model testing. The results of this study indicate that the permanent magnet generator and rotor of the NERDC system were not matched properly, which resulted in low overall system efficiency. In addition, the design parameters of the rotor were not appropriate for sites with low wind potential. Other finding of this study was suitable wind rotor for extract more energy from low wine potential, should be· with higher diameter and higher solidity.