The starting and low wind speed behaviour of a small horizontal axis wind turbine

In order to extract the maximum possible power, it is important that the blades of small wind turbines start rotating at the lowest possible wind speed. The starting performance of a three-bladed, 2 m diameter horizontal axis wind turbine was measured in field tests, and compared with calculations employing a quasi-steady blade element analysis. Accurate predictions of rotor acceleration were made for a large range of wind speeds, using a combination of interpolated aerofoil data and generic equations for lift and drag at high angles of incidence. Also, significantly different values for the wind speeds at which the turbine rotor starts and ceases to rotate were determined, indicating limitations in the traditional method of describing starting performance with a single ʹcut-inʹ wind speed based on 10-min averages of wind speed and turbine power. The blade element calculations suggest that most of the starting torque is generated near the hub, whereas most power-producing torque comes from the tip region. The significance of these results for blade design is discussed.