Performance of Downwind Turbines in Complex Terrains

Abstract

This study verified an advantage in the performance of downwind-turbines in complex terrain, compared with upwind-turbines. The comparison, for otherwise identical machines, was by wind turbine simulations, field tests, and local area wind predictions. A three-dimensional power calculation function was formulated based on momentum theory. It indicates the advantage of downwind-turbines in up-flow wind, as they have smaller misalignment due to their negative tilt angles. Validities of the function and the downwind-turbine advantage were verified through field tests, in both upwind and downwind configurations of a 100 kW turbine. In similar up-flow wind conditions, the downwind configuration produced significantly more power than the upwind configuration. Local area wind predictions were also conducted for a windfarm in a typical complex terrain; it showed that the utilized wind energy is distributed mainly at positive inclination, and that time and energy average inclinations were respectively +6.0 deg and +7.5 deg. Furthermore, 2 MW downwind-turbines were shown to produce 7.6% more annual energy in complex terrain than upwind-turbines with same dimensions.