Some Effects of Efficiency on Wind Turbine Interference and Maximum Power Production

The effects of finite efficiency on wake interference and power output are studied for identical horizontal-axis wind turbines in line with the wind. Interference occurs whenever turbines reduce the power available to any turbines downwind of them. The analysis uses wake models that are commonly employed in wind farm layout design. The aerodynamic efficiency is varied from 75% to 100% for six identical hypothetical turbines in line parallel to the wind direction with spacing from four to six rotor diameters. Selfish optimization of the power output of individual turbines and co-operative optimization of the total power are considered. For selfish control, all turbines operate at the maximum possible local C-P, based on the aerodynamic efficiency. For co-operative optimization, each turbine operates at a C-P value between zero and the selfish value, and the total power is optimized numerically. The results show that at low efficiency, there is little difference in total power output between the two strategies. As efficiency increases, co-operative optimization produces increasingly more power. As turbine spacing increases, the difference between the strategies decreases. There is, however, a realistic range of efficiencies and spacing over which more power is delivered by co-operative optimization. The simplest form of co-operative optimization requires reducing the power output of the most upwind turbine to allow increased performance from those downwind. This should be an easy strategy to implement in wind farm control.