Synergistic effects of turbine wakes and atmospheric stability on power production at an onshore wind farm
We first discuss the applicability of instrument-derived stability parameters, including the wind shear-exponent, α, turbulence intensity, IU, and turbulence kinetic energy, TKE, against the more physically-based Obukhov length, L, to accurately describe the wind speed and turbulence profiles in the rotor area. Next, we divide the measurement period into five stability classes (strongly stable, stable, neutral, convective, and strongly convective) to discern stability-effects on power output at both upwind and downwind turbines to assess the role of atmospheric stability on turbine wakes and power production. Stability effects at upwind turbines are significant: when IU is considered, the power generated for a given wind speed is twenty percent higher during strongly stable conditions than during strongly convective conditions. Power produced by downwind turbines is more complex due to the interactions between atmospheric stability and turbine wakes. During convective conditions, wake effects on downwind power production are expected to be small because turbulence dissipates turbine wakes. Under stable conditions, in contrast, turbine wakes will not be largely dissipated by turbulence and power production is expected to be attenuated at downwind turbines as compared to upwind turbines. Therefore, although leading-edge turbines at this farm generate more power during stable conditions than during convective conditions, the total farm power collection is more complicated.