The Modification of Wind Turbine Performance by Statistically-Distinct Atmospheric Regimes

Power production from wind turbines can vary from the manufacturer's ratings due to atmospheric stability and wind shear. In this study, meteorological tower and nacelle anemometer data from a wind farm in the High Plains of Central North America were examined to quantify the effects on power generation of atmospheric conditions in the boundary layer. The power law exponent α and the bulk Richardson number RB were used in combination to define a metric for characterizing the 10-60m layer stability. This classification was then used along with the turbine nacelle winds to generate stability-dependent power curves. We observed underperformance during stable/night regimes and overperformance during convective/day regimes at moderate wind speeds (7-12m/s). Statistical testing using the Monte Carlo approach indicated that these results were robust despite the use of nacelle wind measurements. The derived curves and wind data from a separate month were used to predict power output. Predictions that accounted for the stability at the site were ~23% more accurate than those using the manufacturer's power curve. The success in diagnosis and forecasting of power production using boundary layer data demonstrate that non-waked power output is strongly influenced by boundary layer stability, but further research is required using measurements taken across the rotor-disk to obtain a generalized understanding of atmospheric influences.