Mountain wave and downslope winds impact on wind power production

Abstract. Vertically propagating mountain waves, accompanied by strong downslope winds, occur frequently along the coast of Norway and cause accelerated surface winds on the lee side and downstream of the mountain. Mountain waves form when stably stratified air flows over a mountain and can potentially impact the power production in wind parks located in complex terrains. Although mountain waves and downslope windstorms have received significant attention within the meteorology community, they have received less focus within the wind energy industry. Taking advantage of wind and power production data from a grid of 67 wind turbines spread across two nearby mountains, this study documents accelerated wind speeds and enhanced power production on the lee side of the mountains compared to at the mountain crest. The result of this study suggests that considering mountain waves in the planning phase of future wind parks may allow for an optimal layout of the wind turbines and improve the profitability. The non-dimensional mountain height Ĥ, is a key parameter for describing the development of mountain waves, and this study finds a strong relationship between Ĥ and the accelerated downslope winds. The results of this study suggest that mountain-wave-induced accelerated downslope winds tend to occur in the wind park when Ĥ < 3, above this value, the airflow is more likely to be blocked and diverted around the barrier. Finally, the Weather Research and Forecasting model reproduces the spatial variations in the wind speeds within the two wind parks relatively well during periods of strong downslope winds and blocking. However, the differences in the wind speeds at the windward side, the mountain top, and the lee side, are not as pronounced as in the observations.