Wind Energy Potential in Complex Terrain: Discovering Localized Thermo-Topographic Flows and Associated Wind Resources

Much of the current wind resource assessment in Switzerland at the regional and national scale is based on mean decadal wind speeds statistically interpolated onto a 1 km grid using approximately 200 measurement stations spread across the country. This methodology is however unsatisfactory to account for the complex, highly localized thermo-topographic flow phenomena occurring at sub-diurnal timescales that could be harnessed for wind energy production.

Prime examples of such flows are katabatic and anabatic winds in Alpine valleys. Katabatic winds form when outgoing long wave radiation cools air at higher elevations. The cooled, high density wind then drains downslope under the influence of gravity. These winds combined with channeling effects of valleys they can reach speeds up to 50m/s. Anabatic winds form under the influence of solar heating, which lead to up-valley winds during the day. Due to their topography and the jet-stream, the Alps also form a barrier that often separates colder air from warmer air. The pressure gradient that is caused by this temperature difference accelerates the air when it flows through this barrier resulting in ‘pass-winds' that have been shown to be attractive sites for wind energy generation.

Using the example of Switzerland, this study explores the potential in wind energy that arises from topographic wind maxima. We perform high-resolution simulations using the WRF-LES for certain canonical topography features in the Swiss Alps – namely, (a) Valleys ( e.g: Rhine Valley), (b) Mountain Passes ( e.g: Flüelapass) and (c) Glaciers (e.g: Aletsch glacier system). We force these simulations using the Meteoswiss COSMO-2 reanalysis data to study ‘real-world' scenarios. The simulations are validated using relevant weather station data and standard exclusion principles for wind resource development are applied to provide a realistic picture of the additional wind resource discovered.