Characterizing the impact of spatial scales on near-surface wind speed and wind power generation in a mountainous environment

Near-surface wind fields are altered over mountainous topography, giving rise to complex wind flow patterns due to sheltering, acceleration, channelling, deflections, blocking or recirculation. However, the impact of the resulting spatio-temporal wind fields on wind energy potential remains largely unknown. While wind modelling approaches can describe highly resolved spatio-temporal wind fields in mountainous terrain rather well, wind fields cannot be generated in a reasonable amount of computational time. Models are therefore strongly limited in space and time for many applications. In mountainous regions, wind farm planning is thus much more challenging than in flat regions.

To investigate the variability of wind fields and its impact on wind energy production in mountainous terrain, we applied a computationally efficient statistical downscaling model approach to a small region in the Swiss Alps. This allowed us to analyze the impact of horizontal resolutions on spatial wind speeds and energy yield in a mountainous area. We applied the statistical approach of Helbig et al., 2017 to downscale coarse wind speed values to the fine scale based on local terrain parameters. This approach introduces two dominant local wind-topography interactions: sheltering and speed-up on coarse wind speed. Then, based on the resulting spatio-temporal near-surface wind fields and a common theoretical power curve, we calculated long-term wind energy yield. Through a sensitivity analysis, we assessed the impact of varying horizontal spatial resolutions in the mountainous environment on overall and local wind energy yield. Specifically, we addressed the impact when decreasing horizontal resolutions from grid cell sizes of 100 m down to 5 m. Resulting spatial variations will be discussed as functions of local terrain parameters, as well as wind speeds.

Helbig, N., Mott, R., van Herwijnen, A., Winstral, A. and Jonas, T. (2017): Parameterizing surface wind speed over complex topography. J. Geophys. Res., 122, 651–667.