Wakes from Offshore Wind Farms Observed with Aircraft and Simulated with WRF

Large offshore wind farms are usually clustered around transmission grids to minimize transmission expenses. However, this close proximity can undermine power production in downwind wind farms due to wakes from upwind wind farms. Further, these wind farms represent an additional source of turbulence and, hence, influence the stratification of the marine boundary layer (MABL). Therefore, the wind industry has great interest in determining the spatial dimensions of offshore wind farm wakes to assess the economical potential of planned wind farms, and policymakers are interested in possible changes in the temperature and moisture budget of the MABL which can affect the stratification of the ocean and, hence, the food web of marine life.

To explore the downwind impacts of offshore wind farms, we use wake measurements conducted by a research aircraft and evaluate the performance of the Weather Research and Forecasting (WRF) model’s wind farm parameterization (WFP) in a mesoscale model during stably-stratified atmospheric conditions, in which the wake is expected to be the strongest. The observations were conducted on the 10 September 2016 within the project WIPAFF (Wind PArk Far Field) at the North Sea. The observations allow evaluation of the horizontal and the vertical dimensions of the wake, as well as temperature and moisture changes within the wake. The aircraft measurements and simulations show a warming of 0.6 K and a drying of 0.5 g kg−1 even 45 km downwind of a wind farm cluster, in a region that experiences a wind speed deficit. The model simulates the length and the spatial dimensions of the wake. The temperature and moisture impacts of wind farms are only observed in case of a strong inversion near rotor height, allowing wind turbines to mix air across the inversion.