Assessment of Engineering Models for Large-Scale Cluster Wakes Using In Situ Airborne Measurements

Germany is to be climate-neutral by 2045, with important interim targets set for 2030. This includes a 65% reduction in greenhouse gas emissions compared to 1990 and a significant increase in the proportion of renewable energies in the electricity mix to at least 80% by 2030. This share currently stands at around 56%. A key element of this strategy is the Renewable Energy Sources Act (EEG 2023), which provides for an accelerated expansion of renewable energies. This includes wind and solar energy, with particularly ambitious targets for offshore wind energy: at least 30 gigawatts by 2030, 40 gigawatts by 2035 and 70 gigawatts by 2045. 

This strong expansion of offshore wind energy brings with it several challenges. The biggest is certainly the space required in the German Bight and in the Baltic Sea. Studies are already showing long wake lengths of wind farms and wind farm clusters, which can reach wind farms located downstream and thus reduce their energy production. With the increasing expansion of wind energy in the German Bight, the influence of wind farms on each other will increase and lead to greater power losses. This influence must be considered in future planning. The models often used by industry are so-called engineering models. They have low computational costs due to their fast calculations but are made for power yield calculations within a wind farm and not for modelling the wake in the far field. An approach was taken to use different setups of this model to evaluate the results against measurement flights of a research aircraft in the lee of large wind farm clusters in the German Bight. As part of the X-Wakes project, the wakes of wind farm clusters were measured and evaluated under different meteorological conditions using the D-IBUF research aircraft operated by the Technische University of Braunschweig. This data was then used to evaluate the performance of the Weather Research and Forecasting Model with Wind Farm Parameterization (WRF-WF) and the engineering model "FOXES" (Farm Optimization and eXtended yield Evaluation Software) with four different setups.