Modelling large-scale wind farms and their climatic effects in the North and South Baltic Seas

The operation of large offshore wind farms decreases wind speeds in and around the wind farm areas. Wind farm wakes can significantly impact annual energy production, especially in areas with high installed capacity density. We simulate the atmospheric flow during one typical year to estimate the wind resources for the North and South Baltic Seas using three scenarios: no wind farms, wind farms as installed in November 2021, and future wind farm deployment in 2030. We use two wind farm parameterisations in the WRF mesoscale model to model the wind farm wakes. The simulation’s wind speed climatology with and without wind farms is evaluated against a few available tall mast observations. Maps and spatial transects are created to illustrate the potential reductions in wind speed, capacity factors, load hours, and the distances needed for the wind to recover to its background values.

Based on simulations from this study (the first of its kind using nearly 40,000 individual wind turbines of over 400 different types), the yearly average (or over 20% in some regions). The wake’s impact on the capacity factor reductions can be detected from a distance of 20 up to 80 km downstream of the wind farms. This distance mainly depends on the installed capacity density, the extent of the wind farm and the background wind speed. Using an additional post-processing tool, we can calculate the production for each wind turbine in the domain and compare their production under various scenarios and parameterisations. The simulations also show that large wind farms can affect fields other than wind speed at hub height.  They show a decrease in 2-m temperature and an increase in boundary layer height, particularly in summer. An increase in cloud fraction at the wind farm locations, particularly in winter, can also be detected in the modelling results. Although the mean annual changes in these quantities are not statistically significant at 95%, under particular stability conditions or seasons, they are.