Locating wind farms offshore generally increases the capacity for power generation relative to placement onshore, due to the stronger and more persistent winds over sea compared to land. Such offshore wind farms function by harvesting a part of the wind energy that is itself the main driver of near-surface circulation and mixing. It is thus important to estimate both the local and regional impacts that a basin wide deployment of offshore wind farms could have on the marine environment. In this study we focus on the Baltic Sea, which is one of the main areas for offshore wind farm development within the European Union, and quantify the impact of such large-scale development on the exchange of energy across the air-sea interface. Our approach involves considering the envisaged future wind farm coverage and modifying surface winds accordingly, so as to take account of the combined wind wakes from individual turbines throughout the Baltic Sea. We implement these altered wind fields as forcing for a three dimensional hydrodynamic model of the entire Baltic Sea, and examine the anomaly in several properties relative to a model run with unaltered winds. Based on an idealized mixed layer energy budget, we identify two routes by which the wake effect alters vertical mixing - mechanical wind work and buoyancy forcing - and ultimately show substantial reductions to mixed layer depth in the close vicinity of wind turbines. Our simulations indicate that such changes are mostly limited to areas within a radius of a few kilometres of the nearest wind turbine, further suggesting that moderate changes to wind farm placement may considerably alter the local impact on the marine environment.
Twelves et al. (Fri,) studied this question.