In 2013, a study by the German Federal Environmental Agency (Umweltbundesamt) concluded that almost 7 W of electrical power per m² could be generated from wind energy. However, Axel Kleidon, Max Planck Institute for Biogeochemistry, Jena, Germany, and colleagues have used atmospheric model simulations to calculate that a maximum of 1.1 W of electricity could be generated per m² over a large (105 km²) wind farm in the windy state of Kansas, USA. The correlation between the amount of energy generated and the number of wind turbines is not linear, as more turbines increasingly slow down the wind. This is particularly noticeable in the cases of very high turbine densities. The actual value of the potential depends on the wind conditions in the specific location. Currently, the researchers are investigating to which extend this applys to wind energy generation in Germany.

At the end of 2014, Germany’s wind turbines had a total installed capacity of 39 GW. The German Federal Environmental Agency assumes that it would be possible to build more wind farms that would reach a total capacity of around 1,200 GW, covering an area of 14 % of Germany. These numbers correspond to 23 W of installed capacity per square metre, and is expected to yield an output of approximately 6.7 W of electricity per square metre. Maybe this estimate is far too optimistic: Kansas is almost half the size of Germany and currently has around 2.7 GW of installed capacity, which translates to 0.013 W/m².

• Max-Plank-Gesellschaft, Munich, Germany