More Wind, Falling Efficiency: The Driving Factors of German Onshore Wind Power Generation

ABSTRACT Wind power has become the most important source of electricity generation in Germany, providing more than a quarter of its electricity consumption in 2022. The growth in wind power generation has been mainly driven by an increase in installed capacity, but other factors have also contributed significantly and have been less investigated. Here, we decompose the increase in German wind power generation into its driving factors: rotor swept area, number of operating turbines, available input wind power density and the relation between input wind power and generated electricity—here called system efficiency. Additionally, input wind power density is decomposed into its components: hub height change, new wind profiles due to new locations and annual variations. We find that the increase in average rotor swept area had the biggest positive impact on the change in output, closely followed by the increase in the number of operating turbines. Input wind power density increased moderately due to increasing hub heights; however, output power density remained almost constant as system efficiency, that is, the amount of input wind power converted to electricity, declined by 5.9 percentage points between 2005 and 2022. Approximately 66% of this decrease occurred due to turbine ageing, 16% due to the combined decrease in specific power and 16% due to increase in input power density caused by taller turbines. Lastly, we show that there is a trade‐off between output power density and average capacity factor. The recent decline in average specific power from 400 to 380 W/m 2 has lowered the total output power by about 1.2% compared to a scenario without a change in specific power, but average capacity factors increased by 4.5%.