KfW Research: Wind and solar energy complement each other very well

• Last year, these two sources of energy met 45 per cent of Germany’s electricity needs
• On average, conditions for both wind and solar are unfavourable in Germany on only 15 days of the year
• Increasing battery storage and flexibility of electricity demand offer further expansion potential

Last year, 56 per cent of electricity consumed in Germany was generated from renewables. Wind energy accounted for 29 per cent and solar energy for 16 per cent of the electricity consumed. Both renewable energy sources complement each other extremely well. Solar harvest is highest on days with little wind, and vice versa. In each of the past three years, unfavourable conditions for wind and solar coincided on only around 15 days. That was only around four per cent of all days in the year, and all of these were between October and February.

At the same time, the share of wind and solar electricity is increasingly less likely to fall below a particular absolute threshold. In the year 2025, both types of generation together accounted for low shares of electricity generation (below 15 per cent) on 16 days, whereas four years ago it was 31 days, almost twice as many. In other words, the expansion of renewables is having an impact. The number of days on which the share of wind and solar energy was very low (below ten per cent) has also fallen. It has dropped from nine days in 2021 to only six days last year.

These are some of the findings of a study by KfW Research on wind and solar electricity.

“The strong expansion of wind and solar energy does not pose a cluster risk for Germany. Both sources of energy work together effectively,”

said Dr Dirk Schumacher, Chief Economist of KfW.

The sun generates electricity only during the day. Wind is more constant throughout the day but usually generates slightly more electricity at night. Furthermore, the sun shines more frequently and for longer in the summer while electricity generation from wind reaches its maximum in the winter. But the compensation is not perfect, which means solar and wind energy generates less electricity in the winter half-year.

On the days with little wind and solar generation in 2025, more electricity was imported (15 per cent compared with five per cent on average for the whole year). Besides, more electricity was then generated from fossil fuels in Germany, both from coal (29 per cent compared with 21 per cent) and from other fossil fuels, particularly natural gas (29 per cent compared with 16 per cent).

“Renewables are now the mainstay of electricity supply in Germany. The expansion is already well advanced, but further steps are necessary,”

said Schumacher.

“Looking ahead, electricity generation from biomass could be deployed in an even more targeted manner during periods of low wind and solar output. Making demand more flexible, adding more battery storage and new gas power plants that can run on hydrogen in the medium term are also an important part of the solution.”

The complete study can be accessed at Focus on Economics | KfW (in German)