On the expansion of renewable energies in Germany and the problems related to fluctuation in the German electricity grid

The expansion of renewables energies in Germany especially in the solar and wind sector are key factors for the transformation to net zero carbon emissions. Both sources have significant seasonal fluctuations in production. Even if the technologies complement each other in the sense that solar makes a greater contribution in summer and wind is represented in winter, these contributions are not guaranteed; there may be a poor supply or even a so called "Dunkelflaute" , a period with very low wind and solar energy production. However, it is precisely these periods of poor wind and solar coverage that prevent conventional power plants from being shut down, as they have to fill the gap. In order to raise awareness of the mentioned problems, a further expansion of wind and solar power plants is simulated based on the data of 2023 and the need for storage technologies is calculated to solve imbalances. The calculations are not designed to accurately reflect the energy supply in future years. Instead the aim is to provide the fundamental relationships between production and consumption of carbon neutral/green energy. The calculations show that the expansion of wind and solar power plants alone will not lead to a stable electricity supply and that storage technologies will play an important role in the future. In summer, there is energy that must be frequently stored and retrieved within short cycles (24 hours). However, there is also a substantial energy surplus during the summer months that needs to be shifted to periods of low production in autumn and winter, requiring storage over timescales of weeks to several months. Therefore, the paper analyzes scenarios involving both battery and hydrogen storage. It becomes evident that both technologies contribute in distinct and complementary ways: batteries are well suited for high-frequency, short-term storage with limited capacity needs, while hydrogen plays a crucial role in storing large amounts of energy over extended periods. Future work will include a more detailed analysis of regional differences and financial aspects, aiming to refine and optimize the proposed storage scenarios.