A rapid and large-scale expansion of renewable energy sources is the central prerequisite for a successful energy transition. That much has become more than clear in recent years. With the ambitious goal of generating electricity from 80% renewables by 2030, the Federal Government has clearly focused on expansion. But what happens when all these systems produce at the same time? On very sunny and windy days, solar and wind are already producing so much electricity that the power grids are reaching their capacity limits. Some of the systems must then be switched off to ensure secure network operation. In our article”Battery storage as a key technology in the energy revolution“This is described in detail on an example day. Looking at these shutdowns over the entire year, a full 3% of renewable generation had to be shut down as early as 2021 to avoid overloading the electricity infrastructure. In absolute amounts, this corresponds to 5.82 TWh. By way of comparison, a household has an average annual consumption of 2,800 kWh. With the regulated quantity alone, you could therefore supply over 2 million households with electricity for a year.
The reason for this is that the current electricity infrastructure in Germany is not designed for the high volatility of renewable generation plants. As a result of their strong weather dependency, solar systems, for example, produce primarily during the day on sunny days. If it is also very windy on these days, large amounts of electricity from wind turbines are also pushed into the grid. So much electricity is then produced in certain regions in total that the lines are not sufficient to transport it to consumers. As a result, some of the renewables must be switched off so as not to put excessive strain on the power lines. This is because up to now, these have been designed for a power supply from conventional large power plants that is easily controlled and as close to load as possible. To ensure that the total amount of electricity in Germany is sufficient, generation must be ramped up elsewhere to compensate for the shutdowns. Gas-fired power plants, for example, are used for this purpose.
In technical language, this process of shifting electricity generation due to bottlenecks is referred to as “redispatch.” This is particularly necessary in regions where — such as in northern Germany — many renewables have been built, or in regions where the development of the electricity grid is very lagging behind the expansion of renewables.
The rapid expansion of renewables therefore meets an electricity infrastructure that is not designed to meet the volatile requirements of these plants. This results in measures for grid congestion management, which not only result in a shutdown of around 3% of renewable electricity generation, but also consumed a total of 2.3 billion euros in 2021 — and the trend is rising.
The intuitive solution for adapting the network infrastructure to changing requirements is the expansion of power lines. However, network expansion is lagging behind the expansion of renewables due to a very high level of bureaucracy and time. Network expansion projects such as the Elbe crossing as part of the “SüdLink” project, a 5 km long route below the Elbe, for example, have an estimated completion date of 2028, if everything goes according to plan. It is therefore highly unlikely or impossible that the power grid can be prepared for 80% renewables by 2030 simply by expanding the grid at this rate.
In addition, network expansion “down to the last kWh”, i.e. sizing the grid to meet future extreme renewable generation peaks, is extremely expensive and would cost many billions of euros.
In order to avoid regulations of up to 3% of nationwide renewables, further solutions must therefore be considered. To this end, both research and the regulatory authority BNetzA are increasingly focusing on the large-scale expansion of storage systems in their future scenarios. For example, both the Fraunhofer Institute ISE in the study “Paths to a Climate-Neutral Energy System” and the Federal Network Agency in the scenario framework of the Network Development Plan 2023 predict a significant expansion of energy storage. (Read more in our article”Regulation and research agree: More storage must be built“)
Due to their ability to absorb electricity at any time and feed it back into the grid at a later date, storage systems offer a very effective solution for preventing the regulation of renewables. If storage facilities are built nationwide at sites where there are increasing network bottlenecks, they can absorb the excess electricity during periods of high production and feed it back in later when there is no longer any risk of a grid bottleneck (for example at night when no solar power is being generated). In this way, storage systems, especially large battery storage systems, which can be built quickly and anywhere, can be used effectively to prevent renewables from being regulated and thus use them more efficiently. Renewable power generation is then used instead of regulated.
Large-scale expansion of energy storage systems therefore not only means that the otherwise lost electricity can actually be produced for currently around 2 million households, but also means that fewer renewables such as wind turbines and solar systems have to be built overall in order to achieve the 80% target and complete the energy revolution in the following years.
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