A rapid and large-scale expansion of renewable energies is the key 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 German government has clearly put the expansion in focus. But what happens when all these plants are producing at the same time? On very sunny and windy days, solar and wind already produce so much electricity that the power grids reach their capacity limits. Some of the plants then have to be shut down to ensure safe grid operation. In our article "Battery storage as a key technology for the energy transition", this is described in detail using an example day. Looking at these shutdowns over the entire year, a full 3% of renewable generation already had to be shut down in 2021 to avoid overloading the electricity infrastructure. In absolute quantities, this equates to 5.82 TWh. For comparison, a household has an average annual consumption of 2,800 kWh. So the shutdown volume alone could 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. Due to the strong dependence on the weather, solar plants, for example, mainly produce electricity during the day on sunny days. If it is also very windy on these days, large amounts of electricity from wind turbines also flow into the grid. So much electricity is then produced in certain regions that there are not enough lines to transport it to consumers. As a result, some of the renewables will have to be switched off in order to avoid overloading the power lines. Up to now, these have been designed to ensure that conventional large-scale power plants are able to regulate the power supply as closely as possible to the load. 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 terms, this process of shifting electricity generation due to bottlenecks is referred to as "redispatch". This is particularly necessary in regions where - as in the north of Germany - a lot of renewables have been built, or in regions where the development of the electricity grid is lagging far behind the expansion of renewables.
The rapid expansion of renewables thus encounters an electricity infrastructure that is not designed for the volatile requirements of these plants. This results in grid congestion management measures that not only lead to the shutdown of around 3% of renewable power generation, but also cost a total of a whopping 2.3 billion euros in 2021 - and the trend is rising.
The intuitive solution for adapting the grid infrastructure to the changed conditions is to expand the power lines. However, grid expansion is lagging far behind the expansion of renewables due to the huge amount of bureaucracy and time involved. Grid expansion projects such as the Elbe crossing as part of the "SüdLink" project, a 5 km long route under the Elbe, for example, have an estimated completion date of 2028 if everything goes according to plan. It is therefore highly unlikely, if not impossible, that the electricity grid can be prepared for 80% renewables by 2030 at this rate through grid expansion alone.
In addition, expanding the grid "to the last kWh", i.e. dimensioning the grid for the extreme future generation peaks of renewables, is extremely expensive and would cost many billions of euros.
In order to avoid the curtailment of up to 3% of nationwide renewables, other solutions must therefore be considered. 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 its study "Paths to a climate-neutral energy system" and the Federal Network Agency in the scenario framework of the 2023 grid development plan forecast a strong expansion of energy storage. (Read more in our article "Regulation and research agree: more storage facilities must be built")
Because of their ability to absorb electricity at any point in time and feed it back into the grid at a later time, storage systems offer a very effective solution for preventing renewable curtailment. If storage systems are built nationwide at locations where grid congestions are more likely to occur, they can absorb excess electricity during periods of high production and feed it back into the grid later when there is no longer a risk of grid congestion (for example, at night when no solar power is being generated). In this way, storage systems, especially large-scale battery storage, which can be built quickly and anywhere, can be used effectively to prevent renewables from being curtailed and thus use them more efficiently. Renewable power generation is then used instead of being curtailed.
A large-scale expansion of energy storage, therefore, not only leads to the fact that the otherwise lost electricity for currently about 2 million households can actually be produced, but also to the fact that overall fewer renewables such as wind turbines and solar plants must be built to achieve the 80% target and complete the energy transition in the following years.
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