Why around 3% of all renewables are switched off each year

Why around 3% of all renewables are switched off each year

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.

But why is the power grid already so overburdened with today's share of renewables?

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 their strong dependence on the weather, solar plants, for example, produce electricity mainly during the day on sunny days. If it is also very windy on these days, large amounts of electricity from wind turbines additionally push into the grid. In total, too much electricity is being produced in certain regions and the lines are insufficient in transporting it to consumers. As a result, some of the renewables have to be shut down to avoid overloading the power lines. Up to now, these have been designed to ensure that the power supply from conventional large-scale power plants can be regulated well and is as close to the load as possible. To ensure that the total amount of electricity in Germany is sufficient, generation elsewhere must be ramped up to compensate for the shutdowns. Gas-fired power plants are used for this purpose, for example.
In technical jargon, this process of shifting electricity generation due to bottlenecks is known 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 power grid lags very 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.

How can these shut-downs be prevented?

The intuitive solution for adapting the grid infrastructure to the changed conditions is to expand the power lines. However, due to a very high bureaucratic and time effort, the grid expansion lags strongly behind the expansion of renewables. Grid expansion projects such as the Elbe crossing as part of the "SüdLink" project, a 5km route underneath the Elbe River, for example, have an estimated completion date of 2028, if everything goes according to plan. So, for the power grid to be prepared for 80% renewables by 2030 at this pace through grid expansion alone is highly unlikely to impossible.
In addition, grid expansion "down to the last kWh," i.e., sizing the grid for the future extreme 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 the nationwide renewables, further solutions must therefore be considered. To this end, both research and the regulatory authority BNetzA are increasingly relying on the large-scale expansion of storage systems in their future scenarios. For example, both the Fraunhofer Institute ISE in its study "Ways 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 the Energy storage. (Read more in our article "Regulation and research agree: more storage needs to 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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