Congestion management refers to the measures taken by the transmission system operators (TSOs) to prevent overloading of the nationwide power lines, known as grid congestion.Congestion is caused by surplus electricity production that cannot be transported away due to a lack of capacity on the physical power lines. In order to avoid such bottleneck situations, congestion management measures are used, the most important of which is "redispatch". This is a nationwide option for controlling all large generation plants and throttling or ramping them up as required. If a bottleneck is forecast by the TSOs, generation plants are throttled before the bottleneck and ramped up after the bottleneck. This does not change the absolute electricity production, only the location of production is changed in order to relieve the power line and thus avoid the bottleneck. In 2021, a total of around 21 TWh (10.5 TWh feed-in curtailments & 10.5 TWh feed-in increases) were regulated as part of feed-in management, resulting in costs of around 2.3 billion euros. (Grid congestion management report 2021, BNetzA) Redispatch is therefore used to intervene in the operating times of nationwide generation plants in order to avoid bottlenecks occurring in the grid.
Just like generation plants, storage systems such as large-scale battery storage systems must also be available for the redispatch measures of the TSOs. If they are strategically placed at grid nodes where grid congestion frequently occurs, they can even make a particularly effective contribution to avoiding congestion. In addition to normal redispatch measures, i.e. throttling the output of the large-scale battery storage systems, the storage systems can also function as consumers. In this way, large-scale battery storage systems can not only be throttled to zero before bottlenecks like generation plants, but can also absorb surplus electricity. Once the bottleneck has been avoided, the storage systems can feed this electricity back into the grid with a time delay. With a large-scale expansion of large-scale battery storage systems, which both the BNetzA and the Fraunhofer Institute are forecasting, this potentially more effective Redispatch 3.0 can greatly relieve the nationwide electricity grid. In this way, large-scale battery storage systems can not only avoid bottlenecks, but also minimize the shutdown of renewables such as wind turbines in the north and limit grid expansion.Furthermore, the costs of congestion management measures are drastically reduced by avoiding shutdowns with the help of storage systems, which can reduce our grid fees.
The reason for the emergence of the bottlenecks is that the current electricity infrastructure in Germany is not designed for the high volatility of renewable generation plants. Due to the high dependency on weather, the electricity production of renewable sources fluctuates strongly. However, the power grid has historically been designed for very constant, conventional large-scale power plants and is slow to adapt to rapidly changing electricity production. In the past, the power grid was often referred to as a nationwide "copper plate," describing a power grid that could transmit produced electricity in all directions at all times. That this description no longer corresponds to reality can be seen in the well-known north-south bottleneck. Due to a relatively fast expansion of onshore and offshore wind energy plants in the north of Germany, a considerable surplus of electrical energy is produced there on windy and sunny days. In order not to overload the grid, this surplus must be transported to the south of Germany to large consumption centers such as industrial sites and large cities. Since the physical expansion of the grid, i.e. the expansion of electricity grid capacity, lags significantly behind the expansion of renewable sources, there are often north-south bottlenecks. As a result, renewable generation plants are shut down by redispatch and conventional power plants in the south are ramped up. In 2021, 3% of total renewable generation capacity was already shut down. This amount of electricity could have supplied up to 2 million households. With the ambitious expansion targets of the German government to 80% renewable electricity by 2030, grid bottlenecks will occur even more frequently. For example, from 2020 to 2021 alone, the volume of congestion management measures implemented increased by 19%. (Report Netzengpassmanagement 2021, BNetzA) In today's reality, the German power grid can no longer be described as a nationwide "copper plate". However, such a system is also only desirable to a limited extent in a renewable future. Due to the extremely high fluctuations of renewables, a significant surplus of electricity is produced at peak times. Designing the power grid for this peak kWh production so that all the electricity could be transported without bottleneck even at the absolute peak times would be extremely uneconomical and would cost many billions of euros. An alternative to the resulting redispatch measures, which result in the shutdown of renewables, is the large-scale integration of storage systems, such as large-scale battery storage or pumped storage. These would both limit grid expansion to a realistic level and minimize redispatch measures.
All redispatch measures are carried out and are the responsibility of the 4 TSOs. During the previous day, the TSOs receive both the schedules of all generation plants and the estimated consumption for the following day. With this overview, by means of regional load flow calculations, possible grid congestion in the entire nationwide power grid is forecast. Based on this data, the TSOs determine the redispatch measures for the following day and, if necessary, correct them during the day if short-term fluctuations occur. All generation plants with an installed capacity of 100 kW or more must be available for these measures. This limit was put into effect with the introduction of Redispatch 2.0 on 01.10.2021. Previously, the limit was 10 MW, which meant that only large-scale plants participated in the redispatch. Due to the high addition of smaller renewable generation plants, this limit was adjusted so that the TSOs have adequate intervention options in an energy system dominated by renewable energies. In addition, Redispatch 2.0 focuses on the shutdown of conventional plants. Thus, renewable plants will only be shut down when conventional options are exhausted or the shutdown of renewables is cheaper by a factor of 10.
If generation plants are instructed by the TSOs to throttle or increase their output, this inevitably causes additional costs for the generator. These additional costs are covered by the TSOs, which in turn transfer the costs to all consumers in the form of network charges. These network charges are included in the electricity prices paid.
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