Conventional power plants continue to produce electricity even when there is a high feed-in of renewable energies into the electricity grid. This is shown by a recent study conducted by the consulting firm Consentec on behalf of the four transmission system operators 50Hertz, Amprion, Tennet and TransnetBW. In times of negative exchange prices, around 25 to 30 gigawatts (GW) of conventional power plants are currently connected to the grid. This so-called minimum generation is due to very different circumstances. However, one thing is clear from the study: there is potential and measures that can be taken to reduce minimum generation:
- Around 25 to 30 GW of conventional power plants are connected to the grid even when prices are negative due to various cause
- The transmission system operators are working to reduce the minimum generation through grid expansion and innovative solutions.
The minimum generation is caused by various circumstances: around 0.5 to 2.5 GW of the minimum generation is connected to the grid in order to be available for redispatch measures by the transmission system operators. Because grid expansion has not yet kept pace with the expansion of renewable energies, the transmission system operators have to reduce power plants and ramp them up elsewhere in order to maintain system balance. This proportion of minimum generation can be reduced by swiftly implementing the necessary grid expansion measures.
Around 3.5 to 5.5 GW of the minimum generation is accounted for by the provision of balancing power and its collateralization (approx. 1.5 to 2.5 GW). Control power is procured by the transmission system operators on a technology-neutral and competitive basis. One measure to reduce this type of minimum generation is the integration of renewable energy plants into the balancing energy market. The transmission system operators therefore expressly support the Federal Network Agency's plan to adjust the conditions for this in an ongoing determination procedure. The transmission system operators are also currently carrying out pilot projects with wind energy plants for the provision of balancing power. finally, the data shows a value that cannot currently be broken down further - shown in the study as "PROD_min" - which is around 20 GW on all days analyzed. Based on the data and information currently available, this share cannot be broken down any further. It can be assumed with certainty that own generation plays a role here. Due to the current structure of grid fees and market organization, it may make sense to generate electricity even though the exchange prices are so low that they are below the variable electricity generation costs of the self-generation plant or are even negative. Heat extraction is also a factor. For many CHP plants, electricity generation is only a secondary process. If these power plants are obliged to supply heat for industrial processes or households, they must also generate electricity at negative prices if no other heat sources are available. In addition, there is a technological minimum generation requirement for the power plants, i.e. the power plants must generate a minimum amount of electricity so that a complete shutdown is not necessary. local system services such as voltage maintenance and short-circuit power were not identified as drivers for minimum generation in the study. They are still predominantly provided by conventional power plants. However, there are technical alternatives - such as active compensation elements or rotating phase shifters - that can also provide these services without conventional power plants. Corresponding concepts are already being implemented throughout the grid area of all four transmission system operators. Three very different representative days in 2015 on which negative prices occurred on the electricity exchange were selected for the analysis. The analysis was carried out on the basis of planning data from the power plant operators, which is available to the transmission system operators as part of the energy information network.