The remaining three nuclear power plants in Germany will be shut down on Sunday night. This raises the question of how the increasing demand for electricity will be met in the future. Nuclear physicists and other advocates of nuclear power, such as Götz Ruprecht and André Thess, warn that security of supply is suffering, energy prices are likely to continue to rise and even the climate is being done a disservice. In view of the lack of storage capacity for green electricity, “controllable capacities are needed best low-cost and low-emission nuclear energy“. The resource researcher Henrik Paulitz saw the power supply as “massively endangered” as early as 2021. But there are also other voices in science.
Backup power plants for so-called dark doldrums
Parallel to the nuclear phase-out, the Federal Government and Bundestag formulated a number of new, ambitious expansion targets for renewable energies and created laws and regulations intended to accelerate this initiative. The aim is to replace the performance of nuclear and, in the future, also of coal-fired power plants. At the beginning of 2023, the executive also formulated this for the first time Specifications for so-called backup power plants. These are systems that are supposed to step in when wind power and photovoltaics (PV) do not generate enough electricity, in order to cover the current demand of around 80 gigawatts (GW) in Germany. Such phases can extend over several days, during which the output of renewables would drop sharply – the so-called dark doldrums.
The Science Media Center asked researchers how politics can deal with this challenge. They are largely in agreement: it will not work without sufficiently flexible backup power plants. These would have to cover a large part of the power peaks. However, they are only needed when wind power and PV systems generate too little electricity.
Lots of prerequisites
According to the scientists, gas and, to a limited extent, coal-fired power plants are the most suitable for this. A flexible energy market with opportunities for citizens and companies to feed unlimited electricity from PV and wind systems into the grid, with dynamic tariffs coupled with intelligent electricity meters, virtual power plants and battery pooling, for example via electric vehicles and smart grids, also plays an important role. However, many prerequisites still have to be created for this to happen. Europe-wide planning of the energy transition could also significantly reduce the number of power plants that are rarely in operation. To do this, however, the EU member states would have to plan their energy supply more jointly.
In concrete terms, Christian Rehtanz, head of the Institute for Energy Systems, Energy Efficiency and Economics at the TU Dortmund, calculates: Based on various studies, an annual maximum load of 100 percent – today around 80 (GW), could be estimated in the future – a maximum of up to 10 to 15 percent are covered by the European balancing of renewable energies including hydropower via the grids. Furthermore, it is possible to reduce the peak load by a further 10 to 15 percent by shifting loads during the course of the day. However, this requires appropriate market incentives and “automatic digital implementation”. So you end up with 70 to 80 percent of the power peaks, which would have to be covered by backup power plants during a dark doldrums, for example in winter.
Flexibility and backup services
The required backup capacity “also depends to a large extent on the design of the energy market and how it succeeds in integrating other market players synergistically with renewable energy generation,” says Patrick Jochem from the Institute for Networked Energy Systems at the German Aerospace Center (DLR ). Above all, making electricity demand more flexible should have great potential. If it is possible to integrate electric vehicles directly into the electricity markets – if possible with a vehicle-to-grid (V2G) feedback capability – the flexibility on the demand side could replace a “considerable part” of the backup capacities. To do this, the system must be “supplemented with an appropriate IT infrastructure at all levels”.
Jochem refers to scenarios in which a backup capacity of 40 GW is sufficient. These are characterized “in particular by a high level of flexibility on the demand side and high availability of storage facilities as well as flexible, sustainable power generation, such as geothermal and biogas power plants”. According to other studies, however, backup capacities of up to 90 GW would be required.
Flexible backup power plants needed
According to Rehtanz, “the best alternatives are those power plants that go into operation quickly and can be quickly turned up and down”. Gas is ideal for this. Correspondingly upgraded coal-fired power plants also functioned. Nuclear power plants can only be used theoretically for such purposes, since “for economic reasons they are designed for operation that is as constant as possible”.
Jochem confirms that dark lulls require technologies that can provide energy over a longer period of time. However, since this will only rarely be the case, “these systems do not have high full-load hours”. In this respect, gas turbines that are operated with a renewable gas or hydrogen with good storage characteristics would be the most suitable. From his point of view, nuclear and coal-fired power plants are not suitable as backup due to the low full capacity utilization and high demands on flexible operational management.
Prevention of CO₂ emissions
Jan Wohland, a climate physicist at the Technical University of Zurich, points out one shortcoming: CO₂ is produced if fossil gas or coal is used in backup power plants. Although these emissions can be reduced through the use of CO₂ capture and storage (CSS) technologies, they cannot be completely prevented. Since relevant emissions would have to be reduced to zero “in order to prevent dangerous climate change”, their compensation is necessary. This could be done, for example, via direct air capture, the direct separation of CO₂ from the air. Since this is complex, expensive and energy-intensive, the need for backup power plants should be kept as small as possible.
Batteries allow energy to be stored for short periods of time, lasting hours or days, and so could reduce the need for backup power, Wohland explains. “Pumped storage power plants behave in a similar way, but have the advantage that they can also store energy over a longer period of time.” Furthermore, low-yield phases at one location can be compensated for by simultaneous good yields in other areas. This strategic addition works on many time scales. Solar panels in Spain, for example, are still producing electricity “when the sun has already set in Germany”. PV systems in Greece, on the other hand, are already busy when it is still dark in this country.
“In our results so far we have seen a good natural compensation mechanism at European level,” reports Jochem. “If we experience a calm in the north, the wind turbines in the south are often well utilized. Cloudy in one region is often associated with sun in another.” Offshore wind turbines in particular are important here, “because they usually have higher full-load hours and therefore a correspondingly higher availability”. However, Wohland warns against concentrating wind farms only in the North Sea. The risk of lulls is greater than with stronger spatial distributions in different regions.
(bme)
