Flexibility in the context of the German energy system describes the ability of the power grid as well as the electricity market to balance fluctuations in the demand or supply of electricity and thus to guarantee the stability of the power supply and hence security of supply. This includes the ability to balance both temporal (day-night/summer-winter volatility) and spatial imbalances between generation and demand (local electricity distribution and also supra-regional electricity transport).
With the German government's current energy transition targets of 80% renewable electricity generation by 2030, a large proportion of conventional large-scale power plants will have to be replaced by renewable sources within a few years. This will not only increase the number of individual generation plants and thus the complexity many times over, but will also greatly increase the volatility of electricity production.
The fact that the current energy system will be unable to compensate for this volatility is already evident today in the strong price fluctuations and the lock-in of renewable energies.
A detailed description of the challenge facing the current German energy system can be found in our article "How the electricity grid must be prepared for 80% renewable energies".
Increasing the flexibility of the German energy systems is imperative in order to prepare the system for the high number of volatile generation plants and to guarantee security of supply even in the event of large fluctuations.
But how can the nationwide energy system be made more flexible and what must be done to achieve this?
For simplicity, we divide flexibility into two areas, spatial flexibility and temporal flexibility.
Geographical fluctuations can be balanced out with the help of the spatial flexibility of the energy system. A well-known example of this is Germany's north-south bottleneck. On stormy days, the wind turbines in the harsh north produce a large surplus of renewable electricity. In order to supply the south of Germany with it, the electricity has to be transported to the south via high-voltage lines. Here, bottlenecks regularly occur, which means that more electricity is to be transported from north to south than the lines can carry. As a result, renewable generation plants in the north are shut down and conventional plants in the south are ramped up. It is important that the amount of additional generation in the south is equal to the amount of shutdowns in the north, as this is the only way to generate the total amount of electricity needed.
The best-known challenge that temporal flexibility must solve, in contrast, is the day/night variation of photovoltaic systems, which can produce a significant amount of the electricity needed during the day, but are not available at night. With 80% renewable electricity generation in 2030, the power system needs to be flexible enough to meet demand at night even when electricity production is low.
In addition to this rather short-term temporal flexibility, the system must also compensate for the so-called "dark lulls". These are periods of days or even weeks in which bad weather causes the production of renewable energies, especially wind and photovoltaics, to collapse. The system must also be able to compensate for such long-term fluctuations.
In addition, it is not only generation that varies greatly over time, but also consumption. Typically, there are certain peak times in the morning (7:00-9:00) and in the evening (17:00-21:00) when consumption in households increases sharply. The power system must therefore be able to balance both generation and consumption fluctuations to guarantee a secure power supply.
There are several approaches to building up both the temporal and spatial flexibility of the power system. The possible solutions for increasing flexibility range from the initial generation of electricity to the integration of storage and the flexibilization of the final consumption.
The following infographic presents an overview of the main ways to increase power system flexibility and prepare the system for 80% renewable energy in 2030.
Starting with generation, there is an opportunity to match electricity production to consumption by regulating generation plants. At peak times, for example, plants would have to be ramped up and ramped down at off-peak times.
This approach works well with plants that can produce electricity independently of external influences. These include conventional large-scale power plants or certain renewable energy plants such as biomass and hydropower, but not highly weather-dependent renewables such as wind or solar.
Just as generation can be adapted to consumption, consumption can also be adapted to generation in the opposite direction. For example, there are already smart-home concepts for the near future that can automatically start up household appliances depending on the price of electricity, as well as similar charging concepts for electric cars. Since the price of electricity typically drops when a surplus of renewable power is produced and then rises when expensive conventional power plants take over, such concepts offer a promising part of the solution to the flexibility of the German energy system. However, for these concepts to become reality, a nationwide rollout of smart meter systems for households is needed, which is currently progressing slowly.
Similar concepts also exist in industry on a much larger scale. For example, entire steel or paper production facilities can be operated depending on the price of electricity. Since real-time connection to the electricity markets is already much more advanced in industry, some of these approaches are already being implemented in practice today.
However, the possible flexibilization of both generation and consumption is limited. Particularly due to the massive expansion of comparatively inflexible generation plants such as wind and solar, the possibility of flexibilization of generation will actually decrease rather than increase in the future. And even if the concepts of flexibilization of electricity consumption will be an important part of the solution, there will always be peak times such as mornings or evenings when high consumption must necessarily be covered by supply, regardless of whether the sun is shining or the wind is blowing.
In order to guarantee security of supply at these times as well, the German energy system needs another way of increasing flexibility, which is provided by the large-scale integration of storage systems. The expansion of large-scale storage systems can effectively compensate for both the temporal and spatial imbalances of the energy system. Storage systems can absorb excess electricity and feed it back into the grid on a time-delayed basis, when demand increases. This applies to both short-term fluctuations (day/night balancing through large-scale battery storage) and long-term fluctuations (balancing long-term volatility through power-to-gas, for example). If storage systems are built at strategically important grid nodes, they can also correct spatial imbalances. If there is a surplus in the north, for example, storage facilities in this region can absorb the electricity and storage facilities in the south can simultaneously feed in previously stored electricity (redispatch). Large-scale battery storage systems are particularly suitable for this purpose, as their small footprint means that they can be built almost anywhere and can thus be installed directly at critical network nodes. In this way, grid bottlenecks and the shutdown of renewable energies can be avoided. The expansion of the power grids remains important, but it is flanked by the use of flexibility. Flexibility from large-scale battery storage is available very quickly compared to grid expansion, and an economically nonsensical expansion of the electricity grid "down to the last kWh" is avoided.
Details on the various storage systems and their possible applications can be found in the glossary entry "Electrical energy storage" can be found.
Even though the large-scale integration of storage systems offers one of the most effective ways to make the energy system more flexible, none of the solutions mentioned here can deliver the overall flexibility needed on their own. Both generation and consumption must be made more flexible to the extent technically feasible. In addition, the expansion of storage systems must be accelerated. Only in the combination of all solutions can the German energy system be made flexible quickly enough so that, even with 80 % renewable energies in 2030, generation and consumption can be brought into line at any time and at any place.
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