Flexibility in the context of the German energy system describes the ability of the power grid and the electricity market to compensate for fluctuations in the demand or supply of electricity and thus guarantee the stability of the power supply and thus security of supply. This includes the ability to compensate for both temporal (day-night/summer-winter volatility) and spatial imbalances between generation and demand (local electricity distribution and supra-regional electricity transport).
With the federal government's current goals for the energy transition of 80% renewable electricity generation by 2030, a large proportion of conventional large power plants must be replaced by renewable sources within a few years. This not only increases the number of individual generation plants and thus the complexity many times over, but the volatility of electricity production also increases sharply.
The fact that the current energy system will be overwhelmed to compensate for this volatility is already evident today by sharp price fluctuations and the closure of renewable energies.
A detailed description of the challenge facing today's German energy system is in our article"How the power grid must be prepared for 80% renewable energy"described.
Increasing the flexibility of German energy systems is therefore absolutely necessary 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 major fluctuations.
But how can the nationwide energy system be made more flexible and what must be done to achieve this?
To make things easier, we divide flexibility into two areas, spatial and temporal flexibility.
With the spatial flexibility of the energy system, geographical fluctuations can be balanced out. A well-known example of this is Germany's North-South bottleneck. On stormy days, wind turbines in the rough north produce a large surplus of renewable electricity. In order to supply southern Germany as well, electricity must be transported to the south via high-voltage lines. There are regular bottlenecks here, which means that more electricity is to be transported from north to south than the lines can transport. The result is the shutdown of renewable generation plants in the north and the ramp-up of conventional plants in the south. It is important that the level of additional generation in the south corresponds to the same level of shutdowns in the north, as this is the only way to generate electricity in total.
The most well-known challenge, which, in contrast, must solve time flexibility, is the day/night fluctuation of photovoltaic systems, which can produce a significant portion of the required electricity during the day but are not available at night. With 80% renewable electricity generation in 2030, the energy system must be flexible enough to be able to meet demand even with low electricity production at night.
In addition to this rather short-term flexibility, the system must also compensate for the so-called "dark runs". These are periods of time lasting days or even weeks in which the production of renewable energy, especially wind and photovoltaics, collapses due to bad weather. In this way, the system must also be able to compensate for such long-term fluctuations.
In addition, not only does production fluctuate significantly over time, but also consumption. There are typically certain peak times in the morning (7:00 to 9:00) and in the evening (17:00-21:00) when household consumption rises sharply. The energy system must therefore be able to reconcile both production and consumption fluctuations and thus guarantee a reliable supply of electricity.
There are several starting points for building up both the temporal and spatial flexibility of the energy system. The possible solutions range from increasing flexibility from initial power generation to integration of storage systems to making final consumption more flexible.
The following infographic provides an overview of the most important ways to increase the flexibility of the energy system and how the system can be prepared for 80% renewable energy in 2030.
Starting with generation, it is possible to adjust electricity production to consumption by regulating generation plants. At peak times, for example, the systems would have to be started up and shut down during off-peak times.
This approach works well with systems that can produce electricity independently of external influences. These include conventional large power plants or certain renewable energy plants such as biomass and hydropower, but not heavily weather-dependent renewables such as wind or solar.
Just as production can be adjusted to consumption, consumption can also be adjusted to production the other way around. For example, there are already smart home concepts for the near future that can automatically start up household appliances depending on the electricity price, as well as similar charging concepts for electric cars. Since the price of electricity usually falls as soon as a surplus of renewable electricity 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, in order for these concepts to become reality, a nationwide rollout of smart meter systems for households is necessary, which is currently progressing only slowly.
Similar concepts also exist in industry on a much larger scale. In this way, entire steel or paper productions can be carried out depending on the price of electricity. Since a real-time connection to electricity markets in industry has already made significant progress, some of these approaches are already being implemented in practice today.
However, the possible flexibility of both production and consumption is limited. Particularly as a result of the massive expansion of comparatively inflexible generation systems such as wind and solar, the ability to make production more flexible will decrease rather than increase in the future. And even though the concepts of making electricity consumption more flexible will be an important part of the solution, there will always be peak times, such as morning or evening, when high consumption will have to be covered by supply, regardless of whether the sun is shining or the wind is blowing.
In order to guarantee security of supply even at these times, the German energy system needs a further opportunity to become more flexible, which is provided by the large-scale integration of storage systems. By expanding large-scale storage systems, both the temporal and spatial imbalances of the energy system can be effectively compensated. In this way, the storage systems can absorb excess electricity and feed it back into the grid with a time delay when demand increases. This applies both to short-term fluctuations (day/night compensation through large battery storage) and to long-term fluctuations (balancing long-term volatility, for example through power-to-gas). Storage systems, provided that they are built at strategically important network nodes, can also correct spatial imbalances. If there is a surplus in the north, storage facilities in this region, for example, can absorb 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 they can be built almost anywhere due to their low space requirement and can therefore be installed directly at the critical network nodes. In this way, grid bottlenecks and the shutdown of renewable energy sources can be avoided. The expansion of electricity grids remains important, but is accompanied by the use of flexibility. Compared to grid expansion, the flexibility of large battery storage systems is available very quickly and an economically nonsensical expansion of the power grid "down to the last kWh" is avoided.
Details on the various storage systems and their possible applications can be found in the dictionary entry"Electrical energy storage"to find.
Even though the large-scale integration of storage systems offers one of the most effective options for making the energy system more flexible, none of the solutions mentioned here alone is able to provide the overall necessary flexibility. Both production and consumption must be made more flexible within the limits of technical possibilities. In addition, the expansion of storage systems must be accelerated. Only by combining all solutions can the German energy system be made flexible enough so that even with 80% renewable energy in 2030, generation and consumption can be reconciled at any time and anywhere.
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