(Frankfurt a. M., 21.05.2025) The European interconnected grid stretches from Portugal to Turkey - around 6,000 large power plants and hundreds of thousands of wind and photovoltaic systems feed in electricity. Germany is at the center of this system and is closely connected to the grids of its neighbors. Redundancies secure the supply, which continues to function even if individual lines or power plants fail. However, the reliability of this electricity grid is based on a delicate balance: the electrical power fed into the grid must exactly match the power drawn from it. However, the more plants supply electricity from wind and sun and the fewer conventional power plants with rotating masses remain on the grid, the more vulnerable the entire structure becomes.
"The restructuring of the energy system poses fundamental challenges for grid stability," says Dr. Ralf Petri, Managing Director of the Power Engineering Society within VDE (VDE ETG). Frequency fluctuations, which used to be dampened by the inertia of conventional power plants, now have a more direct effect - and jeopardize the synchronicity of the interconnected grid. "The complex interplay of power electronics, long transmission paths and decentralized feed-in requires new technical answers," Petri demands. The Network Technology and Operation Forum within VDE (VDE FNN) and the German Commission for Electrical, Electronic & Information Technologies (DKE) are involved in the Federal Ministry for Economic Affairs and Energy's System Stability Roadmap together with the VDE ETG, state actors, grid operators, associations, science and industry. This initiative, which was launched at the end of 2023, aims to introduce and implement all necessary measures by the end of 2035 to ensure that a grid with 100% renewable energy can be operated safely.
Fluctuations and instabilities
The larger the grid, the longer it takes for fluctuations to even out - this favors power fluctuations between regions. These are particularly pronounced between northern and southern Europe or between Poland and the Iberian Peninsula. If the oscillation becomes too strong, there is a risk of overloads and, in extreme cases, automatic shutdowns. These complex interactions become more important the more converters and fewer rotating masses there are in the grid.
Wind turbines, photovoltaic systems, battery storage systems and high-voltage direct current (HVDC) transmissions do not feed electricity directly into the grid, but via so-called converters. These electronic converters work with high switching frequencies in order to transform the required power. In addition to the normal grid frequency of 50 Hertz, additional oscillations occur. If many of these so-called harmonics overlap in the grid, grid voltage quality limits can be violated. Such effects have been observed, for example, during the operation of wind farms. They can overload or even damage lines and other equipment - in a critical case, this leads to an automatic shutdown. Whether the faults occur or are intercepted depends largely on how the control technology used in the converters works. To date, there are no proven countermeasures for this new type of instability.
Digitization as the key
Mastering these complex technical challenges requires a decisive leap forward in the development of grid monitoring and control. Reliable coordination of decentralized feed-in sources and new consumers such as heat pumps, electric vehicles or electrolysers requires resilient digitalized grid control centers. Both robust cyber security and communication that takes over in the event of a failure of the central energy supply (blackout-proof) are key prerequisites for resilient overall grid operation. "Blackout-proof" means that the communication systems continue to function even in the event of a complete power failure - backed up by backup batteries or emergency power systems that ensure operation even without an external power supply. Dr.-Ing. Damian Dudek from the Information Technology Society within VDE (VDE ITG) adds: "Without robust information and control technology, can neither process real-time data in the electrical energy grid nor implement effective, suitable measures in the event of a fault."
One thing is certain: The challenges of the energy transition require a coordinated approach from the energy technology and information technology side. The further technical development of converters, increased European cooperation in grid planning and investment in digital infrastructure form the triad for stable energy systems of the future.
The background paper on grid stability is available online (German version).
New guidelines for cross-sector planning of municipal energy systems
In addition, the VDE ETG has published the new guideline "Cross-sector planning of municipal energy systems" (German version). The practice-oriented guide supports cities, municipalities and energy stakeholders in actively shaping the local energy transition and implementing a sustainable energy supply at municipal level.
