The outcome: Grid frequency of 50 Hertz (Hz) is essential. In the context of the distribution grid grid, ethis frequency and almost constant voltage values are required to keep office computers running, ventilators in hospitals working and heat pumps functioning. 50 Hertz is also necessary if, in the course of the energy transition, increasingly smaller amounts of coal and natural gas are burnt, and renewable energies are used instead. The latter naturally lead to greater fluctuations in the grid due to the unpredictability of certain factors such as weather conditions, i.e. the wind does not blow constantly or the sun disappears behind clouds. The question of how these fluctuations can be compensated for was investigated by scientists and industrial partners from four countries within the framework of the “POSYTYF” research project, which was funded by the European Union. The four-year project is due for completion in May 2024. The challenging part for the HTW Berlin team is the development and testing of the power plant systems which are used to feed renewable energies back into the grid.

This was one of a total of five extensive technical work packages on the desk of Prof. Dr. Horst Schulte, Prof. Dr. Jens Fortmann, Prof. Dr. Norbert Klaes, and Prof. Dr. Jochen Twele. The energy experts in Faculty 1 were assisted in their efforts by a number of research assistants. The aim was to design and test control strategies on the basis of which renewable energy sources could be fed into dynamic and virtual power plants capable of assuming the tasks of conventional large-scale power plants in our energy supply system in the future. It is difficult for non-experts in this field to understand the level of complexity of the methods and mathematical models used by the team. Even the consolidated results paper, which is intended for an interested specialist audience, contains many formulae.

“We have recreated a dynamic, virtual power plant on a miniature scale in order to develop methods and models and simulate various scenarios,” explains Prof. Dr Schulte. As the scientific exchange on the topic is conducted almost exclusively in English, he refers to the plant simply as “DVPP”, i.e. “Dynamic Virtual Power Plant”. The DVPP in the university’s test bed system rig is small enough for scientific work, but large enough to map the complex processes in the energy grid. The equivalent of a large conventional power station, it was intended to behave in exactly the same way. This means that, among other things, the system has to react as soon as “load is switched on”, as technical jargon has it, i.e. when electricity demand in the grid increases. It also has to react when the load drops off for any reason.

In order to develop the control strategy, the various types of renewable energies, namely photovoltaics, wind energy, solar thermal energy, hydropower, and biogas, had to be analyzed separately. “They differ considerably in terms of their feed-in dynamics,” explains Prof. Dr. Schulte. Photovoltaic modules react faster than wind turbines, where heavy parts are moved. Hydropower is even slower. Technically speaking, it is easy to take these differences into account. However, they must initially be calculated precisely to a range measuring between one second and 20 milliseconds. “You have to know exactly how quickly the adjustment can be made and where its limits lie,” says Prof. Dr. Schulte, describing the challenge. Only then can the DVPP function like a conventional power plant that runs on gas, coal or nuclear power and is able to compensate for fluctuations with a robust synchronous machine.

The team at HTW Berlin has precisely calculated, simulated, tested and carefully documented the conditions under which the aforementioned renewable energies can be integrated into a dynamic, virtual power plant for the project consortium in a stable manner. Everything is fully accessible and traceable. “Our results take  the DVPP from technology readiness level (TRL) 1-2 to TRL 4,” the scientists write. In the process, they collaborated closely with other universities. Colleagues at the École Centrale de Nantes, which was also responsible for the project’s overall management, as well as those at the Spanish Universitat Politechnica de Catalunya (UPC), and, in the final phase, others at the Swiss Federal Institute of Technology Zurich (ETH Zürich), played a key role. Prof. Dr Schulte did not always find this European cooperation easy. After all, between 30 and 40 participants were involved, including various partners from industry. “However, it was very rewarding, and, as a community, we were far more than merely exploitative,” he says with satisfaction.

A new, subject-specific degree programme has even been created: the interdisciplinary Master’s degree programme “Dynamics of Renewables-based Power Systems” (DREAM). Three partners from the project are on board: HTW Berlin, the French École Centrale de Nantes and the Spanish UPC. They offer the engineering programme in collaboration with the Polytechnic University of Bucharest. It comprises the modeling, simulation, automated regulation, and control of electrical energy systems, has a focus on renewable energies, and leads to a double or triple degree. Prof. Dr. Schulte is delighted with the European Excellence Programme. It gives the university lecturer the opportunity to introduce outstanding students to the subject, to attract doctoral student and to involve the most able participants in large-scale projects such as “POSYTYF”. “In general, we need to think in European terms when it comes to energy supply,” comments the scientist. After all, more solar energy can be generated in the South and more wind energy in the North. These two renewable energies are currently experiencing the strongest growth and, according to Prof. Dr. Schulte, will also play a crucial role in the energy transition.

The POSYTYF partners will disseminate their findings and results in specialised committees and at other levels. The energy sector has many stakeholders with an interest in this. The so-called “dissemination” even constitutes a separate work package.

It goes without saying that a research project wouldn’t be a research project if the scientists had not already identified new questions to which answers need to be found. One is the interlinking of electricity with the heat supply. During the energy transition, not only the generation of electrical power needs to be “orchestrated,” as Prof. Dr. Schulte puts it. Instead, this process must also occur by involving the actual consumers of electrical energy, as in the case of heat pumps, which also include private households and municipal facilities - all this to ensure that the heating turnaround succeeds at some point in the future.