Ensuring grid stability is a critical pillar of the energy transition, as renewable generation continues to expand worldwide. Recognizing this need, Fraunhofer Institute for Solar Energy Systems ISE has developed a new test procedure to evaluate the performance of grid-forming inverters. The work was carried out under the “GFM Benchmark” project on behalf of Germany’s four transmission system operators (50Hertz Transmission GmbH, TransnetBW GmbH, Amprion GmbH, and TenneT TSO GmbH).
The project provided the first comprehensive practical check on the market readiness of grid-forming inverters while also feeding into ongoing national and European standardization efforts. “We wanted to see what manufacturers understand by grid formation and how they implement this in the programming of their devices,” explained Dr. Sönke Rogalla, department head at Fraunhofer ISE.
Seven manufacturers participated, submitting storage inverters ranging from a few kilowatts to 5 MW. The devices were exposed to a range of operating conditions at Fraunhofer ISE’s laboratories, including rapid frequency changes, short circuits, and phase jumps. The results revealed that while devices performed consistently under defined requirements, significant differences emerged in critical scenarios. “We were able to provide suggestions for optimization for almost every device,” added Roland Singer, project manager at Fraunhofer ISE.
These findings are expected to have far-reaching implications. The test procedures developed during the project have already informed the VDE FNN note “Grid-forming properties,” a key guideline that will serve as the normative basis for participation in Germany’s new instantaneous reserve market set to begin in early 2026. This creates a new revenue pathway, particularly for battery storage systems.
With European-level standardization also advancing through ENTSO-E’s implementation guide, Fraunhofer ISE’s expertise positions it as a leading partner for manufacturers and users in certifying grid-forming units. The initiative marks an essential step toward ensuring that renewable and storage-based systems can reliably provide the grid services once dominated by conventional generators.
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