Grid-Forming Inverters: “Fast Players Reap the Biggest Rewards”

Interview with Sönke Rogalla, Head of the Power Electronics and Grid Integration Department at Fraunhofer ISE

How important are grid-forming inverters for Europe’s energy transition and what was the reason behind launching the GFM Benchmark project?

An energy mix consisting entirely of renewables at all times is only possible with grid-forming inverters. As the energy transition progresses rapidly – and some countries are already powered entirely by renewables at times – their use is increasingly gaining in importance. At present, we still rely almost entirely on conventional power plants to maintain frequency and voltage in the power grid. In the future, grid-forming inverters will need to take over these system services. For about a decade, grid operators, inverter manufacturers and researchers have been working intensively on this challenge through various research and development projects. The solution lies in a fundamental change in the control engineering of inverters: moving away from simply feeding into an existing grid and toward actively contributing to grid voltage formation. To this end, grid-forming regulations have been developed, tested in laboratories and have undergone simulations. However, since there has been no standard definition or regulation of “grid-forming”, we launched the GFM Benchmark project. The aim was to establish a clear, applicable definition of grid-forming inverters using a comprehensive test procedure capable of testing all grid-forming capabilities of an inverter.

According to a PV Magazine article from September 2025, the results of the test procedure are being incorporated into national and European standardization. What market developments are these standards intended to promote and what impact would their mandatory application at the EU level have – for example, on investors, manufacturers and grid operators?

Parallel to the GFM Benchmark project, standardization work began in Germany and at the European level on technical standards for components as well as for the connection and operation of grid-forming systems. Our experiences and interim results from the project were extremely helpful in this process, as we were able to contribute our real-world insights from measuring grid-forming inverters. In Germany, the VDE FNN guideline Grid-Forming Capabilities has been in place since May 2025, regulating the requirements and verification for grid-forming units for the first time. This guideline now also forms the basis for the emerging market for the provision of power system inertia.

Unfortunately, at the European level, the path toward implementing grid-forming inverters has recently stalled. Tt is only a matter of time, however, before normative requirements are introduced. This makes the market outlook for grid-forming inverters particularly exciting with fast players reaping the biggest rewards. The established test procedure for assessing the behavior of grid-forming inverters – to which we contributed significantly – can now be used both by component manufacturers and project designers as a basis for their development.

What additional service and revenue models are emerging as a result of the market readiness and certification of grid-forming inverters for PV&BESS?

Implementing the required number of grid-forming inverters is based on a three-pillar model. First, transmission system operators are building their own power converter plants – above all, high-voltage direct-current transmission systems (HVDC) and reactive power compensation units (STATCOMs) – now exclusively using grid-forming technology. Second, a very exciting market for the provision of power system inertia will start in Germany in 2026. Attractive conditions are expected for large-scale battery storage systems and large wind and PV farms equipped with grid-forming capabilities. As the current demand for power system inertia is high, it is likely that all valid offerings will be accepted. The final pillar is mandatory grid-forming capabilities, which will be introduced over the next five years.

Looking ahead to the next three to five years, what political, regulatory and market framework conditions do you think will be essential for the widespread implementation of grid-forming inverters in Germany and across Europe? Are there risks related to delays in grid expansion, approval, certification, etc.?

Thanks to the System Stability Roadmap, which was created in 2023/2024 and now serves as a roadmap, Germany is moving at a good pace in deploying grid-forming technology. Unfortunately, the same is not the case at the EU level. The delay in adopting the Requirements for Generators RfG 2.0 network codes is problematic – especially because, once they come into force, there will be a national implementation period of several years.

What technological developments can be expected in the field of grid-forming inverters? Will grid-forming inverters become the industry standard in the future?

The technology is ready, but system fine-tuning is only just beginning. In order for grid-forming inverters to become the industry standard, we must closely monitor and scientifically evaluate the first pilot plants that are now being connected to the grid. We need to analyze how their parameterization affects system stability and use these insights when developing the next generation of plants and policies. For example, we also need to investigate how grid-forming units interact with protective devices in distribution systems. Additionally, we are examining the capability of these components to form local microgrids in emergency situations. This represents a major opportunity, but also requires careful consideration of the associated risks.