Germany’s Fraunhofer Institute for Energy Economics and Energy System Technology IEE (Fraunhofer IEE) says in a new position paper that large-scale battery storage systems in medium-voltage grids should be technically prepared for future grid-forming operation, aiming to bridge the gap between current regulations and potential system stability requirements.

February 25, 2026
Marian Willuhn

From pv magazine Germany

Germany’s Fraunhofer IEE has published a new position paper calling for early technical preparation of distribution networks for grid-forming functions. Under the term “grid-forming readiness,” the authors outline a concept in which large-scale battery storage systems connected to medium-voltage grids could, in future, contribute to system stability, islanding capability and resilience – without being required to operate in grid-forming mode today.

As the energy transition advances, conventional rotating masses that historically supported frequency and voltage stability are declining. They are being replaced by power electronics-based generation and storage technologies, including photovoltaic, wind and battery systems. As a result, services such as frequency control, short-circuit power, fault management and post-disturbance recovery are increasingly delivered through inverter-based control systems.

At the same time, regional resilience strategies – such as temporarily separating grid sections from the main network and operating them in stable island mode – are gaining importance. Battery energy storage systems could enable this functionality, provided their control architecture is designed accordingly. With several gigawatts of new large-scale battery capacity expected in the coming years, the institute warns that failing to prepare these assets would mean missing a strategic opportunity to strengthen resilience.

Readiness concept

To date, regulatory and technical discussions have largely focused on a binary distinction between “grid-following” and “grid-forming” systems. Grid-following units synchronize with an existing voltage and frequency reference, while grid-forming units can establish these references themselves. According to Fraunhofer IEE, this distinction is overly simplistic.

The institute identifies a gap between today’s operating framework and potential future requirements for grid-forming functionality. Investment decisions are being made without clarity on which system services may be required in 10 or 20 years. Retrofitting assets later could prove technically complex and economically inefficient.

The proposed “grid-forming readiness” concept aims to address this gap. It calls for systems to be designed and categorized so they can assume grid-forming roles when required, even if those capabilities are not activated during normal operation. Technical preparedness is thus separated from immediate operational obligations.

In an initial phase, the institute recommends prioritizing large-scale battery storage systems in medium-voltage networks. These installations are considered particularly suitable for grid-forming applications due to their communication infrastructure, controllability and long asset lifetimes.

Their localized impact may also make regulatory implementation more manageable. While the concept could later extend to other technologies and voltage levels, Fraunhofer IEE suggests first building practical experience in the medium-voltage segment.

The position paper outlines several use cases to consider at the design stage, including islanded operation and regional supply capability, black start and system restoration support, stabilization of weak grids, provision of instantaneous reserves and energy reserves for emergency scenarios.

To ensure transparency and comparability, the authors propose standardized functional classes and defined testing procedures through which plants could verify their grid-forming capabilities.

Standards integration

A central recommendation is to formally define “grid-forming readiness” in technical standards and application rules. The paper assigns a key role to the VDE Association for Electrical, Electronic & Information Technologies and its standardization arm, the DKE German Commission for Electrical, Electronic & Information Technologies, as well as VDE FNN. These bodies would specify technical classes, verification methodologies and activation parameters, and embed them into the existing regulatory framework.

Beyond technical aspects, the paper examines stakeholder perspectives, including manufacturers, asset operators, grid operators, policymakers and regulators. It addresses financing, investment certainty and long-term system responsibility.

According to Fraunhofer IEE, the main advantage of grid-forming readiness lies in anticipating future stability and resilience requirements early. By decoupling technical capability from immediate operational mandates, the approach seeks to avoid costly retrofits while safeguarding long-term system operability.

The position paper is available for download on the institute’s website.

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