European regulators have introduced a framework mandating grid-forming inverter requirements and harmonized interconnection rules to support cross-border long-duration energy storage (LDES) pilot projects in the EU. The European Network of Transmission System Operators (ENTSO-E) published its Phase II technical report in November 2025, establishing requirements for new storage and renewable plants above 1 MW to provide voltage control, inertia response, and frequency regulation using grid-forming functionality1Europe moves to mandate grid-forming capability for new storage over 1 MW - Energy Storage. The European Commission is expected to include these standards in the forthcoming RfG 2.0 network code, after which member states will adopt national transition schedules1Europe moves to mandate grid-forming capability for new storage over 1 MW - Energy Storage.
Background
Grid-forming inverters (GFMs) operate as active voltage sources with internal impedance, allowing inverter-based resources to replicate synchronous machines in frequency and voltage control during both normal and disturbed conditions2COMMISSION REGULATION (EU) 2016/631. Previously, the EU lacked consistent standards for this functionality. In Germany, the VDE-FNN guideline "Grid-Forming Capabilities" took effect in May 2025, supporting new markets for inertia and system services3Standardization of Grid-Forming Inverters in the EU. Concurrently, ENTSO-E's report provides the foundation for mandatory grid-forming capability in new installations exceeding 1 MW across the EU1Europe moves to mandate grid-forming capability for new storage over 1 MW - Energy Storage.
Details
ENTSO-E's report formalizes requirements for storage systems and power conversion systems (PCS) to operate like synchronous machines, delivering voltage control, inertia response, and frequency regulation even during grid disturbances1Europe moves to mandate grid-forming capability for new storage over 1 MW - Energy Storage. The new technical rules will apply to new and substantially modified plants rated above 1 MW once NC RfG 2.0 is adopted by the European Commission1Europe moves to mandate grid-forming capability for new storage over 1 MW - Energy Storage. Member states will set national transition periods for technical adaptation1Europe moves to mandate grid-forming capability for new storage over 1 MW - Energy Storage.
Belgium's transmission system operator (TSO) Elia has launched a fast-track public consultation on grid-forming battery energy storage systems (BESS) for transmission-connected sites, citing delays in the formal adoption of NC RfG 2.0. Elia aims to accelerate national implementation to maintain system strength as inverter-based resource (IBR) integration accelerates420251210_Public Consultation on Additional Technical Requirements. In Germany, the four TSOs started procuring inertia services through fixed-price contracts in January 2026, opening new revenue opportunities for certified grid-forming BESS5Germany to Launch Inertia Service Market in 2026 – New Revenue Stream for Grid-Forming BESS | Herbert Smith Freehills Kramer | Global law firm. The service, known as Momentanreserve or instantaneous reserve, will feature fixed pricing and contracts lasting up to ten years, with contracted volumes published starting in 20276Germany’s TSOs begin inertia procurement with long-term contracts for grid-forming BESS - Energy-Storage.News.
Outlook
After European Commission approval of NC RfG 2.0 and national implementation, mandatory requirements will apply to new projects above 1 MW. Early-adopting markets such as Germany and Belgium are deploying certification and procurement mechanisms to support GFM BESS adoption. As technical definitions and testing standards evolve, cross-border pilots for long-duration storage are expected to advance under unified requirements.
