Europe is taking steps to require grid-forming capabilities for new storage systems over 1 MW.

The European Network of Transmission System Operators for Electricity (ENTSO-E) has released its Phase II technical report on grid-forming requirements, detailing how generators, including inverter-based storage systems, must stabilize the European grid.

This report significantly amends the upcoming Network Code on Requirements for Generators (NC RfG 2.0), which will impose binding grid-forming obligations on new storage and renewable plants over 1 MW. Notably, these requirements will apply only to new connections and major modifications of existing installations.

After the European Commission adopts NC RfG 2.0, ENTSO-E will issue an Implementation Guidance Document (IGD) to assist national regulators and grid operators, with each country regulating according to its own approach and timeline.

For battery developers, the report presents immediate implications: it mandates that storage and the associated power conversion systems (PCS) must perform voltage control, inertia response, and frequency regulation functions akin to a synchronous machine via grid-forming inverter functionality, even amid grid disturbances. Unlike grid-following inverters, which merely track grid conditions, grid-forming units must create them.

As each EU country adopts the new regulations, transitional periods may be implemented to facilitate the process and ensure technical understanding and technology align with the rules.

The report provides clear technical definitions: storage systems must maintain stable voltage while grid frequency or phase shifts occur, deliver reactive current almost instantaneously, and remain synchronized without external reference. Compliance testing will confirm that the storage plant can handle voltage sags, step changes, and phase-angle jumps without losing stability.

It specifies a reaction time of under 10 milliseconds for current response and a damping ratio of at least 5% for power oscillations. The requirements are technology-neutral, but ENTSO-E has set maximum impedance values and adjusted requirements beyond droop control and frequency-watt functions.

The rules may favor technologies that can handle rapid bidirectional power changes, potentially benefiting lithium-based batteries with high charge rates, more modular power converters, and possibly supporting DC-coupled hybrid approaches. Battery technology is evolving quickly.

ENTSO-E has maintained its definition of synthetic inertia, with compliance based on mechanical starting time, calculated from a given equation, which corresponds to the inertia constant of a synchronous machine. For storage, this entails maintaining energy reserves that can provide millisecond-scale frequency support, though the specific capacity required varies based on several factors noted by the grid operator.

Next steps include the Phase II report being part of the ongoing process to implement grid regulations in the EU, making it non-binding yet effectively final. The standard references developments in Great Britain and Australia, which have shown that grid-forming batteries can enhance system strength.

Once NC RfG 2.0 is adopted, the criteria will be integrated into national grid codes through regulatory approval and the framework of each country’s grid operator, potentially including transitional periods depending on the type of plant.