Europe will mandate 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 is crucial for the upcoming Network Code on Requirements for Generators (NC RfG 2.0), introducing binding grid-forming obligations for new storage and renewable plants over 1 MW. Importantly, this applies only to new connections and significant modifications of existing facilities.

Once 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 managing this in its own way and timeline.

For battery developers, the implications are immediate: the report establishes that storage and the associated power conversion systems (PCS) must perform voltage control, inertia response, and frequency regulation akin to a synchronous machine via grid-forming inverter functionality, even during grid disturbances. Unlike grid-following inverters, grid-forming units must create grid conditions.

As each EU nation implements the new rules, transitional periods may be introduced to ease the process and ensure technical understanding and technology developments keep up with regulations.

The report provides clear technical definitions for the industry: storage systems must maintain steady voltage during grid frequency or phase shifts, deliver reactive current almost instantly, and stay synchronized without external references. Compliance testing will ensure that the storage plant can endure voltage sags, step changes, and phase-angle jumps without losing stability.

The report specifies a reaction time of under 10 milliseconds for current response and a damping ratio of at least 5% for power oscillations. While the requirements are technology-neutral, ENTSO-E has established maximum impedance values and shifted 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 C-rates, more modular power converters, and possibly DC-coupled hybrid systems. Battery technology is also rapidly evolving.

ENTSO-E continues to define synthetic inertia, measuring compliance through mechanical starting time, equivalent to a synchronous machine's inertia constant. For storage, this means retaining energy reserves capable of providing millisecond-scale frequency support, although the exact capacity required will depend on various factors, as noted by the grid operator.

Next steps include this Phase II report being a part of the ongoing process for enacting grid regulations in the EU, making it non-binding, though the framework is almost finalized. The standard cites developments and projects in Great Britain and Australia that have shown grid-forming batteries can enhance system strength.

Once NC RfG 2.0 is adopted, these criteria will be integrated into national grid codes through each country's regulatory approval and grid operator framework, and as noted, may enter a transitional period based on the type of plant.