Europe moves to mandate grid-forming capability for new storage over 1 MW
Source：pv magazine
-87792857.jpg)
The European Network of Transmission System Operators for Electricity (ENTSO-E) has published its Phase II technical report on grid-forming requirements, outlining how generators, including inverter-based storage systems, will be mandated to stabilize the European grid.
The report is an enormously important amendment for the upcoming Network Code on Requirements for Generators (NC RfG 2.0), which introduces binding grid-forming obligations for new storage and renewable plants rated above 1 MW. A key aspect is that this will apply only to new connections and substantial modifications of existing installations.
Once adopted by the European Commission as it finalizes NC RfG 2.0, ENTSO-E will then publish an Implementation Guidance Document (IGD) to aid national regulators and grid operators and each country will regulate this in its own approach and timeframe.
For battery developers, the implications are immediate: the report formalizes that storage and the associated PCS must perform voltage control, inertia response, and frequency regulation functions comparable to a synchronous machine through grid-forming inverter functionality, including through grid disturbances. (Unlike grid-following inverters, which simply track grid conditions, grid-forming units must create them.)
Also, as each EU country brings in the new rules, transitional periods may be implemented to smoothen the process and allow for technical understanding and technology to keep pace with regulations.
Storage as a virtual generator
The report’s technical definitions have the clarity needed for the industry: storage systems must hold steady voltage while grid frequency or phase shifts, deliver reactive current almost instantaneously, and remain synchronized without external reference. Compliance testing will verify that the storage plant can ride through voltage sags, step changes, and phase-angle jumps without losing stability.
The report specifies a reaction time of less than 10 milliseconds for current response and a damping ratio of at least 5% for power oscillations. The requirements are technology-agnostic but ENTSO-E has set maximum impedance values and shifts requirements past droop control and frequency-watt functions.
The rules may also be considered to favor approaches that can sustain rapid bidirectional power changes, which may suit lithium-based batteries with high C-rates, more modular power converters, as well as potentially benefitting DC-coupled hybrid approaches. That said, battery technology is evolving rapidly.
ENTSO-E has also stuck to its definition of synthetic inertia with the metric for compliance being the mechanical starting time, which is calculated from a provided equation and is equivalent to the inertia constant of a synchronous machine. For storage, this means holding energy reserves capable of sustaining millisecond-scale frequency support, though the exact capacity to be reserved depends on many factors, as the grid operator notes.
Next steps
The Phase II report is a step along the well-trodden process of enacting grid regulations within the EU, so it is non-binding but the framework is effectively final. The standard references developments and projects in Great Britain and Australia which have already demonstrated grid-forming batteries can deliver measurable system strength.
Next, once NC RfG 2.0 is adopted, the criteria will flow into national grid codes through each country’s regulatory approval and grid operator framework, and as mentioned, may then be placed into a transitional period depending on the type of plant.