Portugal makes grid-forming mandatory for large battery storage plants

Few battery plants connected to Portugal’s transmission grid, or rated at 45 MW or more, must provide grid-forming capability and synthetic inertia under a new regulatory ordinance. Plants of 500 kW or more must also switch automatically from charging to discharging when grid frequency falls.

The rules took effect on Oct. 23 and apply to connection requests filed from that date. Existing plants are covered only if they undergo a significant expansion, modernization or equipment replacement.

The ordinance, signed by Jean Paulo Gil Barroca, Portugal’s secretary of state for energy, applies the requirements for generating units under the EU network code on requirements for generators to storage, whether plants are discharging, charging or powering their own auxiliary systems.

The grid-forming obligation also covers plants connected at 110 kV or above, on terms the grid operators will set. The ordinance extends it to plants of 10 MW to 45 MW, although its technical annex ties the obligation for that class to provisions in grid capacity titles, permits or tender documents.

Smaller plants must provide grid-forming capability only where those documents require it. Plants on the distribution grid must also be able to operate in grid-following mode, with the operator deciding which mode applies.

The technical parameters are based on a joint report by the European transmission and distribution operator bodies ENTSO-E and the EU DSO Entity, industry associations SolarPower Europe, WindEurope and Energy Storage Europe, and the standards body CENELEC. Plants must hold additional power and energy to provide synthetic inertia during frequency deviations between 47.0 Hz and 52.5 Hz and rates of change of up to 2 Hz per second.

The mechanical starting time, which sets the level of inertia a plant emulates, must be adjustable from 1 to 20 seconds, with a default of 12 seconds. Plants must also achieve a damping ratio of at least 10% for power oscillations between 0.1 Hz and 10 Hz. Pumped hydro and other storage that provides synchronous inertia is excluded from the grid-forming requirements.

All plants of 1 MW or more must be technically able to provide frequency containment and restoration reserves, as well as voltage and reactive power control. For the automatic switch to discharging, the default underfrequency relay setting is 49.2 Hz while charging.

Plants must ramp load changes outside reserve activation over 10 minutes unless the system operator instructs otherwise. Plants above 1 MW must give the system operator real-time monitoring and remote control. Grid operators can issue power instructions during congestion or supply-demand emergencies, but the ordinance does not require plants to hold back state of charge to respond.

The government said it is setting the requirements now, while the European Union’s generator connection code is under revision, because of the storage growth expected from Portugal’s national storage strategy and from storage funding calls under its EU-backed recovery plan, which together cover more than 1 GW of projects. It said the ordinance does not prevent the revised EU rules from being implemented once they are published.

Portugal’s draft national storage strategy, put to public consultation in August, targets 6.9 GW of storage by 2030 and highlights grid-forming inverters as a tool for the stability of the Iberian power system. The government has also said it plans a dedicated auction for 750 MVA of battery storage capacity, and in June scheduled it for September alongside a 300 MW round for storage paired with renewable energy projects.

The rules arrive while Portugal’s battery fleet is still small. The country had 20 MW of battery storage in operation at the end of 2025, according to renewable energy association APREN, which expects deployment to accelerate from that base. In January 2025, the government awarded €100 million ($112 million) to 43 storage projects totaling about 500 MW.

From ESS News