The regime requires all new battery storage plants connecting to the transmission system (or those of 45MW and above) to have grid-forming capability and synthetic inertia. The ministerial order signed by the Secretary of State for Energy, Jean Paulo Gil Barroca, came into force on 23 October 2026.

It applies to all connection applications submitted from that date onwards and only to existing installations where there is a major expansion, modernisation or replacement of equipment. The regulation takes the EU grid code requirements for generators and extends them to energy storage (in all phases of operation i.e. discharging, charging and powering of auxiliary systems).

It also applies to installations connected at 110kV and above, and to projects with a capacity between 10MW and 45MW as per their capacity rights, licences or auction documentation. All energy storage installations with a capacity of 500kW and above will be required to switch from charging to discharging automatically when the grid frequency drops below a pre-defined threshold of 49.2Hz.

The technical specifications are derived from a joint report by a number of European entities (ENTSO-E, the EU DSO Entity, CENELEC and a number of the renewable energy industry associations) which states that such installations must have sufficient power and energy reserves to be able to provide synthetic inertia in response to frequency deviations between 47.0Hz and 52.5Hz and rates of change up to 2Hz/s.

The requirements specify an adjustable mechanical start-up time (1 to 20 seconds, default 12 seconds) and a minimum damping ratio of 10% for power oscillations.

Technologies which already provide synchronous inertia (e.g. pumped storage hydro) are exempt from these 'grid-forming' requirements.

All installations of 1MW and above must be technically able to provide frequency containment and restoration reserves as well as voltage and reactive power control and will be subject to real time remote monitoring and control by system operators. Operators are permitted to issue power limiting instructions in the event of congestion or emergency but there is no requirement to maintain a particular prior state of charge for that purpose.

Any load changes (apart from those for the provision of reserves) must be implemented in a gradual manner over a 10-minute period. The government is under no illusions as to the urgency of this requirement given the very strong growth projections for the sector under the National Storage Strategy (which aims for 6.9GW by 2030, with dedicated auctions for 750MVA of capacity) and the EU funding under the Recovery and Resilience Plan which is supporting over 1GW of projects. The national fleet of operational batteries was at just 20MW at the end of 2025.

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