G99 Issue 2's storage requirements came into force in March

ENA EREC G99 Issue 2 is dated 10 March 2025, and its requirements for Power Generating Modules incorporating Electricity Storage came into force on 1 March 2026. That is not a horizon to plan for. It is the regime a British storage or hybrid product is inside now.

The unusual thing about this standard

Most standards describe an outcome and leave the method to you. G99 does something more specific. Annex A.7.1.2.2 sets out over- and under-voltage type verification carried out by operating the module in parallel with a variable AC test supply, with the test voltage applied in steps of 0.5% or less, held for longer than the trip delay, then stepped in a single jump so trip time can be measured — and ride-through confirmed at each setting.

The document also states that a fully integrated package can be tested in a factory environment, for example on a grid simulator. A British grid code has written down the class of instrument you need.

Why that makes it a duty cycle rather than a demonstration

Stepping voltage in half-percent increments, holding past a trip delay, and repeating across settings and phenomena is not a morning's work. Interface Protection, LFSM-O and LFSM-U, RoCoF, Fault Ride Through and Vector Shift each have their own procedure. The bench runs for days.

That is where regeneration stops being a specification-sheet line and becomes an operating cost. A source that returns absorbed power to the grid rather than dissipating it does not need the room, the ventilation or the electricity bill that a load bank does.

Two things that catch people out

• The G98 threshold is 16 A per phase. A product that sits just above it falls into G99 and a materially heavier type-test programme — a design decision, not a paperwork one.
• Northern Ireland runs its own variant. NIE Networks publishes ENA EREC G99/NI. Even within the UK the standard forks.

It is not IEEE 1547

The American interconnection regime is IEEE 1547 with UL 1741 SA and SB — different tests, different trip settings, a different certification culture. Evidence generated for one does not transfer to the other, and a supplier who only knows the American regime will not recognise half the procedures above.