Connecting distributed generation - including solar PV inverters, AC-coupled battery storage, and vehicle-to-grid (V2G) systems - to the UK electricity distribution grid requires compliance with Energy Networks Association (ENA) Engineering Recommendations G98 and G99.

The Capacity Thresholds: G98 vs G99

The dividing line between whether you can "Fit and Inform" or must "Apply and Await Approval" comes down to the total combined registered capacity per phase of all generating equipment:

ENA Capacity Limits:

• Single-Phase: Up to 16 A per phase (3.68 kW at 230 V) → ENA G98

• Three-Phase: Up to 16 A per phase (11.04 kW across 3 phases) → ENA G98

• Above 16 A per phase: Any system capable of exporting > 3.68 kW (single-phase) → ENA G99

Engineering Recommendation G98 ("Fit and Inform")

  • Process: The installer commissions the system and notifies the local Distribution Network Operator (DNO) within 28 days of commissioning using G98 Form A.
  • Requirement: The micro-generator must be fully type-tested and certified to ENA G98 standards (including loss-of-mains anti-islanding protection).
  • Combined Solar + Battery: If a hybrid inverter exports ≤ 3.68 kW to the grid, it qualifies for G98 even if the solar panels and battery storage have higher internal DC capacity.

Engineering Recommendation G99 ("Apply and Wait")

  • Process: The installer or client must submit a formal G99 application to the DNO before installation begins. Connection cannot take place until the DNO grants formal written permission.
  • Fast-Track G99 (Form A1-1): Applicable where a pre-existing G98 solar system is expanded with an AC-coupled battery storage system, provided an export limitation scheme restricts maximum grid export to ≤ 3.68 kW.
  • Standard G99 (Form A2 / A3): Full technical assessment required for commercial installations (> 16 A per phase), often requiring network reinforcement studies and connection fees.

Key DNO Notification Pitfalls to Avoid

  1. Separate Solar Inverter + Separate AC Battery Inverter: If a customer has a 3.68 kW solar inverter and adds a separate 3.0 kW AC-coupled battery inverter, the combined export capacity is 6.68 kW (29 A). This is strictly G99, not G98, unless a G100-certified export limitation device is installed.
  2. Failure to Notify Within 28 Days: Failing to register a G98 installation breaches the Electricity Safety, Quality and Continuity Regulations (ESQCR) and can void building control certificates.