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Solar PV & Battery Storage: G98 vs G99 Sizer

Under ENA Engineering Recommendation G98, generation connected to the distribution network must not exceed 16 A per phase (3.68 kW on single-phase 230V; 11.04 kW on three-phase 400V) to qualify for "Fit and Notify". When adding battery storage to existing solar, total generation capacity often breaches 16 A, legally requiring ENA G99 prior DNO approval before commissioning.

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Statutory DNO Gate: You cannot energise or commission a system exceeding 16 A per phase without prior written consent from your DNO. ENA G100 export limitation assists DNO connection assessment but does not reclassify a system with over 16 A installed inverters as G98.

1. Grid Supply & ArchitectureSupply Phase ConfigurationInverter Coupling ArchitectureAC-coupled inverters must be summed because both can export at full power simultaneously.

2. Inverter Continuous RatingsSolar PV Inverter AC Rating (kW)Continuous AC output rating of the solar inverter.Battery Storage Inverter AC Rating (kW)Continuous AC discharge power of the battery storage inverter (0 if solar only).Battery Storage Energy Capacity (kWh, Optional)Usable storage capacity (informational; DNO threshold is governed by inverter kW, not kWh).

3. ENA G100 Export Limitation

Install ENA G100 Export Limitation Scheme

Regulatory Pathway & Sizing

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Statutory DNO Connection Route--

Total Continuous AC Generation--

Continuous Current per Phase--

ENA G98 De-Minimis Limit--

ENA G100 Export Scheme Status--

BS 7671 AC Circuit & Safety Requirements

Recommended AC Conductor Size--

AC Voltage Rise Limit (≤ 1.0%)--

RCD Selection (BS 7671 Reg 712.530)--

Required DNO Application Forms:

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PAS 63100:2024 Domestic Battery Safety Checklist

Location Restrictions: Domestic battery storage units must NOT be installed in escape routes, landings, corridors, or protected stairways (PAS 63100 §5.1).
Loft Installations: Strongly discouraged due to fire service access, extreme ambient summer temperatures, and structural floor joist loading (PAS 63100 §5.2).
Fire Safety Interconnection: A smoke or heat detector (BS 5839-6 Grade D1) must be installed directly in the battery location and interconnected with dwelling fire alarms.
Bidirectional Protection: Consumer unit breakers must be rated by the manufacturer for bidirectional power flow. Do not use legacy unidirectional electronic RCBOs.

ENA EREC G98 vs G99 & G100 Formulation

ENA EREC G98 Issue 1 Amd 7, ENA EREC G99 Issue 1 Amd 9 & ENA EREC G100 Issue 2

AM2 PORTFOLIO & DESIGN AUDIT FORMATTRANSPARENT FIRST-PRINCIPLES MATHS

The Battery Retrofit Trap: When an existing 3.68 kW single-phase solar PV installation is retrofitted with an AC-coupled 3.0 kW battery storage inverter:

Total Generation Capacity: Solar (3.68 kW) + Battery (3.00 kW) = 6.68 kW total connected AC generation.
Operating Current: 6,680 W / 230 V = 29.04 A per phase.
Regulatory Classification: Because 29.04 A exceeds the statutory 16.0 A de-minimis threshold, ENA G98 Fit & Notify is strictly illegal. The installation is classed as ENA G99.
Export Limitation Role: Installing an ENA G100 export limitation scheme restricted to 3.68 kW qualifies the job for ENA G99 Fast-Track (Form A1-2). It expedites DNO assessment, but written consent prior to commissioning remains legally mandatory.

DNO Legal Authority Notice: This tool provides technical guidance under ENA EREC G98, G99, and G100. The local Distribution Network Operator (DNO: UK Power Networks, National Grid, Northern Powergrid, SP Energy Networks, SSEN) maintains sole legal authority to approve or refuse grid connections. Always verify before energisation.

Statutory Standards: ENA EREC G98 Issue 1 Amd 7 • ENA EREC G99 Issue 1 Amd 9 • ENA EREC G100 Issue 2 • BS 7671:2018+A2:2022 Section 712 • PAS 63100:2024