What is the difference between G98 and G99 grid applications?

EREC G98 allows a 'Fit and Inform' process for fully type-tested generators up to 16 A per phase (3.68 kW single-phase, 11.04 kW three-phase), where the installer notifies the DNO within 28 days of commissioning without prior permission. EREC G99 applies to any generation exceeding 16 A per phase, non-type-tested equipment, or multiple aggregated installations, requiring formal application and written DNO approval before connection.

What is EREC G100 Issue 2 and when is it required?

EREC G100 Issue 2 specifies technical requirements for Customer Export Limitation Schemes. When an installation's total generating capacity exceeds the maximum export capacity permitted by the DNO, G100-compliant controllers dynamically restrict export. The scheme must be fail-safe within less than 5 seconds, feature tamper-proof password protection, and monitor CT health continuously.

Solar & Battery Grid Connections: ENA EREC G98, G99

Connecting distributed generation equipment (solar photovoltaic arrays, battery storage inverters, and micro-hydro) to the UK public electricity network is governed by strict statutory rules enforced by Distribution Network Operators (DNOs). Understanding the legal dividing line between ENA Engineering Recommendation G98 ("Fit and Inform") and ENA Engineering Recommendation G99 (Prior Application Required), alongside EREC G100 Issue 2 Export Limitation, is essential to avoid unlawful grid connections and network curtailment fines.

The Legal Framework: BS 7671, Distribution Code & ESQCR

Connecting generating plant to private and public networks operates under a dual statutory and wiring regulations framework:

BS 7671:2018+A2:2022 Regulation 551.7 & Section 712: Generating sets and solar photovoltaic (PV) power supply systems.Mandates automatic disconnection of generating facilities in event of loss of the public supply or deviation of voltage/frequency beyond declared limits, and sets rules for bidirectional overcurrent coordination.
SI 2002/2665 (ESQCR 2002): Under Regulation 22 of the Electricity Safety, Quality and Continuity Regulations 2002, no person may connect a source of electrical energy in parallel with a public distributor's network without the distributor's formal notification or agreement.
ENA Engineering Recommendations: The technical requirements for connection are codified by the Energy Networks Association (ENA) under EREC G98 and EREC G99.

ENA EREC G98: The "Fit and Inform" Standard

EREC G98 applies to micro-generators of up to and including 16 A per phase connected at low voltage. This covers standard domestic solar and small battery storage systems:

Single-Phase Limit: 16 A × 230 V = 3.68 kW maximum continuous AC output.
Three-Phase Limit: 16 A per phase × 230 V × 3 = 11.04 kW maximum continuous AC output.
Mandatory Pre-Condition: The equipment (inverter) must be Fully Type Tested and registered on the ENA Type Test Register.
Procedure ("Fit and Inform"): The installer commissions the system and submits the formal G98 Commissioning Form to the local DNO (e.g. UKPN, National Grid, SSEN, SP Energy Networks, ENW, or NIE) within 28 days of commissioning. No prior permission is needed.

ENA EREC G99: Prior Approval Application Required

If an installation exceeds the G98 thresholds or fails to meet the strict type-test criteria,the installer is legally prohibited from connecting or commissioning the equipment before receiving formal DNO written approval:

Trigger Condition	Governing Process	Required DNO Workflow
Total inverter capacity > 16 A per phase (> 3.68 kW 1-phase / > 11.04 kW 3-phase)	EREC G99	Submit Standard Application Form (A1-1, A1-2, or A1-3) prior to installation. DNO performs network study. Connection offer must be accepted before energisation.
Non-Type-Tested Inverter Equipment (Regardless of size!)	EREC G99	Even a small 2 kW generator that lacks an ENA Type Test Certificate automatically defaults to a full G99 bespoke application!
Multiple installations in close geographic proximity (e.g. housing estate rollout)	EREC G99 (Fast Track / Multi-Installation)	Advance notification required to evaluate cumulative local substation voltage rise.

Combined Solar PV + Battery Storage Installations

A frequent compliance trap occurs when a property installs a 3.68 kW solar PV inverter alongside an independent 3.68 kW AC-coupled battery storage inverter.

The Combined Generation Rule:

DNOs calculate capacity as the sum of all parallel generating units. Two separate 3.68 kW inverters total 7.36 kW (32 A on single phase). This automatically pushes the installation into EREC G99, unless an integrated hybrid inverter is used that guarantees combined output cannot exceed 16 A, or an approved EREC G100 Export Limitation Scheme is installed.

EREC G100 Issue 2: Customer Export Limitation Schemes (ELS)

Where a consumer wishes to install a large generation system (e.g. 10 kW solar PV + 8 kW battery) but the local DNO network has constrained export capacity (e.g. limited to 3.68 kW or zero export):

The installer may deploy an EREC G100-compliant Export Limitation Scheme (ELS) that dynamically throttles inverter generation to keep net grid export within the agreed DNO ceiling.

Strict G100 Issue 2 Design Rules:

5-Second Fail-Safe Curtailment: If the export limit is breached (or if communication with the intake CT meter is interrupted), the system must reduce export to or below the agreed limit within < 5 seconds.
Password Protection: Export limit settings in the inverter firmware must be protected by an installer-level password to prevent consumer tampering.
CT Health & Polarity Check: The system must continuously monitor CT circuit integrity. If a CT is unplugged or reversed, the inverter must immediately default to zero export.