G98 vs G99 Explained: DNO Approval, Timelines & What Homeowners Need to Know
Every grid-connected solar system in the UK must comply with either G98 or G99. Here's what that means for your installation.
What Are G98 and G99?
G98 and G99 are Engineering Recommendations published by the Energy Networks Association (ENA). They govern how small-scale generation systems (like solar panels) connect to the local electricity distribution network.
G98 — Most Homes
- Inverter capacity ≤ 16A per phase (up to 3.68 kW single-phase)
- Notification only — no DNO application needed
- Installer notifies DNO after commissioning
- No waiting period — install can proceed immediately
G99 — Larger Systems
- Inverter capacity > 16A per phase (above 3.68 kW single-phase)
- Requires DNO application before installation
- Fast-track process for systems under 50 kW
- DNO responds within 10 working days (fast-track)
DNO Approval Timeline
G98: Notification After Install
No delayYour installer submits a notification to the DNO after commissioning. No approval needed beforehand. Most domestic systems (≤3.68 kW) fall here.
G99 Fast-Track (Under 50 kW)
10 working daysApplication submitted before install. DNO must respond within 10 working days. If no response, deemed approved. Covers most larger domestic systems (4–12 kW).
G99 Full Application (50 kW+)
45–90 working daysDetailed network study required. Rare for domestic — mainly commercial. May require grid reinforcement works at homeowner's cost.
What Homeowners Need to Know
Who Handles the Application?
Your MCS-certified installer handles all DNO paperwork — both G98 notifications and G99 applications. You should never need to contact your DNO directly.
Can G99 Be Refused?
Yes, but it's rare for domestic systems. If the local grid is congested, the DNO may request export limitation (e.g., zero-export or capped at 3.68 kW) rather than outright refusal.
Does This Affect Battery Storage?
Battery storage alone doesn't usually trigger G99. But if your combined solar + battery export exceeds 3.68 kW per phase, G99 applies to the total system.
Three-Phase Supply?
Three-phase homes can install up to 11.04 kW (3.68 kW × 3 phases) under G98. This is becoming more common with larger systems and EV chargers.
UK Distribution Network Operators (DNOs)
Your DNO depends on your location. Your installer will identify the correct one, but for reference:
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