Definition: G99 is the grid connection application your installer submits to the local DNO for solar panels, batteries or other generation above 16 amps per phase (about 3.68 kW). It must be approved before installation. Smaller systems use the simpler G98 “fit and inform” process instead.

G98 or G99 — which applies?

G98 covers systems up to 3.68 kW of inverter capacity on a single-phase supply: your installer can fit the system first and notify the DNO within 28 days, normally free of charge. Anything larger — including most modern 4–6 kWp solar arrays with battery storage — needs G99 approval before work starts. Decisions typically take 4–8 weeks (a fast-track route for small domestic systems can cut this to around two), and fees range from nothing to several hundred pounds for typical domestic systems — larger schemes can run into the thousands — depending on the DNO (Capture Energy guide, checked July 2026).

A third document is worth knowing: G100 covers export limitation. If the local network cannot accept your system’s full output, your installer can propose capping what you export while still letting you generate — and store — more for your own use. Outright rejections are rare for domestic systems, but constrained rural networks can require this compromise.

What it means in practice

Your MCS-certified installer should handle the paperwork — but the approval clock affects your project. Build the DNO decision time into your timeline before committing to an installation date, and ask whether your solar panel quote assumes G98, G99 or an export-limited design.

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