DNO Approval for Solar: G98 vs G99 Explained

Planning permission gets most of the attention, but it’s rarely the thing that holds a solar install up. The step that actually causes delays is one most homeowners have never heard of: getting your local electricity distributor to sign off on the connection. That’s what G98 and G99 are.

What G98 and G99 actually are

Every DNO (Distribution Network Operator, the company that owns the physical wires and substations in your area, not your electricity supplier) has to know about any generator connecting to its network. G98 and G99 are the two Engineering Recommendations, published by the Energy Networks Association, that set out how that works. Which one applies comes down to a single number: how much your system can export.

• G98 is the simple route: install first, notify within 28 days. No approval needed before you switch it on, no fee, no site visit.
• G99 is the approval-first route: you apply, the DNO assesses your local network’s capacity, and you wait for a formal connection offer before you can commission the system.

The threshold: 3.68kW, not the size of your panels

G98 covers generating equipment up to 16A per phase, which works out to 3.68kW on a single-phase household connection, or roughly 11kW across a three-phase supply. Above that, you’re into G99.

The part that trips people up: this is about your inverter’s rated export capacity, not the size of your panel array. Panels are commonly oversized behind a smaller inverter (a 6kW or 8kW array paired with a 3.68kW-rated inverter is a normal, well-established setup), and it still qualifies for G98, because the inverter physically can’t export more than 3.68kW regardless of how much the panels generate on a sunny day.

Where it gets genuinely inconsistent is a bigger inverter (rated above 3.68kW) with its export artificially limited down to 3.68kW in software. Some DNOs treat that the same as a small inverter and accept G98. Others take the view that G99 applies to anything that’s capable of exporting more, even if it’s currently dialled down, on the logic that a software limit could be changed later. There’s no single rule here, it depends on your specific DNO, so it’s worth confirming directly with them (or asking your installer to) rather than assuming either way.

How long each route actually takes

Route	Who decides	Typical timescale
G98	You notify, no approval needed	Instant, notify within 28 days of commissioning
G99 Fast Track (type-tested systems up to 17kW per phase)	DNO	Usually 15-20 working days
G99 standard	DNO	Up to 45 working days by the statutory window, though real-world reports range from a few days to several months if the local network needs reinforcement

G99 also carries an assessment fee, which scales with system size, anywhere from roughly £350 for a small domestic system up into five figures for something that needs network reinforcement work. G98 is free.

Who actually submits it

In practice, most homeowners never deal with their DNO directly, a competent installer designs the system to sit under 3.68kW where possible and handles the G98 notification themselves as part of the job. Where a system does need G99, the installer normally submits that too, capping the inverter’s export at 3.68kW so the system can still be installed and used while the full application is pending, then releasing the cap once approval comes through.

The catch: this isn’t universal. Some cheaper quotes leave DNO paperwork as the homeowner’s own responsibility rather than folding it into the install. It’s worth asking directly, and getting it confirmed in writing, whether your quote includes handling the DNO application, before you sign anything.

Batteries change the calculation too

Adding a battery to an existing solar system usually needs its own DNO notification, even if the original solar-only install was a straightforward G98. If the battery adds export capability that pushes your combined total above 3.68kW, that can tip the whole system into needing a G99 application, not just an update to the existing G98 notification. See our battery storage cost and payback guide for whether adding one is worth it for your setup regardless of the paperwork.

Bottom line

For most household-sized systems this is a formality your installer handles without you noticing, but it’s the reason a straightforward-looking install can occasionally take months rather than weeks, and it’s worth asking about upfront rather than discovering it after your panels are already on the roof. See our solar cost and payback guide for the numbers this timeline sits alongside, or get matched with vetted installers who can tell you which route your own system falls under before you commit to anything.

Frequently asked questions