G98 vs G99: DNO Rules for Solar Explained

The paperwork that decides more than the panels do

Every grid-connected solar system in Great Britain connects to a network owned by a Distribution Network Operator — and the DNO’s rules, not your installer’s diary, decide when and how your system can be switched on. Those rules come in two flavours, G98 and G99, and the difference between them is the single most consequential piece of paperwork in a solar project. It is also the piece most installer websites either ignore or get wrong.

This guide explains the boundary, the two processes, why adding a battery usually changes which side of the line you sit on, and the order-of-operations mistake that leaves people with inverters turned down to half power.

First: your DNO is not your energy supplier

The company you pay for electricity — the supplier — does not own the wires. The DNO does, and it is the DNO that G98 and G99 concern. Great Britain is divided into regional DNO licence areas operated by companies including UK Power Networks, Northern Powergrid, Electricity North West, National Grid Electricity Distribution, SP Energy Networks and SSEN. You do not choose your DNO and switching supplier never changes it.

If you do not know yours, the Energy Networks Association’s connection guidance includes a postcode lookup and explains both connection routes. A competent installer names your DNO unprompted at survey — it is a small tell that they have done this before in your area.

G98: connect, then notify

G98 is the route for small systems: up to 16 amps per phase, which at 230 volts works out to roughly 3.68 kW of inverter output per phase. For a standard single-phase UK home, that means a system whose inverter is rated at 3.68 kW or below qualifies — and note carefully that the limit is measured at the inverter, not the panels. An array of, say, 4.4 kWp of panels feeding a 3.68 kW inverter still sits within G98, and this panel-oversizing arrangement is common and legitimate.

The G98 process is deliberately light-touch: the installer fits and commissions the system, then notifies the DNO within 28 days of connection. No advance permission, no waiting, no connection study. This “connect and notify” route exists because a 3.68 kW export is small enough that the network can absorb it without individual assessment.

One wrinkle worth knowing: the 16 amp limit is per phase. A house with a three-phase supply — rarer in the UK, but not exotic — can host up to about 11 kW of inverter capacity across the three phases and still use the G98 route. If you have three-phase, say so early; it changes the design conversation in your favour.

G99: approval before energisation

G99 covers everything above the 16 amps per phase line — larger solar arrays, most solar-plus-battery combinations, and commercial systems. The process inverts completely: the installer submits a G99 application to the DNO before installation, and the system must not be energised until the DNO has approved the connection.

The DNO studies whether the local network — the transformer, the cabling in your street, the other generators already connected — can accept your export. Three outcomes are possible:

1. Approved as applied for. The common outcome for domestic-scale G99 applications in most areas.
2. Approved with an export limit. The network can take your system but not its full export, so the DNO requires an export limitation scheme — the system caps what it pushes to the grid (governed by the associated G100 requirements). You still self-consume everything you can; only the surplus flowing out is capped.
3. Reinforcement required. Rare at domestic scale, more common commercially: the network needs upgrading before the full connection can be accepted, with cost and time implications that belong in the project plan from day one.

Domestic-scale G99 approvals commonly take a few weeks; larger commercial applications can run months, which is why on commercial projects the G99 application belongs at feasibility stage, not after procurement. On those larger jobs — three-phase supplies, sub-main alterations, export metering — the grid application is routinely handled end-to-end by specialist commercial electrical contractors working alongside the solar designer, because the DNO conversation and the electrical infrastructure design are the same conversation.

Why a battery usually tips you into G99

Here is the trap that catches more households than any other, because it is genuinely counter-intuitive: you can be within G98 with your solar system, add a battery, and find the combination needs G99.

The DNO assesses the aggregate capacity of all generation and storage inverters at the property. A battery’s inverter counts, because a battery can export to the grid just as panels can. So:

• A 3.68 kW solar inverter alone: G98. Fine.
• Add an AC-coupled battery with its own 3.6 kW inverter: the property now has roughly 7.2 kW of inverter capacity. That is a G99 application — and it must be approved before the battery is energised, even though the original solar system was legitimately notified under G98.
• A new combined install with a 5 or 6 kW hybrid inverter: over the line from day one. G99 from the start.

This is why “most solar-plus-battery systems are G99” is the honest general statement, and why a battery retrofit quote that never mentions the DNO should worry you. It also interacts with siting and design decisions covered in our battery installation guide and in where a home battery should go — the G99 application belongs at survey stage, alongside the siting conversation, not after the boxes arrive.

There are smaller-print routes an experienced installer will know — export-limited applications that can streamline approval, and DNO-specific processes for storage — but they all share the same principle: the DNO agrees the arrangement before the equipment is switched on.

The order-matters warning

Now the part that justifies this article’s existence. Some installers — under schedule pressure, or because the sale closed faster that way — fit G99-scale systems and promise to “sort the paperwork after”. Here is what that gamble actually risks:

• The DNO can refuse the connection as installed. Approval was never guaranteed; that is what the application is for. If the local network cannot take the export, the after-the-fact answer may be an export limit you were never told about.
• You can be forced to run export-limited. An inverter commissioned at 6 kW and then capped can leave you with a system that never earns what the sales projection promised. The projection assumed exports that the network never agreed to accept.
• Your paperwork chain breaks. Smart Export Guarantee registration — the mechanism that pays you for exported units, overseen by Ofgem’s SEG scheme — requires an MCS-certified installation, and the certification and DNO evidence travel together in your handover pack. Gaps surface at the worst moments: SEG registration, insurance claims, house sale.

The fix costs nothing: sequence. A professional installer establishes at survey which route applies, submits the G99 application before installation where one is needed, and hands you the DNO evidence — the G98 notification confirmation or the G99 approval — with the rest of your documents at handover. Slower by a few weeks sometimes. Right, always.

What this means for your quotes

Three questions to put to any installer, verbatim:

1. “Is this system G98 or G99, and why?” The answer should reference inverter capacity per phase, arrive without hesitation, and match the maths above.
2. “If G99 — when do you submit, and do we wait for approval before energising?” The only acceptable answer: submitted at or shortly after survey, energised after approval.
3. “Who is my DNO and what are their current timescales?” Tests local, recent experience. A firm working your area weekly knows whether the local DNO is turning domestic G99s around in three weeks or eight.

An installer who answers all three cleanly is very unlikely to be cutting corners elsewhere — the paperwork discipline and the fixings-and-commissioning discipline tend to travel together.

Common G98/G99 questions

Does G98 or G99 cost me anything? G98 notification is effectively administrative and bundled into any honest quote. Domestic-scale G99 applications are typically handled within the installer’s price as well, though DNO charges can apply in some circumstances and commercial connection studies carry real fees. What actually costs money is doing it in the wrong order — see above.

My installer says the DNO stuff is “just a formality”. True? For a sub-3.68 kW single-inverter system, close enough — G98 genuinely is notify-and-done. For anything with a battery or a bigger inverter, no: G99 is a real application with a real possibility of conditions attached. “Formality” is the word people use when they intend to do it afterwards.

Can I export to a different company than I buy from? Yes. Your SEG export tariff does not need to be with your import supplier, and shopping the export rate separately is often worth real money. The DNO is unaffected either way — it deals in wires, not tariffs.

If you are weighing up a system — with or without a battery — request a free quote and we will put the G98/G99 position in writing at survey, or start with the FAQs for the rest of the connection questions answered straight.