Local Battery InstallersRules · Memo
G98 and G99 for a home battery
Updated
G98 is the connect-and-notify route most often used at or below 16 amps per phase, which is 3.68 kW. Above that, G99 is an application before you energise.
The claim, without the fog
Plenty of home batteries are 5 kW or more, so G99 is normal, not a sign something is wrong. The DNO can also limit export. Order equipment after the connection strategy is known. This is a decision about paperwork, money or safety. It is not a product ranking.
Take a 13.5 kWh pack, cycled about 340 times, at 90% round trip. Charge at 13.0p, and value what comes back at 30.8p. Export given up is priced at 12.0p. About 3213 kWh a year of the charge is treated as spare solar from 6 kWp that might otherwise have been exported. Delivered energy is about 4131 kWh. After charging cost and lost export, the sketch saves about £785 a year. Set that against £8,805 fitted, which is a September 2026 illustration at the temporary 0% residential rate, not a quote. That is a simple payback of about 11.2 years on these assumptions. Nudge the night rate up by 4p and see if you still like it.
What the rules actually bite on
In most single-phase houses in Britain, 5 kW sits above the 3.68 kW G98 line, so this wants a G99 application before anyone energises it. Export can still be capped. Agree that before the inverter is ordered. The sketch uses 13.5 kWh and 6 kWp, which is enough to tell two quotes apart if they assumed something else.
Where the job is a qualifying install in a home, the 0% rate runs to 31 March 2027 and is due to become 5% after that. This sketch prices the work at £8,805 on that basis. It does not apply to a shop, and it does not apply to a battery you buy and fit yourself.
What I would do next
I would not compare a £8,805 headline with another until usable kWh and the fate of any existing inverter match. Photograph the board, the meter and the wall you have in mind.
Then get two written scopes. If they describe different machines, you do not have two quotes yet.
Before a deposit, I would want usable capacity, the warranty counterparty and a G99 note for this 5 kW inverter. The cupboard has to be a place you can stand in, at a temperature the datasheet allows. A five-minute video is not that.
Questions worth asking out loud
Is the price on this page a quote?
No. £8,805 is a September 2026 illustration for a 13.5 kWh example at the temporary 0% residential rate. Your survey replaces it.
Will it stay on in a power cut?
Only if a gateway or essential-load board was designed and paid for. A standard grid-tied battery turns off with the grid. On this 13.5 kWh sketch the inverter is 5 kW, and backup is still a separate line.
What paperwork should I keep?
Keep the MCS certificate where the job is certified, the electrical certificate, the DNO record, the schematic, the warranty registration and a photo of the schedule. For an illustrated £8,805 job, that folder is part of what you bought.
What if the cheap rate is not 7p?
Then the sketch changes. This page used 13.0p as a charge rate and 30.8p as the rate avoided. A smaller gap means a worse payback. Read the live tariff.