Homes · Site note
A home battery beside a high-mileage EV
Updated
A car that takes 15 to 20 kWh a night will dominate the cheap window and the supply. The home battery is a side decision.
On the actual building
Get the charger and the tariff right first. Add storage if solar surplus or backup still has a job after the car is served. The cupboard, the supply and the tariff decide it. A national package price skips all three.
In Oxford, on SSEN, 3.6 kW is in the band where G98 connect-and-notify is often enough. Export can still be capped. Agree that before the inverter is ordered. The figure uses 10 kWh and 4 kWp, which is enough to tell two quotes apart if they assumed something else.
If the house is in Oxford
Oxford is only an example for "A home battery beside a high-mileage EV", not the only place the point applies. SSEN would be the network if the survey were there, and the cupboard rules would still win.
The money
Take a 10 kWh pack, cycled about 320 times, at 90% round trip. Charge at 11.0p, and value what comes back at 29.6p. Export given up is priced at 10.0p. About 1829 kWh a year of the charge is treated as spare solar from 4 kWp that might otherwise have been exported. Delivered energy is about 2880 kWh. After charging cost and lost export, the figure saves about £555 a year. Set that against £7,293 fitted, which is a September 2026 illustration at the temporary 0% residential rate, not a quote. That is a simple payback of about 13.1 years on these assumptions. Nudge the night rate up by 4p and see if you still like it.
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 figure prices the work at £7,293 on that basis. It does not apply to a shop, and it does not apply to a battery you buy and fit yourself.
When to stop
I would not treat backup as included on a 10 kWh quote unless the circuits are listed.
If the only place for a 10 kWh cabinet is an escape route, a hot boiler cupboard or an unapproved balcony, stopping is a successful survey.
Before a deposit, I would want usable capacity, the warranty counterparty and a G98 note for this 3.6 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.
Common questions
Is the price on this page a quote?
No. £7,293 is a September 2026 illustration for a 10 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 10 kWh example the inverter is 3.6 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 £7,293 job, that folder is part of what you bought.
What if the cheap rate is not 7p?
Then the figure changes. This page used 11.0p as a charge rate and 29.6p as the rate avoided. A smaller gap means a worse payback. Read the live tariff.
Sources
Want a price for your house?
The figures above are a rough guide. An installer still needs to see your fuse board, where the battery will go, and whether you want power during a blackout.