Hardware · Comparison
Fox ESS: should you install one?
Updated
Fox ESS hybrids such as the H1 and H3 families are widely fitted in the UK with modular high-voltage batteries. They suit new solar and inverter-replacement retrofits.
Where this kit fits
An older string inverter can stay only if you choose an AC-coupled design instead. Households that want modular capacity, a mainstream hybrid and a price below the Powerwall, with an installer who fits this range every week. It is a weak buy when buyers who need guaranteed whole-home backup on day one, or who pick the cheapest quote from a firm that has fitted two batteries ever.
Buyers who need guaranteed whole-home backup on day one, or who pick the cheapest quote from a firm that has fitted two batteries ever.
A September 2026 figure for Fox ESS
Take a 10.2 kWh pack, cycled about 280 times, at 90% round trip. Charge at 11.0p, and value what comes back at 27.2p. Export given up is priced at 6.0p. About 1600 kWh a year of the charge is treated as spare solar from 4 kWp that might otherwise have been exported. Delivered energy is about 2520 kWh. After charging cost and lost export, the figure saves about £477 a year. Set that against £6,880 fitted, which is a September 2026 illustration at the temporary 0% residential rate, not a quote. That is a simple payback of about 14.4 years on these assumptions. Nudge the night rate up by 4p and see if you still like it.
In most single-phase houses in Britain, 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 10.2 kWh and 4 kWp, which is enough to tell two quotes apart if they assumed something else.
At a steady 600 W evening load, 10.2 kWh lasts about 17.0 hours. A 3 kW kettle only works if the inverter can deliver it. Capacity on the badge does not answer that.
VAT, paperwork, refusal
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 £6,880 on that basis. It does not apply to a shop, and it does not apply to a battery you buy and fit yourself.
I would not sign off a 10.2 kWh install from a video call. Someone has to open the consumer unit.
Ask the installer for the last Fox ESS they commissioned: postcode area, inverter size, and whether G99 was required. A first-ever install of this range is a risk you can choose not to fund.
Common questions
Is the price on this page a quote?
No. £6,880 is a September 2026 illustration for a 10.2 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 10.2 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 £6,880 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 27.2p 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.