Hardware · Comparison
Fox ESS versus Sigenergy
Updated
Both are modular, both are current UK contenders, and both depend heavily on the installer. Fox is often the value hybrid.
The difference that should decide it
Sigenergy pushes an all-in-one stack and EV integration harder. Compare inverter power, usable capacity, the backup drawing and the warranty contact, not the finish of the brochure. Ignore the brochure finish until you know usable kWh, continuous power, whether the existing solar inverter stays, and who answers in year eight.
A cheaper cell behind a small inverter can win a per-kWh table and still be the wrong machine.
The same house, two scopes
Take a 10 kWh pack, cycled about 340 times, at 90% round trip. Charge at 11.0p, and value what comes back at 30.8p. Export given up is priced at 12.0p. About 1943 kWh a year of the charge is treated as spare solar from 4 kWp that might otherwise have been exported. Delivered energy is about 3060 kWh. After charging cost and lost export, the figure saves about £596 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 11.5 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 kWh and 4 kWp, which is enough to tell two quotes apart if they assumed something else.
Pick with the building, not the advert
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 treat backup as included on a 10 kWh quote unless the circuits are listed. One option may need a certified installer and the other a wider trade. That is a real difference on the day it fails.
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. £6,880 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 £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 30.8p 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.