Money · Cost note
Finance, loans and the 0% VAT window
Updated
Interest on a loan can wipe out a modest arbitrage saving. A 0% promotional finance offer needs the same scope check as a cash quote, and the VAT tax point still needs a written answer.
The figure, and what it leaves out
Monthly comfort is not a payback. People still want a number. A fair illustration for this 10 kWh example is £6,880 fitted at the temporary 0% residential rate, before a new board, scaffold, a long cable or a gateway.
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.
Lines that move the total
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.
A consumer unit with no spare way is extra. A gateway is extra, and only if backup was the brief. Exclusions are fine when they are written down. Hidden ones are why two quotes sit thousands apart.
A number I would not chase
Notice 708/6 is the document. The zero rate on qualifying home installations runs to 31 March 2027, then the notice points to 5%, not a bounce back to 20%, unless the law changes. A deposit can pull the tax point forward. On an illustrated £6,880 job, ask how the invoice will be dated.
I would not treat backup as included on a 10 kWh quote unless the circuits are listed. Price per kWh is a blunt tool. Put inverter kilowatts and the name that honours the warranty back into the comparison.
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.