The Short Answer
We'd only buy a battery to go with a time-of-use tariff, or for backup in a power cut: on a standard tariff it doesn't pay back on our figures. The Energy Saving Trust says battery storage tends to cost around £5,000 to £8,000, and on a standard tariff a 10 kWh battery adds only about £163 a year to a 4kW solar system.
A time-of-use tariff changes the sums. On Octopus Flux, a battery filled at 16p overnight and emptied in the 30p evening export window earns about £336 a year on our assumptions, which would repay the Energy Saving Trust's range in 15 to 24 years. Batteries are zero-rated for VAT until 31 March 2027, including one added to panels you already have.
What a Battery Costs
The Energy Saving Trust puts battery storage at around £5,000 to £8,000. DESNZ's solar cost figures leave batteries out, so they don't give an average by size. Installing a battery in a home is zero-rated for VAT until 31 March 2027, whether it goes in with new solar panels, is added to an existing system, or stores electricity from the grid on its own (HMRC). From 1 April 2027 the rate goes to 5%.
Would One Pay for Itself?
Put in your own quote, tariff and export rate:
Battery payback calculator
Would a solar battery pay for itself?
The honest version: on solar alone, a battery only earns the gap between what you pay for power and what you'd be paid to export it.
Battery size
Makes about 3,800kWh a year, south-facing in central England
Intelligent Octopus Go needs an electric car or charger that Octopus can control.
Payback
40 years
Earns about £163 a year. That's longer than many battery warranties (Tesla's Powerwall 3, for example, is 10 years), so check the one you're quoted.
Working: it moves about 1,139kWh of solar a year from export to your own use (self-use rises from 26% to 56% on the government's SAP 10.2 self-use formula, in a home using Ofgem's typical 2,500 kWh a year), each worth 14.32p, the gap between your import and export rates.
The thing that changes it most is a time-of-use tariff you charge it on. Try the overnight option above, and check your export rate: if you're on 5p, look at a 12p export tariff (Octopus pays it to its own supply customers on certain tariffs) before relying on a battery.
Our view: buy one for the tariff it lets you use or for backup power, not on a payback promise you can't check.
On a Standard Tariff
On the government's SAP 10.2 self-use formula, a 4kW system with no battery in a home using Ofgem's typical 2,500 kWh a year uses about 26% of what it makes and exports the rest. A battery stores some of the midday surplus for the evening; a 10 kWh battery (8 kWh usable, our assumption) lifts that to about 56%. A home that uses more, with an electric car or a heat pump, uses more of its solar either way. Every kWh the battery moves is worth only the gap between what you'd pay for it and what you'd have been paid to export it: 14.32p, between the 26.32p price cap rate and a 12p export rate.
| 4kW solar system | Worth a year (our estimate) |
|---|---|
| No battery | £599 |
| With a 10 kWh battery | £762 |
| What the battery adds | £163 |
At £5,000 to £8,000, £163 a year takes 31 to 49 years to repay the battery, longer than Tesla's 10-year Powerwall 3 warranty. That's at the 1 October to 31 December 2026 cap rate and a 12p export rate; if you're paid less than that for exports, each kWh the battery keeps is worth more. But switching to a better export tariff costs nothing, so do that before buying a battery to make up for a poor one.
On a Time-of-Use Tariff
A battery earns more when it can buy cheap electricity from the grid and use or sell it when electricity is dear.
- Octopus Flux is built for solar and battery owners. On 24 October 2026 its rates, averaged across the 14 regions, were 16p from 2am to 5am, 37p from 4pm to 7pm and 26.5p the rest of the day. It paid 30p for exports from 4pm to 7pm, 11p in the day and 4.67p overnight. Filling a battery at 16p and exporting at 30p is a gap of 14p a kWh; using it at home instead of buying at 37p is 21p.
- Intelligent Octopus Go gives 8p electricity from 11:30pm to 5:30am for your home, but you need an electric car or charger Octopus can control. The calculator above models it.
- Agile Octopus sets prices every half hour from the wholesale market, updated daily, and Octopus says they sometimes drop below zero. A battery can charge in the cheapest half hours, but the savings move with the market, so we don't put a figure on them.
Our Flux example: a 10 kWh battery with 8 kWh usable, filled off-peak and emptied at the peak on 300 days a year (our assumptions, before charging losses), earns about £336 a year if it all goes to export, or up to £504 if your home uses it all in the evening peak. Against £5,000 to £8,000, that's 10 to 24 years. Tariff rates change, and these are Octopus's rates on one day.
Comparing the Batteries You're Quoted
When you compare quotes, check the usable capacity in kWh, how much power it can deliver at once in kW, the warranty in years, and whether a solar inverter is built in. For example, Tesla lists the Powerwall 3 at 13.5 kWh, up to 11.04 kW, with a solar inverter built in and a 10-year warranty.
Check who stands behind the warranty, too: GivEnergy Ltd is in administration (Companies House), so a GivEnergy warranty from that company may not be honoured. Ask your installer what happens if the manufacturer stops trading.
When We Think It's Worth It
We think a battery is worth it if you'll go on a time-of-use tariff and use most of its capacity every day, or if you want backup power in a power cut. For backup, ask the installer whether the system they're quoting will keep your home running when the grid is down. It isn't worth it on a standard tariff for the bill saving alone. If you're fitting panels and think you'll want a battery later, ask for a hybrid inverter that can take one. Our solar panel costs guide has the panel side of the sums.
See if a battery pays off for your home
Battery payback depends on your tariff, usage pattern, and panel size. Get personalised quotes from MCS-certified installers to see the numbers for your setup. Free, no obligation.
