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BatteriesHow much a home battery saves, unit by unit
Three numbers decide what a battery is worth to you: what you pay for a unit in the cheap window, what that unit would have cost at the standard rate, and what the round trip takes off on the way through. Here they are, multiplied out.
Updated 4 August 2026 · from the OVO Solar & Battery team
The answer first
Charge a battery at 8p per kWh and use that electricity when the standard rate is 26.11p, and you save about 17p on every usable unit that passes through it, after the round trip losses have been taken off. On a 5.2 kWh usable battery that is just under 90p a day. Nothing about that depends on the weather.
It pays the same in January
Solar output collapses in a British winter. Off peak charging does not. The gap between the overnight rate and the standard rate is there every night of the year, which is why we size a battery against your usage rather than your roof.
The arithmetic, one unit at a time
Buy the unit cheap
The cheapest smart overnight tariffs start around 8p per kWh. Which rate you can actually get depends on your supplier, your postcode and whether there is an electric car on the drive, and our round-up of off peak tariffs lists the windows, the rates and the conditions on each.
Take the losses off
No battery gives back everything you put in. Round trip losses run about 6 to 8% where the battery shares a hybrid inverter with solar, and 8 to 10% where it has its own inverter. We model 10%, the pessimistic end, so a unit delivered to the house actually cost 8.9p to buy.
Compare it with the alternative
Without the battery, that same unit comes off the grid at whatever the standard rate is at the time you need it. The Ofgem price cap for 1 July to 30 September 2026 averages 26.11p per kWh.
Bank the difference
26.11p minus 8.9p is 17.2p saved on every usable unit the battery delivers. Multiply that by the number of units you actually move through it each night, then by the number of nights a year you genuinely do it.
Our battery is 5.2 kWh usable, so emptying it fully saves about 90p. Do that 300 times in a year, which allows for the days when your evening load is light or your solar has already covered it, and that is roughly £269 from the battery alone. Do it every single night and it is £327. The number you should use is not the size of the pack, it is how much of it you genuinely empty.
| Usable kWh you move each night | Saved that night | Over 300 nights | Over 365 nights |
|---|---|---|---|
| 2 kWh | 34p | £103 | £126 |
| 3.5 kWh | 60p | £181 | £220 |
| 5.2 kWh, a full cycle of our pack | 90p | £269 | £327 |
| 8 kWh | £1.38 | £413 | £503 |
Worked at 17.2p saved per usable kWh: an 8p off peak import rate, a 10% round trip loss which is the pessimistic end of the 6 to 10% range, and the Ofgem price cap average of 26.11p per kWh for 1 July to 30 September 2026. The October cap is published by 26 August 2026, and the saving is a gap rather than a fixed figure, so it moves when either end of it moves. The capacities above 5.2 kWh are shown to scale the arithmetic, not as a product list.
Why our calculator models 13p, not 8p
The savings figures elsewhere on this site are built on a 13p off peak rate. That is deliberate. The very cheapest overnight rates are tied to particular suppliers and to electric vehicle plans, and tariffs move. Modelling the conservative number gives you a figure to beat rather than one to chase. At 13p the same 5.2 kWh pack saves about 11.7p a unit, so roughly 61p a night and £182 over 300 nights. Your local OVO expert runs it on your actual tariff on the design call.
Bring your last annual statement to the free 45 minute video design and we will run this arithmetic on your real usage and your real tariff, then give you a written quote on the call. No home visit.
Get your free quote →Which rate to put into the sum
Use the rate you can actually be billed at, not a headline. That means checking what is open to you on your postcode and your supplier, which off peak tariffs and battery charging sets out window by window. It also means having a smart meter installed and reporting, because time of use pricing is billed from half hourly readings and no supplier can charge you an off peak rate without one. Sort that before the battery goes in rather than after. It is one of the first things we check, and you can find your regional partner by postcode.
The one thing not to do
Charging from the grid at 8p and selling the same electricity back at a higher export rate looks like free money. Do not build a plan around it. Electricity that came off the grid rather than off your roof is not covered by the Smart Export Guarantee obligation, so suppliers are not required to pay for it and the terms differ from one tariff to the next. Export rates are there for what your panels generate. Our guide to how the Smart Export Guarantee works sets out what qualifies and what does not.
Where your own solar fits in the same sum
Once panels are on the roof there are two competing uses for every unit they make, and the export rate decides which one wins. Where the rate is high enough, exporting your generation and filling the battery from the cheap window instead is worth more than using your own solar in the house. The 20p export rate explained puts money on both sides of that choice, and the strategy page carries the month by month working.
Before you commit
- Take your annual kWh from a bill or your smart meter app and divide by 365. That daily number, not your roof size, decides how much usable capacity is worth buying.
- Work out how much of that day lands outside daylight hours. That is the part the battery is being bought to cover.
- Check which off peak rate you can actually be billed at, then run the sum on that number rather than on ours.
- Read the battery warranty for a throughput limit as well as a year count. Charging from the grid every night is heavier use than solar only, and some warranties cap the total energy put through the pack.
- Get the export terms in writing if any part of your plan involves selling stored electricity.
Put your postcode in and we will tell you which local OVO expert covers your area, then book the free 45 minute design call and get your written quote on the same call.
Get your free quote →Battery storage installed in a home in Great Britain currently attracts 0% VAT. That relief is scheduled to run until 31 March 2027, after which the rate is set to return to 5%.
The savings arithmetic, answered
Do I need solar panels to charge a battery off peak?
No. The saving comes from the gap between the off peak rate and the standard rate, and that gap is there whether or not you have panels. Solar makes the overall picture better because your surplus becomes export income on top, but a battery charged purely from a cheap overnight rate still earns every night of the year. If your roof is shaded, north facing or not yours to use, this is the part of the system that still works.
How many full cycles a year should I assume?
Fewer than 365. Some evenings your load is light, some days your solar has already covered it, and some nights you will not empty the pack. We use 300 full cycles as a working figure, which is why the 5.2 kWh row above shows £269 rather than the £327 you would get from cycling every single night. If you want a conservative number, model 300 cycles at the rate you can actually get rather than 365 at the cheapest rate on the market.
Will charging from the grid every night wear the battery out faster?
It is heavier use than solar only charging, but well within what current products are built for. Mainstream home batteries publish cycle ratings from around 6,000 upwards, and at one full charge and discharge a day 6,000 cycles is more than sixteen years. The clause to read is not the cycle count but the throughput limit some warranties carry, which caps the total energy put through the pack over the term. Ask for it in writing if you plan to cycle fully every day.
Is Economy 7 good enough for this?
It works, but it earns you materially less. The average Economy 7 night rate was about 15.43p per kWh on April 2026 data, with the cheapest around 12.5p. At 15.43p a unit costs 17.1p by the time it comes back out of the pack, so the saving is about 9p rather than 17.2p, and a 5.2 kWh pack cycled 300 times a year returns roughly £140 instead of roughly £269. If a smart time of use tariff is available to you, it is the better home for a battery.
What does the battery itself cost?
Our published price is £2,444 for 5.2 kWh usable, fitted and commissioned, and it is flat across all our system sizes. Full pricing, including solar, sits on the costs page, and every installation carries the OVO guaranteed 10 year workmanship warranty.
Figures and specifications in this guide are sourced below and were checked on the date shown. Rates and product specifications change; we confirm the current picture on your free design call.
Sources
- Ofgem, energy price cap 1 July to 30 September 2026, electricity unit rate 26.11p per kWh, October cap published by 26 August 2026 ofgem.gov.uk
- Intelligent Octopus Go, off peak smart charging from 8p per kWh octopus.energy
- Next Drive Smart, 8p per kWh off peak, midnight to 6am whole home window eonnext.com
- Average Economy 7 night rate, April 2026 data energyplus.co.uk
- Round trip efficiency for AC coupled and DC coupled home battery storage greenreachenergy.co.uk
- Smart meter requirement for time of use tariffs haboenergy.co.uk
- Smart Export Guarantee obligation and the treatment of grid charged electricity which.co.uk
- Published cycle life and warranty terms for current UK home battery ranges switchtogether.co.uk
- OVO Solar and Battery published pricing and battery specification ovosolarandbattery.co.uk
- Zero rate VAT relief on domestic battery storage to 31 March 2027 solarenergyuk.org
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Read the guide →A home battery without solar panels, honestly assessed
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Read the guide →Off peak tariffs and battery charging, window by window
The cheap windows on offer in August 2026, what they cost, and how much fits into one.
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