What a home battery takes off a bill in year one
Any figure for what a battery saves depends on two or three prices on your own tariff and on how much of your power it can actually shift. So instead of a headline number, this guide gives you the sum and a tool to run it.
Quick answer
With solar, each kWh a battery lets you use at home instead of exporting is worth your import price minus your export price. Without solar, each kWh it shifts from off-peak to peak is worth the peak price minus the off-peak price divided by the battery's round-trip efficiency. Multiply by the kWh shifted in a year: that is the year-one bill effect.
Run it with your own figures
The tool needs figures you already hold: your annual use from your bills, your tariff's prices, and the self-use estimate or specification from your quote. Nothing you type leaves your screen.
Fill in every box with figures from your own bills, tariff and quote to see a year-one figure. The import price is prefilled with Ofgem's cap average for 1 October to 31 December 2026 (26.32p per kWh, Direct Debit); replace it with your own.
With solar panels: the gap between import and export
On a sunny day, panels make more power than most homes use at the time. Without a battery the surplus is exported, and you are paid your export rate for it. With a battery some of that surplus is stored and used in the evening instead of power you would otherwise buy. So the value of each stored kWh is not your import price; it is your import price minus the export price you gave up.
The second ingredient is how much extra solar the battery lets you use. Installers estimate it with a self-use figure: the share of your solar generation used at home, without and with the battery. Installers registered with MCS work it out with a lookup-table method; a secondary source says that method does not cover generation over 6,000 kWh a year, use outside 1,500 to 6,000 kWh a year, or batteries over 15.1 kWh. Take the two shares from your quote and the tool does the rest.
Two caps we always apply
We never let the share of solar used at home go above 75% without a battery or 90% with one, however a quote words it, and a home can never use more solar than its total use. These are our house rules for honest estimates, and the tool tells you when they have changed your figure.
Without solar: the gap between peak and off-peak
A battery on its own charges from the grid when power is cheap and supplies the home when it is dear. Each kWh it shifts is worth the peak price minus the off-peak price, less what is lost charging and discharging: the round-trip efficiency on the specification sheet. The tool also limits the shift to the use you have outside the cheap window, and to the battery's usable size.
There is a catch worth knowing. Moving from a single-rate tariff to a time-of-use one changes what you pay for all your electricity, not just the part the battery shifts. That change can be positive or negative and has nothing to do with the battery itself, so we show it separately rather than folding it in. We don't prefill any off-peak rate: the only one we read on 3 November 2026 was an electric-vehicle tariff whose terms don't say a home battery may charge at it.
Where the prices come from
- Import price. Your bill shows it. For reference, Ofgem's price cap set the average Direct Debit unit rate at 26.32p per kWh, with a standing charge of 54.83p a day, from 1 October to 31 December 2026, quoted without VAT. HMRC has removed VAT from household electricity in Great Britain until 30 June 2027.
- Export price. Smart Export Guarantee tariffs are set by each supplier and must be above zero. One supplier's examples, read on 3 November 2026: Octopus Energy's Outgoing tariff paid 12p per kWh (variable), and its Prime Outgoing tariff paid 16p between 4pm and 7pm and 9p at other times. Those are examples from one supplier on one date, not "the" export rate.
- Usage. Your bills or smart meter. Ofgem's typical figures from 1 July 2026 are 1,600, 2,500 and 3,800 kWh a year for low, medium and high use on a single-rate meter.
Why we stop at one year
Tariffs change several times a year, export rates change, households change, and a battery slowly holds less as it ages. A figure for year one, on today's prices, is something you can check against your own bills. A payback period or a lifetime total built on today's prices is a guess presented as a fact, and the Advertising Standards Authority has upheld complaints against savings claims whose basis wasn't disclosed. So we don't publish them.
What you can do is set your year-one figure beside the price. The battery price calculator gives a modelled price for any size, the price per kWh page works out what each warranted kWh costs, and paying for a battery covers loans and what isn't a grant.
Sources (page last reviewed 3 November 2026)
- Ofgem: energy price cap unit rates and standing charges (1 October to 31 December 2026), checked 3 November 2026.
- HMRC: VAT on fuel and power (Notice 701/19, updated 28 October 2026), checked 3 November 2026.
- GOV.UK: Smart Export Guarantee, checked 3 November 2026.
- Ofgem: Smart Export Guarantee (SEG), checked 3 November 2026.
- Octopus Energy: Outgoing export tariffs (one supplier, an example only), checked 3 November 2026.
- Ofgem: review of typical domestic consumption values, decision (May 2026; values from 1 July 2026), checked 3 November 2026.
- Easy PV help: limits of the MCS self-consumption lookup method (secondary), checked 3 November 2026.
- ASA ruling on British Gas Services Ltd (savings claim, 4 March 2026), checked 2 November 2026.
- DESNZ: MCS certified domestic battery installation statistics (April 2024 to March 2026 workbook, published 28 May 2026), checked 3 November 2026.
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