A home battery stores spare solar power so you can use it later. It does not make electricity, and it does not always save money. This page explains when a battery adds value, how to size one and when to skip it.
Solar Yield is not an installer. We estimate openly, and we pass enquiries to MCS-certified installers.
What a battery does
On a sunny afternoon your panels may make more power than your home uses. Without a battery, however, that surplus goes to the grid, and you are paid your export rate. With a battery, the surplus charges the battery first, and you use it in the evening.
Each kWh you store replaces a kWh you would otherwise buy. Currently the Ofgem price cap sets the unit rate at 26.32p per kWh, a Great Britain average. Fixed tariffs can be higher or lower, so check your own bill.
When a battery adds value
The case is strongest when your use is mostly in the evening and overnight. For example, a household that is out all day and cooks after work leaves most of its solar output unused. A battery moves that output into the hours you need it.
A big gap between import and export prices helps too. Each supplier sets its own Smart Export Guarantee rate. At the time of writing, Outgoing Octopus pays 12p per kWh, and Energy Saving Trust says around 12p is typical.
Our explainer on the Smart Export Guarantee compares the options. The scheme covers Great Britain only.
Time-of-use tariffs can add a second benefit. For instance, some suppliers charge less for power at set off-peak hours. A battery can charge then and supply the home at peak times, even on a day with little sun. Tariffs change often, so treat any offer as a snapshot and read the terms.
Winter is the weak spot for solar, and a battery cannot fix that. Meanwhile, our guide to solar panel output in winter shows how little you may have to store from December to February. Any winter value then comes mainly from cheap-rate charging, not solar.
How to size a battery
Start with your use. Ofgem’s typical values for a single-rate meter are 1,600 kWh a year (low), 2,500 kWh (medium) and 3,800 kWh (high). A medium home therefore uses about 6.8 kWh a day.
Next, look at the evening share. Say you use 3 kWh after sunset, as an example. A 5kWh battery then covers it, while a larger one will rarely fill in a UK winter.
Then check your panels. PVGIS data puts a 4kWp south-facing array at about 4,092 kWh a year, as our page on solar output in Bristol shows. Summer output can fill a battery early, but December output may not.
Use the solar yield calculator to see how much of your output you already use directly. A higher self-use share leaves less surplus for a battery to store. Therefore a lower share gives a battery more to capture.
What a battery costs
In 2025/26, DESNZ data shows median retrofit costs, with installation, of about £1,300 per kWh for batteries of 1kWh to 6kWh. For 6kWh to 11kWh it is about £890 per kWh. For 11kWh to 30kWh it is about £630 per kWh.
In practice, that makes a typical 5kWh battery roughly £6,000 to £6,500 and a 10kWh battery roughly £9,000. Energy Saving Trust says battery storage tends to cost around £5,000 to £8,000. Which? gives a wider range, from under £2,000 to £10,000, depending on capacity, type and brand.
Larger batteries cost less per kWh, but they only help if you can fill and use them. Buying a battery together with panels may also cost less than adding one later. Ask each installer to price both routes.
The VAT rule
Installing solar panels and batteries in a home is zero-rated for VAT until 31 March 2027, according to HMRC. Standalone and retrofit batteries have qualified since 1 February 2024. The relief applies to installation by a contractor, so a materials-only purchase pays standard VAT.
The reduced rate of 5% returns from 1 April 2027 under current legislation. Therefore a contract signed late may cost more. Check for any extension before you decide.
When a battery does not pay
The sums are simple, but they are tough. A 5kWh battery can move at most about 1,825 kWh a year, which is 5kWh a day for 365 days. If each unit saves the gap between 26.32p import and 12p export, that is 14.32p. The ceiling is therefore about £261 a year, before losses.
Against a cost of £6,000 or more, that is a payback of over 20 years, even in the best case. Energy Saving Trust says an inverter needs replacing after around 12 years, well before a 20-year payback.
A battery is also a poor fit in some homes. Examples include a home with low evening use or a small array. A flat that sits empty all day needs little storage. In those cases, spend on the panels first.
Batteries can still make sense for other reasons. Some people want backup power or lower grid use, or expect tariffs to change. Those are valid goals, but they are not savings, so keep them separate in your comparison. Our longer piece on whether a solar battery is worth it goes through more cases.
Panels first, battery second
For most homes the panels deliver the main saving. Our guide to the solar panel payback period shows how a battery changes the sums. Read the page on solar panel installation for the steps, costs and the MCS process. The same MCS certification applies to a battery.
When you collect quotes, ask for a version with a battery and one without. Compare the extra cost with the extra yearly saving the installer predicts. If they cannot explain the gap in plain numbers, be cautious.
Next steps
Begin with your own numbers. Try the solar yield calculator to see your output and self-use share. When you are ready, ask for quotes and request both options, so you can see what the battery adds.