Cost of adding a battery to solar panels you already have
The official battery prices are, by design, retrofit prices: batteries added to homes that already exist. That makes them the most direct benchmark there is for adding storage to an existing solar system.
Quick answer
Adding a battery to existing solar panels costs about £6,500 for 5 kWh, £8,800 for 10 kWh and £9,400 for 13.5 kWh, modelled from DESNZ's 2025/26 figures for batteries fitted in existing homes, at 0% VAT (to 31 March 2027). The final quote depends mostly on whether your current inverter stays or is replaced.
Why the official figures fit a retrofit so well
DESNZ's battery statistics cover batteries registered with MCS in homes that were already built, and their costs leave out any device fitted alongside, panels included. A battery added to a roof that already has panels is exactly that case: the battery, the work to fit it and the connection, with nothing else mixed in.
The three medians for 2025/26 are £1,300 per nominal kWh under 6 kWh, £890 for 6 to 11 kWh and £630 for 11 kWh and over. Our battery price calculator turns any size into a modelled price; the three most common retrofit sizes come out at about £6,500, £8,800 and £9,400. Half of recorded installs in each band cost more per kWh and half cost less.
Since 1 February 2024, a battery retrofitted to an existing solar system counts as an energy-saving material for VAT when it is installed in a home, so it is zero-rated until 31 March 2027 and 5% from 1 April 2027. A battery bought without installation gets no relief.
The inverter decides most of the difference between quotes
Your panels already feed an inverter, which turns their direct current into the alternating current your home uses. A battery can be connected to that system in two broad ways, and quotes for the same battery can differ a lot depending on which one the installer proposes.
| On the quote | AC-coupled battery | Hybrid inverter (DC-coupled) |
|---|---|---|
| Your existing solar inverter | Usually stays as it is | Usually replaced by one unit that handles panels and battery |
| Extra hardware | A battery inverter, often built into the battery unit | The hybrid inverter itself |
| Work on the existing system | Less: the solar side is left alone | More: the old inverter comes off the wall and the panels are rewired to the new one |
| Worth asking | How the two inverters will be set up to work together | What happens to the warranty you hold on the old inverter |
Which?, quoting the Energy Saving Trust, says AC systems tend to be the more expensive of the two, but gives no figures, so we can't put a number on it. What we can say is that a hybrid swap makes more sense when the old inverter is near the end of its life anyway. If yours is young and working, ask for an AC-coupled price as well, so you can see what replacing it costs you.
The Warm Homes Loan Scheme rules (section 4.17) list what a typical battery quote may include, and the list is a useful check for any retrofit: integration with an existing solar system, setting up monitoring apps or control systems, and isolators, breakers or protection devices. If one quote has these as separate lines and another doesn't, the two totals aren't comparable yet.
Other things a retrofit changes
The network application now covers both
Your panels were notified to the network operator when they went in. Adding storage changes what is connected, and MCS points out that solar plus battery is likely to be above the 16 A per phase limit of the simpler G98 route, so a G99 application before installation is common. That adds time rather than a published fee, but it is worth knowing before you agree an installation date. See G98 and G99 in a battery quote.
Where the battery can go
Existing homes rarely have a spot designed for a battery. PAS 63100 rules out lofts, roof spaces, bedrooms, escape routes and cupboards opening into bedrooms, and prefers outdoors or a separate outbuilding where practicable. A garage is one option, with impact protection if a car parks beside it. The siting works are often the biggest variable on a retrofit quote; what adds to a battery quote lists them.
Your export payments
If you are paid for exported power under the Smart Export Guarantee, a battery will usually mean you export less, because more of your midday solar is stored for the evening. GOV.UK notes that storage able to import and export could also be used under the SEG; the rules and rates vary by supplier, so ask yours before you assume anything about export income.
If your panels are on the Feed-in Tariff
Older systems may still receive Feed-in Tariff payments. GOV.UK's guidance on the SEG says its export payments can't be combined with FiT export payments, so adding a battery doesn't open a second export income on the same system. Before you change anything on a FiT system, ask your FiT licensee how a battery affects your arrangement and your meter readings, and get the answer in writing. The battery price itself is the same either way: the official retrofit medians still apply.
What to have ready before you ask for retrofit quotes
Installers can quote more accurately, and you can compare quotes more fairly, if you have these to hand:
- The make and model of your solar inverter, and its age.
- The size of your panel system in kWp, from your original paperwork or the MCS certificate.
- Your annual electricity use from your bills, and, if you have one, a year of export readings from your SEG statements or export meter.
- Where you think a battery could go, and whether that spot is outdoors, in a garage or inside the house.
- Whether you want any circuits kept running in a power cut.
The export figure matters for sizing: a battery fed by solar only stores what you would otherwise export. Divide a year's export by 365 for a daily average, then remember that summer days produce several times what winter days do. The year-one bill effect guide takes those figures and gives a year-one figure using your own tariff.
Then set each quote against the official median with the quote checker. If you are thinking of replacing panels at the same time, compare with fitting a battery with new panels instead, because the two jobs price differently.
Sources (page last reviewed 3 November 2026)
- DESNZ: MCS certified domestic battery installation statistics (April 2024 to March 2026 workbook, published 28 May 2026), checked 3 November 2026.
- HMRC: extension of the energy-saving materials relief to electrical batteries (from 1 February 2024), checked 3 November 2026.
- HMRC: VAT on energy-saving materials and heating equipment (Notice 708/6), sections 2.1, 2.3 and 2.19, checked 3 November 2026.
- Which?: solar panel battery storage (secondary source, page updated 30 October 2026), checked 3 November 2026.
- DESNZ: Warm Homes Loan Scheme rules, version 3 (September 2026, PDF), sections 2.6 and 4.4 to 4.19, checked 3 November 2026.
- MCS: notifying distribution network operators (G98 and G99), checked 3 November 2026.
- BSI / DESNZ: PAS 63100:2024, battery energy storage systems in dwellings (PDF), checked 3 November 2026.
- GOV.UK: Smart Export Guarantee, checked 3 November 2026.
- European Commission JRC: PVGIS solar yield tool, checked 30 October 2026.
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