Adding a battery to existing solar panels: cost and options

The short answer

Yes, you can add a battery to solar panels you already have. The Energy Saving Trust puts a typical 5kWh battery system at about £4,600, and batteries added to existing panels pay 0% VAT until 31 March 2027. For existing panels an AC battery is usually the better fit, as it won’t affect Feed-in Tariff payments, but on solar savings alone a battery can take longer to pay back than it lasts.

What adding a battery costs

These are the most reliable published prices we found when we checked in October 2026:

The last two rows show the catch with adding a battery later. The Energy Saving Trust says you should be able to save money by fitting a battery at the same time as solar panels, because the installer is already on site. If your panels are already up, you pay for a separate visit. “From” prices are for the smallest option, so a quote for your home may be higher. For full prices when panels and a battery are bought together, see our guide to what solar panels with a battery cost.

AC or DC: the two ways to connect a battery

Solar panels make direct current (DC), and your home runs on alternating current (AC). An inverter converts one to the other. Where the battery joins the system matters:

• AC battery. Connected after the generation meter (the meter that records what your panels make), with its own converter. Which?, citing the Energy Saving Trust, says AC systems cost more, but they won’t affect Feed-in Tariff payments because the generation meter still records everything the panels make.
• DC battery. Connected directly to the panels, before the generation meter. Which? says DC systems aren’t usually recommended when adding a battery to an existing system, and that charging and discharging this way is less efficient, which could cut Feed-in Tariff payments.

Which? also warns that adding a battery to existing panels may mean a new inverter. Ask each installer whether yours can stay, and if not, put the inverter cost on its own line so you can compare quotes fairly.

If you get Feed-in Tariff payments

Many older systems still earn Feed-in Tariff (FIT) payments. The scheme closed to new applications on 1 April 2019, but Ofgem says installations already accredited keep being paid. Adding a battery does not end those payments on its own. Ofgem’s guidance (version 19, published 1 April 2026) says battery storage can be added without affecting accreditation, as long as the system still meets the metering rules.

What you need to do:

• Tell your FIT supplier. Ofgem says adding storage should be reported to your FIT licensee (the energy supplier that pays you), as with any other change.
• Send the paperwork. That means an updated wiring diagram showing how the battery and meters are connected, the meter readings you use to claim, and evidence of the date the battery was installed and commissioned. If your system was accredited through MCS, Ofgem says you should also send a declaration form.
• Keep the generation meter honest. The meter must measure only what your panels generate. If the battery can also charge from the grid, Ofgem says this can be met with a special two-way meter that shows the net figure.
• Use an MCS installer. For batteries up to 50kW, Ofgem recommends an MCS installer and installation to the MCS battery standard.

Export payments and the network operator

If you are paid for exports under the Smart Export Guarantee rather than the FIT, a battery means you export less, so those payments fall. Which? also says a battery may make you ineligible for some export tariffs. On the other hand, some suppliers pay much more to homes with solar and a battery. In April 2026 Which? found one paying 23p per kWh to its customers with panels and a battery, though you have to buy your electricity from that supplier too, and the battery charges when power is cheapest and exports between 4pm and 7pm. Our guide to the Smart Export Guarantee explains how export tariffs work.

Your local electricity network operator also needs to know. SP Energy Networks, for example, says you should tell it about a battery even if you don’t plan to export. Under its rules, solar and a battery totalling up to 7.36kW can get approval to connect within 10 days if certain conditions are met, including limiting exports to 3.68kW per phase. Larger batteries come under a different set of connection rules (called G99). Your installer normally handles this, but check it is in the quote.

Worked example: a 3kWp system from the Feed-in Tariff years

To see what a battery adds, we worked through one household. They have 3kWp of panels, use 3,500kWh to 3,999kWh of electricity a year, are out during the day, and add a 5kWh battery.

• Solar output: about 2,418kWh a year. Government figures give a median solar load factor of 9.2% for 2024/25, which is about 806kWh for each kWp of panels (9.2% of the 8,760 hours in a year).
• Share used at home: 21% without a battery and 59% with one, from the MCS self-consumption table for a home that is out all day. We treated the battery as having 4.1kWh to 5kWh usable.
• Extra solar used at home: 38% of 2,418kWh, which is about 919kWh a year.
• Electricity price: 26.32p per kWh, Ofgem’s price cap rate for Direct Debit from 1 October to 31 December 2026.

The 6p column uses the best export rate Which? found in April 2026 that anyone can get without conditions. The FIT column is for homes whose export is “deemed”: Ofgem explains this is a set percentage of what you generate, worked out from the generation meter, so with an AC battery, keeping more solar at home does not reduce it. We have ignored energy lost in charging and any change in prices, so treat these as estimates.

The Energy Saving Trust puts a battery’s typical lifespan at about 10 to 12 years, and Which? says batteries often come with a 10-year warranty. So in this example, the battery only gets close to paying for itself on solar savings if you find a low price and keep deemed FIT export. The Energy Saving Trust says battery savings can be significant but won’t always be enough on their own to justify the cost. Charging from a cheap overnight tariff can add to the savings. Our guide to whether battery storage is worth it goes through this.

VAT and timing

HMRC says batteries installed in homes have been zero-rated since 1 February 2024, and this includes adding a battery to existing solar panels. The zero rate runs until 31 March 2027. From 1 April 2027 it goes back to 5%, which would add about £230 to a £4,600 battery. Our guide to the end of 0% VAT on solar explains the deadline.

What to do next

Before you ask for quotes, find three things: your yearly electricity use (on your annual statement), whether you get FIT payments, and whether your export is deemed or metered. Then compare solar battery quotes from an MCS-certified installer who covers your area. Ask each one whether the battery is AC or DC, whether your inverter needs replacing, the usable capacity, and whether they will notify the network operator. You can also check what your panels make in our solar savings calculator. It’s free and there’s no obligation.