Solar battery storage: how it works and when it pays in the UK

At a glance

• A battery shifts electricity to later. It can store spare solar and, on a suitable tariff, charge from the grid.
• Measure what the battery adds. Compare the same home with and without storage, allowing for losses and export income forgone.
• Choose capacity for actual use. Check usable energy, power, compatibility and whether backup equipment is included.

A solar battery stores the electricity your panels make during the day that you would otherwise export, so you can use it in the evening instead of buying from the grid. On a time-of-use tariff it can also charge from the grid overnight when electricity is cheap. What a battery is worth depends mostly on how much electricity you use.

For a typical home, a battery mainly moves daytime solar into the evening. Take a household using 2,500 kWh a year (Ofgem's typical figure), out for part of the day, with 4 kWp of panels and a 10 kWh battery. At today's prices, our worked example values the battery's extra solar use at about £184 a year with Fuse's variable 13p export tariff, £201 with Octopus Outgoing's 12p, or £304 with E.ON Next Flex Export's 6p. Fuse and E.ON accept eligible export-only customers; Outgoing needs Octopus electricity supply. The better your export deal, the less you give up by choosing panels without a battery. Under the dated Octopus Flux rates below, the battery and tariff together add about £192 against a single-rate, 12p-export baseline. A ten-year payback would need an extra battery cost of roughly £1,840 to £3,040 across these examples.

For a home with an electric car, overnight charging is where a battery earns most. In our calculator's example, a Birmingham home using 4,500 kWh a year with an electric car, with 6 kWp of panels and a 10 kWh battery (£13,500 in our calculator's price model), saves about £1,542 in the first year, panels and battery together, with Intelligent Octopus Go 12M Fixed, an overnight tariff that needs an electric car or compatible charger and Octopus as your supplier. The panels alone (£9,300) save about £951 on the same tariff, so the battery's share is about £591 a year. These use 12p export. The same model at E.ON Next Flex Export's 6p gives about £1,407 for panels and battery together; that is a lower export-rate sensitivity, rather than the best export-only offer.

How a solar battery works

During the day your panels power your home first and any surplus charges the battery. In the evening the battery supplies your home until it reaches its minimum charge level, and the grid covers the rest. With a time-of-use tariff, the battery can also be set to charge from the grid overnight.

The chart follows our calculator's standard household, 4,000 kWh a year with 5.1 kWp of panels, through an average day hour by hour: what the panels produce, what the home uses, when the battery charges and empties, and what goes to or comes from the grid. Switch the battery off, change its size or pick winter or summer to see how much the season limits what any battery can store. Its default battery is 5.2 kWh, smaller than the 10 kWh in our worked example below, so its figures will not match that example.

Four specifications decide what a battery can do for you:

• Usable capacity (kWh) is the energy you can actually draw, which is less than the total.
• Power (kW) is how fast the battery can charge or discharge. Enphase's IQ Battery 5P delivers 3.2 kVA continuously from 5 kWh.
• Round-trip efficiency is the share of energy you get back. Enphase quotes 90% (AC) for the IQ Battery 5P and E.ON Next quotes 89% for the Tesla Powerwall 3. At 90%, 10 kWh in gives 9 kWh out.
• Coupling. An AC-coupled battery has its own inverter and can sit beside almost any existing system; the IQ Battery 5P has six built-in microinverters. A DC-coupled battery shares a hybrid inverter with the panels.

Where a battery's value comes from

A battery earns its keep in two ways.

1. Storing solar surplus. Each kWh you store and use later saves your import price, but you give up the export payment for it and lose some energy on the way in and out:

value per kWh delivered to your home = import price − (export rate ÷ round-trip efficiency)

At 90% round-trip efficiency, delivering 1 kWh to your home takes about 1.11 kWh of solar that you could otherwise export. At the October to December 2026 import price of 26.32p/kWh, each delivered kWh adds 11.88p with 13p export, 12.99p with 12p export or 19.65p with 6p export. A lower export rate makes storage more valuable, but choosing a better export rate can still lower the home's total energy cost. Fuse's variable 13p is available to eligible export-only customers; Octopus's 12p needs compatible Octopus electricity supply; E.ON Next Flex Export pays a variable 6p. Our Smart Export Guarantee guide compares export tariffs.

2. Charging from the grid at cheap times. On a time-of-use tariff, the battery charges cheaply overnight and covers your home when prices are higher. The value per kWh is the rate you avoid minus the cheap rate, after losses. This matters most in winter, when there is little solar to store, and in homes that use more electricity than their panels and battery can supply, such as those with a heat pump or electric car. So choose the battery and the tariff together.

Time-of-use tariffs and grid charging

Battery-friendly tariffs change often and some close to new customers. The main options:

Octopus Flux is a three-rate import and export tariff for homes with solar panels and a battery, with a cheap period from 02:00 to 05:00 and a peak from 16:00 to 19:00 for both buying and selling. You need panels (from any installer), a home battery, a smart meter sending half-hourly readings, your import and export both with Octopus, and your installation's MCS certificate. Flux is variable. Octopus's published rates for the London region in September 2026, without VAT (electricity VAT in Great Britain is 0% from 1 October 2026 to 31 March 2027):

Rates vary by region. These are Octopus's September 2026 Flux rates. Its standard variable tariff in London rises from 25.09p to 26.60p per kWh without VAT on 1 October, and Flux may change too, so check your region's rates before relying on them. See our Octopus Flux guide.

Intelligent Octopus Flux, where Octopus controls the battery, is open only to customers who bought solar panels and a battery from Octopus.

Overnight tariffs. Intelligent Octopus Go 12M Fixed, open to new customers, charged 8.00p per kWh without VAT from 23:30 to 05:30 in London in September 2026 and 35.48p at other times. It needs Octopus supply and a compatible electric car or charger. Its day rate is above the price cap, so without a car to charge cheaply, moving to it is not a saving in itself. Economy 7 and other multi-rate tariffs charge less at night, and their combined rates are covered by the price cap; ask your supplier whether a battery can charge at the night rate.

These tariffs are for Great Britain. The Smart Export Guarantee does not apply in Northern Ireland, where export payments depend on your supplier's own tariff.

What a battery is worth: two homes

These estimates show the method, not your result.

Typical home: 2,500 kWh a year, Ofgem's typical ("medium") figure, out for part of the day (MCS's "in half the day" pattern), with 4 kWp of south-facing panels in Birmingham producing about 3,872 kWh a year (PVGIS) and two Enphase IQ Battery 5P units (10 kWh usable, 90% round-trip efficiency). MCS's self-consumption tables (guidance note MGD 003), which installers use for their written estimates, estimate about 1,549 kWh more solar used in the home each year, leaving about 215 kWh of household demand for the grid. We treat that uplift as energy delivered to the home. At 90% efficiency, charging for it takes 1,549 ÷ 0.9 ≈ 1,721 kWh, whose export payment is given up. The solar-only value at 12p export is therefore (1,549 × 26.32p) − (1,721 × 12p) ≈ £201 a year. On Flux, the battery also covers the home's remaining grid use from the cheap overnight rate. Because Flux needs a battery, we compare it with the same home without a battery on a single-rate tariff with 12p export. The value is what the battery adds after lost export, before wear, maintenance or finance.

The break-even price is the most a battery can cost if you want the money back within that time. In the price-rise case, import prices, including Flux's cheap rate, go up 2% a year from the second year, in line with the Bank of England's 2% inflation target; it is an assumption, not a forecast, and export rates stay at today's levels. Capacity loss as the battery ages is ignored, so real break-even prices are lower. On Flux, the solar you still export earns 9.80p rather than 12p; that is included. The home's other electricity is priced as on the single-rate tariff, and Flux rates differ by region, so compare your whole bill.

The example below runs our calculator for the same 2,500 kWh household at each battery size it offers, with panels it sizes itself and a single-rate tariff and a 4% yearly rise in import electricity prices, with export rates held flat. It shows payback for panels and battery together, while the table above isolates the battery's extra value. Use the full calculator's prices-today comparison to see the effect of the price-rise assumption; change the yearly use to see which size pays back soonest.

Higher-use homes: our calculator's examples. These are whole-system figures from our calculator: what the panels and battery together save in the first year, and the years to repay the installed cost in our calculator's price model (not a quote). Each saving is measured against the same tariff without panels or battery, at Octopus's London rates for September 2026 and today's prices. Both homes are out for part of the day.

In the EV home the battery adds about £591 a year on the overnight tariff (£1,542 − £951), against about £328 on a single-rate tariff (£1,183 − £855 for panels alone). The car's charging is counted as ordinary night-time use, not smart charging. The Manchester home has no car, so it couldn't join Intelligent Octopus Go; that tariff's 35.48p day rate would also make its bill without solar dearer than on the single-rate cap (£1,141 against £947). The Flux estimate doesn't sell stored energy at the peak export rate, so a battery run for peak export could earn more. With 2% yearly price rises, these paybacks are 0.5 to 1.1 years shorter.

For current battery prices by size, see our solar battery cost guide.

Winter: why a battery runs short

PVGIS estimates that 4 kWp of south-facing panels in Birmingham produce about 468 kWh in June but 133 kWh in December: about 15.6 kWh a day against 4.3 kWh. So there is far less surplus to store in winter, and winter value depends on cheap overnight charging.

The example below shows that gap month by month for a 2,500 kWh household with a battery; change the yearly use, or add an electric car or heat pump, to see how much winter use is left for the grid.

Should you get panels with or without a battery?

How much storage you need

Size a battery to the energy you use between late afternoon and the start of any cheap overnight rate, and to your summer surplus. A larger battery than you can fill or empty most days adds cost without adding value: for the typical home above, MCS's tables show a single 5 kWh IQ Battery 5P would add about 1,278 kWh of solar used in the home a year, against 1,549 kWh with 10 kWh.

Batteries and power cuts

A standard grid-connected battery system does not keep your lights on in a power cut. The grid connection rules require solar and battery inverters to disconnect when the mains supply fails. Backup needs a system designed for it, with equipment that separates your home from the grid. If you want backup, ask in writing which circuits it covers, how much power it provides, whether the panels can recharge the battery during an outage, and the full cost.

Adding a battery to existing panels

You can usually add a battery to an existing system, either as an AC-coupled battery or by swapping your inverter for a hybrid one. The drawings show the difference: with DC coupling the panels and the battery share one hybrid inverter; with AC coupling your existing solar inverter stays and the battery brings its own.

The connection rules count the combined output of your solar and battery inverters. Up to 16 amps per phase (3.68 kW on a normal single-phase supply), your installer can connect and then notify the network operator; above that, the network operator must approve the connection first.

VAT on solar batteries

A battery supplied and installed in your home by an installer carries 0% VAT until 31 March 2027. From 1 April 2027 the rate is due to return to 5%, not 20%, unless the government extends the relief. Since 1 February 2024 the relief covers a battery fitted with new panels, one added to existing panels and a standalone battery charged from the grid. A battery bought without installation is charged at 20%. The same zero rate applies in Northern Ireland. For work finishing around 1 April 2027, ask your installer which rate applies to your invoice.

Warranties, and the GivEnergy administration

A battery warranty usually has three parts: the number of years, a limit on cycles or energy throughput, and the share of capacity the battery must keep. Whichever limit you reach first ends the cover. Check which UK company honours it, and what happens if that company fails.

GivEnergy Ltd, a UK battery and inverter maker, went into administration on 9 April 2026. Its administrator said in April that the company will not honour further hardware warranties, or user and software support. Your statutory rights are separate. If your installer supplied the battery, the Consumer Rights Act 2015 requires it to be of satisfactory quality, including durability, so contact the installer first. If you paid by credit card, or with finance arranged by the seller, section 75 of the Consumer Credit Act 1974 may also help. A consumer code's insurance-backed guarantee covers the installation work, not a product fault. Our GivEnergy page sets out the full claim order, and our best solar batteries guide compares batteries on sale now.

What to check in a battery quote

Ask for the same solar system with and without the battery, then check each point in writing.

• Exact models. Battery, inverter and any backup equipment, with datasheets.
• Usable capacity and power. Usable kWh (not only total), continuous kW, and round-trip efficiency.
• Extra cost. The difference between the two quotes, including VAT, and what it covers.
• Tariff fit. Whether the battery works with the tariff you plan to use, including automated tariffs.
• Network connection. Whether your system will be over 3.68 kW combined, and who applies to the network operator.
• Backup. Whether it is included, which circuits it covers and what it costs.
• Warranty. Years, cycles or throughput, retained capacity, and the UK company that honours it.
• Paperwork. The MCS certificate for the installation, needed for Octopus Flux and export tariffs.
• Control. Which app runs the battery, any subscription, and whether it can be controlled locally.

Estimate your own figures

Our calculator estimates how much of your solar output you would use with and without a battery. You can choose a single-rate tariff, a cheap-overnight tariff or an import-export tariff such as Flux, using example rates you can edit, and add planned use for a heat pump or electric car. Its results are estimates, not a quote.

Solar battery FAQs

Is a solar battery worth it in the UK?

It depends on your usage and tariff. For a household using 2,500 kWh a year with 4 kWp of panels, our worked example values a 10 kWh battery at about £184 a year with Fuse's variable 13p export, £201 with Octopus's 12p export and £304 with E.ON Next Flex Export's 6p. Fuse and E.ON accept eligible export-only customers; Outgoing needs Octopus electricity supply. The dated Flux example adds about £192 against a single-rate, 12p-export baseline. In our calculator's example of a home with an electric car on Intelligent Octopus Go 12M Fixed (which needs an electric car or charger and Octopus), panels and battery together save about £1,542 a year and panels alone £951, so the battery adds about £591 (12p export; £1,407 for panels and battery at 6p in the E.ON export scenario). It pays if its extra cost is below that value over the years it lasts.

What are the disadvantages of a solar battery?

It adds cost that can take longer than the warranty to recover. About a tenth of the energy stored is lost on the way in and out, and every kWh you store is one you don't get paid to export. In winter there is little solar surplus to store, and tariffs can change or close to new customers. A standard battery doesn't keep your lights on in a power cut, its capacity fades with age, and a manufacturer can fail, as GivEnergy did in 2026.

How long will a 10 kWh battery last?

If 10 kWh is its usable capacity, it delivers about 9 kWh after losses at 90% efficiency. That runs a 500 W average load for about 18 hours, or a 1 kW load for about 9 hours.

Will a solar battery work in a power cut?

Only if the system is designed and installed for backup. A standard grid-connected battery shuts down with the grid.