Solar battery storage: costs, sizes and whether it pays

How does home battery storage work?

A home battery is usually used with solar panels, a smart time-of-use tariff or both [1]. It stores spare solar electricity, or charges when the tariff is cheap, and you use that stored energy at night or when prices are high [1]. Some energy is lost on the way in and out, so using stored electricity is less efficient than using it directly [1]. A home battery can be fitted with new panels, added to existing solar panels, or used without solar panels.

How much does a solar battery cost?

Using the government's median prices for 2025-26, a 5 kWh battery works out at about £6,500 installed and a 10 kWh battery about £8,900 [2]. These are our illustrative calculations, each size multiplied by the median price per kWh of nominal capacity for its size band, not quoted prices for those exact sizes. Larger batteries cost less per nominal kWh: the median falls from £1,300 under 6 kWh to £630 from 11 to under 30 kWh [2]. A battery installed in a home is zero-rated for VAT until 31 March 2027, then 5 per cent [3]. Prices by size are on solar battery cost.

Is a solar battery worth it?

It depends on your export tariff, how much electricity you use in the evening, and whether you can charge cheaply overnight. In our worked examples, stored solar alone did not repay the estimated battery cost within a typical 10 to 12 year life; by our calculation it would need to cost under roughly £1,600 to £4,500 to do so. A lower quote, or charging on a cheap overnight rate, can change that. The working, with every assumption, is on is a solar battery worth it. The Energy Saving Trust gives a typical battery life of about 10 to 12 years, shorter than solar panels [1].

What size battery do you need?

For your own use, roughly your evening and overnight electricity use, limited to what spare solar or an off-peak window can refill, plus any charge kept back for power cuts. Your smart meter data shows that evening use. The Energy Saving Trust says a typical home system might be 10 kWh [1], but your own figures decide it: see what size solar battery you need.

Can you add a battery to existing solar panels?

Usually, yes [6]: with its own inverter (AC coupling) or wired to a hybrid inverter's battery connection (DC coupling) [7]. If you get Feed-in Tariff payments, tell your FIT supplier and choose a set-up that keeps the generation meter counting solar only, or generation payments can stop [8]. See adding a battery to existing solar panels.

Home battery storage without solar panels

A battery can charge from the grid when electricity is cheap, but it only saves money on a time-of-use tariff. For a gas-heated home on a standard tariff, the Energy Saving Trust modelled a median saving of about £320 a year from a battery plus a switch to a dynamic tariff, at 2024 prices: around 20 years to pay back, twice the battery life it assumed [4]; the full comparison is on home battery storage without solar.

Choosing a home battery

Compare usable capacity, power output, warranty and compatibility with the inverter you have or plan to fit, and get complete installed quotes. Backup during a power cut is a separate reason to buy and can need extra equipment: Tesla's Powerwall 3, for example, needs its Backup Gateway 2 for backup [5]. Three models are compared in best home batteries, and the checks on a firm are in how to check an installer.