Are Solar Batteries Worth It? The UK Numbers for 2026

A home battery earns its money in one of two ways, and they are worth very different amounts. It can hold your own solar so you use it in the evening instead of exporting it. Or it can buy electricity from the grid at night when it is cheap and run the house on it during the day.

Put plainly: are solar batteries worth it? Bought to store your own solar on a flat-rate tariff, the payback usually runs past the battery's own lifespan. Bought to shift when you buy from the grid, on a time-of-use tariff, the same hardware typically pays for itself inside its warranty.

On current rates that is a difference of a few hundred pounds a year on identical hardware, and it accounts for most of the spread you will see in published payback periods.

What a battery is worth per unit of electricity

Both jobs are the same trade: move a kilowatt-hour from a moment when it is cheap to a moment when it is expensive. What differs is the size of the gap you are trading on.

Ofgem's price cap for 1 October to 31 December 2026 sets electricity at 26.32p per kWh for a typical Direct Debit customer, with a 54.83p daily standing charge (Ofgem, covering 1 October to 31 December 2026). That is the number both jobs are measured against.

Two things fall out of that table. The first is that the overnight trade is worth more per unit than the solar trade. The second is less obvious: the better your export deal, the less a battery is worth for storing solar, because you are giving up more to keep each unit at home.

Octopus publishes an off-peak rate from 8p per kWh on Intelligent Octopus Go, applied to the whole house between 23:30 and 05:30, and reports that customers on it saved a typical £771 against its standard variable tariff over the year to April 2026 (Octopus Energy). British Gas takes a different route on Charge Power, discounting the unit rate by 50% between midnight and 5am, and applying it to everything the house uses in that window rather than the battery alone (British Gas).

Measure the battery on its own, not the whole system

The figures below are for the battery alone, not for a solar-and-battery installation.

Take a 4 kWp array producing roughly 3,500 kWh a year, in a house that uses about half of it directly. A battery lifts self-consumption into the 70–80% range, which moves 700 to 1,050 kWh a year from export to self-use — worth £98 to £147 at a 14p spread, or £42 to £63 if you are on a good peak-export tariff.

Note what sets that ceiling. It is the surplus your roof produces, not the size of your battery. A larger battery does not raise it.

Now give the same 10 kWh battery the overnight job. Shifting 7.5 kWh a day at an 18p spread, after a 10% round-trip loss, returns about £440 a year — enough to pay back a £4,000 installation in roughly nine years, inside a typical ten-year warranty.

The spread is only part of that. 18p against 14p is a difference of a third; the difference in throughput is nearer threefold, because storing solar gives the battery something to do for part of the year while the overnight trade gives it something to do every night.

One caution: the two jobs compete for the same space. In summer the panels fill the battery and there is no room left to buy cheap units overnight; in winter the panels cannot fill it and the overnight trade carries the year. Treat the two figures as the ends of a range, not as a total.

How much do solar batteries cost in the UK?

Solar battery storage prices span a wide range, because capacity, chemistry and installation complexity all move the figure. The Energy Saving Trust puts domestic storage between £1,500 and £10,000 and uses around £4,600 as its benchmark for a 5 kWh system. EDF lists its Sunsynk battery from £3,995 for 5.12 kWh (EDF).

Two costs are easy to miss. The first is the second battery: cells last around 10 to 15 years against 25 or more for panels, so a full-lifetime comparison includes buying one again. The second is the work itself — adding storage to an existing array is a separate job from fitting it at the same time as panels, and you pay separately for the visit.

Modular solar battery systems sit at the lower end and are sold by capacity. The Zendure SolarFlow 2400 AC+ is one example of the AC-coupled approach. It sits alongside an existing inverter rather than replacing it, starts at 2.4 kWh and stacks to 16.8 kWh, with 2,400 W of bidirectional AC and an IP65 rating for outdoor siting. Its current UK listings run from £899 for the base unit to £4,394 for the full stack, which is roughly £375 per kWh at the bottom of the ladder and £262 per kWh at the top, before any installation work you choose to have done. 

What size solar battery do I need?

Size the battery to the job, then sanity-check it against what can actually fill it.

If the job is the overnight trade, match usable capacity to what you draw between the end of the cheap window and the start of the next one. A home using the national average of about 3,400 kWh a year gets through roughly 9.3 kWh a day, which is why 9 to 10 kWh is the size most often recommended for a typical household.

If the job is storing solar, the ceiling is your surplus rather than your consumption. There is no value in capacity your panels cannot fill, and in December they will not fill much of anything — a 4 kWp array can produce under a kilowatt-hour on a genuinely dark day.

Four specifications decide whether the capacity on the label is usable in practice:

• Usable capacity: most systems hold back a reserve rather than discharging to zero, so a stated 10 kWh commonly delivers 9 kWh or so. Compare batteries on the usable figure.
• Power rating in kW: capacity decides how long the battery runs, power decides what it can run at once. A large store with a modest output still leaves you importing when the oven, kettle and dryer overlap.
• Round-trip efficiency: about 10% of what goes in does not come back out. Build that into any saving you calculate.
• Expandability: if you may add a heat pump or an EV later, check whether the system takes further modules, and whether adding one later costs more than buying it now.

When a battery is not worth it

There are households where the numbers do not come together, and they are worth recognising early.

If you are on a single-rate tariff and intend to stay on one, the overnight trade is closed to you and only the narrower solar spread remains. If you are at home through the day and already use most of what you generate, a battery has little left to capture. If your array is small relative to your consumption, there may rarely be a surplus to store in the first place.

And if the money would have to be borrowed at interest, compare the interest against the annual saving before anything else. A trade worth £400 a year does not survive being financed at a rate that costs more.

Frequently asked questions

What does it cost to add a battery to an existing solar system?

The cost to add a battery to an existing solar system is the battery price plus a separate installation visit, since the scaffolding, wiring and commissioning are not already in progress the way they are on a combined job. An AC-coupled unit is the usual retrofit route because it sits alongside your current inverter rather than replacing it. 

Will a battery reduce my export payments?

Yes, and that is the point — every unit you keep is a unit you do not sell. Export rates are set by each supplier rather than nationally, and they range from a few pence to around twenty, so the income you give up varies enormously from one household to the next. Check what you are paid before you buy: on a high peak-export deal, the export you lose cancels much of what self-consumption gains you.

Do solar batteries work in winter?

The battery works fine; the panels are the constraint. Through December and January a domestic array often cannot fill even a modest battery, which is when households charging from the grid overnight keep their savings and households relying on solar alone lose most of theirs.

How long will a battery last before it needs replacing?

Ten to fifteen years is the usual expectation, with warranties commonly set at ten years or a stated number of cycles, whichever comes first. Read which of the two applies to you, because heavy daily cycling on a time-of-use tariff reaches a cycle limit sooner than light seasonal use does.

The practical answer

Buy a battery to change when you buy electricity, and it stands up: roughly £400 a year on current off-peak rates for a 10 kWh system, available every day of the year, paying back inside a typical warranty.

Buy one purely to hoard summer sunshine, on a flat tariff and with a good export deal already in place, and the same hardware returns closer to £100 a year against several thousand pounds spent. That is the case that struggles, and it is the case most often pictured when people imagine a solar battery.

So the deciding question is not how much storage costs or how big it should be. It is which tariff you will be on the day after it is commissioned — and whether the battery you are quoted for can charge from the grid at all. Settle those two, and the rest of the arithmetic follows.