If you have solar panels, someone has quoted you for a battery. The quote came with a payback figure, and that figure was almost certainly calculated in the way that made the battery look best. Working out solar battery payback UK homeowners can actually rely on is not complicated, but it does mean replacing the installer’s assumptions with your own numbers - and the result in 2026 is genuinely different from what it was three years ago, in both directions.
The short answer
A home battery pays back by letting you use electricity you generated but would otherwise have exported for very little, and by letting you buy cheap off-peak electricity to use at peak times. Its payback depends on four things: the installed cost, the gap between your import price and your export price, how many kWh you actually shift through it each year, and how long it lasts. Get those four and you can do the sum in two minutes. Everything else is noise.
The four numbers, and how to get them
1. Installed cost
Not the battery price - the installed cost, including the inverter or hybrid inverter if you need one, the installation labour, the electrical works, the DNO notification and any scaffolding. Ask for it as one figure from an MCS-certified installer. Domestic battery storage currently falls within the zero VAT rate for energy-saving materials in the UK, so check that your quote reflects that rather than adding 20%.
2. The spread between what you pay and what you are paid
This is the number that decides everything, and almost nobody looks it up.
Your import rate is what you pay per kWh. If you are on a time-of-use tariff, you have more than one - a cheap overnight rate and an expensive day rate.
Your export rate is what your supplier pays you per kWh under the Smart Export Guarantee. Suppliers set their own SEG rates and the difference between the worst and best available is large. Many households are still on the rate they were given when the panels were commissioned and have never switched.
Every kWh you push through the battery earns you the spread: the import price you avoided, minus the export price you gave up. If you are on a flat tariff with a decent SEG rate, that spread may be modest. If you are on a time-of-use tariff with a very cheap overnight window, the spread is much larger - and it applies even on days the sun does not shine, because you can charge from the grid.
3. Annual throughput
Capacity is what gets sold. Throughput is what pays.
A battery only earns on the kWh that actually pass through it. A 10kWh battery that cycles fully every day moves about 3,650kWh a year. The same battery that only fills halfway from October to March, and sits idle on a sunny June day because the house is empty and the battery filled by 10am, might move less than half that.
Ask any installer quoting you for the modelled annual throughput in kWh, not the capacity. If they cannot give you one, they have not modelled your house, they have modelled a spreadsheet.
4. Lifespan, measured properly
Battery warranties are written in cycles or throughput, whichever comes first, with a guaranteed remaining capacity at the end - typically a stated percentage of the original. A ten-year warranty is meaningless on its own. A warranty of a stated number of full cycles, or a stated total MWh throughput, tells you how much work the battery is guaranteed to do.
Divide the warranted throughput by your modelled annual throughput. That is your realistic life in years, and it is the number to use - not the marketing ten or fifteen.
The sum
Annual saving = annual throughput (kWh) x spread (£ per kWh), minus round-trip losses of roughly 10 to 15%, because a battery does not give back everything you put in.
Payback in years = installed cost / annual saving.
Then sanity-check it against the warranted life. If the payback period is longer than the warranted throughput life, the battery does not pay back. It is a resilience purchase or a comfort purchase, and there is nothing wrong with that - but call it what it is.
Where this goes right, and where it goes wrong
A battery is worth it if: you are on a time-of-use tariff with a genuinely cheap overnight rate; you have a decent-sized array and a household that is out during the day, so you currently export a lot; your export rate is poor; you have an EV or a heat pump adding significant, shiftable load; or you have a real need for backup power and have specified an inverter that actually provides it.
A battery is marginal or poor if: you are at home all day and already self-consume most of what you generate; your array is small; you are on a good SEG rate and a flat import tariff, so the spread is thin; or you are being sold a large capacity that your modelled throughput will never use.
That last one is the commonest mistake by a distance. Oversizing is where battery economics go to die: you pay for capacity in full and use a fraction of it, so cost per useful kWh doubles. Most UK homes are better served by a smaller battery that cycles hard every day than by a large one that never fills - and the fact that installers consistently quote the larger unit should tell you something about who the sizing serves. Ask for quotes at two sizes and compare cost per warranted kWh of throughput, not headline capacity.
A battery without solar panels
This surprises people: in 2026 it can work. If you are on a time-of-use tariff with a wide gap between the overnight rate and the day rate, a battery can pay back on tariff arbitrage alone - charge cheap at night, discharge through the expensive evening peak, repeat every day of the year with no dependence on weather.
It hangs entirely on that tariff gap continuing to exist, which is a commercial decision by suppliers rather than a law of nature. Treat it as a good deal with a policy risk attached rather than a guaranteed one.
The practical things that trip people up
DNO notification. Your installer must notify or apply to the distribution network operator. Small installations are usually notified after the fact under G98; larger combined systems need prior approval under G99, which takes time. Ask which applies before you agree a date.
Inverter compatibility. Adding a battery to an existing array may mean an AC-coupled battery with its own inverter, or replacing your existing inverter with a hybrid. These are different quotes. Make sure you are comparing the same scope.
Backup is not automatic. Most grid-tied batteries shut down in a power cut for safety. If you want the lights to stay on you need an inverter with an islanding or EPS function and a properly wired backup circuit, specified up front.
Siting and ventilation. Where the unit goes affects cost and performance, and cold garages reduce output in winter. Agree the location before the quote, not on the day.
MCS certification. Use an MCS-certified installer. It is what gives you access to SEG and a recognised warranty route, and it is the paperwork a buyer’s surveyor will ask for.
What to do in the next 30 minutes
Open your energy account and write down your current import rate, your peak and off-peak rates if you have them, and your SEG export rate.
Find your last twelve months of generation and export figures from your inverter app or your export meter readings.
Work out roughly how much you exported last year. That is the ceiling on what a battery can recover from solar.
Email your installer and ask for two things in writing: modelled annual throughput in kWh, and the warranted cycles or total MWh.
Check whether switching your SEG tariff alone would get you a better export rate, before you spend anything.
Once it is installed, the paperwork is what you will need in five years and cannot find. Home+ gives you a free place to keep the MCS certificate, the DNO notification, the warranty terms and the commissioning data against the property, so a warranty claim or a house sale does not start with a search through old emails. Log your solar system in Home+ the week it is commissioned.
FAQ
How big a battery do I need? Size it to the kWh you actually shift in a day, not to your total daily consumption. For most UK homes that means matching typical daily export plus the evening peak load you want to cover. An installer who cannot show you the throughput model behind their recommended size has not done the work.
Do batteries improve my EPC rating? Battery storage on its own has historically had little or no effect on the EPC score, which is modelled on the building fabric and fixed services rather than on how you buy electricity. Ask your assessor how the current methodology treats it before you buy a battery expecting a band change.
How long do home batteries last? Look at the warranted cycles or total throughput rather than the years. Divide that by how much you will realistically cycle it annually to get a working life. Capacity degrades gradually rather than failing suddenly.
Can I add a battery to solar panels installed years ago? Usually yes, either as an AC-coupled unit with its own inverter or by replacing the existing inverter with a hybrid. Older systems on legacy Feed-in Tariff arrangements need checking first, because altering the system can affect the arrangement.
Will a battery keep my house running in a power cut? Only if it has been specified to. Standard grid-tied systems disconnect during an outage. Backup requires an inverter with an EPS or islanding function and dedicated wiring, agreed at quote stage.
Is there VAT on a home battery? Domestic battery storage currently falls within the zero VAT rate for energy-saving materials in the UK, including retrofit to an existing system. Check the current position before you sign, as the relief has a defined end date.
