On solar self-consumption alone, a UK home battery does not pay for itself. A 5 kWh battery costs about £4,000 and adds only £247 a year on a 4 kW system — 16.2-year payback and a £1,229 loss over ten years. Switch to a time-of-use tariff and the picture changes: charging overnight on Octopus Go at 8.63p and using that power during a 30.99p day is worth about £352 a year, an 11.4-year payback. The battery is a tariff product first, a solar accessory second.
⚡ The 30-second answer
- Solar-only gain: ~£247/year on a 4 kW London system with 5 kWh storage → 16.2-year payback, 10-year net position −£1,229.
- Time-of-use arbitrage is the real lever: ~£352/year on Octopus Go, ~£307/year on Flux → payback 11.4–13.0 years, roughly the length of the warranty.
- Best case: bigger battery + Octopus Go + EV → under 10 years. Worst case: 2.5 kW in Scotland on a flat tariff → ~31 years. Skip it.
- 0% VAT on batteries until 31 March 2027 — saves £200–800 across the old 5% and standard 20% rates.
- Honest verdict for a typical home in 2026: a battery is a bet that sits right at the edge of its own warranty. That is the maths, and we are not going to dress it up.
What a battery actually does to your savings
Without a battery, a typical UK solar home self-consumes about 45% of what it generates; a battery lifts that to about 75%. Each extra self-consumed kWh is worth the full import rate (26.32p, Ofgem Q4 2026 cap) instead of the export rate (6p), so it is worth 20.32p more than exporting it.
On a 4 kW system in London that generates 4,060 kWh a year, shifting 30% more generation into self-use moves 1,218 kWh from export to self-consumption. Gross gain £321, minus £73 of lost export income, equals £247 a year. That is the honest solar-only number, and it is the figure our battery ROI calculator reports.
Real UK battery costs in 2026
A 5 kWh LiFePO4 home battery costs about £4,000 installed — roughly £800 per kWh — and that is the figure we use consistently across this site. A 10 kWh unit is about £8,000; a Tesla Powerwall 3 (13.5 kWh) is about £9,000. 0% VAT applies in Great Britain until 31 March 2027.
| Battery | Usable capacity | Installed cost | £/kWh | Best for |
|---|---|---|---|---|
| Fox ESS / GivEnergy 5 kWh | 5 kWh | £3,500–4,500 | £700–800 | Typical 3-bed home |
| Tesla Powerwall 3 | 13.5 kWh | £8,500–9,500 | £630–700 | Large homes, EV owners |
| Sigenergy SigenStor 8 kWh | 8 kWh | £5,500–6,500 | £690–810 | Modular expansion |
| Budget LiFePO4 (no-name) | 5 kWh | £2,800–3,500 | £560–700 | Tight budgets (check warranty) |
Prices include installation and 0% VAT (Great Britain, until 31 March 2027; Northern Ireland rules differ — confirm with your installer). Cost per kWh falls with capacity, so if you are buying a battery at all, 5 kWh is the smallest size that makes sense.
Payback: what the numbers actually say
On our standard assumptions — 4 kW in London, 26.32p import, 6p export, self-consumption rising 45% to 75%, 90% round-trip efficiency — a 5 kWh battery paying back in 16.2 years on a flat tariff is the baseline. The same battery on a time-of-use tariff pays back in 11.4 to 13.0 years. Only the time-of-use cases come close to the warranty.
| Scenario | Extra saving/yr | Payback | Verdict |
|---|---|---|---|
| 4 kW London + 5 kWh, flat standard variable (26.32p) | ~£247 | 16.2 years | No — falls outside the 10–12 year warranty |
| 4 kW London + 5 kWh, Octopus Go (8.63p / 30.99p) | ~£352 | 11.4 years | Marginal — roughly warranty-length |
| 4 kW London + 5 kWh, Octopus Flux (15.29p / 35.66p) | ~£307 | 13.0 years | Marginal — past a 10-year warranty |
| 6 kW London + 10 kWh (£8,000), flat tariff | ~£371 | 21.5 years | No — bigger battery, worse maths |
| 2.5 kW Scotland + 5 kWh, flat tariff | ~£128 | 31.2 years | No |
The pattern is unmistakable: the battery is paid for by the tariff, not by the panels. If your supplier sells cheap overnight electricity, the battery earns money every night of the year — including the dark winter months when solar gives you nothing at all.
How much does a home battery cost in 2026?
About £4,000 for 5 kWh, £8,000 for 10 kWh and £9,000 for a 13.5 kWh Tesla Powerwall 3, all installed and all at 0% VAT until 31 March 2027. That works out at £630–800 per kWh, and the unit price falls as capacity rises — which is why a 2.5 kWh battery is rarely worth quoting.
Two cost traps are worth knowing about. First, most quotes include the inverter, so a hybrid inverter you already own does not always reduce the price. Second, the 0% VAT window ends on 31 March 2027: after that, expect quotes to rise by roughly 5% unless the relief is extended.
How long does a home battery take to pay back?
It depends almost entirely on your tariff, not your battery. The same £4,000, 5 kWh battery pays back in 16.2 years on a flat tariff, 11.4 years on Octopus Go and 13.0 years on Octopus Flux. A larger 13.5 kWh Powerwall 3 at £9,000 on Octopus Go is the fastest case we model at about 9.5 years.
Two caveats keep that honest. First, arbitrage and solar self-consumption compete for the same capacity — a battery that filled up on cheap overnight power cannot also absorb the day's solar, so the two gains are largely mutually exclusive on the same day rather than additive. Second, the arbitrage figures assume you cycle the battery essentially every day; skip days and the payback stretches proportionally.
Can you make money from a home battery on a time-of-use tariff?
Yes — this is the only scenario where a battery reliably pays, and it works even without solar panels. Octopus Go in London (September 2026) charges 8.63p/kWh between 00:30 and 05:30 and 30.99p/kWh the rest of the day. Filling a 5 kWh battery overnight and discharging it at 90% round-trip efficiency nets about 96p a day — roughly £352 a year.
| Tariff (London, 14 Sep 2026) | Off-peak | Peak | Net gain/yr, 5 kWh | Payback on £4,000 |
|---|---|---|---|---|
| Octopus Go — off-peak 00:30–05:30 | 8.63p | 30.99p | ~£352 | 11.4 years |
| Octopus Flux — flux 02:00–05:00, peak 16:00–19:00 | 15.29p | 35.66p | ~£307 | 13.0 years |
| Octopus Cosy — heat pump tariff, eight cheap hours a day | Priced for heat pump households | Varies | Check your region | |
The arbitrage maths is simple: gain per day = capacity × 90% × peak price − capacity × off-peak price. For Octopus Go that is 5 × 0.9 × 30.99p − 5 × 8.63p = 96p.
Battery vs no battery: the 25-year difference
Over 25 years, using the same assumptions and 3% annual price inflation, a 4 kW London home without a battery earns £14,561 net from its solar. The same home with a £4,000, 5 kWh battery earns £18,999 after paying for the battery — a difference of £4,438, or about £178 a year.
That is a real gain, but notice the shape of it: £4,438 over 25 years on a £4,000 outlay. You tie up £4,000 for a quarter of a century to earn roughly the same as a savings account would. On a 6 kW system the same battery is worth £7,375 over 25 years, because there is more surplus to capture. The bigger your system, the better a battery looks — which is the opposite of how most quotes are pitched.
How long does a home battery last and what does the warranty cover?
Yes, all lithium batteries degrade. Modern LiFePO4 cells are warranted for 10 to 12 years — GivEnergy quotes 12 years on its current UK datasheets — and typically retain most of their capacity across that period. Real-world service life is 12–15 years, and LFP chemistry holds up better than the older NMC cells.
Read the warranty document rather than the marketing line, because the terms differ in ways that matter:
- GivEnergy lists 12 years on its All in One and Giv-Bat 9.5 Gen 3 datasheets, uses LFP chemistry with 100% depth of discharge. Its published general terms show the domestic 12 years is reached in stages — a five-year standard term extended by paid remote service checks — so the headline figure depends on you completing them. Commercial battery packs are capped separately, at 10 years or a throughput limit of 10 MWh per kWh of capacity.
- Cycle vs throughput: a "6,000-cycle" warranty sounds generous but means little without knowing the cycle depth. A throughput limit in MWh is the stricter, more honest measure.
- Depth of discharge: LFP tolerates 90–100% discharge. Older NMC cells preferred 80–90%, which is why their usable capacity was lower than the label.
- Round-trip efficiency is about 90%: every 10 kWh you put in gives you roughly 9 kWh back. Both our calculator and the arbitrage figures above already account for it.
Can you install a home battery without solar panels?
Yes, and on a time-of-use tariff it is the only case where a battery pays entirely on its own merits: charge at 8.63p overnight, use the power during a 30.99p day, and a 5 kWh battery earns about £352 a year — an 11.4-year payback with no panels involved. There is no technical barrier: any qualified installer can fit an AC-coupled battery to a home with no solar.
The honest caveat is that a battery with no solar and a flat tariff earns nothing. There is no price spread to capture, so the payback is infinite. If you are considering a battery before solar, the sequence that makes financial sense in 2026 is: get the smart meter and the time-of-use tariff first, then the battery, then the panels. Starting with the battery on a flat tariff is the most expensive way to do it.
Four situations where a battery IS worth it
A battery is worth it when you are on a time-of-use tariff (worth ~£350/year), your solar system is 4 kW or larger, you use most of your power in the evening, or you need backup power. Miss all four and the maths does not work.
- You're on a time-of-use tariff. Octopus Go (8.63p overnight) or Flux (15.29p off-peak) let the battery arbitrage: charge cheap, discharge at peak. Worth roughly £300–350/year on a 5 kWh battery — even without solar, every night of the year.
- Your solar system is 4 kW or bigger. You need surplus to store. A 4 kW system in London generates ~4,060 kWh/year; about 2,200 kWh of that is exportable surplus a battery can capture.
- You use power in the evening. Home from 5pm, cooking, TV, EV charging, heat pump — exactly when solar alone gives you nothing.
- You value backup. Most UK batteries can island your home during a power cut (4–8 hours of essentials). Rarely needed — but if you run medical equipment or a home office, it is real value.
Three situations where it's NOT
Skip the battery if your system is under 3 kW, if you are on a flat tariff with a high export rate, or if the payback runs longer than the warranty. On a 2.5 kW system in Scotland on a flat tariff the payback is 31.2 years — longer than the battery will physically last.
- Small system (under 3 kW). Not enough surplus to fill the battery most of the year. You would be paying £4,000 to shuffle a few hundred kWh around.
- Flat-rate tariff + high SEG. If your supplier pays 12–15p export and you pay 24–26p import, the per-kWh gain from storage shrinks sharply and payback stretches past 15 years.
- Payback longer than warranty. Most LiFePO4 batteries are warranted for 10–12 years. If your payback runs past the warranty, you are betting the battery outlives its guarantee. Sometimes it does. It is still a bet.
Where the battery goes matters too — see our guide to home battery installation locations and fire rules for the permitted positions and clearances.
The 0% VAT window (and what happens after)
Since February 2024 HMRC has charged 0% VAT on domestic battery storage in Great Britain, whether installed with solar or retrofitted. The relief runs until 31 March 2027. On a £4,000 battery that is a £200–800 saving across the previous 5% and standard 20% rates.
If your payback maths currently look marginal, the VAT holiday is a genuine reason to act before April 2027 — after that, expect quotes to rise around 5% unless the policy is extended. Full detail on the deadline and what qualifies is in our solar VAT 2027 guide.
How to calculate your own payback
The formula our calculator uses is deliberately short, so you can check it by hand. Solar-only gain: extra self-use = generation × (75% − 45%), capped at battery capacity × 365 × 90%, then gain = extra self-use × (import rate − SEG rate). Arbitrage gain: capacity × 90% × peak rate − capacity × off-peak rate, multiplied by the days you actually cycle.
payback = battery cost ÷ annual gain
Worked example, 4 kW London, 5 kWh battery, flat tariff: 1,218 kWh × (26.32p − 6p) = £247/year, so £4,000 ÷ £247 = 16.2 years. Swap in Octopus Go and the gain becomes 5 × 0.9 × 30.99p − 5 × 8.63p = 96p/day = £352/year, so £4,000 ÷ £352 = 11.4 years.
Region, system size, battery and tariff — see your payback in 20 seconds.
Open the battery ROI calculator →Frequently asked questions
Are solar batteries worth it in the UK in 2026?
On solar self-consumption alone, no — a 5 kWh battery on a 4 kW system adds about £247/year, a 16.2-year payback that falls outside the 10–12 year warranty. On a time-of-use tariff, possibly — Octopus Go turns the same battery into roughly £352/year and an 11.4-year payback. It is a tariff decision, not a solar one.
How much does a home battery cost in the UK?
Around £4,000 installed for 5 kWh, £8,000 for 10 kWh and £9,000 for a 13.5 kWh Powerwall 3 — £630–800 per kWh depending on brand and size. 0% VAT until 31 March 2027.
How long does a home battery take to pay back?
16.2 years on a flat tariff, about 11.4 years on Octopus Go and about 13.0 years on Octopus Flux, for a £4,000 5 kWh battery. The tariff moves the answer by more than the battery does.
What size battery do I need?
Match capacity to your evening usage, not your solar size. A typical UK home uses 5–10 kWh between 4pm and midnight. A 5 kWh battery covers most homes; 10 kWh suits larger homes with EVs or heat pumps. Oversizing wastes money, because an empty battery earns nothing — our calculator caps daily gains at the battery's capacity × 365 × 90%.
Can a battery work without solar panels?
Yes — and on a time-of-use tariff it is the only case where a battery pays on its own merits: about £352/year on Octopus Go, an 11.4-year payback with no panels. On a flat tariff with no solar it earns nothing at all.
Can I add a battery to existing solar panels?
Yes — retrofitting is routine in 2026. AC-coupled batteries work with any existing inverter. Your installer will check your consumer unit and may need to notify your DNO, usually a formality for storage under 16A per phase.
Do I need planning permission for a home battery?
No — home batteries are permitted development in the UK when installed inside or against a wall by a competent installer. Only listed buildings, flats and conservation areas may need extra checks.
Is vehicle-to-grid (V2G) a better option than a home battery?
Useful only if your car is plugged in at home during peak hours. A V2G-capable EV holds roughly 40 kWh — eight times a 5 kWh home battery — but it cannot arbitrage when it is out on the road. A dedicated battery works every night regardless.
Can you make money from a home battery on a time-of-use tariff?
Yes, and it is the single biggest lever. Octopus Go in London (September 2026) charges 8.63p/kWh between 00:30 and 05:30 and 30.99p/kWh the rest of the day. Filling a 5 kWh battery overnight and discharging it at 90% round-trip efficiency earns about 96p a day — roughly £352 a year. Octopus Flux pays 15.29p off-peak and 35.66p at the 16:00-19:00 peak, worth about £307 a year on the same battery.
How long does a home battery last and what does the warranty cover?
Modern LiFePO4 batteries are warranted for 10 to 12 years, with GivEnergy quoting 12 years on its current UK datasheets and limiting throughput rather than cycles. Real-world service life is 12-15 years, and LFP chemistry degrades more slowly than the older NMC cells. Always read the warranty document for your exact model: some manufacturers extend cover in stages and require a paid service check.
Sources
Figures on this page are taken from primary sources, not resellers:
- Ofgem — Q4 2026 default tariff cap, unit rate 26.32p/kWh, typical annual bill £1,723.
- Octopus Energy — published unit rates for Octopus Go and Octopus Flux, London region, 14 September 2026, read from Octopus Energy's own public product data. Off-peak windows (Go 00:30–05:30) as stated on Octopus Energy's Octopus Go tariff page.
- GivEnergy — All in One datasheet (13.5 kWh, 12-year warranty, 100% depth of discharge) and Giv-Bat 9.5 Gen 3 installation manual (LFP chemistry); warranty structure and the staged extension terms as published in GivEnergy's general terms document. UK and EU documents can differ — check the warranty for your territory.
- HMRC / GOV.UK — 0% VAT on qualifying energy-saving materials, including battery storage, in Great Britain until 31 March 2027.
- Energy Saving Trust — solar generation, self-consumption and storage guidance.
- PVGIS 5.2 (European Commission) — regional solar yield figures, including the 4,060 kWh/year used for 4 kW in London.