⚡ The 30-second answer
- On solar self-consumption alone, payback is slow — a 5 kWh battery (~£4,000) on a 4 kW system saves only ~£110–150/year from extra self-use, a 20-year-plus payback.
- The real money is tariff arbitrage — add a time-of-use tariff (Octopus Go/Agile) and total savings rise to ~£280–450/year → payback 9–14 years, inside the 10-year warranty window for larger setups.
- Best case: 6 kW+ solar + Agile + EV → under 10 years. Worst case: small system, flat tariff, high SEG rate → never. Skip it.
- 0% VAT on batteries until 31 March 2027 — saves £400–800 vs the old 5% rate.
What a battery actually does to your savings
Without a battery, a typical UK solar home self-consumes about 45% of what it generates. The other 55% is exported to the grid at the SEG rate — around 13p/kWh on a good tariff, as little as 3p on a bad one.
A battery raises self-consumption to ~75% by storing daytime solar for the evening. That matters because every kWh you self-consume saves you the full import rate (26.11p, Ofgem Q3 2026 cap) instead of earning you the export rate (~13p).
Real UK battery costs in 2026
| 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 drops with capacity, so if you're getting a battery at all, 5 kWh is the minimum sensible size.
Payback: three real-world scenarios
Using our battery ROI calculator assumptions (26.11p import, 13p SEG, 45%→75% self-consumption, capacity-capped):
| Scenario | Extra saving/yr | Payback | Verdict |
|---|---|---|---|
| 4 kW solar, South East, flat tariff, 5 kWh battery | ~£110 (self-use only) | 20+ years | No — self-use alone doesn't pay |
| 4 kW + Octopus Go (off-peak charging) | ~£280 | ~14 years | Marginal — just past warranty |
| 6 kW + Agile + 10 kWh battery, EV + WFH | ~£600+ | ~10 years | Yes |
| 2.5 kW, Scotland, out all day, 15p SEG | ~£50 | Never (50+ years) | No |
The pattern is clear: a battery is a tariff product first, a solar accessory second. If your supplier offers cheap overnight electricity, the battery earns money every single night of the year — including the dark winter months when solar gives you nothing.
Four situations where a battery IS worth it
- You're on a time-of-use tariff. Octopus Go (7.5p overnight) or Agile (half-hourly pricing) let the battery arbitrage: charge cheap, discharge at peak. Worth roughly £150–400/year depending on capacity and tariff — 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 the Midlands generates ~2,800 kWh/year; roughly 1,500 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 — that's 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's real value.
Three situations where it's NOT
- Small system (under 3 kW). Not enough surplus to fill the battery most of the year. You'd be paying £4,000 to shuffle a few hundred kWh around.
- Flat-rate tariff + high SEG. If your supplier pays 15p export (e.g. Octopus Outgoing Fixed) and you pay 24p import, the per-kWh gain from storage shrinks to ~9p — payback stretches past 15 years.
- Payback longer than warranty. Most LiFePO4 batteries are warrantied for 10 years / 6,000–10,000 cycles. If your payback is 14+ years, you're betting the battery outlives its guarantee. Sometimes it does. It's still a bet.
Battery lifespan and degradation
Modern LFP (lithium iron phosphate) batteries — used by Powerwall 3, GivEnergy, Fox ESS and most 2026 models — are rated for 6,000–10,000 cycles and typically retain 70–80% capacity after 10 years of daily cycling. Depth of discharge of 90–100% is normal for LFP (unlike older NMC chemistries that preferred 80–90%).
Round-trip efficiency is ~90%: for every 10 kWh you put in, you get ~9 kWh out. Our calculator accounts for this when capping daily cycling gains.
The 0% VAT window (and what happens after)
Since February 2024, HMRC charges 0% VAT on domestic battery storage in Great Britain — whether installed with solar or retrofitted. This runs until 31 March 2027. On a £4,000 battery that's a £400–800 saving versus the previous 5%/20% rates.
If payback maths currently look marginal for you, the VAT holiday is a genuine reason to act before April 2027 — after that, expect quotes to rise ~5% unless the policy is extended.
How to calculate your own payback
The formula we use (shown in full on the calculator page):
extra self-use = solar generation × (75% − 45%), capped by battery capacity × 365 × 90% efficiency
extra savings = extra self-use × import rate − extra self-use × SEG rate
payback = battery cost ÷ extra savings
Then add tariff arbitrage if you're on a time-of-use rate: (peak rate − off-peak rate) × capacity × ~300 cycles/year.
Region, system size, tariff — see your payback in 20 seconds.
Open the battery ROI calculator →Frequently asked questions
Is a home battery worth it in the UK in 2026?
On solar self-consumption alone, no — the ~£110/year gain on a typical 4 kW system gives a 20+ year payback, well past the 10-year warranty. The honest case for a battery in 2026 is tariff arbitrage: on Octopus Go or Agile, charging cheap overnight and discharging at peak lifts total savings to £280–450/year, bringing payback to 9–14 years. The bigger your system and the smarter your tariff, the better it gets.
How much does a home battery cost?
Around £4,000 installed for 5 kWh, £9,000 for a 13.5 kWh Powerwall 3 — £560–800 per kWh depending on brand and size. 0% VAT until March 2027.
Can I add a battery to existing solar panels?
Yes — retrofitting is common in 2026. AC-coupled batteries (Powerwall, GivEnergy AC) 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).
What about vehicle-to-grid (V2G) instead?
If you own a V2G-capable EV (e.g. Nissan Leaf) and a compatible charger, your car can act as a ~40 kWh battery. But it needs to be plugged in at home during peak hours to help — great for some households, impractical for many. A dedicated battery works regardless of whether the car is home.
Do I need planning permission?
No — home batteries are permitted development in the UK when installed inside or against a wall by a competent installer. Only listed buildings or flats may need extra checks.
Related guides
- Is solar worth it in the UK? (2026) — the full solar economics breakdown.
- SEG explained: best export rates 2026 — why your export rate matters for battery maths.
- UK solar panel costs 2026 — full installation price breakdown.
- Solar EV charging calculator — if you're adding an EV to the mix.