Solar Battery Payback Calculator
Work out if home battery storage is worth it - savings, payback & net return
Last updated: June 2026
What this solar battery payback calculator does
A home battery only saves you money when the electricity it stores is cheaper than the electricity it replaces. This solar battery payback calculator works out whether battery storage is worth it for your UK home by comparing the price of the energy you put into the battery with the much higher price of grid electricity you avoid buying. It estimates your annual saving, the payback period in years, and your net financial position after 10 and 15 years.
It is built for two real-world situations: a battery paired with solar panels (where the "cost" of charging is the Smart Export Guarantee income you give up by storing surplus instead of exporting it), and a standalone, grid-charged battery on a time-of-use tariff such as Octopus Go or Agile (where the cost is the cheap off-peak rate). It is ideal for homeowners weighing up a quote, solar owners considering a retrofit battery, and anyone asking "is battery storage actually worth it?"
How it works
The maths behind the calculator is the self-consumption arbitrage that makes batteries pay:
- Energy delivered = daily kWh cycled × round-trip efficiency (a battery loses roughly 10% charging and discharging, so 90% is typical).
- Value of each unit = your import rate minus your charging cost. In solar mode the charging cost is the SEG export rate you forgo (around 5p); in standalone mode it is your off-peak rate (around 7p).
- Annual saving = daily kWh cycled × (efficiency × import rate − charging cost) ÷ 100 × 365.
- Payback = installed battery cost ÷ annual saving. We also project the 10- and 15-year net position so you can see lifetime value.
The default import rate of 26.11p/kWh is the Ofgem price-cap electricity unit rate for 1 July to 30 September 2026 (Direct Debit, GB average). Remember that VAT on domestic battery storage is 0% until 31 March 2027, which keeps installed prices lower than they will be afterwards.
Worked example
Suppose you install a 10 kWh battery for £5,000 alongside existing solar panels. You cycle about 80% of its capacity each day, so 8 kWh/day. Your import rate is 26.11p, your SEG export rate is 5p, and round-trip efficiency is 90%.
- Value per kWh cycled = (0.90 × 26.11p) − 5p = 23.499p − 5p = 18.499p
- Annual saving = 8 × 18.499p × 365 ÷ 100 = £540.17
- Payback = £5,000 ÷ £540.17 = 9.3 years
- Net position after 15 years = (£540.17 × 15) − £5,000 = +£3,102.56
At 9.3 years the battery pays back just inside a typical 10-year warranty, then earns roughly £540 a year of "free" savings for the rest of its life. A higher import rate, a cheaper battery, or more daily cycling all shorten the payback.
Frequently asked questions
Is a home battery worth it in the UK?
It depends on the gap between your import rate and your charging cost. With the import price cap at 26.11p and SEG export around 5p, a solar-paired battery typically pays back in 8–11 years — close to the 10-year warranty. A standalone battery on a cheap off-peak tariff can pay back faster if you cycle it fully every day. Use the calculator with your own quote and tariff to see your figure.
Do I pay VAT on battery storage?
No. The government applies a 0% (zero) rate of VAT to electrical battery storage installed in residential homes in Great Britain from 1 February 2024 until 31 March 2027. This covers standalone batteries, retrofits and solar-plus-battery installs. After 31 March 2027 the rate is expected to revert, so installing before then locks in the lower price.
What is round-trip efficiency and why does it matter?
Round-trip efficiency is the share of energy you get back out of a battery compared with what you put in. Modern lithium home batteries are around 90% efficient, so storing 10 kWh delivers about 9 kWh. The 10% loss slightly reduces your saving, which is why the calculator lets you adjust it.
How is solar-paired different from a standalone grid-charged battery?
With solar, you charge for free from your panels, but the real "cost" is the export income you give up (around 5p per kWh under SEG). With a standalone battery you buy cheap off-peak electricity (around 7p on Octopus Go) and use it during expensive peak hours. Both strategies profit from the same import-versus-charging-cost gap; the calculator handles each with the toggle.
Sources: HMRC VAT Notice 708/6 – Energy-saving materials (0% VAT on battery storage to 31 March 2027) and the Ofgem energy price cap unit rates (26.11p/kWh electricity, 1 Jul–30 Sep 2026). Figures are estimates for guidance only.