Real numbers for solar PV with or without battery storage. Conservative install costs, current SEG export rates, and 0.5% annual degradation factored in.
Calculates the realistic payback for a solar PV array — with or without battery storage — based on your roof size, electricity consumption, and the import/export tariff you're on. Uses 2026 install costs and the Smart Export Guarantee floor of 1p (most suppliers pay 5–15p).
No marketing inflation. We use mid-range installer pricing, conservative annual yield (kWh per kWp, derated for shading and inverter losses), and assume PV degradation of 0.5% per year. Battery cycles capped at 6,000.
Roof
Usage
Tariff
Storage
Result
How much usable roof space do you have?
Approximate is fine. South-facing or east/west works best.
South
East/West
South-East/West
North-facing
None
Light
Moderate
Heavy
Annual electricity use
Look on a recent annual statement, or estimate from monthly bills.
UK average is ~3,500 kWh/year.
Mostly evenings (~20%)
Some during day (~35%)
Work from home (~55%)
Heavy daytime use (~75%)
Your electricity tariff
Import and export rates determine real-world savings.
Default 27p (Ofgem cap, April 2026 estimate).
1p (legal floor)
5.5p (typical)
8p (better suppliers)
15p (Octopus Outgoing Lite)
No SEG
Battery storage?
A battery shifts daytime generation to evening — only worth it if your import price is much higher than your export rate.
None
5 kWh
10 kWh
13.5 kWh (Powerwall)
How we model this. Annual yield assumes 950 kWh/kWp before orientation/shading derating (PVGIS UK central estimate). Battery cycles capped at 250/year (~6,000 lifetime). Install cost: £1,500 base + £1,250/kWp PV, +£800/kWh battery — mid-range MCS-certified installer pricing 2026. PV degradation 0.5%/year. Export revenue at the SEG rate you select. We don't model the 0% VAT relief expiry beyond 2027 (still a moving target) — when it returns, prices will rise ~5–15%.