How this calculator works
This calculator estimates how much of your EV's annual electricity need can be covered by your solar panels, and the resulting savings compared to charging from the grid or running a petrol car.
The maths
EV annual need = annual mileage × EV consumption (kWh/mile)
Solar surplus for EV = system size (kW) × sun hours × solar-to-EV share
Solar coverage = min(solar surplus, EV need) ÷ EV need × 100%
Where:
- EV consumption — real-world figures from EV Database (0.26–0.35 kWh/mile depending on model)
- Sun hours — PVGIS 5.2 regional net generation values (840–1,113 kWh/kWp per year)
- Solar-to-EV share — 35% without battery (you're not always home when solar generates), 60% with battery (stored for evening charging)
Cost comparisons used
- Grid standard — 26.32p/kWh (Ofgem price cap, Q4 2026)
- Off-peak EV tariff — 7.5p/kWh (Octopus Intelligent Go, 2026)
- Solar — effectively 0p/kWh after system payback (marginal cost)
- Petrol equivalent — 14p/mile (average UK petrol car, 2026)
Why solar + EV is the strongest combination
An EV roughly doubles your home electricity usage — a typical 3-bed home goes from 3,400 kWh to 6,400 kWh when you add 10,000 miles of EV driving. This is actually good news for solar economics, because:
- Higher usage = higher self-consumption — you use more of your own solar instead of exporting at low SEG rates
- EV charging is flexible — you can schedule charging for sunny midday hours, maximising solar use
- Double savings — you save on both home electricity AND fuel (petrol → free solar)
- Shorter payback — the extra panels for EV charging pay back faster than home-only solar, because petrol displacement is worth 14p/mile vs 26p/kWh electricity
For most UK homeowners with an EV, a 5–6 kW solar system (with battery) covers 70–90% of combined home + EV electricity needs during April–September, and 30–50% during winter. Over a full year, solar typically covers 50–70% of EV charging.