Solar calculators
that actually work.
Six interactive tools for planning your DIY solar setup. Enter your numbers, get real answers - no email, no account, no nonsense.
Pick your tool
Each one does a single job properly. Start with the MPPT calculator if you are choosing a charge controller, or the savings calculator if you are still deciding whether to go ahead.
Victron MPPT Calculator
2 min · 14 models
Enter your panel specs and string config. Tells you exactly which Victron SmartSolar MPPT fits, with cold-weather voltage adjustment so a January morning cannot cook your controller.
Calculate nowSolar String Calculator
3 min · pass / warn / fail
Validate a panel string against your inverter or MPPT limits. Temperature-adjusted Voc, Isc and power checks with a clear verdict on each.
Open toolDC Cable Size Calculator
2 min · all standard sizes
Work out the cable cross-section your DC runs need. Compares every standard size and estimates voltage drop and power loss for each.
Open toolBattery Payback Calculator
2 min · tariff-aware ROI
See how fast a home battery pays for itself by charging on cheap off-peak electricity. Compare TOU tariffs and work out your annual saving from load shifting.
Open toolUK Solar Irradiance Lookup
1 min · 15 regions
Estimated annual generation for your part of the country, from Cornwall to northern Scotland, with a monthly breakdown and the optimal tilt angle.
Open toolSolar Savings Calculator
3 min · 25-year ROI
Estimate payback period, annual saving and 25-year return. Accounts for Smart Export Guarantee payments and your actual tariff rate.
Open toolNot sure where to start?
The tools answer specific questions. These guides answer the big ones.
Complete Installation Guide
From sizing your system to wiring the inverter, every step explained against UK regs.
Read guideVictron MPPT Comparison
Every SmartSolar model from 75/15 to 250/100 compared on specs, price and real-world fit.
Compare modelsGrants & Incentives 2026
ECO4, the Smart Export Guarantee and 0% VAT - exactly what you can claim this year.
Check eligibility