Solar payback estimator.

Drop in your assumptions. The calculator shows every step it takes to reach the payback figure, and updates as you change the numbers.

Inputs

Your roof and tariff

System sizeTotal kWp installed

Install cost (£)All-in, after VAT

OrientationCompass direction

Shading factor0 = none, 0.4 = heavy

Import rate (p)Your tariff's day rate

Export rate (p)SEG or smart export rate

Self-consumption (%)Share used directly

Working

The maths, shown

Annual generation3,491 kWh

— used at home1,222 kWh

— exported to grid2,269 kWh

Bill savings (year 1)£336

Export income (year 1)£340

Year-one total return£677

Headline figure

Payback: 10.0 years

Assuming 0.5% panel degradation per year and stable tariffs in real terms.

Assumptions: annual generation from a UK baseline of 1040 kWh/kWp adjusted for orientation and shading. Real systems vary ±10% against this baseline. We do not factor in inverter replacement at year 12-15.