Solar payback estimator.

Drop in your assumptions. The calculator shows every step it takes and updates as you change the numbers.

Inputs

Your roof and tariff

System sizeTotal kWp installed

Install costAll-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 one)£336

Export income (year one)£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. Most sensitive to the import rate.

Assumptions: annual generation derived 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, which would push payback out by roughly a year.