Solar Simple Payback Calculator

How the solar simple payback calculator works

Annual self-used generation multiplies the entered avoided import price, and annual export multiplies the entered export value. Those two currency amounts round separately before annual maintenance is subtracted. The generation split is supplied; it is not inferred from annual load or a resource model.

Simple payback is net installed cost divided by positive constant annual net saving. The installed amount already reflects whatever adjustments you have chosen, so grants or credits should not be counted again. Zero or negative annual saving gives an unavailable finite-payback ratio. Zero cost with positive saving gives zero years.

This is undiscounted recovery arithmetic, not a full financial return or tariff model. Incentive eligibility, tax, degradation, replacement, financing, changing prices and generation are not predicted. No solar yield or on-site self-consumption level is guaranteed by the example.

Worked example

Self-use of 4,000 kWh at 0.20 is worth 800; export of 2,000 kWh at 0.05 adds 100. Less 100 maintenance, annual net saving is 800. Net installed cost 10,000 gives 12.5-year simple payback. At net cost 8,000, simple payback becomes 10 years.

Sources and assumptions

The source material explains the underlying calculation or pricing structure. Entered prices, costs, schedules and scenario choices are your assumptions; this tool does not obtain supplier quotes or predict actual results.

• SAM: PVWatts model inputs and scope
• SAM: energy, demand and time-matched export billing