Solar panel and battery payback calculator

Compare the first year's benefit from solar panels alone or solar panels with a battery. The estimate shows how much grid electricity you avoid, how much solar electricity remains for export, and how long those benefits could take to cover your quote.

Start with a full year's solar generation from your inverter, an installer report or PVGIS. PVGIS is a solar estimate for the selected site and array. It is not a meter reading. Array size alone does not tell the calculator your yearly generation.

Enter the share of solar your home uses straight away before adding a battery. For a battery quote, enter electricity delivered to the home after losses and the full-system round-trip efficiency. This efficiency is the share of charging energy returned for use, including inverter losses. Leave grid-charged battery energy out of this solar calculation.

The optional panel count uses the quoted array size and one panel’s rated watts. Check both against the same quote. It is a count calculation, not confirmation that the panels fit your roof.

Generation comes from PVGIS, installer reports or inverter records. Direct use = generation × direct-use share without battery. Battery charging = annual delivered battery energy ÷ full-system round-trip efficiency. Remaining export = generation minus direct use minus charging. Annual benefit = avoided imports plus remaining export income minus maintenance. Simple payback = net total quote ÷ positive annual benefit. Optional panel count rounds up array watts ÷ module watts.

Convert percentage inputs once: 40% direct use means generation × 0.40. The avoided import price values electricity you no longer buy. The export price values electricity you sell. Using more solar at home also leaves less to sell, so export income must not be counted twice.

Subtract the confirmed quote discount once, then divide the remaining cost by the positive yearly benefit. If that benefit is zero or negative, there is no finite simple payback. The optional panel count rounds up to a whole panel; it does not estimate roof fit or yearly generation.

These illustrative inputs are separate from your saved answers. Prices, use and performance are held constant for this worked scenario; they are not personal defaults.

Use figures for the same year and equipment setup. Battery charging, including its losses, plus direct solar use cannot exceed generation. Delivered battery energy needs a matching record or installer model; a battery's storage capacity is not an annual energy total.

Simple payback keeps the first year's benefit unchanged. It leaves out borrowing costs, changing prices, battery wear, equipment replacement and the time value of money. It is a useful comparison, not a forecast of every future bill.

Imported source files stay on your device. Unsupported formats, missing information or invalid units stop the import. The calculator does not fill gaps. Personal fields start empty, and example figures are only guides. An incomplete edit keeps the last valid result visible with a warning.

Use the import and export prices in your UK supply contracts, in pence per kWh. These may come from different suppliers and may change at different times. Include the tax treatment that applies to your bill.

Existing standing charges are outside this comparison because using less grid electricity does not by itself end the supply account. Keep the quote, source report and tariff dates with your estimate so you can check the same scenario later.

Ask a qualified solar installer to check roof space, shading, electrical work and the expected timing of household use. Ask for an estimate that separates direct solar use, battery charging losses and battery delivery.

Before accepting a quote, confirm what installation, maintenance and replacement costs it covers. Check any discount in writing. The calculator cannot confirm installation safety, grant eligibility or whether the system will meet your backup-power needs.