A useful solar payback period checklist should include the installed price, any eligible Small-scale Technology Certificate discount, expected system output, household electricity use, grid rates and feed-in tariff. Check whether the estimate allows for changing energy prices, export limits, panel degradation, inverter replacement and loan interest if you are financing the system. Compare quotes using the same assumptions and ask the installer to explain how shading, roof orientation and future electricity use affect the calculation. The actual payback period will depend on your circumstances and should be confirmed with the installer or an independent energy adviser.