Compare each option by dividing its total installed cost, after any applicable incentives, by the estimated annual bill savings and export income. A basic solar-only system often has a different payback period from a larger system or one with a battery, because batteries add upfront cost but may increase self-consumption. Use your actual electricity usage, tariff, export rate, system size, shading and maintenance assumptions rather than relying only on advertised estimates. Payback calculations are estimates, so compare quotes carefully and ask an accredited installer to explain the assumptions; current incentive details can be checked through the official energy.gov.au website.