Your solar payback period is the estimated time for energy-bill savings to cover the system’s upfront cost. A simple calculation is the net purchase price, after any applicable rebates or Small-scale Technology Certificates, divided by your estimated annual savings. Savings depend on your electricity use, system size, feed-in tariff, energy rates, export limits and whether you include a battery, so the result is only an estimate. Ask a licensed installer to show the assumptions behind their calculation and compare them with your recent bills before making a decision.