Estimate how many years a rooftop solar system takes to repay its cost from bill savings and feed-in credits.
Rooftop solar saves money in two ways: each kWh you use yourself avoids buying a kWh at your usage rate, and each kWh you export earns the feed-in tariff, which is usually much lower. This calculator compares that yearly saving with the net cost of the system.
Formula. Net cost = system price − incentives. Yearly saving grows by the price change you enter. Payback is the point at which cumulative savings equal the net cost. Net saving = total savings over the period − net cost.
Working out the yearly saving. Example (illustrative): a 6.6 kW system produces 9,000 kWh a year; the household uses 30% itself (2,700 kWh) and exports 6,300 kWh. At a 30 c/kWh usage rate and a 4 c/kWh feed-in tariff: 2,700 × $0.30 = $810 plus 6,300 × $0.04 = $252, total about $1,062. If the feed-in tariff drops to 1 c/kWh, the export part falls to $63, showing why self-use matters more than the feed-in rate.
Worked example (defaults). $7,500 − $2,200 = $5,300 net; $900 a year rising 2% gives payback in a little under 6 years.
Limits. Real output depends on roof orientation, shading, location and system condition. Feed-in tariffs are set by retailers and can change; in Victoria there has been no minimum feed-in tariff since 1 July 2025. Time-of-use plans, two-way export charges and free-midday-power offers change the value of exports; see the feed-in tariff guide and the solar worked example. Inputs are illustrative.
Worked Examples and Comparison Checklists
An illustrative worked example of how household gas and electricity bills change when you go all-electric in Australia — supply charges, MJ to kWh, tariffs and timing.
Worked Examples and Comparison Checklists
Work out what rooftop solar saves on an Australian bill — self-consumed kWh, export credits, a lower feed-in tariff scenario and simple payback — with every step of the maths shown.
Price Factors, Tariffs and 2026 Rules
How solar feed-in tariffs are set in each state in 2026, why Victoria no longer has a minimum, flat versus time-varying rates and why self-consumption usually matters more.
