The solar payback period is how long your bill savings take to cover what the system cost you. In 2026 a 6.6 kW system in Sydney costs $5,116-$7,416 after the federal rebate and pays back in about 4.3 to 7.6 years on a $450 quarterly bill, on our solar cost calculator (prices checked 10 October 2026).
How to calculate solar payback
Payback (years) = net system cost ÷ annual bill savings
Worked example, using the middle of each band: a 6.6 kW system at $6,266 after the STC rebate, saving $1,080 a year, pays back in 5.8 years. The band of 4.3 to 7.6 years pairs the cheapest price with the highest saving, and the dearest with the lowest.
Assumptions: Sydney (STC zone 3), a $450 quarterly bill, grid power at 32c/kWh, 1,450 kWh a year per kW, price after the federal rebate only, bill savings only (no VPP income), savings ±10%. Installed prices from the Solar Choice Price Index, October 2026, checked 10 October 2026. General information, not financial advice. Run your own bill through the solar cost calculator, which uses the same calculation.
Payback by system size
| System | Typical bill it suits | After STCs (Sydney) | Bill saving a year | Payback |
|---|---|---|---|---|
| 5 kW | $250 a quarter | $3,952-$5,652 | $540-$660 | 6.0 to 10.5 years |
| 6 kW | $375 a quarter | $4,674-$6,674 | $810-$990 | 4.7 to 8.2 years |
| 6.6 kW | $450 a quarter | $5,116-$7,416 | $972-$1,188 | 4.3 to 7.6 years |
| 8 kW | $650 a quarter | $6,219-$8,919 | $1,404-$1,716 | 3.6 to 6.4 years |
| 10 kW | $850 a quarter | $7,764-$11,164 | $1,836-$2,244 | 3.5 to 6.1 years |
| 13.2 kW | $900 a quarter | $10,292-$14,692 | $1,944-$2,376 | 4.3 to 7.6 years |
| 15 kW | $1,000 a quarter | $11,716-$16,816 | $2,160-$2,640 | 4.4 to 7.8 years |
| 20 kW | $1,400 a quarter | $15,528-$22,328 | $3,024-$3,696 | 4.2 to 7.4 years |
Each size is run at the middle of the bill range it suits (the floor, where the range is open-ended), so the rows compare sizes on the bills they are meant for.
What changes your payback
- Daytime self-consumption, the biggest lever. Power you use yourself avoids the full import rate; exported power earns only the feed-in tariff, which is a few cents in most states.
- Your bill. Solar alone can only offset the daytime and shiftable part of a bill, so a system sized well past your bill exports more and pays back more slowly. Compare the 10 kW row above with what a 10 kW system does on an average bill in is 10 kW solar enough.
- State rebates. Victoria has a point-of-sale solar rebate of $1,400, income-tested and not included above. See your state rebate page.
What about battery payback?
A battery pays back more slowly than panels. The state-by-state figures, with VPP income kept separate, are in is a solar battery worth it.
Common questions
What is a good solar payback period?
One that finishes well inside the panels' warranty term. On our calculator a 6.6 kW system pays back in 4.3 to 7.6 years and an 8 kW system on a $650 quarterly bill in 3.6 to 6.4 years. Shorter paybacks come from using more of the power yourself.
How is solar payback calculated?
Net system cost after rebates divided by your annual bill savings. A 6.6 kW system at $6,266 saving $1,080 a year pays back in about 5.8 years.
Why is my solar payback longer than the calculator's?
Usually low daytime self-consumption (you export most of your solar for a small feed-in tariff), a system sized past your bill, or a shaded or poorly oriented roof. Shifting usage into daylight or adding a battery improves it.