How to use the solar calculator
Choose your state and zone
The zone is set to your capital. Change it if you live elsewhere: most of NSW, Queensland, SA and WA is zone 3; Victoria and Tasmania are mostly zone 4.
Set the system size
Use the panel capacity from your quote. See what size system you need.
Enter your price and rates
Replace the defaults with your quote and the usage rate and feed-in tariff from your bill.
Estimate your self-use
The share of solar you use as it is made. The more you run during the day, the higher it goes.
Sun zones used in the calculator
| Zone | Rating | Per kW a day | 6.6 kW STCs | Covers |
|---|---|---|---|---|
| Zone 1 | 1.622 | 4.44 kWh | 53 | Alice Springs and the arid centre |
| Zone 2 | 1.536 | 4.21 kWh | 50 | Darwin, Broome and the tropical north |
| Zone 3 | 1.382 | 3.79 kWh | 45 | Sydney, Brisbane, Adelaide, Perth, Canberra and most of NSW, QLD, SA and WA |
| Zone 4 | 1.185 | 3.25 kWh | 39 | Melbourne, Hobart, Geelong and the rest of Tasmania and southern Victoria |
Your exact zone depends on your postcode. The Clean Energy Regulator publishes the full postcode list.
How the maths works
Yearly output = system size × zone rating × 1,000. Saving = output used at home × usage rate + output exported × feed-in tariff. Payback = price ÷ yearly saving.
What the estimate leaves out
Roof direction, shade and hot weather lower output. Panels lose a little output each year, prices change each July, and time-of-use rates change the value of each kWh. For more detail see solar payback periods and orientation and shading.
Questions about the solar calculator
It depends on output, how much you use at home and your rates. A 6.6 kW system in Sydney is deemed to make about 9,100 kWh a year. Using 30% of that at 33c and exporting the rest at 3c saves roughly $1,100 a year.
It uses the Clean Energy Regulator zone ratings, the same figures used to work out STCs. They give the average yearly output per kW of panels for each sun zone in Australia.
Households out during the day often use 20 to 30% of their solar. Homes with people at home, timers on appliances or a heat pump on a timer can reach 40 to 50% or more. Smart meter data shows your real figure.
Yes. The pre-filled price is after the federal STC discount, and the calculator shows how many STCs the system creates. Take off any state rebate, such as Victoria's, yourself.
Sources
Output and STCs use Clean Energy Regulator figures. Prices are from the Solar Choice Price Index, an industry source. Last checked October 2026. Prices include GST unless we say otherwise.