Zone rating is the sunshine multiplier in the STC formula. A system in zone 1 earns more certificates than the same system in zone 4.
The ratings
| Zone | Rating | Example areas |
|---|---|---|
| 1 | 1.622 | Northern Territory and the sunniest inland areas |
| 2 | 1.536 | Parts of inland Queensland, WA and NSW, and other northern and central areas |
| 3 | 1.382 | Most major population centres, including Sydney and Melbourne |
| 4 | 1.185 | Tasmania and some southern coastal areas |
The examples are rough. Always look up the actual postcode.
How to look it up
- Go to the Clean Energy Regulator’s postcode zone table for small-scale systems.
- Enter the install postcode.
- Note the zone and its rating.
Many calculators and our own do this lookup automatically from the postcode.
How it enters the formula
STCs equal system capacity in kW times the zone rating times the deeming period, rounded down. For a 6.6 kW system with a five-year deeming period (2026 installs):
- Zone 1: about 53 STCs
- Zone 2: about 50 STCs
- Zone 3: about 45 STCs
- Zone 4: about 39 STCs
See how many STCs a 6.6 kW system makes.
Checking a quote
To check a quote, take the system size, the zone rating for the postcode and the deeming period for the year, multiply them, and round down. If your figure differs from the installer’s by more than a certificate or two, ask why. Sometimes the answer is a different system size, sometimes a different zone. Occasionally it is a mistake, and the correction can work for or against you. Either way, a customer who understands the numbers is a customer who trusts you.
What this means for installers
Quote with the correct zone from the start, and use the same number on the claim. A mismatch is a common cause of validation failure. The deeming period and zone ratings guide goes into more detail, and the map view gives a visual. Check today’s rate on pricing and see the STC trading page.