Every small-scale solar system is assigned to one of four zones based on the postcode where it is installed. Each zone carries a rating that reflects average sunshine, and that rating is one of three numbers multiplied together to get the STC count. The map is a guide; the Clean Energy Regulator’s postcode table is the rule.
The four zones and their ratings
| Zone | Rating | Typical regions |
|---|---|---|
| 1 | 1.622 | Central Australia, including Alice Springs, and the sunniest arid inland |
| 2 | 1.536 | The tropical north, including Darwin |
| 3 | 1.382 | Most of the populated coast: Sydney, Brisbane, Perth, Adelaide, Canberra, Gold Coast, Newcastle, Wollongong, Cairns, Townsville |
| 4 | 1.185 | The cooler south: Melbourne, Geelong, Hobart, Launceston |
Zone 1 postcodes
Zone 1 is the smallest and is dominated by the Alice Springs region and surrounding desert postcodes. If your site is in central Australia, check the table, because the jump from zone 3 to zone 1 is meaningful.
Zone 2 postcodes
Zone 2 covers Darwin and the Top End, plus some northern and inland postcodes. It is a thin band, so a site only a few hundred kilometres away can sit in zone 3.
Zone 3 postcodes
Zone 3 is where most Australian installs happen. It includes the capital cities of New South Wales, Queensland, Western Australia, South Australia and the ACT, along with large regional centres such as Newcastle, Wollongong, Cairns and Townsville.
Zone 4 postcodes
Zone 4 takes in Melbourne, Geelong, Hobart and Launceston, and most of Victoria and Tasmania. It has the lowest rating, which is why a Melbourne system earns roughly 14 per cent fewer certificates than the same system in Sydney.
How the zone feeds into the STC number
The formula is system kW x zone rating x deeming period. For a 6.6 kW system installed in 2026 (five-year deeming period), certificates are rounded down:
- Zone 1: 6.6 x 1.622 x 5 = 53 STCs
- Zone 2: 6.6 x 1.536 x 5 = 50 STCs
- Zone 3: 6.6 x 1.382 x 5 = 45 STCs
- Zone 4: 6.6 x 1.185 x 5 = 39 STCs
At the time of writing the STC spot market has been roughly $38 to $40, so that is the difference between about $1,500 and about $2,100 in certificate value for the same hardware. See what an STC is worth for the current range.
What this means for installers
Use the postcode on the installation address, not the customer’s billing postcode, and check it against the CER table for every job near a boundary. A wrong zone changes the certificate count and can trigger a rejection or a later correction. The STC calculator applies the zone automatically, and the deeming period and zone ratings guide explains the maths in full.
For a city-by-city list, see which zone is my city in. For how payment works once the certificates exist, read the STC trading overview and check current rates.