There is a common mix-up: people ask for “zone ratings by year” when the number that moves by year is the deeming period. The zone rating is a fixed multiplier for the four solar zones. Together they set STCs per kW.
The zone ratings
| Zone | Rating | Example locations |
|---|---|---|
| 1 | 1.622 | Alice Springs |
| 2 | 1.536 | Darwin |
| 3 | 1.382 | Sydney, Brisbane, Perth, Adelaide, Canberra |
| 4 | 1.185 | Melbourne, Geelong, Hobart |
To find which one applies, see what is my STC zone.
The deeming period by year
The deeming period is the number of years of expected generation that the system is credited for upfront. For small-scale solar it declines by one year each January until the scheme ends on 31 December 2030:
| Install year | Deeming period |
|---|---|
| 2026 | 5 years |
| 2027 | 4 years |
| 2028 | 3 years |
| 2029 | 2 years |
| 2030 | 1 year |
Mid-scale systems above 100 kW and up to 1 MW installed from 1 October 2026 have a fixed five-year deeming period. See the 1 MW expansion.
STCs per kW by year
Multiply the rating by the deeming years:
| Year | Zone 1 | Zone 2 | Zone 3 | Zone 4 |
|---|---|---|---|---|
| 2026 | 8.110 | 7.680 | 6.910 | 5.925 |
| 2027 | 6.488 | 6.144 | 5.528 | 4.740 |
| 2028 | 4.866 | 4.608 | 4.146 | 3.555 |
| 2029 | 3.244 | 3.072 | 2.764 | 2.370 |
| 2030 | 1.622 | 1.536 | 1.382 | 1.185 |
So a 6.6 kW system in zone 3 creates 45 STCs in 2026 and about 36 in 2027 (6.6 x 5.528 = 36.5, rounded down). The 2027 and later figures follow from the schedule at the time of writing, which could change if the legislation does. Read what changes in January for the practical effect.
Why the rating is higher in the north
The ratings are tied to how much a kW of solar is expected to generate in each zone. Alice Springs gets more sun than Hobart, so each kW is credited with more certificates. It is the same logic as the deeming period, which credits a number of years of output.
What this means for installers
Selling before the January step helps customers and your pipeline, but the date that counts is the install date, not the contract date. Make sure the job is installed and complete before 31 December. For the numbers on specific sizes, see STCs by system size, the STC calculator and deeming period and zone ratings.
If you want to see what the certificates are worth to you, check pricing.