The number of small-scale technology certificates (STCs) a system creates is a formula, not an estimate: rated panel capacity in kW, multiplied by the zone rating for the postcode, multiplied by the deeming period in years. For installs in 2026 the deeming period is 5 years. The result is rounded down to a whole certificate.
Zone 3 has a rating of 1.382, so each kW is worth 1.382 x 5 = 6.91 STCs. Zone 4 is 1.185, so each kW is worth 5.925. Zone 3 covers Sydney, Brisbane, Perth, Adelaide, Canberra, the Gold Coast, Newcastle, Wollongong, Cairns and Townsville. Zone 4 covers Melbourne, Geelong, Hobart and Launceston. Darwin is zone 2 (1.536) and Alice Springs is zone 1 (1.622).
STCs by system size, 2026 installs
| System size | Zone 3 (Sydney, Brisbane, Perth, Adelaide) | Zone 4 (Melbourne, Hobart) |
|---|---|---|
| 3 kW | 20 STCs | 17 STCs |
| 5 kW | 34 STCs | 29 STCs |
| 6.6 kW | 45 STCs | 39 STCs |
| 8 kW | 55 STCs | 47 STCs |
| 10 kW | 69 STCs | 59 STCs |
| 13.2 kW | 91 STCs | 78 STCs |
| 15 kW | 103 STCs | 88 STCs |
| 20 kW | 138 STCs | 118 STCs |
| 30 kW | 207 STCs | 177 STCs |
| 50 kW | 345 STCs | 296 STCs |
| 99 kW | 684 STCs | 586 STCs |
| 100 kW | 691 STCs | 592 STCs |
The table covers the sizes people search most: 3 kW, 5 kW, 6.6 kW, 8 kW, 10 kW, 13.2 kW, 15 kW, 20 kW, 30 kW, 50 kW, 99 kW and 100 kW. For anything between, multiply your kW by 6.91 (zone 3) or 5.925 (zone 4) and drop the decimals. For zones 1 and 2, use 8.11 and 7.68 per kW.
Worked example: 6.6 kW in zone 3
6.6 x 1.382 x 5 = 45.6, rounded down to 45 STCs. A 6.6 kW system is the common residential size because 6.6 kW of panels sits comfortably on a 5 kW inverter at the 133 per cent limit. There is a longer walk-through in how many STCs for a 6.6 kW system.
What moves the number
- Postcode. The zone is set by the postcode of the installation, not the owner’s address.
- Install date. The deeming period counts down, so STCs per kW fall each January. At the time of writing it is 5 years for 2026 and 4 for 2027. The detail is in deeming period and zone ratings.
- Panel rating. The kW figure is the total rated output of the panels as listed on the approved product list, not what the roof will produce. See panel size or inverter size.
- Size cap. Up to and including 100 kW the system creates STCs. Above that, the 2026 mid-scale change matters; see what installers need to know about the 1 MW expansion.
What this means for installers
Every certificate you create is worth roughly the spot price, so the count is your discount to the customer or your margin. At the time of writing the STC market has been about $38 to $40 against a clearing house ceiling of $40, so a 6.6 kW zone 3 job is worth in the order of $1,700 to $1,800 before any trader spread. The dollar view of the same table is in STC rebate value by system size. To check a specific job, run it through the STC calculator.
Rates for what a trader pays on top of the spot picture are published on pricing. If you are working out cash flow across a run of jobs, how STC trading works covers settlement.