The solar rebate for a 6.6 kW system is a number of STCs, then a dollar value on top. Because STCs trade on a market, the dollars move a little, but the count is fixed by the formula: kilowatts, times your zone rating, times the deeming period.
The calculation
For a system installed in 2026, the deeming period is five years. The zone ratings are 1.622, 1.536, 1.382 and 1.185. So for 6.6 kW:
| Zone rating | STCs (rounded down) | At $38 | At $40 |
|---|---|---|---|
| 1.622 | 53 | $2,014 | $2,120 |
| 1.536 | 50 | $1,900 | $2,000 |
| 1.382 | 45 | $1,710 | $1,800 |
| 1.185 | 39 | $1,482 | $1,560 |
At the time of writing the STC spot market has been roughly $38 to $40, and the clearing house ceiling is $40. Your installer may apply a slightly lower figure to cover their costs and risk.
Which zone are you in
The zone depends on your postcode. Zone 3, rated 1.382, includes most of Sydney, Brisbane, Perth and Adelaide, while Melbourne and Hobart sit in zone 4 at 1.185, so 45 STCs is the figure you will see most often. Hotter northern areas sit in zones 1 and 2, and cooler southern areas such as Tasmania and Alpine regions are in zone 4. Our deeming period and zone ratings guide has the postcode ranges and the solar rebate calculator page shows how to check yours.
What changes in 2027
On 1 January 2027 the deeming period drops to four years. A 6.6 kW system in zone 3 then earns 36 STCs, a drop of nine certificates, or roughly $350 at current prices. See what changes in January.
From the desk: the date that counts is the installation date, not the signing date. If your install slips past 31 December, the lower count applies.
If your system is not exactly 6.6 kW
The same formula works for any size. A 6.6 kW system is just the most common, built from 15 panels of 440 W. Count your panels, multiply by their rated watts, divide by 1,000, and use that figure. A 10 kW system in zone 3 earns 69 STCs in 2026, for example, which is roughly $2,600 to $2,760.
What this means for you
Use the table to sense-check the discount on your quote. If it is much lower than the figure for your zone, ask why. The resources hub and STC trading give the background on how those certificates are valued and sold.