The deeming period is set by the year a system is installed. Looking back is useful for installers dealing with late claims or audits, and for anyone comparing an old quote with today’s.
The historical schedule
| Install year | Deeming period | 6.6 kW, zone 3 STCs |
|---|---|---|
| 2016 | 15 years | 136 |
| 2017 | 14 years | 127 |
| 2018 | 13 years | 118 |
| 2019 | 12 years | 109 |
| 2020 | 11 years | 100 |
| 2021 | 10 years | 91 |
| 2022 | 9 years | 82 |
| 2023 | 8 years | 72 |
| 2024 | 7 years | 63 |
| 2025 | 6 years | 54 |
| 2026 | 5 years | 45 |
The STC count is 6.6 kW x 1.382 x deeming years, rounded down. Zone 3 here covers Sydney, Brisbane, Perth, Adelaide and Canberra. The count for a given system has more than halved since 2020, purely from the shorter period.
Why look at old years
- Late claims. STCs generally must be created within 12 months of the install, so most old claims are lost. Check the CER’s current guidance if you find an old job.
- Audits. If the CER audits an older job, the STC count is checked against the period for the year of installation, not the claim date. See how STC audits work.
- Quote comparisons. A neighbour who got 100 STCs on the same system in 2020 got them under an 11-year period. It is not a sign you are being shortchanged.
What this means for installers
Match every claim to the install date, not the lodgement date. If your records show a job that straddles New Year, confirm which date the commissioning and electrical sign-off fall on. The deeming year follows the installation date, and a wrong year means a wrong STC count and a rejected claim. Read the deeming period resource and the pillar.
For the current and future years see solar deeming period by year 2026 to 2030. Rates are on pricing and accounts open at start trading.