A bundled quote can hide how many certificates are involved. Under the surface there are two different schemes’ worth of rules.
How the two sets of STCs work
Solar panels. A new small-scale solar system creates STCs based on its kilowatt size, the zone rating for the postcode and the deeming period. For 2026 installs the deeming period is five years, falling to four for 2027 and one in 2030, and the scheme ends on 31 December 2030. Zone ratings are 1.622, 1.536, 1.382 and 1.185. Sydney, Brisbane, Perth, Adelaide and Canberra are zone 3; Melbourne and Hobart are zone 4. The STC calculator does the sum.
Battery. The battery creates STCs from usable capacity times the factor, 6.8 at the time of writing, with the first 14 kWh at 100%, 14 to 28 kWh at 60% and 28 to 50 kWh at 15%. The battery STC calculator does that one.
The two are independent. Having the battery does not reduce the solar certificates, and the solar does not change the battery factor, except that the battery needs solar behind it to qualify at all.
The same-day solar upgrade
A common job is expanding an older solar system and fitting a battery in the same visit. Three things to keep straight:
- The solar side. Additional panels on an existing system are an “additional” installation, and a swapped-out set is a “replacement”. The treatment affects the certificate count. See installation type: new, replacement, additional.
- The battery side. It is a battery commissioned with an existing or new solar system. Evidence is separate. See adding a battery to old solar.
- The paperwork. Two assignment forms, two sets of serials, two sets of photos. Combining them is how claims get rejected.
Timing and the commissioning date
Both claims fall under the rules for their commissioning dates. A job that is completed in late December and commissioned in January can sit under a lower solar deeming period and a lower battery factor than the one quoted. See the 2027 deeming change and why the battery factor falls.
What this means for installers
Settle the two claims as two jobs, even if the customer sees one invoice. Our compliance desk pre-checks both, and the account manager sees the batch as a whole. See the battery STCs pillar, /start-trading/ and /pricing/ for how the rate is published and locked on lodgement of a complete claim.
What this means for you
Ask for the STC count for the panels and for the battery separately, and compare each with the calculators. A bundle price should make sense when you add the certificate values to the net price.