A granny flat does not need to piggyback on the main house’s solar. The scheme treats a new, separate system at an address that already has solar as an “additional system”, and that can earn certificates in its own right.
Why it works
The CER describes four installation types: new, replacement, extension and additional. A fresh system for a secondary dwelling is additional. The test is that the new system is made of new components, is installed by an accredited installer, and that the combined capacity of systems at the address is under 100 kW.
Worked example
A 3 kW system on a granny flat in Sydney (zone 3) in 2026 earns 3 x 1.382 x 5 = 20 STCs, rounded down. At the time of writing STC spot has been roughly $38 to $40, which is about $760 to $800 in certificate value. In Melbourne (zone 4) the same system earns 17.
Extension or additional
If the granny flat’s panels connect to the main house’s existing inverter, the job is an extension. That can still earn STCs, but the extra capacity must suit the inverter, and the inverter must be on the approved list at the time. A separate inverter and meter arrangement is usually cleaner for a dwelling that may be rented. The details of extension jobs are on the add panels page; the wider question of a second system is on the second system page.
Who owns the STCs
The certificates belong to the owner of the system. In a granny flat setup that is usually the landlord or property owner. Make sure the signed assignment form names the right person.
Batteries
A secondary dwelling can also have a battery under the Cheaper Home Batteries Program, one battery per property being the key limit. See battery rebates for granny flats.
What this means for installers
Record the system type correctly: choosing “additional” when it is really an extension is a common cause of questions. The installation type guide explains the options. Keep the address of the granny flat consistent across the quote, assignment form and photos, and note whether it has a separate meter.
Next steps: start trading once the job is lodged, or compare current rates.