Adding panels is the most common reason an owner reaches out after the original installation, whether for an electric vehicle, a new pool or a bigger battery. The scheme allows it, with conditions.
The rule for extensions
The CER describes an extension as components added to an existing system. It is eligible when:
- the total capacity of the system stays under 100 kW;
- the new panels and the inverter are on the Clean Energy Council approved list at the date of the addition;
- the inverter has enough capacity for the larger array; and
- all components meet current standards.
Only the added capacity earns certificates. The old panels do not.
How many STCs
Added kW x zone rating x deeming period. The deeming period for 2026 installs is five years and falls to four for 2027, so timing matters. Extending in December 2026 locks in five years’ worth; the same job in January 2027 earns a fifth less. Adding 3 kW in zone 3 in 2026 earns 3 x 1.382 x 5 = 20 STCs; the same job in 2027 earns 3 x 1.382 x 4 = 16. See what changes in January 2027.
Extending a system
An “extend solar system” job usually means new panels connected to the existing inverter. If the old inverter is too small, a second inverter is added. A second inverter with its own array may be an additional system rather than an extension, depending on how it connects. See the section below, and a second system on the same property.
Adding a second inverter
When a second inverter is added, the combined capacity of everything at the address still has to be under 100 kW. The new inverter has to be approved. If the new array feeds the old inverter and the new inverter together, the CER will look at it as one extended system. Record the arrangement clearly on the claim.
What this means for installers
Get the old system’s details before quoting: panel capacity, inverter model and approval status, and the original installation date. Then pick the installation type deliberately using the installation type guide. Photograph both the old and new arrays so that the added capacity is clear.
When the extension is lodged, start trading or check current rates. The STC trading overview covers payment.