Four phrases cover this one topic: a second solar system, adding a second system, upgrading, and replacing old solar. The specific rules are set by the Clean Energy Regulator and can change, so treat this as a guide and confirm the current position with your installer.
The three types
The Clean Energy Regulator claim form asks the installer to categorise the job.
| Type | What it means | STC position, at the time of writing |
|---|---|---|
| New | First system at the property | Eligible for the full capacity |
| Additional | New capacity alongside the existing system | Can be eligible, depending on rules for the situation |
| Replacement | Old system removed, new one installed | Can be eligible if the old system is genuinely removed |
Our installer-facing guide to new, replacement or additional installation types lists what is recorded.
Adding a second system or panels
If you add capacity, say a second array or extra panels, the installer must register the addition correctly. See adding panels to an existing system. The STC count is based on the added kW, with the zone rating and deeming years that apply on the new installation date, which shortens every year (5 for 2026, 4 for 2027).
Upgrading and replacing
An upgrade that swaps old panels for new ones is usually a replacement. The new equipment must be new and approved, the old system must be removed, and the installer must record what happened to it. Reusing old panels or taking second-hand panels from another job will not earn certificates.
What does not qualify:
- relocated or second-hand panels
- systems that do not meet the product and installer requirements
- claims where the old system’s earlier STCs conflict with the new claim
How to estimate the discount
Use the formula in how much STC discount you should get on the added or replaced capacity only. Run the numbers in the STC calculator, then ask the installer how many STCs they plan to create and the value per STC. Remember that the discount will be lower than it was on your first system, because the deeming period is shorter each year.
What this means for you
Ask these three questions before you sign: what installation type will you register, how many STCs do you expect, and what happens if the claim is rejected? If you are adding a battery, see getting a battery after solar, since batteries have their own STCs. Wider options are in the homeowners guide. Installers can read how we handle these claims on STC trading and how it works.