Nothing in the STC rules says a system must use one brand. What the rules require is that the panels are CEC listed, that the declared system size is accurate, and that the installation is compliant. Mixed brands pass those tests as long as each model does individually.
Are mixed panel brands STC eligible
Yes. Each model is checked against the CEC list on the installation date, and the system’s capacity is the total of all panels. Record each model and serial number for the photo and form requirements.
Can I mix panel brands on one system
You can, but the engineering matters more than the paperwork. Panels with different voltage, current or power ratings wired together in one string drag each other to the lowest common performance, and can exceed an inverter’s input limits. Installers usually avoid it unless there is a good reason, such as a discontinued model on an existing roof.
Can I use different panels on different strings
This is the clean way to do it. If each string has panels of one type, and the inverter has separate MPPT inputs or the design uses microinverters or optimisers, each string can operate at its own optimum. All panels must still be listed, and the inverter must support the string configurations.
When it comes up in practice
- Roof faces with different panel sizes. A small east roof fitted with a different model is a normal reason.
- Supply shortages. A distributor substitutes part of the order.
- Existing system extensions. The old model is no longer listed or available, which affects how the extension is treated. See adding panels to an existing system.
It is also worth recording why a mix happened. A short note on the job file explaining a substitution, with the dates and the supplier’s advice, makes any later query simple to answer and shows the system was designed deliberately rather than assembled from leftovers.
What this means for installers
Run both checks: listing for each model, and string design for each array. If the customer is paying for a system declared as one brand and you installed two, correct the documents before lodgement. See top STC claim rejection reasons and installation type.
What this means for homeowners
Mixed brands are not a red flag by themselves, but ask the installer to explain how the strings are arranged and whether every model is on the CEC list. Check how the discount is calculated in STC trading and the STC calculator.