What are STCs?
In Australia, Small-scale Technology Certificates (STCs) are a government incentive to help accelerate the adoption of solar on both a residential and commercial scale.
The amount of certificates are calculated based on the region as well as the size (kWp) of the system. The price per certificate can change over time and will be calculated at the time the STCs are processed.
STCs can be created and the settings (such as certificate price & number of years remaining) can be edited in the Control > Other > Incentives section. Read more here.
Residential vs Commercial
There are different tax (GST) treatments for STCs based on whether the project is residential or commercial. Note: you can mark whether a project is residential or commercial in the Project Info page in the Site Details sub-section.
Please refer to this article by the ATO for more information: https://www.ato.gov.au/business/gst/in-detail/your-industry/gst-and-the-small-scale-renewable-energy-scheme/?page=2#System_owner
If a project is marked as residential then the STCs will be treated as GST free, meaning that no GST will be applied to them when calculating the final price of the system.
If a project is marked as commercial then the STCs will attract GST which will then impact the GST on the final price.