STCs are treated as a taxable supply for GST purposes, so the short answer for a GST-registered installer is yes: GST applies when you sell certificates. The practical detail is in how that GST appears on paper.
How it works on a sale
You sell STCs to a trader at, say, a price per certificate. If you are registered for GST, the buyer pays the price plus 10 per cent GST. That GST is not income. It is collected on behalf of the ATO and goes into your business activity statement (BAS), and the buyer claims it back as an input tax credit if they are registered.
If you are not registered for GST (turnover under $75,000 a year, and you have chosen not to register), the buyer pays you the price with no GST added. Most solar installers pass the threshold quickly, so assume you will be registered.
RCTIs and why the buyer invoices you
Most traders run an agreement under which the buyer issues a recipient created tax invoice (RCTI) for the purchase. It saves you raising a tax invoice for every batch. The RCTI shows the certificate count, price, GST and total, and it is the document you give your accountant. Both parties need an ABN, and both need to agree in writing that RCTIs will be used. See RCTI, GST and ABN for STC payments and RCTI explained.
The customer’s discount
The STC discount you give the customer sits inside your job pricing. It is not the same thing as the GST on the certificate sale, and the way the two interact depends on how your quote is structured. This is an accounting question: show your accountant a sample quote and a sample RCTI together and ask for a written view.
What this means for installers
- Give your ABN and GST status to the buyer at sign-up, and update them if either changes.
- Reconcile every RCTI against the registry transfer. A count mismatch is a claim to chase.
- Do not treat the GST portion as profit. Keep it aside until BAS time.
- Do not rely on forum answers for tax treatment. Tax rules are for your accountant, not a trading desk.
For the invoice mechanics and a sample, read charging GST on STCs. Energy Merchants issues RCTIs and charges no fees; current rates are on pricing, and account setup is at start trading. More in the FAQ.