Two of the most common invoice questions are why the STC discount shows as a separate line and why GST seems too high. Both come down to how the Australian Taxation Office treats certificates.
How the ATO treats the discount
When you assign your STCs to the installer, the discount you receive is part of the consideration for the supply, along with the cash you pay. For that reason the ATO’s guidance on the Small-scale Renewable Energy Scheme says GST is based on the price before the discount is applied. The full 10% is added to the total system price, and then the STC discount comes off.
So your invoice can show GST greater than one tenth of the amount you pay. That is expected, not an error.
An example
| Line | Amount |
|---|---|
| System price excluding GST | $9,000 |
| GST at 10% | $900 |
| Total including GST | $9,900 |
| Less STC discount (45 STCs at about $39) | -$1,755 |
| Amount you pay | $8,145 |
The GST of $900 is about 11% of the $8,145 you pay. The numbers are illustrative only, not a quote.
Why a separate line is better
Some installers fold the discount into one lower price. That is legal, but it hides the number of STCs and the dollar value, and it makes quotes hard to compare. Prefer an installer who lists the line, as in how the STC line should read. If your invoice shows the STC discount “inclusive” or “plus GST” in odd ways, ask for a corrected version before you pay.
Is the discount taxable income for you?
For a household with a system on the home, the discount is generally not treated as income. If the system is for a business or investment property, claiming and GST registration questions are different, so speak to your accountant. Our page on whether the solar rebate is taxable goes through the common cases.
What this means for you
Compare quotes on the final amount payable and the STC count behind it, not on a headline price. For installers, the invoicing side of certificate sales is covered in GST on STC sales and our RCTI guide. The homeowners guide and pricing page give more context on what the certificates are worth.
When the figures do not add up
If your invoice total does not match the quote, check three things: whether the system size changed on the day, whether the STC count was recalculated, and whether GST was applied to the discounted or the full price. An honest installer can walk you through each line. Ask for a corrected tax invoice if there is an error, since you may need it for warranty, finance or insurance.