18/10/2026
Solar, battery and hot water installers: GST is worked out on the full price, before the STC discount.
In the ATO's example, a $7,700 system with $1,000 of STCs assigned carries $700 of GST. Calculate it on the $6,700 the customer pays and you are $90.91 short.
The rule, the invoice details and a five-question checklist: https://ap1.hubs.ly/H01rrp60
Why an installer's GST is worked out on the full price before the STC discount, what a correct invoice shows, and the GST when the customer is a business.