STC discounts are not a fixed rebate: the value depends on your postcode, system size, installation date, remaining deeming period and the current STC market price. When comparing quotes, check that each one lists the system’s expected STC quantity, the dollar value applied and whether the installer has already deducted it from the price. A lower advertised discount may reflect different equipment or installation costs, so compare the final out-of-pocket price and inclusions as well. You can check the Clean Energy Regulator’s guidance and use its calculator, while your installer should confirm the system’s eligibility and paperwork.