Three questions are usually bundled here: how many STCs, whether tank size matters, and what the zone ratings are. They share one answer, which is that the model sets the entitlement and the zone and year adjust it.
How many STCs
The Clean Energy Regulator’s register of solar water heaters lists every eligible model, and each entry carries an STC figure for each zone, based on a 10-year system life. The count that applies to you also reflects the install year: the factor is 0.5 for 2026, 0.4 for 2027, 0.3 for 2028, 0.2 for 2029 and 0.1 for 2030. The register shows the result for the install date you select. Expect tens of certificates rather than hundreds. See how many STCs a heat pump gets for the shared logic.
Solar hot water STCs by tank size
There is no litres-to-STC table. A larger tank with more collector area usually has higher tested performance, and so usually registers more energy and more STCs. But two systems with the same tank size can differ, and a bigger tank in a poor zone can create fewer certificates than a smaller one in a good zone. The CER page for the product category says solar water heaters under 700 litres are covered in the normal way, with systems above that needing additional documentation. Check that boundary for your project.
Solar hot water STC zone ratings
Solar water heaters use four postcode zones. Each zone has its own STC figure for each model, and the regulator publishes a postcode zones document. These are not the solar PV ratings of 1.622, 1.536, 1.382 and 1.185, which are for rooftop solar panels. For hot water you read the zone column of the register entry. A system in a sunnier region of the country is credited with more displaced energy than the same system in a cloudier one.
Turning the count into dollars
At roughly $38 to $40 per STC at the time of writing, a system that registers 30 STCs on your zone and date has a value of about $1,140 to $1,200 before any installer margin. The 30 is an illustration only. State rebates can sit on top: see solar hot water rebates in Victoria.
Checking the number
- Identify the model number, not just the brand and range.
- Look it up on the register. See how to check hot water STC eligibility.
- Select your zone and install date.
- Compare the figure with the quote.
What this means for you
If you are buying, ask for the count, the zone and the year on the quote. If you are an installer, the figure you claim must match the registered model, the zone and the install date, and the photos must show the serial plate. Our hot water STCs page walks through how we settle these, and pricing shows the current rate. For the eligibility checklist see solar water heater STC eligibility.