When you are quoting a solar installation, the STC calculation drives the upfront discount. Getting it right keeps your quote honest and your margin predictable.
Step by step
- Confirm the postcode and its zone. Zone ratings are 1.622, 1.536, 1.382 and 1.185.
- Confirm the installation year. The deeming period is 5 years for 2026 and 4 for 2027.
- Take the system capacity in kW from the panels being installed.
- Multiply kW x zone rating x deeming years.
- Round down to a whole number of certificates.
- Multiply by a price to get a dollar value.
For example, 8 kW in zone 2 in 2026 is 8 x 1.536 x 5 = 61.4, so 61 certificates. At around $38 that is about $2,320.
Checks before you quote
Make sure the panels are CEC approved, that the system qualifies as new, replacement or additional (see installation types), and that the installer holds the right accreditation. A calculator tells you the maximum; a rejected claim gives you nothing.
Quoting across the new year
If installation could fall in January 2027, quote both numbers. Dropping from 5 to 4 deeming years cuts certificates by a fifth. That is a visible hit on the discount you can offer a homeowner, and customers like to hear it early. See the 2027 calculator guide.
What this means for installers
Lock in the value as soon as you can. Energy Merchants publishes a daily rate on the pricing page, and it is locked when a complete claim is lodged. The STC trading pillar covers the path from install to payment.
Prices move, so treat any number here as a snapshot and check the live figure before you quote a job.
If a homeowner asks why the discount is smaller than a friend’s, the answer is usually system size, zone or install year. A clear table on your proposal, showing certificates by zone and year, answers most of those questions before they are asked and builds trust in the quote.
One more point for commercial work: for installs from 1 October 2026, systems above 100 kW and up to 1 MW also earn upfront STCs, with a fixed five-year deeming period (see mid-scale solar STCs). Systems above 1 MW, and older systems above 100 kW, earn LGCs instead. Check which scheme applies before you promise an upfront discount, because the two are not interchangeable.