The postcode on the job decides the zone, and the zone decides the multiplier. A higher rating reflects more expected solar generation, so more certificates.
The four zones
| Zone | Rating | Relative output |
|---|---|---|
| 1 | 1.622 | Highest |
| 2 | 1.536 | High |
| 3 | 1.382 | Moderate |
| 4 | 1.185 | Lowest |
Zone membership is by postcode, and it is easy to guess wrong at the edges. Use the Clean Energy Regulator’s published table rather than a general impression of the climate.
Applying it
Take the rating, multiply by the kW of the system and the deeming years (5 for 2026, 4 for 2027), and round down. A 6.6 kW system in zone 3 gives 45 certificates in 2026. The same system in zone 4 gives 39. That 6 certificate difference is worth around $228 at $38.
Common errors
Using the customer’s billing postcode instead of the installation postcode. Using a suburb that spans two postcodes without checking. Quoting from last year’s table. Each can flow through to the claim and cause questions at assessment.
What this means for you
Your zone affects both the discount on a quote and the cash from certificates. Our deeming period and zone ratings guide shows the calculation in full, and the pricing page has the live buy rate to turn certificates into dollars. For the broader picture see STC trading.
Prices move, so treat any number here as a snapshot and check the live figure before you quote a job.
If you service several zones, build a rate sheet for each one so quotes stay consistent between salespeople. It takes ten minutes and prevents the sort of mistake that costs a customer a few hundred dollars and costs you a difficult phone call.
Edge cases are where mistakes cluster. Rural properties can have a postcode that differs from the nearest town, and new subdivisions sometimes carry a recently created postcode. When in doubt, check the regulator’s table directly and keep a screenshot on the job file as evidence of what you used on the day of installation.
It is also worth noting that the ratings reflect the scheme’s own rules, not a promise of how much your customer’s system will generate. Real output depends on orientation, shading and equipment, so keep the certificate calculation and the generation forecast on separate lines of the proposal.