Zone rating (solar STCs)

Written and checked by the Energy Merchants desk · Reviewed 2 October 2026

A zone rating is a number representing how much electricity a kilowatt of solar is expected to produce in a year in a given part of Australia. The country is split into four zones by postcode. Sunnier regions have higher ratings.

The ratings are used in the STC calculation: system size in kW x zone rating x deeming period (in years) gives the number of STCs, rounded down.

Worked example

A 6.6 kW system installed in 2026, with a five-year deeming period.

• Zone 1: 6.6 x 1.622 x 5 = 53.5, so 53 STCs.
• Zone 3: 6.6 x 1.382 x 5 = 45.6, so 45 STCs.
• Zone 4: 6.6 x 1.185 x 5 = 39.1, so 39 STCs.

Same panels, same size, but a 14 certificate gap between the sunniest and the least sunny zone. At roughly $38 to $40 per STC at the time of writing, that is about $530 to $560.

In practice

You do not choose the zone. The postcode of the installation address determines it, using the Clean Energy Regulator’s postcode table. The usual mistake is using the postcode of the customer’s mailing address, or of the business, instead of the install address. That can leave a claim with the wrong STC count, which is a problem either way.

Some postcodes straddle zones, so use the official lookup rather than assuming from the region.

Common confusion

The zone rating is not the same as the real yield of the system. A well-sited array in zone 4 can outperform a shaded one in zone 1. The rating is a regulatory input, not a performance forecast, and it should not be used in a customer’s savings calculation.

For the full table and calculation, see deeming period and zone ratings. More terms are in the certificate trading glossary, and you can see current buying rates on pricing.