What is zone rating (solar postcode zone)?
Zone rating is the classification of a postcode into one of four Australian solar zones (1 to 4), determined by average annual solar irradiance, which directly affects the number of STCs generated and the rebate value of a solar system installation.
The Australian solar incentive system divides the country into four zone ratings based on average annual solar irradiance. Each zone corresponds to expected solar energy generation: Zone 1 receives the highest irradiance (above 5.0 kWh/m²/day), down to Zone 4 with the lowest (below 3.5 kWh/m²/day). Your postcode's zone rating directly determines how many Small-scale Technology Certificates (STCs) a system generates for a given capacity, which translates into the rebate value available at the point of purchase.
Perth Metropolitan postcodes fall predominantly into Zone 2 or Zone 3. Zone 2 (4.0 to 5.0 kWh/m²/day average) encompasses most of Perth's southern and coastal areas, while Zone 3 (3.5 to 4.0 kWh/m²/day) covers some inland pockets. A 5 kW system installed in a Zone 2 postcode generates more STCs than the same system in a Zone 3 postcode, resulting in a higher upfront discount. The Clean Energy Regulator sets the STC value annually; suppliers and installers use your postcode's zone rating to calculate your system's rebate eligibility before installation.
Zone ratings matter because they standardise STC calculation across postcodes with different solar potential. If your postcode straddles a zone boundary, installers should confirm the exact zone classification with the regulator's postcode tool. Government rebate specialists can verify your zone and explain how it affects your specific rebate entitlement.