How to Calculate STCs and Maximise Your Solar Rebate in Australia (2025 Guide)
What Are STCs and Why Do They Matter?
If you’re considering solar in Australia, you’ve probably heard about the government solar rebate. This rebate is delivered through the Small-scale Renewable Energy Scheme (SRES) in the form of Small-scale Technology Certificates (STCs).
Each STC has a market value, and the total number of STCs your system generates is applied as an upfront discount on your installation cost. Understanding how to calculate STCs helps you estimate your rebate and compare quotes with confidence.
Factors That Affect STC Calculation
1. System Size (kW)
Bigger systems produce more electricity, which means more STCs—and a larger rebate.
2. Solar Zone (Location)
Australia is divided into four STC zones, based on average sunlight:
- Zone 1 – highest rebate (e.g., Northern & Central Australia)
- Zone 4 – lowest rebate (e.g., Melbourne & Tasmania)
3. Deeming Period (Years Remaining Until 2030)
The SRES scheme is scheduled to phase out in 2030. Each January, the deeming period drops by one year, reducing the number of STCs (and your rebate) by about 4–5% annually. The Clean Energy Regulator provides conversion multipliers for each postcode zone to make this simpler.
4. How to claim STC
In most cases, solar installers calculate the number of Small-scale Technology Certificates (STCs) your system is eligible for and include their value as an upfront discount in your quotation. This means you don’t have to claim the certificates yourself. After installation, the installer or their agent will submit the STC claim on your behalf through the Clean Energy Regulator’s system, transferring the certificates to a registered trader or aggregator. The installer then receives the rebate value directly, while you enjoy the savings immediately as part of your system price.
How to Calculate STCs?
The formula to estimate your STCs is:
STCs = System size(kW) x Zone Rating x Deeming Period(years)
Example (Sydney, Zone 3):
- System size: 6.6 kW
- Zone rating: 1.382
- Deeming period: 6 years
- STCs = 6.6 × 1.382 × 6 = 54 STCs
At the March 2025 STC price of $38, that’s a rebate of about $2,052
STC Price in 2025
- Current price: ~$38 per STC (trading range $35–$40)
- Applied at the point of sale: Most installers trade STCs for you and apply the rebate as an upfront discount.
- Tip: Always compare the final system price between installers, not just the STC value.
Example Rebates for a 6.6 kW Solar System (2025)
| Location | Zone | Ratings | STCs | Rebate (@$38/STC) |
|---|---|---|---|---|
| North West & Central Australia | 1 | 1.622 | 64 | $2432 |
| Darwin, Central Australia | 2 | 1.536 | 60 | $2280 |
| Brisbane, Sydney, Adelaide, Perth | 3 | 1.382 | 54 | $2052 |
| Melbourne & Tasmania | 4 | 1.185 | 46 | $1748 |
Remember: Your rebate amount reduces with each passing year.
The amount of STCs a system is eligible for is based on:
- The type of system
- The capacity of the system (kW)
- Where the system is located
- When the system was installed
- If STCs are created over one or 5 years or a single maximum deeming period
Key Takeaway
- Install solar sooner to lock in higher STC rebates.
- Your rebate depends on system size, zone rating, and deeming years remaining.
- In 2025, a standard 6.6 kW system can save homeowners $3,000–$4,000 upfront, depending on location.