Panel capacity, not inverter size.
Set by postcode, not state.
Usable, not nameplate. Minimum 5 kWh.
6.8 for May–Dec 2026.
Installers rarely pass on the full $40.
0 to skip. Enter the price before rebate.
This STC calculator works out your Small-scale Technology Certificate entitlement using the Clean Energy Regulator’s zone ratings and deeming schedule — and rounds down, as the regulator does, rather than up like several published examples.
The short answer
STCs = system kW × zone rating × deeming years, rounded down. A 6.6 kW system in Sydney installed in 2026 gives 6.6 × 1.382 × 5 = 45.6, so 45 certificates — about $1,710 at $38 each.
Install the same system in 2027 and you get 36 certificates. That’s a 20% cut, not the “4–5%” still quoted widely.
On this page
How to use this STC calculator
Enter your system size in panel kilowatts — not inverter size, which is often smaller. A 6.6 kW system with a 5 kW inverter earns certificates on 6.6.
Pick your zone (set by postcode, not state), your installation year, and the STC price your installer is using. Enter the quoted system cost and it’ll show the net figure with the rebate applied.
Switch to Battery for the Cheaper Home Batteries certificates, which use an entirely different calculation.
The formula
STCs = System size (kW) × Zone rating × Deeming years
Rebate = STCs × STC price
Rounded down to a whole certificate — fractions cannot be created
Worked example — 6.6 kW in Sydney, installed 2026
Why waiting costs 20%, not 4%
The deeming period is the number of years between installation and the scheme’s end on 31 December 2030. It drops by one whole year every 1 January.
A lot of solar advice still describes the annual reduction as “around 4–5%”. That was accurate when the deeming period was 14 or 15 years — losing one year out of fifteen is about 7%. With only five years left, losing one is 20%. And it accelerates:
| Install year | Deeming years | STCs on 6.6 kW, Zone 3 | Value at $38 | Drop |
|---|---|---|---|---|
| 2026 | 5 | 45 | $1,710 | — |
| 2027 | 4 | 36 | $1,368 | −20% |
| 2028 | 3 | 27 | $1,026 | −25% |
| 2029 | 2 | 18 | $684 | −33% |
| 2030 | 1 | 9 | $342 | −50% |
Five to four years is 20%. Four to three is 25%. Three to two is 33%. Two to one is 50%. Each year that passes, the next year’s loss is larger in percentage terms than the last.
Critically, the deeming period is set on your installation date, not the date you sign a contract. A quote taken in December for a January install earns the lower figure — worth confirming which year an installer has assumed.
Zone ratings
The zone rating reflects average solar irradiance where you are, and it’s set by postcode, not state. Several states straddle two zones.
| Zone | Rating | Typical locations | STCs on 6.6 kW, 2026 | At $38 |
|---|---|---|---|---|
| Zone 1 | 1.622 | Darwin, central Australia, far north QLD | 53 | $2,014 |
| Zone 2 | 1.536 | Brisbane, Perth, most of QLD and WA | 50 | $1,900 |
| Zone 3 | 1.382 | Sydney, Melbourne, Adelaide, Canberra | 45 | $1,710 |
| Zone 4 | 1.185 | Hobart and most of Tasmania | 39 | $1,482 |
Zone 1 earns 36% more certificates than Zone 4 for an identical system — $532 on a 6.6 kW install. Most of the Australian population sits in Zone 3.
Don’t assume from your nearest capital. Inland NSW and northern WA sit in higher zones than Sydney and Perth do. The Clean Energy Regulator publishes the postcode list.
Rounding down, not up
Certificates are whole units. You cannot create 45.6 of them, and the regulator floors the figure — the remainder is simply not paid.
A live Australian solar site works the same 6.6 kW Zone 3 example and states the answer as 46 certificates. It’s 45.606, which floors to 45. Their figure overstates the rebate by one certificate — up to $40.
Two other sites give 45 correctly. If a quote’s certificate count is one higher than this calculator’s, check whether they’ve rounded up before assuming they’ve found you something.
The rounding also creates dead zones. At Zone 3 in 2026, going from 6.4 kW to 6.5 kW adds no certificate at all — the raw figure moves from 44.2 to 44.9, both flooring to 44. Small size increases sometimes earn nothing.
What an STC is actually worth
There are three different prices in circulation, and quotes use whichever suits:
| Price | Value | 45 STCs | What it is |
|---|---|---|---|
| Clearing house | $40.00 | $1,800 | Fixed, ex GST. A ceiling, with delays |
| Typical market | $38.00 | $1,710 | What most quotes use |
| After agent costs | $37.00 | $1,665 | Net of trading and admin |
| Conservative | $35.00 | $1,575 | Low end of recent range |
That’s a $225 spread on identical certificates. The clearing house price is fixed at $40 excluding GST but comes with settlement delays, so the open market usually trades below it and installers rarely pass on the full amount.
You don’t handle certificates yourself. You assign them to your installer, who applies the value as an upfront discount — which is why most people never see the transaction and can’t easily tell what price was used.
System size
| System | Raw | STCs | At $38 |
|---|---|---|---|
| 3 kW | 20.73 | 20 | $760 |
| 5 kW | 34.55 | 34 | $1,292 |
| 6.6 kW | 45.61 | 45 | $1,710 |
| 10 kW | 69.10 | 69 | $2,622 |
| 13.2 kW | 91.21 | 91 | $3,458 |
| 20 kW | 138.20 | 138 | $5,244 |
Zone 3, installed 2026, at $38 per certificate.
Unlike the battery scheme, solar STCs scale linearly — there’s no tapering by size. A 20 kW system earns almost exactly triple a 6.6 kW one.
6.6 kW is the most common residential size because it’s the largest panel array most networks allow on a 5 kW single-phase inverter, at the standard 133% oversizing ratio.
Battery STCs work differently
Both schemes issue the same certificate, but almost nothing else is shared:
| Solar PV | Battery | |
|---|---|---|
| Based on | System kW | Usable kWh |
| Location factor | Zone rating | None |
| Time factor | Deeming years | Flat factor, currently 6.8 |
| Tapering by size | No | Yes — 100% / 60% / 15% |
| Steps down | Annually, 1 January | Twice yearly |
| Minimum | None | 5 kWh usable |
The battery scheme also calculates on usable capacity rather than nameplate, so a 13.5 kWh battery at 90% depth of discharge claims on 12.2 kWh. The solar battery calculator covers this in full alongside sizing.
Reading a quote
Three things to check, because installers present rebates inconsistently:
- Is the price before or after the rebate? Some quote gross with the discount shown separately, others quote net. Compare like with like
- What STC price did they use? $40 versus $35 is $225 on a 6.6 kW system, and an optimistic price makes a quote look better without changing what you pay
- Which install year? If installation slips past 1 January, the deeming period drops and so does the rebate — find out who absorbs that
The certificate count itself is arithmetic, so it should match between quotes. Where it doesn’t, someone has rounded up or assumed a different zone.
STC mistakes to avoid
- Rounding up. The regulator floors it. 45.6 is 45 certificates.
- Believing the “4–5% a year” figure. It’s 20% now and rising.
- Assuming your zone from your state. It’s by postcode.
- Using inverter size instead of panel size. Certificates follow the panels.
- Assuming $40 per certificate. That’s the ceiling, not the norm.
- Comparing gross and net quotes. Check which each one is.
- Signing in December for a January install. The deeming date is installation.
- Applying the solar formula to a battery. Different scheme entirely.
Frequently asked questions
How do I calculate STCs?
System size in kW × your postcode’s zone rating × the deeming years remaining, rounded down. A 6.6 kW system in Sydney installed in 2026 gives 6.6 × 1.382 × 5 = 45.606, which floors to 45 certificates — about $1,710 at $38 each.
What is the deeming period in 2026?
Five years, covering 2026 to 2030 inclusive. The scheme ends 31 December 2030, so the period drops by one year each 1 January — four years in 2027, three in 2028, two in 2029 and one in 2030. It’s set on your installation date, not your contract date.
How much does waiting a year cost?
20% of the rebate going from 2026 to 2027, and it accelerates — 25% the following year, then 33%, then 50%. Advice describing the annual drop as 4–5% is out of date; that was true when the deeming period was 14 or 15 years, not five.
What are the STC zone ratings?
Zone 1 is 1.622 (Darwin, central Australia), Zone 2 is 1.536 (Brisbane, Perth), Zone 3 is 1.382 (Sydney, Melbourne, Adelaide) and Zone 4 is 1.185 (Tasmania). They’re set by postcode rather than state, and Zone 1 earns about 36% more certificates than Zone 4 for the same system.
Are STCs rounded up or down?
Down. Certificates are whole units and fractions can’t be created, so 45.606 becomes 45 and the remainder is not paid. Some published examples round up — one live site gives 46 for this exact case, overstating the rebate by up to $40.
How much is one STC worth?
Between about $35 and $40. The clearing house price is fixed at $40 excluding GST but comes with settlement delays, so open-market trading usually sits below it and installers commonly use $37–38. On 45 certificates that range is a $225 spread.
Do I have to apply for STCs myself?
No. You assign them to your installer, who claims them and applies the value as an upfront discount on the system price. It isn’t a cash payment from the government — it’s a tradeable certificate entitlement, which is why most people never see the transaction.
Is it panel size or inverter size that counts?
Panel size. A 6.6 kW array with a 5 kW inverter earns certificates on 6.6 kW. That combination is the most common residential setup because 6.6 kW is the largest array most networks allow on a 5 kW single-phase inverter at the standard 133% oversizing ratio.
Do bigger solar systems get proportionally fewer STCs?
No — solar certificates scale linearly, so a 20 kW system earns almost exactly triple a 6.6 kW one. That’s different from the battery scheme, which tapers sharply above 14 kWh of usable capacity.
How are battery STCs calculated?
Differently. Batteries use a flat factor per usable kWh — currently 6.8 — with no zone rating and no deeming period, tiered by size at 100% to 14 kWh, 60% to 28 and 15% to 50. There’s a 5 kWh minimum, and the factor steps down twice a year rather than annually.
What happens to STCs after 2030?
The Small-scale Renewable Energy Scheme ends on 31 December 2030 and no further certificates are created for solar PV. A system installed in 2030 earns just one deeming year — around 9 certificates on 6.6 kW in Zone 3, against 45 in 2026.
Can I claim STCs on a DIY solar install?
No. Certificates require installation by a Clean Energy Council accredited installer using approved products, and the regulator monitors installation dates and can take enforcement action over improperly created certificates. Solar installation is also licensed electrical work in every Australian state.
Sources and method
- Clean Energy Regulator — postcode zone ratings and zones for solar panel systems, and the deeming period schedule under the Small-scale Renewable Energy Scheme
- Formula: system size (kW) × zone rating × deeming years, floored to a whole certificate, consistent with how the regulator’s own calculator creates certificates
- Deeming schedule: 5 years for 2026 installs, reducing by one each 1 January to scheme end on 31 December 2030
- STC clearing house price fixed at $40 excluding GST; open-market prices have ranged roughly $30–42 in recent years
- Battery certificates follow the separate Cheaper Home Batteries Program structure, tiered by usable capacity and stepping down six-monthly
- This estimates entitlement. The regulator’s own calculator produces the binding figure, and eligibility requires CEC-accredited installation and approved products
Related calculators
Solar Battery CalculatorSizing and the tiered battery rebate
Electricity Cost CalculatorWhat your power really costs
Cable Size CalculatorAmpacity and voltage drop
Roof Pitch CalculatorTilt for panel output
Roof Area CalculatorHow much roof you have for panels
How this STC calculator works out its numbers
Solar entitlement multiplies system size by the zone rating and the deeming years for your installation year, then floors the result — because certificates are whole units and the remainder is not paid. The raw figure is shown alongside so you can see exactly what rounding costs.
The year table re-runs the same system across every remaining install year, showing the percentage drop between each. That drop is calculated from the floored certificate counts rather than the raw figures, so it reflects what you would actually receive.
Battery mode applies the separate tiered structure to usable capacity: full factor to 14 kWh, 60% from 14 to 28, and 15% from 28 to 50, with nothing below the 5 kWh threshold.
This estimates your entitlement rather than determining it. The Clean Energy Regulator’s own calculator produces the binding figure, and eligibility depends on CEC-accredited installation and approved products. Zone ratings and the deeming schedule are stable and published, but the STC price is market-determined and what your installer passes on is a commercial decision. Confirm both the certificate count and the price used before signing, and check which installation year a quote assumes — the difference across a 1 January boundary is currently 20% of the rebate.