For years the commercial solar market had a hard edge at 100 kW. A system at or below it earned STCs the day it was commissioned, paid as a lump sum off the customer’s price. A system just above it earned LGCs a year at a time as it generated, and only after a power station accreditation process. That was true for installs before 1 October 2026. From that date, systems above 100 kW and up to 1 MW create STCs too, with a fixed five-year deeming period, so the edge has moved to 1 MW. Pillar page: mid-scale solar STCs.
This article puts dollars on each side of the old line and shows how to quote the new band. The shorter answer on the 100 kW STC limit covers the definitions. Here we assume you know them and want the maths.
The tests, from 1 October 2026
Which certificate a system creates now depends on size and install date:
- 100 kW or less, and annual output under 250 MWh: small-scale STCs, with the deeming period that shortens each January (5 years for 2026 installs, 4 for 2027).
- Above 100 kW and up to 1 MW, installed on or after 1 October 2026: STCs with a fixed five-year deeming period. The Clean Energy Regulator says applications open mid to late November 2026, so hold the claim until then.
- Above 1 MW, or installed before 1 October 2026 above 100 kW: LGCs for actual generation.
Always confirm the exact tests with the Clean Energy Regulator before design, and note that the regulator looks closely at attempts to split one system into several.
Side one: 99 kW with STCs
A 99 kW system in zone 3 (rating 1.382) installed in 2026 with a five-year deeming period:
- 99 x 1.382 = 136.818 per year
- x 5 = 684.09, rounded down to 684 STCs
- At about $38.50 an STC (the market has been roughly $38 to $40 at the time of writing): about $26,300, paid upfront
That is a discount of about $26,300 on day one, which for a system costing around $99,000 installed is roughly a quarter of the price. In 2027 the same system earns 4 x 136.818 = 547.27, so 547 STCs, about $21,000. The drop is $5,300. See deeming period 2027.
Side two: 120 kW, before and after 1 October 2026
A 120 kW system in the same location, producing about 1.4 MWh per kW a year (an illustrative yield), generates about 168 MWh a year.
Installed before 1 October 2026, it was an LGC project:
- 168 LGCs a year
- At about $7.50 each (LGC spot has been roughly $6 to $9 in September 2026): about $1,260 a year
- Over the years to the end of 2030: a few thousand dollars in total, received over time, after accreditation, metering and reporting
Installed from 1 October 2026, it creates STCs:
- 120 x 1.382 x 5 = 829.2, rounded down to 829 STCs
- At about $38.50 an STC: about $31,900, paid upfront
So the 120 kW system now earns more than the 99 kW one, and the same way: a discount on day one. The LGC route is the exception, not the default, for this band.
| 99 kW (STCs) | 120 kW (STCs from 1 Oct 2026) | 120 kW (LGCs, installed earlier) | |
|---|---|---|---|
| Certificate type | STCs | STCs | LGCs |
| When paid | Upfront | Upfront | Yearly, as generated |
| Value (illustrative) | about $26,300 | about $31,900 | about $1,260 a year |
| Deeming period | 5 years (2026), 4 (2027) | Fixed 5 years | None, actual output |
| Admin | One claim | One claim | Power station accreditation and ongoing reporting |
What this does to the decision
The old reason to hold a system at 99 kW has gone for installs from 1 October 2026. Size the system to the customer’s load and roof, then show the certificate value at that size. Questions to ask:
- What is the customer’s load? If a 99 kW system already covers daytime use, the extra kilowatts export at a low price.
- What is the cost per watt at each size? Compare the extra equipment and labour against the certificate difference.
- How is it financed? An upfront discount reduces borrowing. LGC revenue arrives slowly and may not count in a lender’s model.
- What is the customer’s tax position? GST and depreciation treatment differ for a business. They should check with their accountant.
- When is it being installed? Small-scale systems lose certificates each January as the deeming period shortens, while mid-scale systems keep a fixed five years. Installs before 1 October 2026 above 100 kW sit on the LGC side.
From the desk: do not design to 99.9 kW as a reflex any more. A system at the threshold with a high-yield site can approach the 250 MWh output test under 100 kW, and the mid-scale route avoids the problem. Run the yield estimate for the specific site, confirm the install date, and if a quote depends on mid-scale STCs, say so, because the regulator has not opened applications yet.
Quoting a commercial STC job
Present the numbers clearly so the customer sees the discount and the assumptions (shown here for a small-scale system):
| Line | Example |
|---|---|
| System, 99 kW, installed (ex GST) | $99,000 |
| Less STC discount (684 STCs x $38.50) | -$26,334 |
| Net price (ex GST) | $72,666 |
Add the assumptions: zone, deeming period, price per STC and the date at which the count changes. Add a line saying the final number depends on the registered certificate count at the time of claim. For GST on the business side, see STC GST treatment for installers.
Evidence and paperwork on larger jobs
A larger job is a larger claim. The Clean Energy Regulator audits systems of all sizes, and an error is worth more on a $26,000 certificate batch. Keep:
- The signed assignment form naming the owner, with evidence of authority for a company. See STC assignment form.
- Photos of the arrays, inverters, serial numbers and installation, per the photo requirements.
- Single line diagrams, commissioning records and network approvals.
- A record of who was on site and their accreditation numbers.
Cash flow on commercial jobs
At $26,000 or more per job, a slow settlement is a serious cost. A crew doing four commercial jobs a month at $26,000 has $104,000 in certificates a month. At a seven-business-day settlement, roughly $35,000 is waiting on the trader at any moment. At 24 hours it is about $5,000. That is the working capital difference between taking on a fifth job or not. See how to improve cash flow as a solar installer.
If you are working out whether to sell larger systems’ certificates through one desk, our STC trading page explains how claims are checked and settled, and pricing has the published rate.
When LGCs are still the right route
Large sites above 1 MW, and anything above 100 kW installed before 1 October 2026, follow the LGC path, covered in how to sell LGCs and how to create LGCs. For them the question is how to run the power station well and sell the certificates for a fair price. Those between 100 kW and 1 MW should read the mid-scale solar STCs page first.
What to do next
- For every commercial quote above 100 kW, check the install date and show the STC value alongside any LGC alternative.
- Estimate annual output for the site before you promise small-scale STCs, and confirm the claim timing for mid-scale ones.
- Quote with explicit assumptions on zone, deeming year and price per STC.
- Keep complete evidence for the larger claim.
- Read the mid-scale solar STCs page and the 100 kW limit answer, check today’s rate and start trading when your next job is ready to claim.