Small-scale Technology Certificates (STCs) explained for Perth solar

Nearly every Perth solar installation involves STCs — Small-scale Technology Certificates — yet many homeowners are unclear on what they are, how the value is calculated, and whether they're getting the full benefit. Here's how the STC system works in practice for Perth solar.

What are STCs?

STCs are certificates issued under Australia's Renewable Energy Target (RET) legislation. Each STC represents one megawatt-hour (1,000kWh) of renewable electricity that a solar system is expected to generate (or displace) over its deeming period.

Solar installers assign the STCs on your behalf when you install a system. They sell those certificates (or bundle them) to liable entities (electricity retailers and large energy users) who must surrender them to meet their RET obligations. This creates a market for STCs with a fluctuating spot price.

In practice: the STC value is applied as an upfront discount on your installation quote — you don't receive a cheque; the installer clips the rebate and reduces your price accordingly.

How STCs are calculated for Perth

The STC quantity assigned to a Perth solar installation depends on three variables:

1. System capacity (kW): The inverter or panel capacity, whichever is lower.

2. Zone rating (zone factor): Australia is divided into 4 solar zones based on solar irradiance. Perth is in Zone 3 — which has a zone rating of 1.382 under current CER (Clean Energy Regulator) tables. This means Perth solar systems generate more STCs per kW than Zone 4 cities (Melbourne, Hobart).

3. Deeming period: The STC scheme runs until 31 December 2030. The deeming period at any given installation date is the number of whole calendar years remaining until then, rounded down to whole years. A system installed in June 2026 gets a deeming period of 4 years (2027, 2028, 2029, 2030). A system installed in January 2026 also gets 4 years (same calculation — only whole remaining years count). [Note: at installation time in 2026, verify the exact deeming period with your installer or the CER calculator.]

The formula:

STCs = (System capacity in kW) × (Zone 3 factor: 1.382) × (Deeming years)

Example for a 10kW system installed in Perth in mid-2026 (4 deeming years):

10kW × 1.382 × 4 = 55.28 STCs

Rounded down (CER rounds down): 55 STCs

What is one STC worth?

The STC price is set by market — liable entities pay the spot price, currently typically around $35–$40 per STC (fluctuating; spot price changes daily on the open market). The CER also operates a clearing house at a fixed price of $40 per STC (the legislative cap), which provides a price ceiling.

For a Perth 10kW system mid-2026 with 55 STCs at $38/STC:

55 × $38 = $2,090 STC value applied as an upfront discount

This is less than in prior years — in 2023 with 6 deeming years, the same 10kW system would have generated 10 × 1.382 × 6 = 82.9 STCs ≈ $3,150 at $38/STC. The STC value declines each year as the deeming period shortens.

Why "after rebate" prices can mislead

Perth solar quotes typically show pricing "after STCs" or "after rebate." This presentation is standard but conceals important detail:

What installers may quote differently:

• Some installers price at the clearing house rate ($40/STC) — this is the maximum, and only achieved if the clearing house is used (which adds processing time vs spot market)
• Some use the current spot price ($35–$40)
• Some discount a fixed STC value and absorb the price risk

What you should ask:

1. "What STC price are you using in this quote?"
2. "How many STCs did you calculate, and what system capacity and zone factor did you use?"
3. "When does the STC assignment happen — will you use today's STC price or lock it at contract signing?"

A reputable installer should be able to show you the STC calculation on request.

The deeming period decline — STC value over time

| Year of installation | Deeming years (until 2030) | STCs for 10kW Perth | Value at $38/STC | |---|---|---|---| | 2022 | 8 | 110 | $4,180 | | 2023 | 7 | 96 | $3,648 | | 2024 | 6 | 82 | $3,116 | | 2025 | 5 | 69 | $2,622 | | 2026 | 4 | 55 | $2,090 | | 2027 | 3 | 41 | $1,558 | | 2028 | 2 | 27 | $1,026 | | 2029 | 1 | 13 | $494 | | 2030 | 0 | 0 | $0 |

The STC scheme ends on 31 December 2030. After that date, no federal upfront solar subsidy exists under the current legislative framework (a successor scheme hasn't been confirmed as at mid-2026).

How STCs interact with Perth's battery incentive

The WA Battery Scheme ($130/kWh, maximum $1,300 for battery storage) is separate from the federal STC scheme:

• STCs: cover solar panels only (not batteries)
• WA Battery Scheme: covers battery storage only (not solar panels)
• Both can be claimed in the same installation

A combined 6.6kW solar + 10kWh battery installation in Perth mid-2026 would attract:

• STCs for the solar component (6.6kW × 1.382 × 4 deeming years = 36 STCs ≈ $1,368 at $38)
• WA Battery Scheme for the battery ($1,300, subject to battery SSL eligibility and Synergy registration)

Small-print: STC scheme conditions

• System must be ≤ 100kW (residential and small commercial qualify)
• Installed by a Clean Energy Council (CEC) accredited installer
• Using CEC-approved components
• Grid-connected (off-grid systems use a different mechanism)
• The installer manages the STC assignment and Rec Agent paperwork — you sign an assignment form

STCs represent a real upfront discount on Perth solar, declining year-by-year as the scheme approaches its 31 December 2030 end date. For a 10kW Perth system in mid-2026, the STC discount is approximately $2,000–$2,200. Each year you wait reduces this by roughly $500–$700. The federal scheme declining toward zero is a genuine incentive to install sooner rather than later — though system pricing and installer quality should weigh more than chasing the STC value.