How the STC solar rebate works in Perth: what installers don't always explain

When you get solar quotes in Perth, the quoted price already has a rebate applied — you don't see a higher number with a rebate subtracted. This is by design: the installer assigns the Small-scale Technology Certificates (STCs) to a registered trader on your behalf, receives payment, and passes the saving to you as a discounted quote price.

The rebate is real and significant ($2,000–$4,000+ for most Perth systems). But the lack of transparency around how it's calculated creates confusion and occasional inconsistency between quotes.

What STCs are

Small-Scale Technology Certificates (STCs) are the mechanism behind Australia's residential solar incentive. They're created under the federal Small-scale Renewable Energy Scheme (SRES) and exist because the government requires large energy users (retailers, generators) to purchase certificates from renewable energy installations. The demand from this obligation is what gives STCs their value.

Each STC represents 1 MWh (1,000 kWh) of renewable energy. When you install solar, you can create a certain number of STCs based on:

1. Your system's expected generation over the deeming period
2. Your geographic zone (Perth is in STC Zone 3, which has more peak sun hours than southern cities)

You don't deal with STCs directly. Your CEC-accredited retailer/installer does. You assign the STCs to them, they sell them on the spot market or to an aggregator, and the discount appears in your quote.

The deeming period (the most important number)

STCs are calculated using a deeming period — the number of years of future generation used in the calculation. The deeming period is 15 years minus the current year, counting from the SRES scheme start in 2001. The scheme is scheduled to end in 2030.

Deeming periods by year of installation:

| Year installed | Deeming period | Impact | |---|---|---| | 2026 | 4 years | Lower STCs, smaller rebate | | 2027 | 3 years | Even lower | | 2028 | 2 years | Dropping further | | 2029 | 1 year | Small rebate | | 2030 | 0 years | Scheme ends |

In 2026, the deeming period is 4 years. This is significantly lower than it was in 2020 (10 years) or 2015 (15 years). The rebate has already declined substantially and continues to do so each January.

This creates a real but modest incentive to install sooner rather than later — each year the rebate decreases.

STC calculation for a Perth solar system

The formula is:

STCs = System capacity (kW) × Zone rating × Deeming period

For Perth (Zone 3):

• Zone 3 rating: 1.382 (this reflects Perth's higher solar resource vs southern cities)
• 2026 deeming period: 4 years

Example: 6.6kW system in Perth in 2026:

STCs = 6.6 kW × 1.382 × 4 = 36.5 → 36 STCs (rounded down)

STC spot price: The STC spot market price fluctuates but typically trades at $35–$40 per certificate in 2026. At $38/STC:

Rebate value = 36 × $38 = $1,368

For a 6.6kW system installed in 2026, the STC rebate is approximately $1,200–$1,500 depending on the spot price at time of installation.

This is noticeably lower than what buyers received in 2020 (when the deeming period was 10 years, yielding 90+ STCs worth $3,000–$4,000 on the same system). The rebate has roughly halved since then as the scheme winds down.

Why STC values differ between quotes

Several legitimate reasons cause variation:

1. Timing relative to the January deeming-period reduction. The deeming period drops each January 1. Installers sometimes quote in December knowing the rebate will fall in January — they may quote the higher deeming period (this year's) or the upcoming lower one depending on the expected installation date.

2. STC spot price at time of assignment. Installers may assign STCs to a trader immediately after installation, or may have a forward contract. If they lock in STCs at $38 but the market drops to $34 by assignment time, the saving they passed to you may not fully materialise in their model.

3. Deliberately different treatment. Most installers deduct the STC value from the quote upfront (point-of-sale assignment). Some quote "before STC" and show the rebate separately. Ensure you're comparing quotes on the same basis — both should show the final price you pay, with STC already applied.

4. Small rounding differences. The STC calculation rounds down to whole certificates. A 6.6kW system and a 6.58kW system may produce different STC counts despite similar practical capacity.

When you're at risk of losing the rebate

To receive STCs, your installation must meet requirements:

• Installed by a CEC-accredited installer (verify at solaraccreditation.com.au)
• Using CEC-approved products (panels and inverter on the CEC product eligibility list)
• Meets AS4777 grid connection standards
• STCs must be created and assigned within 12 months of installation

Non-compliant installations (unlicensed installer, non-approved equipment) are ineligible. The STCs are assigned by your installer — you should receive documentation confirming the assignment at settlement of the account.

What this means for your quote

When comparing quotes, ask each installer:

1. How many STCs does this quote include?
2. What STC price have they used in the calculation?
3. Is the quoted price final (STC already deducted), or do you pay this amount and then receive a rebate?

A legitimate quote will have the STC value already deducted from the displayed price. You should not need to claim anything separately.

The rebate exists whether or not the installer mentions it explicitly. If one quote is significantly lower than another for the same system, check whether both have applied STCs — or whether one is quoting "before STC" while presenting it as a lower total.

The WA Battery Scheme is separate

The STC scheme covers solar panels (and some batteries). The WA Battery Scheme ($130/kWh, up to $1,300 for a 10kWh battery, via Synergy) is a separate state government rebate for battery storage, administered by Synergy — not through the federal SRES. Both can be claimed on the same installation.

STC calculations use the current deeming period effective from 1 January 2026 (4 years). The deeming period reduces by 1 each January 1 and the scheme ends on 31 December 2030. STC spot prices fluctuate; the figures above are indicative of mid-2026 market pricing.