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

When you get solar quotes in Perth, the price you see already has a rebate built in: you won't see a higher number with a discount subtracted. The installer assigns your Small-scale Technology Certificates (STCs) to a registered trader on your behalf, gets paid for them, and passes that saving on as a lower quote price. On a typical Perth system, that's worth roughly $1,700 to $4,000 or more, depending on system size and the STC price on the day.

The rebate is real and it's worked into your price automatically. What causes confusion is the lack of transparency around how it's calculated, why it can look slightly different from one quote to the next, and how quickly it's shrinking as the scheme winds down to its legislated close at the end of 2030.

What's an STC, actually?

Small-scale Technology Certificates (STCs) are the mechanism behind Australia's residential solar incentive. They exist under the federal Small-scale Renewable Energy Scheme (SRES), which requires large energy retailers and generators to buy certificates from renewable energy installations. That obligation creates the demand that gives STCs their value.

Each STC represents 1 MWh (1,000 kWh) of renewable energy. When you install solar, the number of STCs your system can create depends on two things:

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

Rather than waiting years to see how much electricity your system actually generates, the scheme "deems" (pre-calculates) a fixed number of years of expected output up front and issues all the certificates at once, at installation. That deemed number of years is what shrinks annually as the scheme approaches 2030.

You never deal with STCs directly. Your installer does: you assign the certificates to them, they sell them on the spot market or to an aggregator, and the discount shows up in your quote.

Why does the STC rebate shrink every year?

STCs are calculated using a deeming period: the number of years of future generation the calculation assumes. The deeming period counts down by one year every 1 January, and it's the biggest single lever on your rebate's size.

Deeming periods by year of installation:

In 2026, the deeming period is 5 years. That's already well down from 2020, when it was around 11 years, and lower again than the scheme's early years, when it ran to 15 years or more. The rebate has been shrinking every January for a long time, and it will keep shrinking until the scheme closes for good.

How many STCs will your system generate?

The formula is:

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

For Perth (Zone 3):

• Zone rating: 1.382, reflecting Perth's higher solar resource than the southern cities
• 2026 deeming period: 5 years

Example: a 6.6kW system installed in Perth in 2026

STCs = 6.6 kW x 1.382 x 5 = 45.6, rounded down to 45 STCs

How much is the STC rebate worth on your system?

The STC spot market price moves around, but it's recently traded in the high $30s to $40 per certificate. At $38 a certificate:

Rebate value = 45 x $38 = $1,710

For a 6.6kW system installed in 2026, that puts the STC rebate at roughly $1,700 to $1,800, depending on the spot price on the day the certificates are assigned. Larger systems generate proportionally more STCs, so an 8 to 15kW system lands well above that, up toward the $4,000-plus end of the range.

In 2020, the same 6.6kW system would have generated around 100 STCs on an 11-year deeming period, more than double today's 45, worth several thousand dollars more. The rebate has roughly halved since then, and it keeps shrinking as the scheme winds down toward its 2030 close.

How much do you actually lose by waiting?

Here's the year-by-year picture for a 6.6kW Perth system, at a certificate price of around $39.90:

The 2026 rebate is about two and a half times the 2029 rebate for the same system, and the step-down costs more each year in percentage terms as the scheme runs down: roughly 20% shaved off at first, then 25%, then a third, then half. For a larger 10kW system, each January step currently costs about $551 in lost discount.

Does waiting actually change your payback? A 6.6kW solar system without a battery in Perth typically pays for itself in roughly six and a half to seven and a half years. A smaller rebate pushes that out a little further each year you wait, because you start from a higher effective cost, but for most households the difference is months rather than years. The sharper point is simpler: if you're already planning to install, there's no upside to waiting on rebate grounds alone, and a clear cost saving in going ahead sooner.

Should you wait for panel prices to drop instead? Panel prices fell a long way over the 2010s and have levelled off more recently. Installed prices in Perth haven't moved much over the past few years, while the STC rebate keeps shrinking on a fixed schedule. If installed prices stay flat while the rebate keeps falling, waiting doesn't buy you a cheaper system, it just buys you a smaller rebate on the same price.

Is there ever a good reason to wait? Yes, one: if you're planning other home changes in the next 12 months that touch the roof or the switchboard, adding a battery, installing EV charging, building an extension that could shade panels, or replacing the roof itself, it's usually worth finishing those first. Installing solar twice costs more in labour and disruption than a year of shrinking rebate costs you in dollars. Outside that, the maths favours going sooner. To build the sum for your own roof and usage, see the solar payback calculation guide.

Why do STC prices go up and down?

STCs trade on a market. The Clean Energy Regulator's Clearing House will buy any certificate at a fixed price of $40, which acts as a ceiling. In practice, most installers and aggregators sell on the open market instead, at a price that runs a little below that $40 Clearing House rate, because it settles faster.

The open-market price moves with supply and demand: supply is how many STCs are being created (tied to how much solar is being installed nationally), and demand is how many liable entities, mostly electricity retailers, need to buy them to meet their obligations. A surge in solar installations tends to soften the price; a shortfall tends to firm it up.

For Perth households: the STC discount shown in your quote is locked in at the time you sign the contract. If the market price moves between your quote and your installation date, most installers absorb the difference and guarantee the STC value they quoted.

Why do STC values differ between quotes?

Several legitimate reasons cause variation:

1. Timing around the January deeming-period drop. The deeming period falls each 1 January. Installers quoting in December, knowing the rebate will drop in the new year, may quote this year's higher deeming period or the upcoming lower one, depending on your likely installation date.

2. STC spot price at time of assignment. Installers may assign STCs to a trader right after installation, or work from a forward contract. If they've priced your quote assuming $38 a certificate but the market has dropped to $34 by the time they assign, the saving they modelled may not fully land.

3. How the quote is presented. Most installers deduct the STC value upfront, so the number you see is already net of the rebate. Some quote "before STC" and show the discount as a separate line. Make sure you're comparing quotes on the same basis: both should show the final price you pay, STC already applied.

4. Rounding. STCs are calculated in whole certificates, rounded down. A 6.6kW system and a 6.58kW system can produce slightly different STC counts despite near-identical capacity.

What actually happens when you buy solar with STCs?

1. You sign a contract for a solar system at a price that already has the STC discount built in.
2. After installation, your installer (or an aggregator working with them) creates the STCs through the Clean Energy Regulator's REC Registry.
3. The certificates are sold, either on the open market or to the Clearing House.
4. The sale proceeds offset your invoice, so you only pay the net, discounted price.

You don't manage any part of this yourself. Your installer handles the certificate creation and sale, and you should get documentation confirming the assignment when you settle the account.

What could disqualify your install from the rebate?

To receive STCs, your installation needs to meet these requirements:

• Installed by an SAA-accredited installer (verify at saaustralia.com.au)
• Uses CEC-approved products: both the panels and the inverter need to be on the CEC product eligibility list
• Meets the AS4777 grid connection standard
• STCs created and assigned within 12 months of installation

An unaccredited installer or non-approved equipment makes the installation ineligible for STCs. Our pre-purchase checklist for Perth solar buyers covers exactly what to verify before you sign.

What should you ask when comparing quotes?

When you're weighing up 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, with STC already deducted, or do you pay the full amount and claim a rebate separately?

A legitimate quote has the STC value already taken off the displayed price. You shouldn't need to claim anything yourself.

The rebate applies whether or not the installer spells it out. If one quote looks noticeably lower than another for the same system, check that both have applied STCs the same way, rather than one quoting "before STC" and presenting it as a lower total.

What happens when STCs end in 2030?

The Small-scale Renewable Energy Scheme is legislated to end on 31 December 2030. From 1 January 2031, new solar installations no longer receive a federal STC discount.

What this means in practice:

• A system installed in 2030 still receives one deeming year of STCs.
• A system installed after 31 December 2030 receives no federal STC discount.
• Once that discount disappears, the upfront cost of a comparable system is likely to rise for anyone installing after 2030.

As of mid-2026, no federal replacement for the SRES has been legislated.

How is the WA Battery Scheme different from STCs?

STCs cover solar panels, and some batteries under a separate federal battery program. The WA Battery Scheme, worth $130/kWh up to $1,300 for a 10kWh battery via Synergy, is a separate state government rebate for battery storage, and it isn't part of the federal SRES or tied to its 2030 end date. You can claim both on the same installation. For the full walkthrough of eligibility and paperwork, see how to claim your WA Battery Scheme rebate.

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Figures above use the deeming period effective from 1 January 2026 (5 years). The deeming period drops by one year every 1 January and reaches zero from 2031, once the scheme is fully closed. STC spot prices fluctuate day to day; the figures here are indicative of mid-2026 market pricing.