Understanding STCs — the federal solar rebate, plainly.

The 30-second take

• STC = Small-scale Technology Certificate. The federal solar rebate, applied as an upfront install discount.
• STC count = system kW × zone rating × deeming period. Each STC trades on the open market at ~$36–$39.
• Deeming period drops 1 year every 1 January — scheme ends in 2030.
• Sydney (Zone 3, 1.382 rating) × 6.6 kW × 5 years deeming = ~46 STCs ≈ $1,700 discount.
• STCs apply nationwide. State rebates stack on top in NSW, WA, NT, ACT, VIC.

What an STC actually is

A Small-scale Technology Certificate (STC) is a tradeable certificate created by the federal Small-scale Renewable Energy Scheme. Every kilowatt-hour of electricity your solar system is expected to produce over its deemed lifetime is converted into STCs. Installers (or their accredited agents) sell those STCs into a market and pass the proceeds to you as an upfront discount on the install cost.

You don’t see the STCs yourself. You see a quote that says "system price $X, after STC discount $Y." The difference is the STCs.

The three numbers that drive your STC count

STC count = system kW × zone rating × deeming period.

• System size in kW. Capped at 100 kW for STC eligibility — anything larger goes through a different (LGC) scheme.
• Zone rating. Australia is split into 4 STC zones based on average sunshine. Zone 1 (Darwin, far north) = 1.622. Zone 2 (Townsville) = 1.536. Zone 3 (Sydney, Brisbane, Perth, Adelaide, Canberra) = 1.382. Zone 4 (Melbourne, Hobart, southern VIC) = 1.185.
• Deeming period. The number of years of forward production that gets certificated. In 2026: 5 years. 2027: 4 years. 2028: 3. 2029: 2. 2030: 1, then scheme ends.

Worked example: 6.6 kW in Sydney

Sydney sits in Zone 3 (rating 1.382). A 6.6 kW system installed in 2026 (5-year deeming): 6.6 × 1.382 × 5 = 45.6 STCs. At a spot price of $37 each: ~$1,687 upfront discount.

Same system installed in January 2027 (4-year deeming): 6.6 × 1.382 × 4 = 36.5 STCs ≈ $1,350. About $337 less for an identical install — just because you waited 4 weeks past 1 January.

This is why late-December installs tend to sell out — homeowners who book late November get the next year’s smaller deeming.

“A 6.6 kW Sydney system installed December 2026 is worth ~$337 more in STCs than the same system installed January 2027. Same hardware, same install, smaller rebate.”

STC spot price — and why it floats

STCs trade on the Clean Energy Regulator-administered market. The clearing price has hovered around $36–$39 for most of 2024–2026, but it can move 5–10% within a quarter based on supply (volume of new installs) and demand (how many liable retailers need certificates).

Your installer’s quote uses an assumed price — usually the rolling 30-day average. If install slips past the quote validity window, the discount can shift slightly. Reputable installers will lock the STC value in writing for installs within 30 days.

What stacks with STCs

STCs apply nationwide, and they stack with every active state rebate. Notable stacks in 2026: the NSW VPP incentive, the WA Residential Battery Scheme, the ACT Sustainable Household Scheme loan, and the VIC Solar Homes panel rebate. The NT battery scheme has closed. VIC, QLD, SA, TAS run federal-only on panels.

STCs also stack with the federal Cheaper Home Batteries Program — but they’re separate certificate streams. Solar panels get solar STCs; batteries get battery STCs (CHBP). Both apply to the same install.

Read next

• Federal rebate page (full STC + CHBP)
• Cheaper Home Batteries explained
• System size guide

Sources

• cer.gov.au — STC entitlement calculation
• cer.gov.au — postcode zone ratings