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STC calculator: how the capacity taper affects your battery

Compare federal rebate values across each half-year period of the step-down schedule. The capacity taper in force since 1 May 2026 affects larger systems most.

Your battery size

Enter your planned battery capacity to see timing impacts

Battery Capacity (kWh)

Common sizes: 10kWh (small), 13.5kWh (Tesla Powerwall), 20kWh (large), 40kWh (commercial)

Strategic recommendations for your 13.5kWh battery

Your 13.5 kWh battery gets the full rebate rate

The rebate still steps down every six months, but the lower rate for bigger batteries doesn't apply to yours.

Step-down schedule:

• Current (May-Dec 2026): 6.8 STCs/kWh
• 2027: 5.7-5.2 STCs/kWh
• 2028-2030: Continuing annual decline through scheme end

Additional considerations:

• Most Perth installers have 2-4 month wait times, so book early if you're aiming for a specific rebate factor
• The Clean Energy Regulator sets your rate by the factor in force on the installation date, not the quote or deposit date — ask installers to keep quotes current rather than to “lock in” a superseded rate
• WA state rebate (up to $1,300, 10kWh max eligible) is separate from federal STCs
• STC market price (~$39.9) can fluctuate, affecting final value slightly

Understanding the capacity taper

The Australian Government introduced tapered STC rates on 1 May 2026 to address taxpayer waste from oversized systems that would never fully cycle. The three-tier system, now in force, encourages right-sizing batteries to actual household needs.

5-14Kwh tier

100% STCs (optimal for most homes)

14-28Kwh tier

60% STCs (for larger households)

28-50Kwh tier

15% STCs (commercial/special cases)

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Where next

WA battery rebate: are you eligible?

Synergy customers get $130/kWh back, capped at $1,300.

Synergy Battery Rewards: what the VPP pays

Activation events credit 70¢/kWh on top of DEBS exports, and signing up is a WA rebate condition.

How federal and WA rebates stack

Worked examples of combining both schemes on a single install.

The 1 January 2027 step-down in dollars

What changes on the date, what does not, and a worked 10 kWh example.

Explore your options

Answer a few questions and see systems and installers that fit your home.