A larger battery can attract more federal support while receiving less support for each extra kilowatt-hour. That is the practical effect of the tiered calculation, and it is why multiplying a headline rate by the entire battery size can overstate a quote's discount.
A larger battery can attract more federal support while receiving less support for each extra kilowatt-hour.
That is the practical effect of the tiered calculation, and it is why multiplying a headline rate by the entire battery size can overstate a quote's discount.
This worksheet uses the rules checked on 27 October 2026 for installations in May to December 2026. It compares hypothetical usable capacities, not particular products or recommended battery sizes.
The Clean Energy Regulator's battery guidance lists a 6.8 STC factor for May to December 2026.
The first 14 kWh of usable capacity receives the full factor. The next 14 kWh receives 60 per cent, and usable capacity above 28 kWh up to the supported 50 kWh limit receives 15 per cent.
For this period, that means unrounded calculation rates of 6.8, 4.08 and 1.02 respectively. The thresholds use usable energy, not simply the largest capacity number in a product advertisement.
Ask your battery supplier to identify nominal and usable capacity separately. Do not assume that adding modules preserves a particular usable fraction across every product family.
At 14 kWh usable, the unrounded calculation is 14 × 6.8, which equals 95.20. At 28 kWh, it is 95.20 plus 14 × 4.08, which equals 152.32.
At 40 kWh usable, add another 12 × 1.02 to the 28 kWh result, giving 164.56. These are intermediate arithmetic results, not fractional certificates that can be issued or a confirmed customer entitlement.
Use the regulator's current calculator and the approved product information for the final whole-certificate result.
The examples assume the system satisfies the program's other requirements; capacity arithmetic alone does not establish eligibility.
Moving from 14 to 28 kWh adds 14 kWh of storage and 57.12 to the unrounded calculation. Moving from 28 to 40 kWh adds 12 kWh but only 12.24 to that calculation.
That second increase may still suit a household with a documented need. It simply should not be priced as though every extra kilowatt-hour receives the first tier's support rate.
Compare the incremental installed price with the extra useful storage, charge/discharge power, available charging energy and intended backup loads. A larger energy capacity does not automatically increase the inverter's power output.
The CER certificate-assignment guidance explains the agent's role in turning assigned rights into an upfront discount. Ask what value and fees the retailer uses.
An invented example of 100 certificates assigned at $35 each gives $3,500; at $32 each it gives $3,200. Those prices are arithmetic illustrations, not current market prices, an offer or a calculation for the systems above.
Our STC assignment explainer covers the paperwork.
Keep the gross installation cost, certificate count, assigned value and final customer payment on separate quote lines.
The regulator currently lists a lower factor of 5.7 for January to June 2027. Recalculate if the installation period changes, and ask how the contract allocates any resulting price variation.
The program also limits repeat claims after a premises has received battery STCs. Do not assume a later expansion will receive another discount just because the hardware can be expanded.
For a home with solar, assess seasonal generation and the energy available to charge the proposed storage. Include future EV charging carefully, so the same surplus is not allocated to both the car and the battery.
Ask Lightning Energy for a comparison using your interval data and a consistent installation scope. Choose the capacity for a defensible household use case, with the tier calculation shown transparently afterwards.
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