The factor is a certificate count, not a dollar figure. The dollars come from multiplying that count by what an STC sells for. At the time of writing the factor is 6.8, STCs have been trading around $38 to $40, and the clearing house ceiling is $40.
The formula in one line
STCs = usable kWh counted in each tier x factor x tier percentage, rounded down to a whole certificate.
The tiers, in force since 1 May 2026, are:
| Usable capacity band | Share of the factor | STCs per kWh at 6.8 | Approx. value per kWh at $38-40 |
|---|---|---|---|
| First 14 kWh | 100% | 6.80 | $258 to $272 |
| 14 to 28 kWh | 60% | 4.08 | $155 to $163 |
| 28 to 50 kWh | 15% | 1.02 | $39 to $41 |
Nothing above 50 kWh earns certificates, and the battery must be 5 to 100 kWh usable to qualify at all.
Why the nominal figure is the wrong input
Datasheets often lead with nominal capacity. The program counts usable capacity, which is what the CEC listing records. A 13.5 kWh usable battery is calculated on 13.5, whatever the marketing says. Using nominal capacity is one of the easier ways to overquote a discount.
How the dollar value moves
Two things shift the number independently of each other:
- The factor. It steps every six months now: 6.8 for May to December 2026, then 5.7 on 1 January 2027 and 5.2 on 1 July 2027, continuing down to 2030. At 5.7 the first 14 kWh is worth roughly $217 to $228 per kWh at the same STC price.
- The STC price. A $2 move in the certificate price changes the value of the first 14 kWh by about $13.60 per kWh.
What this means for installers
Quote the discount as a range tied to the certificate price on the day, not as a fixed dollar figure. The rate you will be paid for the certificates is published daily on our pricing page, and it is locked when a complete claim is lodged. Run each job through the battery STC calculator so the count on your quote matches the count you lodge.
What this means for homeowners
The rebate is applied as a discount on your invoice, so the useful question is the final price after the discount. Ask for a quote with the usable kWh, the factor, the STC count and the dollar discount on separate lines. Our battery worked example shows what a 13.5 kWh and a 28 kWh job look like in full. For the wider picture, see the battery STC guide and the insight on the 2026 installer position.