The factor is the multiplier that turns a battery’s usable capacity into certificates. It is 6.8 per kWh for installations in 2026 and 5.7 from 1 January 2027, and it now steps down every six months to 2030 until the program winds down in 2030. For installers and customers, it means a visible drop in discount for the same battery after the new year.
What the drop does
Certificates = eligible usable kWh x factor. The change from 6.8 to 5.7 is a fall of about 16 percent.
| Usable capacity | 2026 STCs | 2027 STCs | Difference |
|---|---|---|---|
| 5 kWh | 34 | 28 | 6 |
| 10 kWh | 68 | 57 | 11 |
| 13.5 kWh | 91 | 76 | 15 |
| 20 kWh | 136 | 114 | 22 |
At roughly $38 per certificate at the time of writing, a 13.5 kWh battery loses around $570 of certificate value across the changeover. Prices move, so recalculate with the live rate.
Install date is what counts
The relevant date is the installation, not the quote or deposit. A battery contracted in November and installed in January gets the lower factor. Supply delays, switchboard upgrades and network approvals commonly push installs back a few weeks, so any job planned for December needs a firm path to completion.
What to tell customers
Show both numbers on the quote and say plainly what happens if the install date moves. Customers are rarely upset by a clear explanation; they are upset by a surprise at invoice time. Where the date risk is real, agree in writing who carries the difference.
What this means for installers
Plan your Q4 around ready-to-go battery jobs, and make sure claims clear quickly. See the battery STC pillar, our installer guide to the program and the battery submission guide. Energy Merchants publishes its battery STC rate on the pricing page.
One further consequence is on pricing strategy. A fall of about 16 percent in the certificate discount will show up as a higher net price for customers in the new year unless battery prices fall to match. Some installers expect a rush in the final weeks of 2026, so being clear with customers about timelines is good service as well as good business.