The legislated cut on 1 January 2027 reduces the battery STC factor from 6.8 to 5.7. Because the certificate count is usable kWh multiplied by the factor, the same battery generates about 16 per cent fewer STCs from that date.
What the cut does to a typical battery
Using the tiered structure, here are approximate counts for the same battery before and after the cut.
| Usable size | STCs at 6.8 | STCs at 5.7 |
|---|---|---|
| 14 kWh | about 95 | about 79 |
| 28 kWh | about 152 | about 127 |
| 50 kWh | about 175 | about 146 |
At a spot price near $40 a 14 kWh battery loses roughly $600 of discount. The exact figure depends on the STC price on the day, which moves.
The part that catches people out
The factor that counts is set by the installation date. Batteries that are quoted in November but delayed by stock, a switchboard upgrade or network approval can slide past 31 December and pick up the lower factor. A discount promised in a quote is only as firm as the install date.
Demand also tends to bunch before a known cut. Expect crowded installer calendars through November and December, and plan site visits, switchboard works and approvals early. See the deeming period and scheme wind-down page for how the broader scheme steps down.
A quick test for any December quote
Ask three questions. What is the commissioning date, who is responsible if it slips, and what STC count does the quote assume? A quote that cannot answer the first question is not a 2026 quote, whatever the discount line says. Installers who want to protect their margin should add the same wording to their terms, so that a customer who delays a switchboard upgrade understands the discount is date dependent.
What this means for you
Homeowners deciding whether to wait should compare the roughly 16 per cent certificate loss against any change in hardware prices and VPP incentives. Waiting rarely helps, because the factor only moves down. Installers should reprice 2027 quotes now and keep an eye on today’s STC rates. The battery STC pillar and the January 2027 deeming period piece give the wider context.