For batteries installed from 1 January to 30 June 2027 the STC factor is 5.7, and from 1 July 2027 it is 5.2. The 2026 factor is 6.8, so the reduction is 1.1 certificates per kWh, about 16 per cent.
Worked examples at 5.7
Applying the same tier rules as 2026 (full factor to 14 kWh, 60 per cent from 14 to 28 kWh, 15 per cent from 28 to 50 kWh):
| Usable size | 2026 STCs | 2027 STCs | Change |
|---|---|---|---|
| 10 kWh | 68 | 57 | -11 |
| 14 kWh | 95 | 79 | -16 |
| 20 kWh | 120 | 101 | -19 |
| 28 kWh | 152 | 127 | -25 |
| 50 kWh | 175 | 146 | -29 |
Counts are approximate and round down on the actual claim.
What to do with the numbers
A 14 kWh battery loses 16 STCs. At roughly $38 to $40 a certificate, that is around $600 less discount. If hardware prices are flat, the customer pays more out of pocket for the same battery after 1 January. If your costs fall, the net price can hold, but the headline discount will still look smaller.
Customers and sales teams often ask whether a delivered-by-31-December promise is honoured when the install slips. It is not, because the factor is tied to the install date. Write that into your terms.
What changes for quoting software
If your quotes are built in a spreadsheet or a CRM, add the install date as a driver of the factor, with 6.8 up to 31 December 2026, 5.7 from 1 January to 30 June 2027 and 5.2 from 1 July 2027. Then add the three tiers and the 50 kWh cap. Many early errors in battery quotes come from applying a single per-kWh figure to every size.
What this means for installers
Re-price the 2027 pipeline, update quote templates, and recheck the factor before every changeover. Install-date discipline is a margin lever. The battery STC pillar and the cheaper home batteries installer guide have further detail. To see what a certificate pays today, check our pricing or read what an STC is worth.