Two questions get asked in different words but have the same answer: which date sets the factor, and whether it locks in at purchase or at install. At the time of writing the rule is that the installation date determines the factor. Buying early, signing early or paying a deposit early does not preserve a higher rate.
Why purchase date does not matter
The STC factor sits in the regulations that govern when certificates can be created. Certificates are created for a battery that has been installed, so the date that counts is the date of that event. A contract is a commercial arrangement between you and the installer. It does not change what the regulator will create.
That is why a quote that says “price held for 30 days” is a price promise from the installer, not a rate guarantee from the scheme. If the factor steps down before install, the STC value falls and someone absorbs it.
Installation versus commissioning
The two events can be days or weeks apart on a battery job, for example when a distributor must approve the connection or the VPP capability setup is not finished. Public guidance and industry commentary describe the factor as following the installation date. Because the rules and the CER’s guidance have been refined more than once since the program began, any job within a few weeks of a changeover is worth a direct check against the CER’s current wording.
Do not treat commissioning as a way to delay. If the installation is complete in December and the commissioning sheet says January, that is a conversation you want to have before lodging, not after a query.
The upcoming changeovers
| Date | Factor from that date |
|---|---|
| 1 May 2026 | 6.8 (tiers begin) |
| 1 January 2027 | 5.7 |
| 1 July 2027 | 5.2 |
Each step costs real money. On a 13.5 kWh battery, the move from 6.8 to 5.7 is about 15 fewer certificates, roughly $580 at $38 to $40.
What this means for installers
- Put the installation date on the job sheet and keep it consistent across the photos, the assignment form and the registry entry.
- Do not quote a rate beyond the changeover unless you have priced the lower factor.
- If a delivery delay pushes a job across a changeover, tell the customer before it happens and reprice in writing.
- Lodge a complete claim promptly. Our pricing page shows the rate for the day, and it locks once a complete claim is lodged.
The battery submission guide lists the evidence that should carry the date, and the photo requirements resource covers the image rules.
What this means for homeowners
If your installer says the current rebate is “locked in” by a deposit, ask them to show you the rule. In practice the discount you receive is calculated at the factor on install day, and the installer is deciding whether to absorb any difference. Ask for that in writing. The pillar page on battery STCs and the insight on the January 2027 cut explain where the program is heading.