Installation date (STCs)

Written and checked by the Energy Merchants desk · Reviewed 3 October 2026

The installation date is the date the system was installed, as stated on the claim. For STCs it is the most consequential date on the file because it sets the rules the system is assessed under.

Why it decides so much

For solar, the deeming period steps down year by year: 5 years for 2026 installs, 4 for 2027, down to 1 in 2030. For batteries under the Cheaper Home Batteries Program, the factor steps down every six months, at 6.8 at the time of writing, then 5.7 on 1 January 2027 and 5.2 on 1 July 2027. The installation date is what places a job in one period or another.

Worked example

A battery with 10 kWh usable installed on 30 December 2026 creates 10 x 6.8 = 68 STCs. The same battery installed on 2 January 2027 creates 10 x 5.7 = 57 STCs. Eleven certificates, roughly $420 to $440 at $38 to $40, turn on a three-day difference.

In practice

The installation date should agree across the written statement, the registry entry, the compliance certificate and the photos. A photo with a metadata timestamp that contradicts the stated date is a typical trigger for a query. See geotagged photo and the STC photo requirements.

Do not pick a date for convenience. If the job ran across two days, record the date the installation was completed according to the rules, and keep the evidence that supports it.

Common confusion

The installation date is not the commissioning date, which is when the system is switched on and running, or the creation date, when the claim is lodged. The three can all differ. See commissioning date and STC creation date.

Read the 2027 deeming period guide, see battery STCs and browse the glossary.