Installation date vs commissioning date

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

Installation date is when the physical work is done. Commissioning date is when the system is tested, connected and switched on. For a household job they are often the same day. On larger or delayed jobs they can be weeks apart, for example when the system is installed and then waits for the network’s approval or a meter change.

Dates matter in certificate schemes because the rules change over time. The deeming period for solar steps down each year: five years for 2026 installs, four for 2027, then lower to one in 2030. For batteries, the STC factor now steps every six months: 6.8 at the time of writing, then 5.7 on 1 January 2027 and 5.2 on 1 July 2027. A date either side of a step changes the number of certificates.

A worked figure

A 10 kWh usable battery installed on 20 December 2026 earns 10 x 6.8 = 68 STCs. The same battery with an installation date of 5 January 2027 earns 10 x 5.7 = 57. Eleven STCs at roughly $38 to $40 each is about $420 to $440, so the date is worth checking.

In practice

Check how the relevant scheme defines the date that counts. The Clean Energy Regulator publishes guidance, and it is the authority on whether the installation or another date applies in a case. Do not assume. Where the guidance and your paperwork could point at different dates, ask before you lodge. See stc deeming period 2027 changes.

Whatever the rule, make the paperwork agree.

• The installation date on the claim, the invoice, the installer’s statement and the assignment form should match. See installer written statement.
• Photos should carry dates consistent with the stated work.
• If the network approval came later, record both dates and explain the gap. See grid connection application.

Common confusion

The date a customer signed the quote, the date of payment and the date of the first export are not the installation date. Neither is the date the claim is lodged, though that is one more date to line up.

See STC photo requirements, battery STCs and the glossary.