Commissioning date

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

The commissioning date is when the system was switched on and confirmed to be working. It is the end of the project in the customer’s eyes, because the panels or the battery are doing their job.

How it differs from installation

Installation is the physical work: panels on the roof, battery on the wall, wiring complete. Commissioning follows. It includes testing, inverter configuration and, where required, network approval and a meter exchange. If the DNSP has not yet approved the connection, the system can be fully installed and not yet commissioned.

In practice

The two dates matter for different reasons. The installation date decides the deeming rules or battery factor. The commissioning date shows up in compliance certificates and in some program paperwork. If the form asks for installation date, give the installation date. Putting the commissioning date there, when the gap spans the start of a new period, can change the STC quantity.

Worked example

An installer finishes the wiring on a 9 kW system on 28 December 2026. The network approval is delayed and the system is switched on on 15 January 2027. The installation date is 28 December and the 2026 rules apply. The commissioning date is 15 January. Mixing them up would move the job into the 4-year deeming period for 2027 and shorten the STC quantity.

Common confusion

Do not assume the two dates must be the same. They often are on a simple job, so the difference gets missed on the complex ones. Also do not back-date either one. The evidence trail, including photos with timestamps and the certificate, will show the true sequence. See CES.

See installation date, how it works, top STC claim rejection reasons and the glossary.