Solar Inverter Commissioning: What It Means and What to Expect

Commissioning is the formal testing and sign-off step that happens after physical installation is complete but before a solar system is switched on for real use. A Licensed Electrical Worker (LEW) tests the system's wiring, earthing, and safety protections, and only signs off once everything checks out correctly. It's a mandatory step by law, not an optional add-on service some installers offer and others skip.

What does a Licensed Electrical Worker actually check?

Commissioning testing covers correct wiring between panels, inverter, and your home's electrical supply, proper earthing throughout the system, safe voltage and current levels under load, and confirmation that safety protections, including anti-islanding, function correctly.

None of these are optional spot-checks, each addresses a distinct way an improperly installed system could genuinely injure someone or damage equipment, which is exactly why the LEW inspects each one individually rather than relying on a single overall pass/fail impression. Anti-islanding specifically is tested by verifying the inverter disconnects properly when it detects a grid outage, since this is a mandatory EMA safety requirement, not an optional feature. The LEW verifies this against defined numeric thresholds, not just a general "does it turn off," confirming the inverter trips within the voltage and frequency tolerances the standards actually specify.

Why can't the installer just switch the system on themselves?

Singapore law requires a Licensed Electrical Worker to sign off on electrical installations including solar systems, specifically because this final check is independent verification that the work was done safely, not just a formality. An installer certifying their own work without this independent check removes the safeguard that catches genuine wiring or safety issues before a system is energised and connected to the live grid for the first time.

What document does commissioning actually produce, and what should I ask for by name?

The Certificate of Compliance, commonly referred to as the COC and submitted on a standard SP Group form (Appendix 37), is the specific document your LEW signs to certify the installation meets the Electricity (Electrical Installations) Regulations and the relevant Singapore Standard. It's submitted directly to SP Group, and it's the specific piece of paperwork that unlocks the next step: SP Group will not activate your export registration, and therefore your SCT or ECIS credit, until this document is on file.

Knowing the document's actual name is useful leverage. Rather than asking an installer the vague "has commissioning been done," asking specifically "can I see the signed Certificate of Compliance" is a harder question to wave away with a verbal assurance.

Does every Licensed Electrical Worker have the right qualification for solar work?

Not automatically, LEWs are licensed in grades, and solar work has a specific minimum. A Grade 8 LEW (Electrical Technician) is the standard qualification for residential solar, competent to design and take charge of installations well beyond what a typical landed home needs, and Grade 9 covers larger or more complex systems. A lower Grade 7 licence, common for general electrical work, doesn't carry the same scope, so confirming your installer's LEW holds at least Grade 8 specifically for solar is a legitimate, concrete question, not an overly technical one to ask.

This is worth asking directly rather than assuming, since not every electrician who does general household wiring work automatically holds a solar-appropriate grade. A reputable installer will have this answer ready immediately, along with the LEW's full name and licence number, rather than needing to go check with someone else first.

How is commissioning different from SP Group's grid connection approval?

Commissioning is a technical safety sign-off on the physical installation itself. SP Group's grid connection approval is a separate administrative step that permits the system to formally export electricity to the grid and begin earning export credit.

Both need to be complete before your system is fully operational, and they typically happen close together in the overall installation timeline, but they are distinct steps performed by different parties for different reasons: one is a technical safety inspection performed by an independent LEW, the other is an administrative registration process performed by SP Group's own back office once that inspection's paperwork reaches them.

Do I need to be home for commissioning, and what actually happens during it?

Not for the entire process, though it's worth being reachable. Your LEW doesn't need to be continuously on site through every stage of installation, but they do need to personally inspect specific critical points: the DC string terminations where panel wiring connects, the inverter's AC connections into your home's supply, the protection relay (the anti-islanding mechanism) actually tripping correctly, and earthing throughout the system. These checks happen at defined moments rather than as one continuous site visit, so coordination between the installer and LEW matters for how smoothly the day goes.

From a homeowner's perspective, the useful thing to track isn't the commissioning check itself, which is largely a technical inspection, but the paperwork it produces and how quickly that paperwork gets filed afterward.

How long does the full process actually take, from installation to being switched on?

Physical installation itself is usually quick, often 1-3 days on site for a typical landed home system.

The gap most homeowners underestimate is what follows: commissioning, Certificate of Compliance submission, and SP Group's grid connection approval together can stretch the full timeline from installation start to genuine, credit-earning operation to somewhere in the range of 4 to 12 weeks. Asking your installer for a realistic estimate of this full window, not just the on-site installation days, avoids the common surprise of panels sitting visibly installed but not yet actually earning anything. Where the timeline actually runs long is rarely the LEW's inspection itself, which is a matter of hours across a few site visits, but the queue and processing time on SP Group's side of the grid connection approval, a step largely outside your own installer's direct control once the paperwork has actually been filed on your behalf.

What should you ask for after commissioning is complete?

Request a copy of the signed Certificate of Compliance itself, not a generic completion letter or invoice marked paid, since this is documentation that your system passed a genuine independent safety check, not just a verbal confirmation. Confirm it was actually emailed to SP Group's install address as part of your grid connection application, rather than simply sitting in your installer's files, since a signed copy sitting unfiled in your installer's own records does you no good if your export credit hasn't actually started.

This document is also worth keeping alongside your warranty paperwork long-term, in case any future maintenance visit, ownership transfer, or warranty claim needs to reference the original commissioning results years down the line.

Further reading: see solar installation safety for the full installation process context, and solar panel maintenance and warranty for what to keep on file. Run the Sunnify solar estimate to start planning your own installation.