Commissioning is where a solar project either confirms its business case or quietly loses part of it.
The failures that surface on energisation day are rarely exotic – a string wired to the wrong input, a torque value nobody recorded, a monitoring gateway that was never configured. Nearly all of them were created weeks earlier, at delivery or during installation, and nearly all of them were cheap to catch at the time.
This checklist follows a project from the container arriving to the handover pack being signed. It is written for EPC and installation teams, and it works equally well as a procurement document – several items here are worth fixing in the purchase order rather than on site.
IEC 62446-1 sets out documentation, commissioning tests and inspection requirements for grid-connected PV systems.
Goods-in inspection, before anything is unloaded
The inspection that matters happens before the equipment leaves the truck. Once pallets are broken down and distributed, damage attribution becomes an argument rather than a fact.
- Photograph every pallet and container before unloading, including seals and any visible impact.
- Check crate and pallet counts against the packing list before signing the delivery note.
- Inspect for crushed corners, punctured wrapping, water ingress and shifted loads.
- Record serial numbers at goods-in. This is the only point where it is easy, and it is what makes the warranty meaningful later.
Note any discrepancy on the delivery document itself, with the driver’s acknowledgement, and notify the supplier in writing the same day. Claims raised weeks later are far harder to support.
Site storage: where most avoidable damage happens
Equipment on a construction site is at more risk than equipment in transit. Modules stacked on uneven ground, inverters stored in a damp container, and cable drums left uncovered are all common and all preventable.
- Store modules on level ground, on the original pallets, protected from standing water and not covered with material that traps condensation.
- Keep inverters and batteries indoors or in a dry, ventilated, temperature-controlled space. Storage temperature range is in the manual and is part of the warranty conditions.
- Keep cable drums upright and sealed until termination.
- Secure the laydown area. Theft from unsecured sites is a real and recurring cost.
Mechanical checks before electrical work starts
- Confirm the mounting structure matches the approved design – rail spans, clamp positions and fixing type for the actual roof or ground condition.
- Verify torque values on structural fixings and record them. Torque that is not recorded was not checked.
- Check roof penetrations are sealed and flashed as specified, and that waterproofing warranty requirements are met where they exist.
- Confirm earthing and bonding continuity across the array frame before modules are energised.
Electrical checks before energisation
This is the stage that catches the expensive mistakes, and it should be done with the system dead.
- Verify string polarity and open-circuit voltage per string, against the expected value for the conditions at the time of measurement.
- Confirm stringVoc at site temperature is within the inverter’s maximum DC input rating.
- Check insulation resistance to earth on DC and AC circuits.
- Verify conductor sizing and termination torque on all DC isolators, combiners and AC connections.
- Confirm protective devices, labelling and isolation points match the single-line diagram.
Energisation and performance verification
- Bring the system up string by string where possible, comparing each against its expected contribution.
- Verify the inverter’s grid settings match the approved interconnection parameters – voltage and frequency trip limits, ramp rates, export limits.
- Test the anti-islanding and shutdown functions, including the rapid shutdown arrangement where the market requires one.
- If storage is present, test each operating mode independently: charge, discharge, and the transition to backup. A battery that has only ever been tested in one mode will fail in another.
- Confirm the monitoring gateway is reporting, at string level, and that the right people have access before the team leaves site.
Documentation pack: what handover should include
A handover pack is not a courtesy – it is what allows the asset to be maintained, insured and eventually repowered. It should contain as-built single-line and layout drawings, string configuration, equipment serial numbers and datasheets, test and commissioning results with the measured values, warranty documentation with registration confirmed, and the O&M manual with maintenance intervals. Where the market requires it, include the interconnection approval and any inspection sign-off.
Training, spares and the first-year plan
Before demobilisation, confirm the site team can perform the basic operations: safe isolation, inverter restart, monitoring access and alarm escalation. Agree the spare parts holding – a spare string fuse and a communications module cost very little compared with a truck roll – and set the first inspection date rather than leaving it open.
The most common causes of failed commissioning
Reference table
Swipe horizontally to view all columns →
| Cause | Where it originates | When it is cheapest to catch |
|---|---|---|
| Grid parameters not set to approved values | Commissioning | Pre-energisation settings review |
| String polarity or wiring error | Installation | String Voc test before energisation |
| Transport damage discovered late | Delivery | Goods-in inspection with photos |
| Inverter derating from poor siting | Design | Design stage, against derating curve |
| Monitoring never configured | Handover | Commissioning test with portal access |
| Missing serial numbers for warranty | Delivery | Serial capture at goods-in |
| Battery mode untested | Commissioning | Per-mode functional test |
Getting the specification right upstream
Several items above are cheaper to fix in procurement than on site: agreed spare parts, serial number capture, documentation requirements and warranty registration terms are all worth writing into the purchase order. If you are sourcing equipment for a scheduled project, the import and documentation checklist covers the shipping side, and our service and quality page sets out what we inspect before dispatch. For project-specific support, use the contact page.
BUYER CHECKLIST
Buyer considerations for this scope
What has to be on site before commissioning can start?
As-built drawings, torque records, string-level current and voltage measurements, insulation resistance results, labelling and signage. Missing any of these turns a commissioning day into a return visit.
Who witnesses and who signs?
The installer, the EPC where there is one, and the utility or authority having jurisdiction. Permission to operate comes before energisation, and the sequence is worth confirming with the utility early because it is the step most often underestimated.
What records protect the warranty later?
The commissioning report with measured values, photographs, and the serial number list. These are what a claim rests on years later, and they are far cheaper to produce on the day than to reconstruct afterwards.
PRACTICAL ANSWERS
Questions buyers ask about this
What is checked before anything is unloaded?
Goods-in inspection: pallet condition, module frame and glass condition, and serial numbers against the packing list. Damage found at goods-in is a freight claim; damage found after installation is your problem.
Where does avoidable damage usually happen?
In site storage. Modules stacked on uneven ground, pallets left in standing water, and cable drums laid on their side cause more loss than transport does.
What happens before energisation?
Mechanical checks first, then insulation resistance, polarity, string open-circuit voltage and current against expectation, then protection settings verified against the design rather than against defaults.
What records close out a commissioning?
Test results per string, torque records, the serial-to-position map, monitoring access confirmed, and the signed commissioning checklist. Those are what a performance claim or a warranty question later depends on.
EXPLORE FURTHER