Solar PV commissioning: tests, IEC 62446-1 and the commissioning records
Deskely Completions team Singapore
Solar PV commissioning proves that a PV system is installed safely and correctly and performs as designed before it is connected and handed over. For grid-connected systems, the reference is IEC 62446-1, which sets out the documentation, inspection and tests a commissioning report should contain.
This guide covers the commissioning sequence, the IEC 62446-1 tests, inverter and grid connection commissioning, performance testing on utility-scale plants, and how to manage the records when a plant has thousands of strings.
- IEC 62446-1 sets the documentation, inspection and test requirements for grid-connected PV systems.
- Category 1 tests apply to all systems: earthing continuity, polarity, Voc, current, functional and insulation tests.
- Category 2 adds I-V curve tracing and infrared thermography for larger or higher-risk systems.
- On a utility-scale plant, every string, combiner and inverter is a tag with its own records.
The commissioning sequence
- 01Documentation check
System data, wiring diagrams, datasheets, the array layout and the operation and maintenance information are in place.
- 02Visual inspection
Modules, mounting, cabling, connectors, labelling, earthing and the DC and AC protection are inspected against the design.
- 03DC tests
String by string: earthing continuity, polarity, open circuit voltage, current and insulation resistance (see below).
- 04Inverter commissioning
Inverters configured and started, usually by or with the vendor, protection and grid settings checked.
- 05AC and grid connection
AC cabling, transformers and switchgear tested; grid protection settings verified; energisation with the network operator.
- 06Performance verification
On larger plants, a capacity or performance ratio test against the expected output.
- 07Handover
Commissioning report, as-built documents and the O&M package handed to the owner.
IEC 62446-1 test categories
IEC 62446-1 (Photovoltaic systems, requirements for testing, documentation and maintenance, part 1: grid connected systems) defines a test regime in categories:
| Category | Tests | Applies to |
|---|---|---|
| Category 1 | Continuity of protective earthing and equipotential bonding, polarity, combiner box test, string open circuit voltage, string current (short circuit or operational), functional tests, insulation resistance of the DC circuits | All systems |
| Category 2 | Category 1 plus string I-V curve testing and infrared (IR) thermography of the array | Larger systems, or where specified |
| Additional tests | For example voltage to ground, blocking diode tests, wet insulation tests and shade evaluation | Where required |
The standard also sets out the content of the inspection and test report, so that results from different installers can be compared and the owner receives a complete record.
Key DC tests
| Test | What it checks | Typical issue found |
|---|---|---|
| Open circuit voltage (Voc) | Each string's voltage against the expected value for its module count and temperature | Missing or reversed module, wrong string length |
| String current (Isc or operating) | Each string's current against expected, corrected for irradiance | Shading, damaged modules, poor connections |
| Polarity | Positive and negative correctly connected before closing isolators | Reversed strings, which can damage equipment |
| Insulation resistance | Between DC conductors and earth, at a test voltage set by the system voltage | Damaged cable insulation, water ingress in connectors |
| I-V curve (category 2) | The full current-voltage characteristic of each string | Degraded or mismatched modules, bypass diode faults |
| IR thermography (category 2) | Hot spots on modules and connections under irradiance | Cell defects, failing connectors and fuses |
See the insulation resistance test guide for how IR testing works and how to read the results.
Inverters, substations and the grid
On utility-scale plants, PV commissioning continues through the inverter stations, the medium-voltage collection system and the plant substation, where the work looks like any substation commissioning: transformer and switchgear tests, protection relay testing, SCADA and power plant controller checks, then energisation and grid compliance tests with the network operator. The plant's single line diagram is the master drawing for that sequence.
Records on a utility-scale plant
A 100 MW plant can have several thousand strings, hundreds of combiner boxes and dozens of inverters. Each string has its own Voc, current and insulation readings; each test can raise a punch item; and the commissioning report has to show all of it. On spreadsheets, readings get typed twice, punch items lose their link to the string, and progress per block is a manual count.
Holding each string, combiner and inverter as a tag, with its test results checked against expected values as they are entered, turns the commissioning report into an export rather than a project.
The Deskely products for this
Frequently asked questions
What standard covers solar PV commissioning?
IEC 62446-1 for grid-connected PV systems: the documentation, inspection and commissioning tests, and the content of the test report.
What tests are done when commissioning a solar PV system?
Category 1: earthing continuity, polarity, combiner box test, string open circuit voltage, string current, functional tests and insulation resistance. Category 2 adds I-V curve tracing and infrared thermography.
What is the difference between category 1 and category 2 tests?
Category 1 is the minimum for all systems. Category 2 adds I-V curve testing and thermography, typically for larger systems or where the owner specifies it.
Why is string Voc measured?
To confirm each string has the right number of modules connected the right way. A low reading points to a missing, damaged or reversed module.
What happens after the DC tests?
Inverter commissioning, AC and grid connection tests with the network operator, then on larger plants a performance or capacity test before handover.
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