IEC 62446-1 is the international reference for testing, documentation and maintenance of grid-connected PV systems. This page explains the main tests in the order they usually happen and what owners should look for in the results.
Before testing: visual inspection
Every commissioning programme starts with a walk-down: module and structure condition, cable routing and support, connector types and mating, labelling, earthing connections, combiner and inverter installation, and safety signage. Many defects are cheaper to find with eyes than with instruments, and some must be fixed before electrical tests are safe to run.
Category 1 tests: required for every system
IEC 62446-1 sets out a baseline group of tests that apply to all systems. In practice they include:
- Continuity of protective earthing and equipotential bonding conductors.
- Polarity of every string, before any connection to the inverter.
- String open-circuit voltage, compared with expected values for the module count and temperature.
- String current, by short-circuit or operating current measurement, compared between strings in similar light.
- Functional tests of switchgear, isolators and the inverter.
- Insulation resistance of the DC circuits.
Results outside tolerance point to wrong module counts, reversed polarity, damaged cables or connectors, or faulty modules, and should be fixed and re-tested before energisation.
Category 2 tests: deeper evidence
For larger and financed plants, owners usually ask for additional tests described in the standard:
| Test | What it shows |
|---|---|
| String I-V curve tracing | Shape of the curve reveals shading, mismatch, cell damage or high series resistance |
| Infrared thermography | Hot spots from damaged cells, bypass diode faults or poor connections, done under adequate sunlight |
Additional tests such as electroluminescence imaging of samples, earth resistance and specific inverter tests can be added by contract.
Inverter, transformer and AC side
On the AC side, commissioning covers inverter start-up and protection settings, transformer tests, cable tests, protection relay testing and the plant controller. Utility-scale plants then go through grid compliance testing to show they meet the network code for power factor or reactive power, voltage and frequency response, and ride-through. Those tests are often witnessed by the grid operator. Our page on grid code compliance covers what is typically required.
Performance testing
Once the plant is running, a performance test compares measured output with expected output over a defined period. The usual measure is the performance ratio, corrected for actual irradiance and temperature, or energy output against a model run with measured weather. The contract should define the test duration, the weather data source, sensor calibration, how outages are treated and the pass threshold. Our performance ratio guide explains the calculation.
Where solar is combined with storage or thermal generation, acceptance also tests the hybrid control functions; see our hybrid acceptance test page.
Documentation and sign-off
IEC 62446-1 expects a system documentation package: design data, datasheets, wiring diagrams, test reports, operation and maintenance information and warranty documents. Owners should receive it before final acceptance, along with the punch list showing every open item, its owner and its deadline. Hold back final acceptance or retention until the critical items are closed.
Commissioning records are also the start of good O&M. Store them in the maintenance system so the next technician can compare a future string reading with the day-one value.
Common defects found at commissioning
| Defect | How it shows up |
|---|---|
| Mismatched or poorly crimped DC connectors | Hot spots in thermography, low insulation resistance, later arcing risk |
| Reversed string polarity | Polarity test failure before inverter connection |
| Wrong module count in a string | Open-circuit voltage outside expected range |
| Cable damage during installation | Low insulation resistance on a string or feeder |
| Cracked or damaged cells | Distorted I-V curve, hot cells in thermography |
| Loose earth bonds | Continuity test failure |
| Incorrect inverter settings | Functional or grid compliance test failure |
Finding these during commissioning is the system working as intended. The aim is that none of them survive into operation.
Who should run the tests
The EPC contractor normally carries out commissioning under its own procedures, witnessed by the owner’s engineer and, for financed projects, the lender’s technical adviser. Independent testing of a sample of strings or modules adds confidence on larger plants. Our power plant EPC page explains how we deliver and commission plants end to end.
Solar EPC by USP&E
Commissioning is where our engineering, construction and O&M teams meet. USP&E designs, builds, commissions and maintains solar and hybrid plants under ISO 9001 and ISO 45001 certification, with 150+ power projects in 45+ countries and 25,000 MW contracted since 2002.
Offices: Colorado Springs (1755 Telstar Dr, Suite 300), Knoxville (800 S Gay St, Suite 700), London (162-168 Regent Street), Johannesburg (22 Kildoon Rd, Bryanston), Cape Town (31 Brickfield Road, Woodstock) and China (No. 1 Ningzhou Road, Wuxi). Regions: USA | AFRICA | UK | UAE | CHINA. ISO 9001 and ISO 45001 certified.
PV commissioning FAQs
What tests are done when commissioning a solar PV system?
A visual inspection, then earth continuity, polarity, string open-circuit voltage, string current, insulation resistance and functional tests, followed by AC-side tests, grid compliance tests and a performance test.
What is IEC 62446-1?
It is the international standard for testing, documentation and maintenance of grid-connected PV systems, setting out required tests and the documentation package.
What is the difference between Category 1 and Category 2 tests?
Category 1 tests apply to all systems and cover the basics such as earthing, polarity, voltage, current and insulation. Category 2 tests add deeper checks such as I-V curve tracing and infrared thermography.
How is a solar plant’s performance tested at handover?
Usually by measuring the performance ratio or energy output over a defined period and comparing it with a model corrected for the actual weather.
Who witnesses solar commissioning tests?
Typically the owner’s engineer, the lender’s technical adviser on financed projects and, for grid tests, the network operator.
Plan your commissioning
Our engineers can write your commissioning plan, carry out or witness tests and close out handover with documentation your lenders and operators can use.
Write to info@uspeglobal.com, phone +27 10 822 2324, or start with the solar EPC team. For firming and backup generation, see our equipment inventory.