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We can’t turn off the sun, so the DC side of a photovoltaic (PV) system cannot be easily switched off or made inactive for electrical testing purposes. What’s more, certain electrical tests require irradiance data (solar power per unit area) to be considered when comparing to Standard Test Conditions (STC).
When verifying any electrical system, the first step tends to be a visual inspection, which should be conducted prior to any electrical testing. A visual inspection helps identify any issues with the system, such as damage to modules, cable connectors, wiring, inverters or combiner boxes. This inspection should be performed not only during the commissioning process but also during periodic testing.
The electrical testing of the DC side of a PV system can be divided into two categories:
1. System testing and measurement
2. System performance testing
System testing and measurement
Testing the DC side of a PV system typically involves the following:
• Continuity or resistance testing is performed to ensure the integrity of protective earth, grounding or equipotential bonding conductors and connections. Proper grounding/earthing is crucial for reducing the risk of electric shock. It should be noted that not all PV systems are grounded or earthed.
• Polarity testing is necessary to ensure correct connections to other components in the system, such as inverters, charge controllers or batteries. Cross polarity can lead to efficiency losses or, in extreme cases, pose serious risks.
• Voltage and current testing is conducted to verify that the PV system operates within the specified design parameters. The Open Circuit Voltage (VOC) and Short Circuit Current (ISC) are commonly used to confirm these characteristics.
• Insulation resistance testing is used to identify faults in insulation by assessing the integrity of wiring and equipment.
• Functional testing ensures that switchgear and other control devices are properly mounted, connected and functioning as intended.
System performance testing
Performance testing of PV systems is essential to ensure that they operate according to the design specifications. This usually involves voltage and current measurements and may include I-V Curve tracing. Comparisons to Standard Test Conditions (STC) must be made, taking into account factors such as temperature, irradiance and spectral data at the time of measurement.
These comparisons, combined with electrical measurements, enable verification of the power and energy output of the PV system and allow for comparison against manufacturers' specifications.