Commissioning: Verification Before Turnover
Commissioning proves the PV system is installed per design, code, and manufacturer instructions and is safe to energize. The exam tests the sequence of visual, continuity, insulation-resistance, polarity, Voc/Isc, IV-curve, and functional tests, plus the records that close out a project. IEC 62446-1 is the reference framework; NEC 690 and 705 govern the electrical installation.
Test sequence and rules
- Review as-builts, string sizing, conductor ampacity, OCPD ratings, labeling, and rapid-shutdown documentation before testing.
- Visual inspection: module orientation, mounting torque, connector mating, clearance, drainage, signage, and equipment grounding.
- Continuity and polarity: verify equipment grounding conductor continuity and DC conductor polarity at each string and combiner.
- Insulation resistance: isolate electronics and surge protective devices, then test PV conductors to ground with a megohmmeter at the specified voltage. Record values; a low reading requires sectionalizing.
- Voc and Isc: compare each string to expected values corrected for cell temperature (Voc) and irradiance (Isc). IV curve tracing adds fill factor and series/shunt resistance evidence.
- Functional tests: inverter startup, grid synchronization, anti-islanding, rapid shutdown, arc-fault and ground-fault response, and monitoring sensor calibration.
Worked example
A string has 20 modules with STC Voc = 41.0 V and a Voc temperature coefficient of −0.30%/°C. At 5°C cell temperature: expected Voc = 20 × 41.0 × [1 + (−0.003)(5 − 25)] = 820 × 1.06 = 869 V. A measured 860 V is within about 1%, acceptable given meter tolerance and irradiance. Do not compare directly to 820 V at STC.
Traps
Testing insulation resistance with inverters or SPDs connected; using an uncorrected nameplate Voc; measuring Isc at low irradiance and expecting STC current; skipping polarity at every string; failing to record meter calibration and test conditions.