Solar PV System Troubleshooting with Test Instruments

Why PV Faults Are Hard to Find

A solar array can lose 20 % of its yield without anyone noticing — string-level monitoring averages the loss across many panels, and a single shaded or defective module silently drags the rest down. Solar PV troubleshooting needs a deliberate workflow with four instrument types, run in the same order every time.

Step 1 — String Voltage Survey

Start with an open-circuit voltage measurement on every string at the combiner box. Record V_oc at the same irradiance for all parallel strings; outliers more than 5 % below the median point to dead modules, reverse-installed cells, or mismatched module counts.

Step 2 — IV Curve Trace

An IV curve tracer sweeps the string from open-circuit to short-circuit and overlays the measured curve on the manufacturer's reference. The shape tells the story:

• Step in the curve → bypass-diode active around shaded cell.
• Curve below reference but same shape → uniform soiling or module degradation.
• Reduced V_oc → cell crack or junction-box fault.
• Reduced I_sc → uniform shading or partial module disconnect.

Step 3 — Insulation Resistance to Earth

Disconnect the string at the inverter input and measure insulation resistance from each polarity to the earthed mounting frame. A 1000 V test should show > 1 MΩ per kW; lower values indicate moisture in connectors, damaged cable insulation, or a cracked module backsheet.

Step 4 — Thermal Imaging Survey

Under load, defective cells run hot. A drone- or pole-mounted thermal imager with 256×192 detector and 50 mK NETD identifies hot-spot cells, bypass-diode failures, and disconnected sub-strings in one fly-over. Always image strings under at least 70 % of rated irradiance — low-light imaging hides faults.

Step 5 — Document and Trend

Capture every reading with GPS coordinates, time stamp and irradiance. Trend year-on-year — a 0.7 %/year degradation is normal; faster decline triggers warranty claim or remediation. EK PV inspection reports follow IEC TS 62446-3 and produce a per-module heat map suitable for insurance and warranty submission.

Common False Alarms

1. String V_oc measured under partial cloud cover.
2. Thermal hot-spot caused by adjacent obstruction shadow, not module fault.
3. Insulation low value cleared after 24 hours of dry weather (condensation).
4. IV curve below reference because of mismatched module count, not degradation.