Canary in Coal Mine: Junction Box Temperature Provides Early Warning of Manufacture, Installation, or Degradation Faults

Junction box (JB) hotspots of an aged solar module are often attributed to JB or bypass diode damage. Unless supported by a physics-based model, this presumption may lead to incorrect diagnostics and overlooked risks. This study investigates the possible physical origin of JB-hotspots observed in infrared thermography and field data. Our electro-thermal modeling-based analysis reveals that JB-hotspot temperature, exceeding the regular module’s temperature by 5–20°C, correlates strongly with connector corrosion, solder joint degradation, and increased series resistance. Contrary to zeroth-order assumptions attributing such anomalies to bypass diode failures, we find that exit contact corrosion and module connection defects are the most probable contributors to JB hotspots. Our predicted JB temperature ranges are consistent with that found in thermal imaging in literature. Thus, infrared thermography, supported by electro-thermal inverse-modeling, can identify the origin of degradation, suggest various risk mitigation strategies, and serve as a powerful diagnostic tool for large-scale solar farm management.