IR Thermography

Key Takeaways

• IR thermography = thermal imaging of operating PV systems.
• Detects hot spots, connector failures, diode burnout.
• Drone-based for utility-scale; handheld for residential.
• Quarterly inspection typical for large plants.
• Complements EL imaging at commissioning.

What Shows Up in a Thermal Scan

A thermal camera doesn’t measure defects directly, it measures surface temperature, and reads a defect wherever something is dissipating power as heat instead of converting it. That makes IR thermography useful across several different failure modes at once. A hot spot from a shaded or cracked cell shows up as a localized bright patch on a single cell or cell group.

A failed or shorted bypass diode runs warmer than a healthy one during bypass diode activation, since a diode that isn’t conducting properly forces the shaded segment to keep dissipating current it should be routing around. On the electrical side, a loose or corroded MC4 connector shows up as a hot point at the connection itself rather than across the module, because resistance is concentrated at that single joint.

Handheld vs. Drone-Based Scans

Which platform makes sense depends mostly on plant size. Handheld thermal cameras are common on residential and small commercial rooftops, where a technician can walk the array during a service visit and check anomalies against the layout by eye.

Utility-scale plants use drone-mounted thermal cameras instead, flying a fixed altitude, typically in the 30-50 m range, to cover several megawatts of array area in a single day, well beyond what a ground-based inspection could manage in the same time.

The tradeoff is resolution versus coverage: handheld scans catch finer detail on individual modules, while drone sweeps are built to flag which sections of a large plant need closer, module-level follow-up.

Related Reading

IR thermography findings are one of the ways a plant’s actual field performance gets reconciled against what was modeled at the design stage, if a string is underperforming the yield a study projected, a thermal sweep is often the first diagnostic step before a deeper root-cause investigation, a process covered in more depth in our piece on P50, P90, and P99 solar yield reports.

Many of the hot spots a thermal scan turns up also trace back to shading that wasn’t fully accounted for at the layout stage, which is why getting the shading model right up front, using the tools discussed in our review of solar shading analysis software, reduces how much a plant depends on catching these issues after the fact.

For a defect-detection method that works the opposite way, applying current to a de-energized module in the dark rather than imaging a live array in daylight, see EL imaging, which is typically used earlier in a module’s life at manufacturing and commissioning.

Aerial IR surveys are covered in the drone survey guide for solar projects.