A solar panel hotspot is a localized area of a module that runs significantly hotter than its surroundings. Hotspots are the single most common finding in solar thermography — and depending on severity, they range from a minor efficiency nuisance to a genuine fire risk. Understanding what causes them, how they're detected, and when they demand action is core to any solar O&M program.
What Causes a Hotspot?
A hotspot forms when one or more cells in a module dissipate energy as heat instead of converting it to electricity. Several mechanisms cause this:
- Cell cracks: Microcracks from hail, transport, or thermal cycling disconnect part of a cell, forcing current through a smaller area that overheats.
- Partial shading: A shaded cell becomes reverse-biased and dissipates the current of the rest of its string as heat.
- Soiling: Bird droppings or localized dirt act like persistent shading on individual cells.
- Manufacturing defects: Poor solder joints, contamination, or cell mismatch present as hotspots from day one.
- Bypass diode failure: When a bypass diode fails, an entire cell-string can overheat.
Why hotspots matter: Beyond the immediate power loss, a hotspot accelerates degradation of the affected cells and encapsulant. Left unaddressed, a severe hotspot can scorch the backsheet and, in extreme cases, initiate a module fire. This is why IEC 62446-3 flags the most severe hotspots as Class 3 — immediate action.
How Thermography Detects Hotspots
Infrared thermography is the ideal tool for hotspot detection because a hotspot is, by definition, a thermal signature. Under load and sufficient irradiance, a healthy cell sits within a narrow temperature band; a hotspot appears as a bright anomaly against that baseline. The inspection measures the temperature differential (ΔT) between the anomaly and a healthy reference area on a comparable module.
The pattern of the thermal signature reveals the cause: a single bright cell suggests a crack or soiling; a bright cell-string suggests a bypass diode issue; a uniform pattern on edge cells suggests PID. Reading these patterns correctly is what separates a useful report from a list of bright spots. The conditions required for valid detection are set out in our IEC 62446-3 guide.
Severity: When Does a Hotspot Demand Action?
Not every hotspot justifies a repair. IEC 62446-3 classifies severity by temperature differential:
| ΔT above reference | Class | Typical action |
|---|---|---|
| Under 10 K | Class 1 | Document, monitor at next inspection |
| 10–20 K | Class 2 | Investigate and repair within months |
| Over 20 K or whole string | Class 3 | Isolate immediately, assess fire risk |
Detecting Hotspots Across a Whole Plant
On a single module, a handheld camera finds a hotspot in seconds. Across a utility-scale plant with hundreds of thousands of modules, systematic aerial capture and analysis is the only practical approach — see utility-scale solar thermography. Either way, the analysis step — detecting, classifying, and mapping every hotspot to a location — is what turns imagery into an actionable report. That's the part we handle remotely.