Hotspot
A localised area of one cell running significantly hotter than its neighbours — the classic PV thermal fault, and a defect that degrades the module further the longer it runs hot.
Thermal signature
A sharply bounded bright spot at cell or part-cell scale, in strong contrast to the uniformly warm cells around it. It stays fixed on the same cell across consecutive frames and viewing angles — a reflection or sun glint moves; a hotspot doesn't.
Typical ΔT
10–25 °C above neighbouring cells, with severe cases exceeding 40 °C (typical industry interpretation aligned with IEC TS 62446-3, measured at ≥600 W/m² irradiance).
What causes it
- Cell microcracks concentrating current through a shrinking active area
- Failing or high-resistance solder joints on the cell ribbons
- Persistent partial shading or hard soiling (droppings, lichen) forcing a cell into reverse bias
- Cell mismatch or localised degradation
- Backsheet or encapsulant damage behind the cell
Power impact
The direct loss is usually modest — often a few percent of one module — but sustained heat accelerates encapsulant browning, backsheet damage and further cracking, so the defect compounds. High-ΔT hotspots are also a recognised fire-precursor and are treated as safety-relevant findings.
Recommended action
Fix: within 30 days
Verify on site within 30 days: confirm the cell (not surface soiling) is the source, clean the module if soiling is implicated, and I-V test the string. Replace the module if the hotspot is severe or recurs after cleaning; escalate very high ΔT findings for immediate attention.
Frequently asked questions
Are solar panel hotspots dangerous?
Most are a performance and degradation problem rather than an acute hazard, but a severe hotspot can damage the backsheet and, in the worst cases, start a fire. That is why very high ΔT findings are graded as safety-relevant and prioritised for immediate action rather than routine maintenance.
What temperature difference counts as a serious hotspot?
Under the typical industry interpretation aligned with IEC TS 62446-3, a ΔT of roughly 10 °C or more against neighbouring cells is an abnormality worth scheduling repair for, and around 40 °C or more is treated as safety-relevant and immediate. Both readings assume the site was flown at ≥600 W/m² irradiance.
Can a hotspot be fixed without replacing the module?
Only when the cause is external — cleaning off hard soiling or removing a persistent shading source can eliminate the hotspot entirely. Hotspots caused by cracked cells or failing solder joints are inside the laminate and cannot be repaired in the field; those modules are monitored or replaced.
Related anomalies
Suspect hotspot on your site?
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ΔT figures and abnormality classes on this page describe the typical industry interpretation aligned with IEC TS 62446-3 — indicative engineering guidance, not normative text from the specification. Temperature differentials are only meaningful when captured at ≥600 W/m² irradiance (per the TS) and verified on site before repair work.