Single bypassed (1 substring)
One of the module's three substrings is being carried by its bypass diode, taking roughly a third of the module out of production. The key question is whether the cause is external (shading, soiling) or internal (cells, diode).
Thermal signature
One substring band — typically a third of the module along its internal wiring layout — reading uniformly warmer than the other two, with a straight boundary between them. The same clean one-third geometry repeated across a row usually points to row-to-row shading rather than module faults.
Typical ΔT
2–5 °C between the bypassed substring and the operating substrings (typical industry interpretation aligned with IEC TS 62446-3).
What causes it
- Persistent shading across one substring (row-to-row, vegetation, fixed structures)
- Hard soiling concentrated on one substring region
- A cracked or degraded cell forcing its substring into bypass
- A shorted bypass diode keeping the substring permanently off
Power impact
Roughly one-third of the module's output is lost while the diode conducts. Shading-driven bypassing comes and goes with the sun; a shorted diode or damaged cell makes the loss permanent until repaired.
Recommended action
Fix: next maintenance window
Check at the next maintenance window: rule out shading and soiling first (the RGB pair and time-of-day help), then test the bypass diode and inspect the substring's cells if the pattern persists in unshaded conditions.
Frequently asked questions
Is a bypassed substring a fault or normal operation?
The diode doing its job is normal; what it reveals may not be. Bypassing that tracks shadows is the system protecting itself. Bypassing that persists on a clean, unshaded module means a cell or diode problem that will not resolve on its own.
Why does the bypassed third look warmer, not cooler?
The bypassed substring stops exporting electrical energy, so the sunlight it absorbs is dissipated as heat instead — the same physics that makes offline modules and strings run warm. The mismatch cell that triggered the bypass can additionally show as a hotter point within the band.
Related anomalies
Suspect single bypassed (1 substring) on your site?
Fly the site, upload the thermal frames, and get every module graded against this taxonomy — severity-ranked, with flagged imagery and per-module locations. Quote your site size in seconds.
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.