Solar Lattice

FailureMode

Bypass Diode Failure

ID
fm:bypass-diode-failure
IRI
https://solarlattice.org/kb/fm/bypass-diode-failure
Status
active
Category
Modules

A bypass diode usually fails in one of two states: shorted or open. A shorted diode keeps the module voltage and output permanently low. It can also pull the other modules in the string away from their maximum power point. An open diode often shows no loss at all until the module is mismatched or shaded. Then cells can be driven into reverse bias, which causes hotspots, burn marks, arcing or fire. Common causes are lightning or static discharge, thermal runaway, undersized or reversed diodes, poor connections, mechanical stress, junction box corrosion and frequent partial shading. To find it, look for low open-circuit voltage or odd IV curves, scan with an IR camera, and check the junction box and module for burn marks. To confirm, test the diode directly with a multimeter in diode or resistance mode. Affected modules are usually replaced, although the diode itself can be replaced. Any module left in service should be watched closely, and the string should be checked after the repair. Reducing partial shading helps bypass diodes last longer.

Claims

affects

c1 drafted · lead Bypass diode

c2 drafted · lead Junction box

Heat from a failed diode can deform or burn the junction box.

caused_by

c3 drafted · lead Partial shading

Frequent shading makes the diodes conduct more often and run hotter, which shortens their life.

c4 verified · fact Lightning strike

verified by: joshuahamsaverified on: 2026-10-16

c5 drafted · lead Electrostatic discharge

Schottky bypass diodes are very sensitive to static high-voltage discharge.

c6 verified · fact Thermal runaway

Happens when the diode cannot dissipate the heat produced as it switches between operating modes.

verified by: joshuahamsaverified on: 2026-10-16

c7 drafted · lead High operating temperature

Failure rate rises with diode operating temperature. Failures are more common in hot climates.

c8 verified · fact Mechanical stress

verified by: joshuahamsaverified on: 2026-10-16

c9 drafted · lead Manufacturing defect

Examples are a wrong specification, a non-functional diode, or a diode that was reversed or wrongly connected during assembly.

c10 drafted · lead Installation error

The diode may be mounted the wrong way round or not properly connected.

c11 drafted · lead Undersized component

An undersized diode cannot withstand continuous current flow.

c12 drafted · lead Junction Box Failure

Corrosion inside the junction box can weaken the diode.

review note: reviewer 2026-10-19: target stressor:junction-box-corrosion merged into fm:junction-box-failure; re-verify against the cited passages

c13 drafted · lead Component aging

presents_as

c14 drafted · lead Low module open-circuit voltage

Points to a short-circuited diode.

c15 drafted · lead Hotspot in IR image

review note: support check: partial - Passages say IR thermography might reveal diode activations or hotspots, but not definitively that failure presents as an IR hotspot.

c16 drafted · lead Burn marks

c17 verified · fact Deformed or burnt junction box

verified by: joshuahamsaverified on: 2026-10-16

c18 drafted · lead Bypassed substring

review note: support check: partial - Substring loss appears only in the overview impact-factor list, without further description.

c19 verified · fact Shifted maximum power point

A shorted diode can move the operating point of the other modules in the string or array.

verified by: joshuahamsaverified on: 2026-10-16

c20 drafted · lead Uneven cell heating

detected_by

c21 drafted · lead Multimeter diode test

Described as the best way to tell whether a diode is shorted or open.

c22 drafted · lead IV curve tracing

c23 drafted · lead Open-circuit voltage measurement

c24 verified · fact Infrared thermography

verified by: joshuahamsaverified on: 2026-10-16

c25 drafted · lead Visual inspection

Look for burn marks.

c26 verified · fact Junction box inspection

verified by: joshuahamsaverified on: 2026-10-16

mitigated_by

c27 drafted · lead Module replacement

In practice, the whole module is usually replaced.

c28 verified · fact Bypass diode replacement

verified by: joshuahamsaverified on: 2026-10-16

c29 verified · fact Avoiding partial shading

verified by: joshuahamsaverified on: 2026-10-16

c30 verified · fact Post-repair verification

verified by: joshuahamsaverified on: 2026-10-16

c31 drafted · lead Close monitoring

For affected modules that are not replaced.

c32 verified · fact Bypass diode functional check

Check that the diodes activate when hotspots or burn marks are found.

verified by: joshuahamsaverified on: 2026-10-16

leads_to

c33 verified · fact Module Hotspot from Cell Damage

With an open diode and a mismatch, current is forced through the affected cell string, which heats it and drives the cells into reverse bias.

verified by: joshuahamsaverified on: 2026-10-16review note: support check: partial - Open diode with mismatch causing heat and hotspots is stated, but the detail of driving cells into reverse bias with current forced through the string is a mix across passages.

c34 verified · fact Junction Box Failure

verified by: joshuahamsaverified on: 2026-10-16

c35 verified · fact Arc fault

Open-circuit diodes can lead to arcing and, in some cases, fire.

verified by: joshuahamsaverified on: 2026-10-16

c36 verified · fact Leakage current

Follows when the junction box or backsheet has burnt through.

verified by: joshuahamsaverified on: 2026-10-16

time_to_onset

c37 drafted · lead ≤ 10 YR

Conditions: Bypass diode failures show up mainly within the first ten years after a PV installation.

review note: support check: partial - Passages say failures are primarily revealed during the first ten years, supporting roughly 10 years as an upper window, not a precise onset time.

Referenced by

Data