Failures in Testing

Why Module Failures Matter

Site acceptance testing was performed by Extel Energy, a member of the Kiwa Group, on a 12 MW rooftop site in Taiwan. The project used 340W half-cut 120-cell mono PERC modules and was commissioned in 2021. Routine drone infrared (IR) imaging revealed hot spots at the junction boxes for some modules, along with some activated bypass diodes. Upon further inspection of the site, Extel found some completely burnt junction boxes. Of the ~35,000 modules on site, ~700 had hot spots at the junction boxes visible in IR images, ~70 had bypass diodes activated and ~10 had extreme junction box burning.

The module manufacturer investigated and determined that these were all due to a soldering issue within the junction box. They updated their quality and process control to implement pull testing on their junction box soldering.

While replacements for the affected modules were provided by the manufacturer, the cost of labor to replace these modules and to diagnose the issue was not covered by the module manufacturer’s warranty. It is unclear if other modules will be affected by this failure mode in the future, given that they will experience natural temperature cycling in the field and its effects on soldering reliability.

PVEL has reported junction box related failure issues in every edition of the Scorecard since 2019. This problem still remains persistent both in the failures identified by PQP testing and on modules in the field.

Infrared image showing junction box hot spots (via the brighter dots on the modules), and one module with an activated bypass diode (via the bright rectangle on module located in the top row, fourth from the right).

An example of one of the ~10 modules with extreme junction box failure due to electrical arcing.

Failure Types

Safety Failure

Modules with safety failures may be hazardous to operate in the field. Throughout PQP testing, safe operation is determined via wet leakage testing using the IEC 61215 standard, which evaluates the electrical insulation of the PV module. BOMs not meeting the IEC 61215 minimum requirements for insulation resistance are included in the Scorecard’s failure statistics.

This module failed wet leakage testing before any stress testing. PVEL’s investigation revealed exposed metal within the junction boxes, due to a process control or workmanship issue.

Visual Inspection

Visual inspections identify issues that cause premature field failure. Modules are examined for delamination, corrosion, broken or cracked surfaces and other ‘major’ defects using the IEC 61215 criteria. BOMs exhibiting ‘major’ visual inspection findings are included in the Scorecard’s failure statistics.

This module broke during the static mechanical load testing portion of the mechanical stress sequence. Glass cracks originated under the module clamp, possibly due to improper frame adhesive application or poor frame profile design.

Power Degradation

Modules with power degradation failures may underperform in the field and ultimately result in financial losses for the asset owner. Although the PQP does not assign specific pass/fail thresholds for degradation, manufacturers may remove products from testing if power loss rates are below their or their customers’ expectations. The manufacturer typically changes BOMs or production processes, then submits new samples for retesting. Retests are clearly noted in PQP reports. BOMs that undergo a retest due to power loss are included in the Scorecard’s failure statistics.

This module degraded almost 13% following 2000 hours of damp heat causing, the module manufacturer to modify their BOM combination.

Electroluminescence

Modules undergo EL imaging throughout the PQP test sequences. No pass/fail thresholds are applied to EL images, but manufacturers may discontinue testing if the level of cell damage observed is higher than
anticipated. In these cases, new samples may be submitted for retesting. Retests are clearly noted in PQP reports. BOMs that undergo a retest due to EL image results are included in the Scorecard’s failure statistics.

From PVEL’s archive, this module arrived at PVEL with a shattered cell and the manufacturer removed it from testing. No modules in the 2023 Scorecard test population experienced EL image-based failures

Diode

PVEL evaluates the functionality of the module’s bypass diodes after TC and MSS testing. A failed bypass diode can no longer protect the module from hot spots, which could lead to fire risk. BOMs with non-functioning diodes in reverse and/or forward bias are included in the Scorecard’s failure statistics.

A junction box where PVEL removed the pottant to investigate a suspected diode or open-circuit failure

Key Takeaways

Click through the key takeaways.

Visual Inspection Failures
Safety Failures
Power Degradation Failures
Junction Box Failures

40% of manufacturers and 22% of BOMs had a failure found during visual inspection.

These failures included modules breaking during MSS, junction box lids falling off, burn marks, melted/failing connectors, delamination, and power labels peeling off or becoming illegible. (Note that HSS failures are not included in this statistic.)

23% of manufacturers and 18% of BOMs had a safety failure.

Most failures found during wet leakage testing occurred during the pre-stress stage, affecting 14% of manufacturers. This is a basic safety test that should be easily passed. These failures were also detected after TC, DH, PID and LETID testing.

17% of manufacturers and 9% of BOMs had a power degradation failure.

The prevalence of DH-related power degradation failures decreased significantly from the 2022 Scorecard, but PID-related power degradation failures increased. Power degradation failures from TC also occurred, caused by open circuits inside the junction box.

29% of manufacturers and 19% of BOMs had a junction box related failure.

Only one manufacturer suffered a failed bypass diode, but there were other catastrophic failures related to junction boxes including melted connectors, exposed wires, wet leakage failures traced to the junction box and failed junction box soldering.

PQP Failure Statistics

This graph shows the percentage of BOMs experiencing a failure in each test sequence of the PQP by failure type.

The most common type of failure is visual inspection major defect, followed closely by safety failures due to low insulation resistance.

Initial failures are those that were detected during characterizations prior to stress-testing.

HSS failures are not shown. Visit the HSS page to learn more.

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