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Mechanical Stress Sequence

Mechanical Stress Sequence

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The PQP’s Mechanical Stress Sequence (MSS) surpasses IEC/UL certification for more thorough module and cell durability testing. It detects potential glass and cell cracking vulnerabilities through static load testing. Dynamic mechanical load and climate chamber assess power output reduction due to cell cracks, crucial for sites facing extreme weather such as heavy snow and high winds. MSS also evaluates how cell damage from manufacturing defects, transportation, handling or environmental stresses will impact module performance.

Key
Takeaways

95% of BOMs completing MSS had < 2% power loss.

The power loss following MSS was quite similar for BOMs produced in 2023 and in 2022 ( see the Power Degradation graph below for more ). However, power loss from this test is expected to increase in the coming year with the test changing from traditional fixed-tilt mounting to more aggressive tracker or corner mounting.

Test Result Spotlight

While glass and cell cracking are key module durability concerns, frame fatigue can also be an issue. In this example, the module’s mounting hole was ripped out of the frame during tracker-mounted ± 1800 Pa SML and DML. This failure mode could result in modules becoming dismounted from racking during high wind events, and is likely due to using a thinner frame flange to save cost. This type of defect is typically not replicated during standalone SML or DML testing, but has been seen on multiple BOMs subjected to the PQP’s combination of SML and DML.

Test Result Spotlight

The module frame failed following static mechanical load testing at ±1800 Pa and dynamic mechanical load for 1000 cycles at ±1000 Pa. The failure occurred on DML cycle #962.

Power Degradation of MSS BOMs

Power degradation chart for mechanical stress sequence

Before 2019, all results are only DML+TC50+HF10. 30% of 2019 results and all post-2019 results are SML+DML+TC50+HF10. Outliers with >10% degradation are not shown. In some cases, these cause a significant reduction in the mean.

View Box Plot Interpretation Guide

A case study on why MSS is important, what PV module materials are assessed, and the test procedure can be found here on kiwa.com/pvel.

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