Thermal cycling

Thermal cycling is the repeated heating and cooling of modules from day and night and from seasonal changes, and it puts thermomechanical stress on module components. It fatigues cell interconnect ribbons and solder joints, which drives cell interconnection failure. Uneven thermal expansion inside the module helps cell cracks form and grow during operation. In the junction box, day-night and seasonal cycling can loosen mechanical contacts, leading to junction box failure. Combined with other stresses such as snow loads or partial shading, thermal cycling can break weakened cell or connection parts, and this damage can end in burn marks. Hot and dry sites can see module temperature swings of up to 40-50°C in one day. In hot and humid climates, frequent cloud passages cause many smaller temperature changes, and these were found to stress solder joints more than the larger day-night cycles in deserts. To limit damage, reduce thermal stressors that drive progression and use site temperature data to decide whether modules need extended thermal cycling tests, because the 200 cycles used in standard qualification have been reported as too few.

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• sentence 8: support check: partial - The mitigation to reduce thermal stressors (u14), the use of temperature monitoring data to decide on extended cycling (u30), and the 200 cycles reported as inadequate (u24) are all present, but u24 says it is unclear how many cycles are needed and u30 mentions IEC 62892 temperature monitoring data, so 'site temperature data' and the causal 'because' framing are slightly stronger than the passages. -->