Sequential Application of Static and Dynamic Mechanical Stresses for Electrical Isolation of Cell Cracks

The static mechanical load test (SMLT; IEC 61215 series) and the dynamic mechanical load test (IEC TS 62782:2016) are widely used in the industry to mimic the mechanical stresses in the installation and operation of PV modules. The DMLT is often followed by thermal cycling and humidity-freeze cycling; the DMLT-TC50-HF10 sequence appears in the CSA/ANSI C450 quality-assurance-testing standard published in 2018. The EL images of field-stressed modules, however, show a higher degree of electrical isolation of cell cracks ("islanding") than what is observed in modules stressed by SMLT or DMLT-TC50-HF10. Such qualitative difference raises questions on the validity of post-MLT power measurements. We investigated different MLT variations of the DMLT-TC50-HF10 sequence and found that a sequential execution of SMLT and DMLT is effective in creating and then electrically isolating the cell cracks.