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Consistency of Hipot Tests on Photovoltaic Modules

The field experience of HARREXCO AG is over 500MW/a and increasing. One of the most common questions which the company is confronted with, concerns the consistency of hipot values either expressed in electrical resistance or leakage current vs time or age. For instance, when a TF module laminated with PVB is in production and screened for hipot failure, the values will usually be more comfortable than 2 weeks after production. Most production and metrology engineers will firstly check that the equipment is working correctly, however it is common knowledge to them that PVB is hygroscopic and that the interface between foil and edge deleted substrate is suffering under initial corrosion. The corrosion and hygroscopy will be stronger in the beginning before consolidating and bringing constant hipot values. We strongly advise to only compare values of modules vs time on the condition of constant climate chamber storage. For instance, the module should be stored in a climate chamber, 1 month after initial manufacturing the module can be measured daily to review the drift in measurement values.