Equating damp heat testing with field failures of PV modules

Damp heat testing is an integral part of the module qualification test sequence. To develop accelerated stress tests for module wear out mechanisms, laboratories have been extending the damp heat tests beyond the qualification level. This paper examines the failure analysis of modules exposed to extended damp heat testing and concludes that there is no evidence that the dominant observed failure mode occurs in fielded modules. Analysis of moisture ingress shows that the damp heat test exposes modules to much higher levels of moisture than will ever be experienced in the field. Humidity driven field failures instead often appear to occur in combination with delamination of the encapsulant, suggesting interfaces should be pre-stressed using UV and/or humidity-freeze before applying damp heat.