This document is intended to provide information to supplement the baseline testing defined in IEC 61215, which is a qualification test with pass-fail criteria. This document provides a standardized method for evaluating longer term reliability of photovoltaic (PV) modules and for different bills of materials (BOMs) that may be used when manufacturing those modules. The included test sequences in this specification are intended to provide information for comparative qualitative analysis using stresses relevant to application exposures to target known failure modes.

A significant constraint imposed was that the test duration was limited, recognizing that customers of the test will proceed with decisions before the test results are available, if the test takes too long. With this business-relevant limitation, some known failure modes cannot be accurately addressed, most notably those related to long-term ultra-violet light (UV) exposures. While failure modes related to UV stress are known to occur on both front and back side of PV modules, the testing time required to achieve a dose of UV stress that causes changes observed in the field during the module’s intended lifetime without overstressing is beyond the scope of this document. The included backside UV stress sequence gives increased confidence for some backsheets with regard to backside cracking, and a frontside UV stress sequence is not included at all, leaving gaps for failure modes, such as encapsulant discoloration, frontside backsheet cracking, frontside delamination, etc.

Other limitations of extended stress testing are described in Annex A. This document identifies vulnerabilities without attempting to gather the information needed to make a service-life prediction, which would require identifying failure mechanisms and their dependencies on all of the stresses. Annex B contains a brief background of the origins of the tests.

Out of scope for this document is its use as a pass-fail criterion. The same module deployed in two different locations may fail/degrade in different ways, so a single test protocol cannot be expected to simultaneously exactly match both results, and will depend upon where and how the product is deployed. Additionally, both false positives and false negatives may occur: due to the highly accelerated and extended nature of some of the stress exposures, the tests may cause some changes that do not occur in the field for some module designs, and degradation which is difficult to accelerate will be missed.

This document was developed with primary consideration for c-Si modules, as reflected in the targeted failure modes. However, the applied stresses are based on the service environment, and as such are relevant to generalized PV modules. Interpretation of the data resulting from these tests should always include the possibility that a design change may cause a new failure to occur. In particular, modules with different form factors (e.g. made without the standard glass frontsheet) may be found to differ in the way they fail. In every case, the data collected in this extended-stress test procedure is used as input to an analysis that may then identify the need for additional testing, to more fully assess module performance relative to the intended deployment conditions.