Progress Update: Task Group 4
Task Group 4 is focused on testing diodes, which are essential to protecting the module during partially shaded conditions.
There is increasing evidence that shading or other non-uniformities in modules causes localized stress that can lead to overheating and, in some cases, to fires. Not only is this failure a serious safety issue, but there is some evidence that aging modules show increasing non-uniformity, implying that this may turn out to be a significant wear-out mechanism. The details of the stresses that lead to these failures are not well understood but may be related to shading (and reverse bias operation associated with shading or other situations), high temperatures, and lightning. Thermal cycling may also be important because thermal fatigue failures can cause stress on the diodes.
A New Work Item Proposal was submitted to IEC in June 2013 related to electrostatic discharge (ESD) testing. The test will apply forward bias, then reverse bias. Studies are attempting to replicate this failure mode in outdoor testing to understand the conditions that are needed for the test. The Task Group has been studying ESD failures in the United States using a human body model; and using a machine model in Japan. Failure analysis has been helpful in predicting failures in the field. Extended thermal tests and thermal cycling tests may be beneficial and studies are ongoing. Studies are also underway to determine quantitative criteria for evaluating thermal runaway of the diodes within the junction box. A New Work Item Proposal has been prepared.
Vivek Gade — Jabil, representing the Americas
Paul Robusto — Miasole, representing the Americas
Yasunori Uchida — JET, representing Japan
Volunteers representing other parts of the world are welcomed.