Thermal and Mechanical Fatigue Including Vibration: Task Group 2
Task Group 2 is focused on thermal and mechanical fatigue.
Failures of cell interconnects and solder bonds have been identified as a key cause of long-term failure of PV modules. The primary stresses affecting the failure rates have been shown to be thermal and mechanical. This task group will study how to induce and quantify these failures.
There is a consensus that 200 thermal cycles do not adequately stress a module, so discussion has focused on how to increase the amount of stress without extending the test for a prolonged time. Dynamic mechanical load (DML) and faster cycling are two options that have been discussed.
Experiments to elucidate the effect of DML on interconnect fatigue failure have been conducted at NREL and the results presented and published (2013 IEEE PVSC). This work demonstrated that DML is effective in evaluating ribbon fatigue durability and may be used to comment on the associated fatigue life given a specific service environment. Work is on going to correlate the equivalency between DML and thermal cycles. DML is not able to evaluate solder bond fatigue durability; therefore there is current interest in creating a more efficient thermal cycling sequence and a higher resolution method to evaluate solder bond fatigue failure.
IEC 62892-1 "Comparative testing of PV modules to differentiate performance in multiple climates and applications—Part 1: Overall test sequence and method of communication," is being developed by IEC Technical Committee 82. The first committee draft is being reviewed. The general concept being proposed for inclusion in the IEC Comparative Testing Standard was presented at the SOPHIA workshop and at the 40th IEEE PVSC:
Wohlgemuth, J. S. Kurtz, T. Sample, M. Kondo, and M. Yamamichi "Development of Comparative Tests of PV Modules by the International PV QA Task Force." IEEE PVSC, Denver, CO. June 2014.
Nick Bosco — National Renewable Energy Laboratory, representing the Americas
Tadanori Tanahashi — Espec, representing Japan
Simon Xiao — Trina Solar, representing China.
Volunteers representing other parts of the world are welcomed.