Thermal and Mechanical Fatigue Including Vibration: Task Group 2

Task Group 2 examines how thermal and mechanical fatigue impact fielded PV modules, and how standardized tests should best apply these stresses to reproduce field-observed behavior.

Progress Update

Over the years, failures of cell interconnects and solder bonds were observed to be a cause long-term failure of PV modules. The primary stresses affecting the failure rates are thermal and mechanical. This task group has studied how to induce and quantify these failures.

There was a consensus that 200 thermal cycles may not adequately stress a module, so discussion focused on how to increase the amount of stress without extending the test for a prolonged time. Finite element modeling (FEM) has quantified the number of thermal cycles in the chamber needed to simulate a lifetime in the field. FEM analyses on the rate of solder fatigue damage has revealed that the number of thermal cycles (required for an equivalent exposure to an envisioned climate) would be significantly reduced by the increase in the maximum cycle temperature. Moreover, since the acceleration factor between the thermal cycling test with the increased maximum temperature and outdoor service was (nearly) identical even when some variables (such as laminate layer thicknesses and thermomechanical properties of materials) were changed, it is expected that this test protocol can apply the adequate thermomechanical stress to PV modules with various designs. Publications were created to detail the relationship between maximum temperature in thermal cycling, number of cycles, and equivalent exposures in different climates.

Standards Activities

Based on the above FEM studies, a New Work Item Proposal was introduced into the IEC standards process in 2015.  IEC working group two and PVQAT task group 2 provided input to the document and eventually achieved consensus.  The document was published as IEC 62892 ED. 1 "Extended Thermal Cycling of PV Modules - Test Procedure" in 2019. The standard provides options for reducing the time for the thermal cycling test by increasing the maximum temperature and/or increasing the sample size being tested.

Related Resources

IEC 62892 ED1 "Extended Thermal Cycling of PV Modules - Test Procedure"

Climate Specific Thermomechanical Fatigue of Flat Plate Photovoltaic Module Solder Joints (2016)
Authors: Bosco, N., Silverman, T. J., and Kurtz, S.
Journal: Microelectronics Reliability

The Influence of PV Module Materials and Design on Solder Joint Thermal Fatigue Durability (2016)
Authors: Bosco, N., Silverman, T. J., and Kurtz, S.
Journal: IEEE Journal of Photovoltaics

Causes of Degradation Identified by the Extended Thermal Cycling Test on Commercially Available Crystalline Silicon Photovoltaic Modules (2017)
Authors: Kawai, S., Tanahashi, T., Fukumoto, Y., Tamai, F., Masuda, A., and Kondo, M.
Journal: IEEE Journal of Photovoltaics

Task Leaders

Task group 2 is currently inactive.  If you are interested in leading an activity in this area, please contact us for further information.