Evaluating the Durability of Balance of Systems Components Using Combined-Accelerated Stress Testing

David Miller, Greg Perrin, Kent Terwilliger, Joshua Morse, Chuanxiao Xiao, Bobby To, Sona Ulicna, Chun-Sheng Jiang, Laura Schelhas, Peter Hacke

Research output: NRELPoster


The degradation of photovoltaic (PV) balance of systems (BoS) components is not well-studied, but the consequences include: offline-modules, -strings, -inverters; system shutdown; arc-faults; and fires. A utility provider experienced a ~30% failure rate in their power transfer chain, attributed to branch connectors. Field-failed specimen assemblies were therefore examined, consisting of cable connector, branch connector and discrete fuse components. Unused field-vintage specimens are presently being examined using combined-accelerated stress testing (C-AST) to clarify the most influential environmental stressors as well as the effect of external mechanical perturbation. A benchtop prototype fixture was used to develop the perturbation capability for C-AST. The benchtop experiments were also used to develop the in-situ data acquisition of specimen: current, voltage, and temperature. A significant increase in operating temperature, ~100 deg C from ~40 deg C, and a different failure mode was observed immediately once periodic mechanical perturbation was applied. The current at failure was decreased from 35 A (with failure occurring in the fuses) to 15 A (failure at the male/female metal pin connection). After initial examination using X-ray computed tomography, the external plastic was machined away from failed specimens to allow failure analysis, including the extraction of the internal convolute springs for morphological examination (optical- and electron-microscopy). Chemical composition analysis included: energy-dispersive X-ray spectroscopy, differential scanning calorimetry, and Fourier transform infrared spectroscopy.
Original languageAmerican English
StatePublished - 2022

Publication series

NamePresented at the 49th IEEE Photovoltaic Specialists Conference (PVSC 49), 5-10 June 2022, Philadelphia, Pennsylvania

NREL Publication Number

  • NREL/PO-5K00-82764


  • balance of systems
  • branch connector
  • C-AST
  • DSC
  • durability
  • DuraMAT
  • FTIR
  • fuse
  • reliability
  • SEM
  • XCT


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