Characterization of Electrical Parameters of Cracked Crystalline Silicon Solar Cells in Photovoltaic Modules

Abstract

In this work we investigate the characteristics of solar cells cracks in photovoltaic (PV) modules for understanding the extent to which the solar cell electrical parameters change due to cell crack degradation. The experimental investigation is performed on two custom nine-cell mini-modules of mono-and multi-crystalline silicon, respectively, where each solar cell in the module has a junction box, allowing individual and module level characterization. Results show that power loss caused by cell cracks is driven primarily by a reduction of the cell's maximum power point current, in particular B type cracks. C cracks also affect the short circuit current of the cells, whereas cells with combined B and C cracks show the most reduction of the short circuit current. Equivalent circuit diode model curve fitting and analysis of the light or dark I-V curves proved of limited used in analyzing degradation of cracked cells, as the model assumptions break down. However, a comparative analysis of dark and light I-V curves with a Suns-Voc curve was better suited for understanding the evolution of diode parameters on cracked cells for increasing levels of degradation.

Solar cell cracks within a photovoltaic module: Characterization by AC impedance spectroscopy

“…demonstrated that the decrease in the I sc was a specific feature in Mode C cells [ 61 ], and it was also confirmed in our study that I sc was decreased in the HC cells ( Fig 9A and Table 1 ), but not in the MC cells. Based on the combination of two independent observations (in [ 61 ] and this study), we infer that I mp reduction is a common signature in HC cells, and the crucial reduction of I sc could be attributed to the occurrence of an electrically inactive area within the HC cells. Furthermore, I mp reduction cannot be regarded as a distinguishing feature of MC cells.…”

“…However, the time constant in the cracked PV cells is confined to one side of the distribution ( Fig 8 ). 3) Significant evolutions of the electrical signatures ( P max , I sc , I mp , FF, and d- R s ) were observed in the cracked PV cells with electrically inactive regions, coinciding with the results reported in previous publications (in particular, in [ 61 ]). Therefore, we conclude that the evolution of these electrical characteristics, which were observed in this study, should be predominantly used to study cell cracks.…”

“…The I–V parameters of the individual PV cells within the PV module subjected to the nonuniform mechanical loading test ( Fig 3 ) were extracted from their I–V curves obtained under the illuminated and dark conditions (hereafter referred to as flash I–V and dark I–V , respectively); these are summarized in Fig 9 , and all p -values estimated by the Steel–Dwass test are added to Table 1 . As potential electrical signature for cell cracks, the critical reduction I mp in the Mode B and C cells laminated in the mini-PV modules has been recently reported [ 61 ]; however the authors did not mention the evolution in the Mode A cells. In this study ( Table 1 ), a significant decrease in the I mp was confirmed in the HC cells (Mode B and C cells), although no significant difference between the MC (Mode A cells) and NC cells was verified.…”

“…In fact, although this combined evolution was clearly confirmed in PV modules with a large power loss, it can be observed that the evolution of the dark I - V curve in the PV module with a small power loss was considerably smaller [ 26 , 65 ]. Moreover, it was suggested in their recent report that these evolutions have limitations when applied in cell-crack analysis [ 61 ]. This implies that microcracks could not be clearly detected by the evolutions of the dark I - V parameters (particularly, J 01 and J 02 ) when they occurred in the PV cells encapsulated in a PV module, as shown in Fig 12 .…”

“…So far, various electrical signatures attributed to cell cracks have been reported, such as a possible decrease in I sc owing to the development of an inactive cell area [ 19 , 22 , 26 ], an increase in R s [ 19 – 27 ], and a reduction in R sh / R p [ 30 , 32 – 35 ]. The J 02 elevation, which reflects the increase in carrier recombination occurring at the p-n junction, has been clearly demonstrated at the PV cell level [ 28 – 31 ]; however, at the PV module level, it may not necessarily apply to all cell-crack modes (including microcracks) [ 26 , 61 , 65 ], as discussed above. At the PV cell level, it is suggested that the evolution of these signatures (excluding carrier recombination and its relevant ones) depends on the progression of the crack modes, that is, the signatures (such as R s -elevation) would appear if the cracks reached the rear side from the front surface of the PV cells [ 30 , 31 ].…”