PID Effect of c‐Si Modules: Study of Degradation and Recovery to More Closely Mimic Field Behavior

Abstract

Recent research demonstrates several failure modes of photovoltaic modules operating under high electric potentials. In crystalline‐silicon modules, the predominant failure mode is potential‐induced degradation (PID), causing dramatic power losses in systems under high voltage and critical polarity. Environmental conditions highly influence the degradation behavior. The ability to reproduce field observation in the laboratory is challenging and not all stressors can be checked simultaneously. PID and its root cause are not fully understood, but we know several mechanisms are working simultaneously and at varying rates. The main mechanisms are degradation, characterized by ion diffusion and cell shunting, and recovery, driven by temperature, voltage, and potential. Most studies have focused on simulating module degradation using a constant set of parameters. However, field exposure to high voltage is variable, measured by the hour. In 2012, Nagel presented a module stability test with varying environmental conditions, notably temperature. To investigate PID remedies, this research develops a testing procedure that reproduces field observations while understanding that some modules do not degrade in real PV installations under high potentials. Conductive foil is applied to the front side of the module and voltage cycling is introduced to examine potential‐induced degradation and potential‐induced recovery behavior. The relationship between the two defines a PID stability criterion. Results show general PID sensitivity and suitable remedies for PID affected systems. PID recovery and protection solutions include applying recovery potential at night, and potential shifting, which regulates potential for the module string. This paper explores possible degradation mechanisms, recovery of module output power and PID stability criteria.

Investigating PID shunting in polycrystalline silicon modules via multiscale, multitechnique characterization

“…Shunting‐type PID can cause significant power loss and even total module failure . Potential‐induced degradation is believed to be caused by the diffusion of metal ions—largely, Na + from the front glass and encapsulation of the cell—that are driven into the silicon by the high voltage present . Currently, it is unclear whether sodium diffuses along stacking faults that are already present in the material or if sodium itself induces a stacking fault from a preexisting defect at the surface of the silicon .…”

From Modules to Atoms: Techniques and Characterization for Identifying and Understanding Device-Level Photovoltaic Degradation Mechanisms

“…Shunting-type PID can cause significant power loss and even total module failure [13]. PID is believed to be caused by the diffusion of metal ions-largely, Na + from the front glass and encapsulation of the cell-that are driven into the silicon by the high voltage present in arrays of PV modules [14][15][16][17][18][19][20][21][22][23][24]. Currently, it is unclear whether the sodium diffuses along stacking faults that are already present in the material or if the sodium itself induces a stacking fault from a pre-existing defect at the surface of the silicon [17].…”

Influence of crystal defect density of silicon wafers on potential-induced degradation (PID) in solar cells and modules

“…For p‐type c‐si modules, on a macroscopic level, many reasons have been proposed that can influence the PID, such as the temperature, humidity, voltage, the materials used during module manufacture and so on . Different methods have been applied to suppress the PID depending on those correlations, including the utilization of advanced materials like sodium‐free glasses, resistive encapsulants , the application of a reverse potential at night , and the improvement in the antireflecting coating (ARC) layer .…”