US scientists lately put totally different bifacial photo voltaic cells and modules by a sequence of assessments at elevated temperature, humidity, voltage and mechanical stress ranges. The assessments revealed a spread of light-induced and potential-induced degradation mechanisms that modules will seemingly endure within the discipline.
The photo voltaic trade’s adoption of bifacial cells, which is predicted to characterize greater than half of all silicon PV cells available on the market this yr, required just a few fast shifts in module design, centered on maximizing the quantity of sunshine that may be absorbed from the module’s rear facet. And modifications to the supplies utilized in a module, in addition to to the way in which it operates, can have an effect on its efficiency within the discipline. A number of efficiency points distinctive to bifacial applied sciences have been famous in analysis and within the discipline, and at the same time as bifacial turns into a mainstream PV know-how, understanding of those issues remains to be creating.
Scientists led by the US Nationwide Renewable Power Laboratory (NREL) have sought to realize a clearer image of those points. They put a spread of various bifacial module configurations by a sequence of assessments designed to imitate essentially the most excessive of situations the modules might expertise within the discipline. This sequence of “mixed accelerated stress testing” (C-AST) exposes modules concurrently to various temperatures, humidities and voltages, in addition to mechanical stress. NREL launched the C-AST testing protocol in 2020 and sees it’s a very important manner for the photo voltaic trade to know efficiency loss in numerous applied sciences.
This newest work put PERC cells in each glass-glass and glass-backsheet setups, and units encapsulated with POE and EVA, by a number of cycles of C-AST testing. The units examined had been “mini modules” every consisting of 4 156 mm x 156 mm cells. The outcomes can be found within the paper “Analysis of bifacial module applied sciences with combined-accelerated stress testing,” which was lately revealed in Progress in Photovoltaics.
The glass-glass modules had been proven to have many extra breaks within the grid fingers in comparison with these utilizing a backsheet – they counted on common 124 breaks in grid fingers for the glass-glass units, in comparison with 42 for glass-backsheet. The group attributes this to elevated rigidity of the glass.
“On the one hand, if the cell is nearer to the impartial airplane of the module laminate and the module is extra inflexible when uniformly encapsulated in glass, it could be anticipated that the stress on cells and cell cracking is diminished,” they stated. “However, this rigidity could also be a drawback resulting in elevated stress if the cell is impeded from deforming, for instance, as a result of pressure related to thermal coefficient of growth mismatch.”
The testing additionally discovered potential-induced degradation, which was highest in glass-glass modules encapsulated with EVA, and that comparable outcomes had been seen with cells examined within the discipline over an extended interval.
“The outcomes of C-AST present that use of bifacial cells and modules can improve the prevalence of failure modes reminiscent of grid finger breaks and PID,” they stated. “Consideration should due to this fact be given to the selection of packaging supplies and processes for his or her mitigation. C-AST indicated that that use of the POE and clear PVF backsheet diminished propensity for polarization-type PID in glass-glass modules.”
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