Scientists from Poland's John Paul II Catholic University of Lublin have analyzed the optical and electrical parameters of textured glass in building integrated photovoltaic (BIPV) systems and have found that this kind of glass may considerably affect PV power generation and increase light reflection.
“In the case of installations in urban spaces, an important parameter is the low reflectance value and, consequently, the reduction of light reflections that can blind drivers,” said the research's lead author, Paweł Kwaśnicki. “Since BIPV is becoming increasingly popular, expanding the scope of installation on facades, building walls and various types of glazing its aesthetics aspects become one of the key parameters.”
Textured glasses are made by heating glass sheets, softening them, and then passing them between engraved rollers. For his research, the academics used two commercially available textured glass sheets. The first sample had a surface topography with height differences of 45 μm, while the second sample was in the range of 10 μm. Sample 1 had a regular pattern, with features with a 400 μm diameter, while in the case of sample 2, the pattern was irregular, with objects ranging from 50 μm to over 1 mm.
Overall, three modules were constructed—one with sample 1, the other with sample 2, and the last with reference clear glass. In all cases, a lamination foil was put between the glass and the cell, which measured 2.89 W encapsulated. The fill factor of the bare cell was measured at 71%, its open circuit voltage 0.699 V, and its short circuit current at 5.83 A.
“From the calculation, the value of solar direct absorptance for the reference sample was almost 13 and 5 times lower than samples 1 and 2, respectively,” the researchers said. “For both textured samples, transmittance was significantly lower in the near-infrared (NIR) region than the reference glass. Furthermore, for the sample with a regular surface pattern (sample 1), slightly lower transmittance in the infrared (IR) region was noticed in comparison to the nonregular one (sample 2). Significantly lower reflection in visible light (VIS) region was measured for: 8,5x lower for sample 1 and 1,6x for sample 2.”
As for electrical performance, the reference cell measured a maximum power of 2.86 W; sample 1 had 2.79 W, and sample 2 had 2.74 W. Fill factor, open-circuit voltage, and short-circuit current for the reference module were 72.4%, 0.73 V, and 5.425 A, respectively. Sample 1 had 72.9%, 0.727 V, and 5.27 A, while sample 2 had 73.2%, 0.728 V, and 5.143 A.
The analysis showed that power yield in the modules using texturized glass could be up to 5% lower compared to modules based on conventional glass, with reflection parameters being up to 88% in the VIS region.
“Since infrared radiation has several negative effects on silicon photovoltaic cells, including limited energy absorption, thermal effects leading to reduced efficiency, material limitations, and optical losses due to carrier recombination – the application of textured glass in PV module is profitable,” concluded the academics.” Additionally, long-term exposure to IR radiation can accelerate material degradation, which affects the stability and lifetime of PV modules.”
Their findings were presented in “Texturized glass in the application of architectural photovoltaics,” published in Cleaner Engineering and Technology. In addition to the John Paul II Catholic University of Lublin, Kwaśnicki is affiliated with Polish PV supplier ML System.
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