How does textured glass perform in BIPV?

Researchers from Poland evaluated how textured glass used as the front cover for building-integrated photovoltaic materials affects performance. They found that power output is 5% lower compared to components based on traditional glass, with reflection parameters reaching up to 88% in the visible light spectrum.

Scientists from John Paul II Catholic University of Lublin, Poland, analyzed the optical and electrical parameters of textured glass in building-integrated photovoltaic (BIPV) systems. They found that this type of glass can significantly impact photovoltaic generation and increase light reflection. “In urban installations, an important parameter is the low reflectance value, which reduces light reflection that could blind drivers,” said Paweł Wanicki, the lead author of the study. “As BIPV becomes increasingly popular, expanding its installation on façades, building walls and various types of glass, its aesthetic aspects have become one of the key parameters.”

Textured glass is made by heating glass sheets to soften them, then shaping them through engraved rollers. In their study, the researchers used two types of commercially available textured glass sheets. The first sample has a surface morphology with a height variation of 45 micrometers, while the second sample falls within a range of 10 micrometers. Sample 1 features a regular pattern with a characteristic diameter of 400 micrometers, whereas Sample 2 has an irregular pattern with features ranging from 50 micrometers to over 1 millimeter.

In total, three modules were built—one with sample 1, another with sample 2, and the last with reference clear glass. In all cases, the laminate foil was placed between the glass and the cell, and the power delivered by the package was measured to be 2.89 W. The bare cell was measured to have a fill factor of 71%, an open circuit voltage of 0.699 V, and a short circuit current of 5.83 A.

"According to calculations, the direct solar energy absorption values of the reference sample are nearly 13 times and 5 times lower than those of samples 1 and 2, respectively," the researchers said. For both textured samples, the transmittance in the near-infrared (NIR) region is significantly lower than that of the reference glass. Furthermore, for the sample with a regular surface pattern (Sample 1), the transmittance in the infrared (IR) region is slightly lower compared to the irregular sample (Sample 2). The measured reflectance in the visible (VIS) region is significantly lower: 8.5 times lower for sample 1 and 1.6 times lower for sample 2. "

As for electrical performance, the reference cell measured a maximum power of 2.86 W; sample 1 had a power of 2.79 W, and sample 2 had a power of 2.74 W. The fill factor, open circuit voltage, and short circuit current of the reference module were 72.4%, 0.73 V, and 5.425 A, respectively. Sample 1 had a voltage of 72.9%, 0.727 V, and 5.27 A, while sample 2 had a voltage of 73.2%, 0.728 V, and 5.143 A.

The analysis showed that the power yield in modules using textured glass was 5% lower and the reflection parameters were up to 88% higher in the VIS region compared to modules based on conventional glass.

"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 photovoltaic modules is profitable," the academics concluded. In addition, long-term exposure to infrared radiation accelerates material degradation, thus affecting the stability and lifetime of photovoltaic modules.

Their findings were published in "Textured Glass in Architectural Photovoltaic Applications," published in Clean Engineering and Technology. In addition to the John Paul II Catholic University in Lublin, Kwanicki is also associated with Polish photovoltaic supplier ML Systems.

In the application of BIPV projects, especially those located in cities, construction designers are also very concerned about the light reflection problem of photovoltaic building materials. For these BIPV projects with strict requirements on light reflection, the surface of the power generation glass can be frosted to achieve a lower light reflection effect.