BIPV color characterization technology

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Swiss scientists have invented a new technique to characterize the color of BIPV panels. The method uses a fiber optic spectrometer to detect the color-characterizing signal.


Picture: Ecole Polytechnique Federales de Lausanne (EPFL), Solar, CC BY 4.0 DEED

Researchers from Switzerland have developed a new color characterization technique for building integrated photovoltaics (BIPV).

The method, known as a large area illumination (LAI) colorimeter, uses a fiber optic spectrometer and large area illumination. In this way, it can overcome the problems of existing color characterization techniques, which are difficult to accurately determine color when behind a transparent layer, such as a solar photovoltaic laminate.

"We are currently working on enhancing the method by testing light sources and designing a portable device to characterize the color of photovoltaic building-integrated components," corresponding author Ledro Borhablock toldpv magazine."We are working on light sources, and calibration procedures, and coming up with a suitable portable tool."

The new LAI method uses a fiber optic spectrometer to detect the color-characterizing signal. It is placed at a 45 degree angle relative to the samples and 7mm above their back. Since the measurement depends on the lightning, the illuminated area must be larger than the measurement point. To achieve this, the researchers used a diffuse light with a visible spectrum signal similar to D65, which is roughly equivalent to the average light at noon in Western and Northern Europe.

To prove the utility of the new method, the scientists measured the difference in color measurements between colored foils without glass and colored foils with glass thicknesses of 3.2mm and 6.4mm. They made eight different types of foil, from highly reflective white to low reflective clay. They then compared the differences detected by the new method with those detected by existing color characterization techniques-scanners, portable colorimeters, and integrated spherical spectrometers.

LAI Colorimeter Components

Picture: Ecole Polytechnique Federales de Lausanne (EPFL), Solar, CC BY 4.0 DEED

They emphasized: "When the sample under investigation is placed in the aperture of an integrating sphere or colorimeter, these devices can produce accurate reflectance measurements." "In the case of integrated photovoltaic modules, the surface layer is based on glass a few millimeters thick, which produces measurement artifacts. The above-mentioned device sends an optical probe through its aperture to process the signal. Due to the thickness of the transparent layer, a decrease in reflectivity is observed."

According to their research results, when using the LAI method, the signal only slightly decreased when the sample was changed from free foil to glass foil. In contrast, for the same sample, the reflectivity of the integrating sphere spectrometer and the portable colorimeter is much reduced. For example, while the commercial portable colorimeter measured the color change at 57, the LAI result was only 3.

In addition, the scientists also found that standard scanners cannot accurately assess the color of photovoltaic modules because the light is trapped in the glass. "Measurements comparing the characterization techniques show that the LAI colorimeter is much better than commercially available solutions in terms of accuracy," the research group emphasized.

Its findings are published in "Accurate color characterization of solar photovoltaic modules for building integration," published in the Journal 《Solar energy.These scientists are from the Federal Institute of Technology in Lausanne (EPFL) and the Swiss Center for Electronics and Microtechnology (CSEM).

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