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Swiss scientists have created a new technique to characterize the color of building-integrated photovoltaic (BIPV) panels. The method uses a fiber optic spectrometer to detect color characterization signals.
Swiss researchers have developed a novel color characterization technique for building-integrated photovoltaic (BIPV) systems.
The method, called large area illumination (LAI) colorimeter, uses a fiber optic spectrometer and large area illumination. This can overcome the problems of existing color characterization techniques, which have difficulty accurately determining color when it is behind a transparent layer, such as a solar photovoltaic laminate.
“We are currently working on improving the method by testing light sources and designing a portable device to characterize the color of BIPV modules,” corresponding author Alejandro Borja Block explains to pv magazine . “We are studying light sources and calibration procedures, and proposing a suitable portable tool.”
The novel LAI method uses a fiber optic spectrometer to detect color characterization signals. It was placed at an angle of 45 degrees with respect to the samples and 7 mm above their rear face. Since measurements depend on lighting, the illuminated area must be larger than the measurement point. To do this, the researchers used a diffuse lamp with a visible spectrum signal similar to D65, which roughly corresponds to the average midday light in western and northern Europe.
To demonstrate the usefulness of the new method, the scientists measured the differences in color measurement between color sheets without glass and with glass thicknesses of 3.2 mm and 6.4 mm. They did it with eight different types of sheets, from white ones with high reflectance to clayey ones with low reflectance. They then compared the differences detected by the new method with those detected by existing color characterization techniques: a scanner, a portable colorimeter, and an integrated sphere spectrometer.
“These devices produce accurate reflectance measurements when the investigated samples are placed in the aperture of the integrating sphere or colorimeter,” they stressed. “In the case of integrated photovoltaic modules, the front layer is based on glass several millimeters thick, which creates measurement artifacts. The mentioned devices send a light probe through its opening to process the signal. A reduction in reflectance is observed due to the thickness of the transparent layer.”
According to their conclusions, when the LAI method is used, the signal only decreases slightly when changing the sample from free sheet to glazed sheet. In comparison, and with the same samples, a large reduction in reflectance is observed with the integrated sphere spectrometer and the portable colorimeter. For example, while the commercial portable colorimeter had measured color change at 57, the LAI results were only 3.
In addition, scientists also discovered that standard scanning machines cannot accurately evaluate the colors of photovoltaic modules because light is trapped in the glass. “Measurements comparing characterization techniques indicate that the LAI colorimeter performs much better than solutions available on the market in terms of accuracy,” highlighted the research group.
Their findings were presented in “ Accurate color characterization of solar photovoltaic modules for building integration ,” published in Solar Energy . The scientists come from the Federal Polytechnic School of Lausanne (EPFL) and the Swiss Center for Electronics and Microtechnology (CSEM). |
