Power loss through decorative elements in the front glazing of BIPV modules
Printed module front covers can be designed to mask the geometry of solar cells for Building-Integrated Photovoltaics (BiPV). Such prints reduce the transmittance of the module front layer, which decreases module power. We performed transmittance measurements with large-area and small-area measurement equipment (220 mm / 620 mm integrating sphere) on different samples and find measurements applying small-area illumination to result in lower transmittance ( = 3.1abs% at 40% coverage) due to lateral losses in the samples. By measuring the power of modules with different design prints we find that the results do not correspond to transmittance measurements of the glass covers alone, even if a large-area transmittance measurement setup is used ( = 16%abs at 40% coverage). We attribute the differences between optical and electrical measurements to module internal reflection, optical coupling of the solar cell, partial transmittance by coatings and diffuse scattering of decorative prints. Differences increase with the share of coated glass area. We perform electrical and LBIC measurements on modules with printed and unprinted reference glass covers and calculate the effective transmittance. Short circuit currents calculated by spatial integration of LBIC results are in good agreement with results from ISC measurements. We predict the effective transmittance for arbitrary prints based on selected ISC measurements and find them to be in good agreement to measurements. In conclusion, we find transmittance measurements on printed glass alone to be insufficient to predict the optical power losses as they overestimate the optical loss.