Abstract
Transparent energy-harvesting windows are emerging as practical building-integrated photovoltaics (BIPV), capable of generating electricity while simultaneously reducing heating and cooling demands. By incorporating spectrally-selective diffraction gratings as light deflecting structures of high visible transparency into lamination interlayers and using improved spectrally-selective thin-film coatings, most of the visible solar radiation can be transmitted through the glass windows with minimum attenuation. At the same time, the ultraviolet (UV) and a part of incident solar infrared (IR) radiation energy are converted and/or deflected geometrically towards the panel edge for collection by CuInSe2 solar cells. Experimental results show power conversion efficiencies in excess of 3.04% in 10 cm × 10 cm vertically-placed clear glass panels facing direct sunlight, and up to 2.08% in 50 cm × 50 cm installation-ready framed window systems. These results confirm the emergence of a new class of solar window system ready for industrial application.
Highlights
All-inorganic photovoltaic solar window systems have been developed, which employ photonic microstructures represented by spectrally-selective transparent diffractive elements placed into direct vicinity of planar luminescent media embedded into glass structure
Experimental results have shown that the demonstrated window systems possess the potential to replace or complement conventional luminescent solar concentrator designs in building-integrated photovoltaic systems, making them suitable for use in future buildings with net-zero energy balance
Framed solar windows of glass panel size 50 cm × 50 cm have been shown to generate up to 2.43 W and up to 3.64 W of electric power output, corresponding to the power conversion efficiency of up to 2.08% measured in field conditions involving CuInSe2 solar modules working at their real operating cell temperature in excess of 40 °C
Summary
The effects of direct lightwave deflection provided by diffractive microstructures were shown experimentally to substantially improve the energy-harvesting efficiency of planar glass-based transparent concentrators, which employed other light deflection mechanisms, including luminescence and multiple scattering. This was confirmed by direct measurements of electric power outputs in multiple samples performed in both the lab conditions and in multiple outdoor sunlight-illumination experiments. Haze measurement results obtained from flat-glass (not containing any microstructured elements) regions of our energy-harvesting window panels were as follows: typically between 3.9–4.2% in systems using low-haze interlayers, and between 8–12% in systems of same luminophore concentration as used in 100 mm × 100 mm samples. Energy harvesting improvements due to using perimeter-mounted diffraction gratings were observed clearly in samples of this size, as has been evidenced by the short-circuit current (Isc) readings increasing from about 140 mA (the samples of Fig. 5(b,e)) up to >2 10 mA (the sample of Fig. 5(f)), in similar weather conditions, and for the same open-circuit voltages of around 40 V
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