Scientists have fabricated and analyzed a new coating for semi-transparent photovoltaic glazing that reportedly delivers remarkable energy yield and low heat gain. Through outdoor experiments, the researchers also found that the glazing also provides satisfactory, high-quality indoor lighting conditions.
Researchers from Hong Kong University of Science and Technology and Hong Kong Polytechnic University have designed and investigated a new coated semi-transparent photovoltaic (CSTPV) glazing for building-integrated photovoltaic (BIPV) applications.
They explained that the novelty of their approach was to equip the glazing with a highly transparent passive radiant cooling coating. “Highly transparent passive radiant cooling paints are also now available, which allow solar radiation to pass through while retaining certain radiant-emotional characteristics,” she said. “The new radiant cooling material has the potential to mitigate the urban heat island effects associated with carbon emissions and reduce energy consumption.”
The experiment started with the fabrication of two samples, a CSTPV glazing and an uncoated glazing (STPV), using cadmium telluride PV modules. They also compared them to traditional and vacuum windows, one of which is a 6.3mm thick vacuum glazing and a 3.2mm thick single glazing.
“The key distinction between CSTPV and STPV is that CSTPV contains an additional cooling layer, while STPV works with a glazing surface without any coating,” the academics explained. “The STPV glazing, which amounts to 40% of the PV coverage, has a total thickness of 7.92 mm. The inside of the sample contains vacuum glazing, consisting of two layers: a 3.2 mm low-emission coated glazing on the front and a 3.2 mm transparent glazing on the rear.”
After constructing the samples, the team measured their electrical, thermal and optical properties and inserted the data into software simulations. They assumed that the glazing would be used in a south-facing hexagonal office with windows 1.5 m wide and high and a sill height of 0.8 m. The data used in the simulation came from Hong Kong . The results were also verified by outdoor experimental measurements.
“The results indicate that the CSTPV windows can significantly reduce heat gain by approximately 15% and achieve excellent electricity generation, with annual production approximately 3% higher than that of STPV windows,” the research group said.
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“All measured samples have correlated color temperature (CCT) values within the neutral light range and color rendering index (CRI) values above 96, demonstrating satisfactory high-quality indoor lighting conditions,” she added. “Photovoltaic vacuum glazing has increased CRI and CCT values, ensuring accurate light transmission without distortion.”
The results are presented in “The overall performance of a new semi-transparent photovoltaic window with passive radiant cooling coating – a comparative study,” published in Energy & Buildings.
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