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The new multifunctional PV window concept aims to produce electricity while providing over-heating protection for better indoor thermal and visual comfort. It consists of an insulating glazing unit with bifacial crystalline silicon solar cells strips and embedded venetian blinds that act as reflectors for the rear side of the cells.
A research group coordinated by the Netherlands Organisation for Applied Scientific Research (TNO) has fabricated a multifunctional PV window concept that is aimed at producing electricity while providing over-heating protection for better indoor thermal and visual comfort.
“The ZIEZO window consists of a unique insulating glazing unit (IGU) with bifacial crystalline silicon solar cells strips and embedded Venetian blinds,” the research’s lead author, Simona Villa, told pv magazine. “When the blinds are deployed they will act as a reflector, redirecting part of the sunlight on the back-side of the bifacial cells, thus boosting the energy generation. To the best of our knowledge, no bifacial PV window for building integration exists on the market to date.”
The system was presented in the paper “Outdoor Performance Analysis of Semitransparent Photovoltaic Windows with Bifacial Cells and Integrated Blinds,” published in RRL Solar, where its authors explained that the system is an evolution of a window technology developed and patented by Dutch glass company Pilkington without the solar cells.
The novel solar window can operate in a “no boost” mode when the blinds are stored in the top storage box or a the “partial boost” mode when the blinds are deployed but kept open. Moreover, it can work in the “maximum boost” mode when the sunlight toward the inside of the room is blocked. Users can automatically adjust the blinds’ position to prioritize either PV yield or thermal and visual control.
The research group, which also comprised scientists from Pilkington itself, deployed 12 small-size demonstrators at the outdoor research facility SolarBEAT, with variations in terms of PV cell types, coverage ratios, and types of Venetian blinds. Additionally, 6 real-size windows were also installed at the office building of Pilkington headquarters in Enschede, Netherlands.
“One full year of outdoor monitoring showed the great potential of this BIPV innovative product,” Villa stated. “The instantaneous energy boost on sunny days can go up to 25%, with the most reflective blind. If we look at the daily average over the total measurement period, the boost is around 13%. The orientation and tilt angle of blinds of course have a significant effect on the results, as well as the irradiance conditions and the sun position.”
The results gathered at the SolarBEAT test site were in line with the results obtained with the bigger ZIEZO windows installed at the Pilkington office in Enschede.
“It is good to realize that the power density of this BIPV window is roughly 100 W/m2, with transparency of 40%, and the boost given by the reflection of the blinds is added on top of this,” Villa went on to say. “This makes this semi-transparent BIPV product extremely competitive, with a power rating comparable to colored opaque PV solutions. The glass company Pilkington will now try to bring the product to the market.”
“We are also looking at the other benefits of this product, such as the visual comfort and thermal control inside the building given by the active shading device,” Villa said, referring to the future directions of the group’s work.
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