The invention of a bifacial PV system capable of keeping homes cooler

The cooling of buildings is a process that consumes a lot of energy. According to the IEA (International Energy Agency), air conditioning accounts for nearly 10% of the energy bills of households and businesses worldwide. While efforts to decarbonize the residential sector are intensifying around the globe, an innovation from Hong Kong could change the game. Researchers from the City University of Hong Kong have developed a revolutionary smart glazing solution. This new system, called TC-BiPV (Thermochromic Bifacial Photovoltaic), consists of a bifacial solar panel and a thermochromic layer. This combination allows for electricity generation while passively regulating the indoor temperature of buildings.

## An innovative multilayer structure

The material used for the thermochromic layer is a hydrogel. This choice is motivated by its low cost, low toxicity, and ease of large-scale manufacturing. The newly designed system is composed of several strategically arranged layers. From the outside in, there is first the bifacial photovoltaic glass panel. This is separated from a second wall by a five-centimeter air gap. The second wall in question is the thermochromic layer. It is 1 mm thick and sealed between two glass sheets.

## A passive energy solution

Before going further, it is worth noting that this invention is described in a study published in the journal Building and Environment. The system’s efficiency lies in its hybrid architecture. The BiPV photovoltaic cells, arranged in a 6×6 matrix covering approximately 45% of the surface, capture solar energy. The air gap, on the other hand, not only serves as insulation but also facilitates installation and allows for simplified maintenance, with each component being replaceable independently. Additionally, it cools the solar cells. As for the hydrogel, this material has optical properties that change with heat. At low temperatures, it remains transparent, allowing natural light to pass through. However, as the temperature increases under the effect of solar radiation, it undergoes a phase transition and becomes translucent.

## Encouraging results

This change in opacity allows the glazing to block a portion of the solar spectrum, thereby reducing the amount of heat entering the habitat. This dynamic modulation offers optimal visual and thermal comfort by relying on a purely passive mechanism. Tests conducted on a prototype have shown highly promising results. The researchers observed a decrease in indoor temperatures of up to 15.1°C and an increase in electricity production by 16.5% due to the recovery of reflected light. Annual-scale simulations have also revealed that for windows, bifacial gains could range from 9 to 18%, compared to 6 to 14% for vertical windows. In both cases, the team from the City University of Hong Kong reports significantly better performance than traditional BiPV systems. What do you think of this innovation? Feel free to share your opinion in the comments! More information on the study can be found at sciencedirect.com.