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Researchers in Saudi Arabia have developed a hydrogel compound that absorbs moisture from solar modules at night and facilitates evaporative cooling during daylight hours. The system has been tested in laboratory and outdoor experiments on two continents. A group led by scientists at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia has developed a low-cost passive cooling technology for photovoltaic panels. It consists of a hydrogel composite of polyacrylic acid sodium salt (PAAS) and lithium chloride (LiCl) applied to the back of the solar module. “We specialize in materials that enable passive cooling,” explained researcher Qiaoqiang Gan. “These materials are thin and can be placed in various systems that require cooling to operate, such as greenhouses and solar cells, without affecting performance.” To create the composite, the researchers combined LiCl and PAAS in a 2:1 ratio. After mixing the materials, they poured the mixture into a mold, where it cured for an hour to form a flat shape. According to the researchers, the specific ratio was selected to ensure the composites resilience under extreme conditions, such as relative humidity levels above 90% and temperatures exceeding 30°C. “The composite takes advantage of the desiccants hygroscopic properties, allowing it to absorb moisture during the night and facilitate evaporative cooling during daylight hours,” they explained. “In this composite, the PAAS molecules increase the water storage capacity through their highly hydrophilic carboxylate groups. While the LiCl crystals act as hygroscopic agents that actively absorb moisture from the environment, the water stored in the composite is gradually released throughout the day due to the balanced LiCl content, eliminating the need to replace the cooling layer.” To test their new development, the team used a 54 mm × 54 mm polycrystalline silicon photovoltaic panel. A 7 mm thick layer was applied to the back, which expanded to about 10 mm once water was absorbed. It was then tested in several locations, in laboratories in both Saudi Arabia and the United States, as well as in field trials. A 21-day field trial took place in the Saudi city of Thuwal, while a month-long field experiment was conducted in Buffalo, New York. “We achieved impressive cooling performance in laboratory tests,” the team noted. “When exposed to continuous solar radiation of 1 kW/m² for 3 hours, the cooling power reached 373 W/m², which decreased to 187 W/m² after extending the operating period to 12 hours. Under real-time simulated outdoor solar radiation, the system delivered an average cooling power of 160 W/m², with a peak of 247 W/m² between 10:00 and 11:00.” In outdoor testing in Saudi Arabia, with a temperature of 37°C and a relative humidity of 53%, a sustained evaporative cooling power of 175 W/m² was achieved. “A significant temperature drop of up to 14.1°C was recorded around midday (12.5°C on average from 12:00 to 13:00), leading to a substantial increase in energy conversion efficiency, from 13.1% to 14.7%, an improvement of approximately 12.2%,” they highlighted. Through testing in the United States, the team also concluded that the improved cooling efficiency extends the operational lifetime of the photovoltaic panels by more than 200% and reduces the levelized cost of electricity by 18%. They also calculated the material cost to be approximately $37/m², noting that this is “lower than most previous studies using hydrogel or non-hydrogel cooling methods.” They presented their novel technique in “ Streamlined fabrication of an inexpensive hygroscopic composite for low-maintenance evaporative cooling of solar panels,” recently published in Materials Science & Engineering R. Scientists from King Abdullah University of Science and Technology in Saudi Arabia and the State University of New York at Buffalo in the United States participated in the research. |
