Researchers in Saudi Arabia have developed a hydrogel composite that absorbs moisture in solar modules overnight and facilitates evaporative cooling throughout daylight hours. The system has undergone lab tests and outdoor experiments on two continents.
A group led by scientists from Saudi Arabia’s King Abdullah University of Science and Technology (KAUST) has developed a novel, low-cost passive cooling technology for PV panels.
It consists of polyacrylic acid sodium salt (PAAS) and lithium chloride (LiCl) hydrogel composites applied to the rear side of the solar module. “We specialize in materials that enable passive cooling,” said researcher Qiaoqiang Gan. “These materials are thin and can be placed on different systems that require cooling to operate, like greenhouses and solar cells, without affecting performance.”
To create the composite, the researchers combined LiCl and PAAS at a ratio of 2:1. After mixing the materials, they poured the mixture into a mold, where it was cured for one hour to form a flat shape. According to the academics, the specific ratio was selected to ensure the composite’s resilience under extreme conditions, such as relative humidity levels of above 90% and temperatures over 30 C.
“The composite exploits the hygroscopic properties of the desiccant, enabling it to absorb moisture overnight and facilitate evaporative cooling throughout daylight hours,” they explained. “In this composite, PAAS molecules increase water storage capacity through their highly hydrophilic carboxylate groups. While LiCl crystals act as hygroscopic agents that actively absorb moisture from the environment, the water stored in the composite is released gradually throughout the entire day due to the balanced content of LiCl, eliminating the need to replace the cooling layer.”
To test their new development, the team used a polycrystalline silicon PV panel measuring 54 mm × 54 mm. A 7 mm thick layer was applied to its back, expanding to about 10 mm once water was absorbed. It was then tested in several locations, in laboratories both in Saudi Arabia and the United States, as well as in field tests. A 21-day field test took place in Saudi Arabia’s city of Thuwal, while a month-long field experiment occurred in Buffalo, New York.
“We achieved impressive cooling performance in laboratory tests,” said the team. “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 work period to 12 hours. Under simulated real-time outdoor solar radiation, the system delivered an average cooling power of 160 W/m2, peaking at 247 W/m2 between 10:00 AM and 11:00 AM.”
Regarding the 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. “Significant temperature decrease of up to 14.1 C was recorded around midday (12.5 C on average from 12:00–13:00), leading to a substantial increase in power conversion efficiency, from 13.1% to 14.7%—an improvement of approximately 12.2%,” they stressed.
Through the testing in the United States, the team also concluded that the enhancement in cooling efficiency extends the operational lifespan of PV panels by over 200% and reduces the levelized cost of electricity by 18%. They also calculated that the material cost is approximately $ 37/m², and highlighted that it is “lower than most of the 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,” which was recently published in Materials Science & Engineering R. Scientists from Saudi Arabia’s King Abdullah University of Science and Technology and the US’s State University of New York at Buffalo have participated in the research.