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Passive solar module cooling tech based on atmospheric water harvesting

Source：pv magazine

Scientists from India's PSG College of Technology have developed a passive solar module cooling technology that utilizes a hygroscopic salt to harvest atmospheric water from the air.

“The objective is to apply the water production technique from atmospheric air to cool the front side of the panel,” researcher R. Jegathishkumar told pv magazine. “Most of the cooling systems were designed to provide rear-side cooling using active cooling techniques. This work was to bring a passive cooling system for a highly humid region where the water absorption rate of hygroscopic salt is high.”

Scientists used a hygroscopic salt, calcium chloride (CaCl₂), commonly applied as a food additive, road de-icer, and in medical fields. They enclosed CaCl₂ solution mixed with sawdust at various concentrations – or without sawdust – in a cloth bag that absorbs moisture from the air in a highly humid location in Coimbatore, Tamil Nadu, India. The salt pack was placed in holes at the module’s base to distribute the regenerated water.

The experiment used a 15 W solar panel equipped with the cooling technology alongside a reference panel without cooling. Scientists measured the module temperature every 15 minutes using an infrared thermometer for 4.5 hours daily over four consecutive days. Results showed the panel with pure calcium chloride and no sand had a maximum power output 18.93% higher than the panel without cooling.

“Using the current water production from atmospheric air, the panel temperature is reduced by 3 C and the efficiency of the panel is increased by about 17.38%,” said Jegathishkumar. 

The experiment also showed that salt sedimentation reduces solar irradiation and PV module performance, making regular cleaning of the panel surface mandatory for the system’s viability.

“The pure salt sample attained a temperature drop of 1.7%, as it absorbed more amount of water from the air,” Jegathishkumar said. “However, it failed to desorb the same quantity due to the demand for high desorption.”

The researchers described the new cooling technique in “Experimental study on passive cooling of photovoltaic panel by harvesting atmospheric water using hygroscopic salt,” which was recently published in Energy for Sustainable Development. 

Looking ahead, the research team plans to optimize additive concentrations and identify suitable nonhazardous additives.