A simple cooling system driven by the capture of passive solar energy could provide low-cost food refrigeration and living space cooling for impoverished communities with no access to the electricity grid. The system, which has no electrical components, exploits the powerful cooling effect that occurs when certain salts are dissolved in water. After each cooling cycle, the system uses solar energy to evaporate the water and regenerate the salt, ready for reuse. //

After comparing a range of salts, ammonium nitrate (NH4NO3) proved to be the standout performer, with a cooling power more than four times greater than its closest competitor, ammonium chloride (NH4Cl). The ammonium nitrate salt’s exceptional cooling power can be attributed to its high solubility. “NH4NO3’s solubility reached 208 grams per 100 grams of water, whereas the other salts were generally below 100 grams,” Wenbin says. “This salt’s other advantage is that it is very cheap and already widely used as fertilizer,” he adds.

The system has good potential for food storage applications, the team showed. When the salt was gradually dissolved in water in a metal cup placed inside a polystyrene foam box, the temperature of the cup fell from room temperature to around 3.6 degrees Celsius and remained below 15 degrees Celsius for over 15 hours. //

Reference: ” Conversion and storage of solar energy for cooling” by Wenbin Wang, Yusuf Shi, Chenlin Zhang, Renyuan Li, Mengchun Wu, Sifei Zhuo Sara Aleida and Peng Wang, 1 September 2021, Energy & Environmental Science.
DOI: 10.1039/D1EE01688A