No more electricity will be needed for efficient cooling, only sunlight. A new experimental electricity-free cooling system is under development at Saudi Arabia’s King Abdullah University of Science and Technology (KAUST). It is not a complex device, but a simple cooling system that captures solar energy and uses it to cool living spaces and food. This cooling system can help a large number of poor people who do not have access to the electricity grid.

Cooling system without electrical components

There are no electronic components in this system. The system 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.

“Hot regions have high levels of solar energy, so it would be very attractive to use that solar energy for cooling,” says Wenbin Wang, a postdoc in Peng Wang’s lab. In many parts of the world, there is a greater need for cooling because of climate change, but not every community can access electricity for air conditioning and refrigeration. “We conceptualized an off-grid solar-energy conversion and storage design for green and inexpensive cooling,” says Professor Wang.

Credit: Wenbin Wang/KAUST

The solubility of the salt is crucial for the effect of the cooling system

The scientific team designed a two-stage cooling and regeneration system. How does cooling actually take place? Dissolving some common salts in water absorbs energy, which cools the water quickly. Each salt has different results, but the best cooling salts are ammonium nitrate (NH4NO3). It has a high cooling power because it has a 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.

Credit: Wenbin Wang/KAUST

An effective solution for the poor

People in poor areas need to store food at low temperatures to keep it from spoiling. This cooling system helps them store food at low temperatures and does not consume any electricity. 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. When the brine reaches room temperature, solar energy is used to evaporate the water. As the water evaporates, crystalline salt accumulates. The process can be repeated over and over again.

As a result of climate change, areas are increasing where high temperatures complicate people’s lives. Used en masse, this simple and efficient cooling system can help many people better manage their daily lives in inhospitable conditions.


Credit: Wenbin Wang/KAUST