Water harvester cycles continuously without intervention

Solar-powered harvesters work in a two-stage cycle: an absorbent material first captures water from the air and, once it is saturated, the system is sealed and heated with sunlight to extract the captured water. Alternating between the two stages requires manual labour or a switching system, which adds complexity and cost.

By contrast, the new harvester developed at KAUST (King Abdullah University of Science and Technology) is said to passively alternate between the two stages so it can cycle continuously without intervention.

Project lead and KAUST post-doctoral student Kaijie Yang said initial inspiration came from observing natural processes, specifically how plants efficiently transport water from their roots to their leaves through specialised structures.

“In our system, mass transport bridges play a crucial role as a connection between the ‘open part’ for atmospheric water capture and the ‘closed part’ for freshwater generation,” Yang said in a statement.

According to KAUST, the mass transport bridges are a collection of vertical microchannels filled with a salt solution that absorbs water.

The water-rich salt solution is pulled up the channel by the same capillary action that pulls water up plant stems, and then the concentrated salt solution diffuses back down to collect more water.

“By optimising the transport of mass and heat within the system, we enhanced its efficiency and effectiveness,” said Tingting Pan, another postdoc who worked on the project.

During testing the system in Saudi Arabia, each square metre is said to have produced 2-3 litres of water per day during the summer, and about 1-3 litres per day in the autumn.

During the tests, the team ran the system for several weeks without the need for maintenance. They also showed that it could be used as a direct point source to irrigate Chinese cabbage and desert trees.

“The materials we used were a water-wicking fabric, a low-cost hygroscopic salt and a plastic-based frame. We chose the materials for their affordability and availability, so we anticipate the cost is affordable for large-scale application in low-income areas,” said Qiaoqiang Gan, one of the study’s senior authors.

The team’s findings are detailed in Nature Communications.