An Atmospheric Water Harvesting System Suitable for Desert Areas
Passive atmospheric water harvesting systems are making significant strides. Driven by the worsening water crisis in various regions of the planet, research is continuously producing new studies and devices to address this challenge. The latest innovation comes from a group of engineers at the King Abdullah University of Science and Technology (KAUST). Led by Professor Qiaoqiang Gan, the team has designed a special moisture-harvesting system capable of operating in arid environments, such as Saudi Arabia.
How Do Passive Atmospheric Water Harvesting Systems Work?
Passive atmospheric water harvesting systems can capture and condense water from the air without the need for electricity. Currently, these devices fall into two main categories:
- Moisture-harvesting systems using special absorbents, such as metal-organic frameworks, silica gels, or zeolites. These systems function during the day and can work even in low relative humidity. Once the absorbent material is saturated, the system is closed and placed under the sun. The heat from the sun causes the water to evaporate, which then condenses on the walls and is collected.
- Dew-harvesting systems using radiative cooling sheets, which require high relative humidity. These devices emit thermal radiation in a wavelength range where the atmosphere is mostly transparent (from 8 to 13 μm). In other words, they send heat in the form of infrared rays directly into space. The radiative effect cools the sheet below the dew point temperature of the air, causing water to condense on its surface.
Radiative Cooling with Gravity: KAUST’s Work
KAUST’s work has focused on atmospheric water harvesting systems using radiative cooling, improving their efficiency.
“A common challenge in atmospheric water harvesting systems is that water droplets tend to stick to the surface of the device, making active condensation collection necessary. Our coating effectively eliminated this sticking, allowing for true passive water collection driven by gravity,” explains Ahmad.
The solution builds on Gan’s previous technology, which he described as a “double-sided vertical architecture.” That system was originally designed to reflect thermal heat into the sky to keep solar cells cool, not to capture the water produced.
The new device maintains the same architecture but coats the surface in contact with the condenser with a layer of elastomer lubricated with silicone oil. This addition allows water droplets to slide down more easily under the force of gravity, instead of sticking to the surface.
Dew Harvesting Systems: How Much Water Do They Produce?
Tested over a year in outdoor conditions in Thuwal, a Saudi city about 100 km north of Jeddah, the results were promising. The passive water collection rate reached 21 g/m² per hour, twice that of the superhydrophobic surface. In indoor tests (20°C and 80% relative humidity), this system achieved a condensation rate of about 87% of the theoretical limit, with 90% of the total condensation being collected passively.
The research was published in Advanced Materials.