Just imagine, you can extract water from the air without being connected to any power grid. Sounds incredible, especially if it works where the air is very dry, such as in deserts and steppe regions of the world. Such a device has indeed been developed and the best thing about it is that it uses almost no mechanical parts or complex electronics and operates exclusively from direct sunlight (not solar cells).
Researchers at the Massachusetts Institute of Technology used a structure known as an organic metal structure (MOF) to collect water directly from the air (at humidity levels as low as 20%). This moisture level is commonly found in the driest regions of the world. The prototype was capable of extracting 2.8 liters of water per day at 20 to 30% humidity.
MOF structure: The yellow balls represent voids in the structure that collect water. Source: UC Berkeley / Berkeley Lab
MOFs are lattice structures composed of organic compounds and metal particles and have been popular since their invention about 20 years ago. Depending on the MOF structure and starting materials, certain molecules can be very reliably deposited in the pores of this structure. These can be gases from hydrogen to methane. Their storage density per unit volume is higher than if the gases were compressed in large hollow tanks. Since their invention at the University of California, Berkeley, over 20,000 different MOF warrants have been developed. The MOF used for this water collector consists of zirconium and adipic acid, which bind water vapor.
In the first picture you can see the construction of the water collector. Inside there are about 1 kg of MOF crystals pressed between the upper light-absorbing layer and the lower capacitor plate. When ambient air passes through the porous MOF, water molecules attach to the interior surfaces. Sunlight entering through a translucent window at the top of the device heats up the MOF and moves the bound water towards the condenser, which is at ambient temperature, through the heat pipe and radiator below the device. The steam condenses and the water flows into the collector. The principle is both simple and effective. If these properties can be made stable, this is a real breakthrough in the intelligent use of solar energy without solar PV cells.
Translation author Sergey Smyshlyaev