Solar-powered device harvest water from dry air: All you need to know

Powering the device with sunlight bypasses that requirement, especially important in developing nations lacking infrastructure. Under the heat of the sun, water molecules begin to vaporize again, eventually condensing into reservoirs created to collect the water. Mechanical engineer Oliver O'Reilly and his UC Berkeley colleagues have just published a scientific paper exploring this mystery of the ages. Harvester photos courtesy of MIT.

Senior author Omar Yaghi demonstrates how the MOF works using a model. After all, dehumidifiers make sure that a room or home does not easily grow mold by sucking out the moisture from the air, and at the end of the day, you will have to pour all of the water away somewhere else.

Professor Yaghi added: 'One vision for the future is to have water off-grid, where you have a device at home running on ambient solar for delivering water that satisfies the needs of a household. Better yet, the new invention does not require electricity and the researchers are attempting to make the device as low-cost as possible. The second method is called "dewing", and it involves using water condensers to pull water vapor out of the air and turn it into liquid form. In the last 20 years, researchers have created over 20,000 different MOFs for a wide variety of applications, such as separating methane and water from other gasses. An MOF being tested by chemical giant BASF, for example, is capable of holding three times more natural gas than can be forced into an equivalent-sized hollow tank.

A schematic of a metal-organic framework. The yellow balls represent the porous spaces that can fill up with water.

The devices made from MOF are not restricted to water dispensers. UC Berkeley, Berkeley Lab image.

The researchers built a small prototype water collector that contains a thin layer of MOF powder. The material, which is sandwiched between a solar absorber and a condenser place, captures water molecules in the air that flows through the open chamber.

As the atmospheric air gets diffused while passing through the porous MOF, the water molecules that are by preference get attached to the interior surfaces. According to X-ray diffraction studies, the water vapor molecules tend to gather in groups of eight to form cubes.

At night setup soaks up water vapor from air, and uses heat from the sun to release it as liquid water during the day.

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It's not that hard to collect condensation in a humid climate, but squeezing H20 from arid, thin air is another story. A new sponge-like device can draw around 3 liters of water out of air per day in the desert like region, researchers say.

The harvester sitting atop a roof at MIT.

How the device works.

The device is billed as a proof of concept by Yaghi, so it's just a starting point. With other MOF materials, they believe it would be able to absorb at least 40% of its weight in water.

Desert like conditions typically have low humidity levels making it hard to extract anything that resembles water from the air. What powers this water harvester?

The next step is to continue scaling up the design into devices that can collect even more water. "It is just a matter of further engineering now".

To do this, they turned to a class of synthetic materials known as metal-organic frameworks (MOFs), which he pioneered more than 20 years ago. The invention has the potential to bring clean drinking water to people living in places that need water desperately, like in countries undergoing drought conditions or areas of the world with a relatively low amount of humidity.

This work was supported in part by DOE's Advanced Research Projects Agency-Energy (ARPA-E).

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