Scientists invent solar-powered device to extract water from dry air

In a new study published in the journal 'Science', scientists have invented a new system that can harvest litres of water from the air everyday using just ambient sunlight. It can work in conditions as low as 20 percent humidity.

Scientists at the MIT technology lab have been working together with the University of California, Berkeley to create this solar-powered harvester.

"This is a major breakthrough in the long-standing challenge of harvesting water from the air at low humidity", said Omar Yaghi, from the University of California, Berkeley.

Yaghi, also a faculty scientist at Lawrence Berkeley National Laboratory in the US said, "There is no other way to do that right now, except by using extra energy. Your electric dehumidifier at home 'produces' very expensive water".

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Using one kilogramme of a metal-organic framework (MOF) - a special material produced at UC Berkeley, the prototype was able to pull 2.8 litres of water from the air over a 12-hour period under conditions of 20-30 per cent humidity, roughly equal to the humidity level in the Sahara desert meaning that the technology could be used to pull water from the air in some of the poorest areas of the globe that have little to no available drinking water. 

Rooftop tests at MIT confirmed that the device works in real-world conditions, researchers said.

"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", said Yaghi.

"To me, that will be made possible because of this experiment. I call it personalised water", he added.

The new approach makes use of a substance called MOF, a metal-organic framework. As the name suggests, these are materials made of metals mixed with organic compounds. Powders made from MOFs are very porous, so researchers have proposed using them to store hydrogen or methane fuels or to capture carbon dioxide.

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The researchers built a small prototype water collector that contains a thin layer of MOF powder. The powder absorbs water vapor until it is saturated.

And when the water is released, it collects in the bottom of the prototype.

In the prototype, the heat needed to drive the water out of the MOF comes from ambient sunlight — no external power supply is needed.

Evelyn Wang, a mechanical engineer at MIT stated that "This work offers a new way to harvest water from air that does not require high relative humidity conditions and is much more energy efficient than other existing technologies".

This proof of concept harvester leaves much room for improvement, Yaghi said. The current MOF can absorb only 20 percent of its weight in water, but other MOF materials could possibly absorb 40 percent or more.

The material can also be tweaked to be more effective at higher or lower humidity levels.

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"To have water running all the time, you could design a system that absorbs the humidity during the night and evolves it during the day", Yaghi said.

“We wanted to demonstrate that if you are cut off somewhere in the desert, you could survive because of this device.” he added.