University Of California Researcher Solves Drought Problems With Solar-Powered 'Water Harvester'

Device pulls water from dry air, powered only by the sun

The solar-powered harvester can provide 2.8 litres of water from the air over a 12 hour period in conditions as dry as the Mojave Desert, where the average humidity is around 20 per cent.

"This is a major breakthrough in the long-standing challenge of harvesting water from the air at low humidity", says Omar Yaghi from UC Berkeley regarding the new device. There is no other way to do that right now, except by using extra energy.

Though researchers at Berkeley and MIT have developed a way to extract clean water from thin air, it will take more research and development to bring the prodct to an affordable enough price that it can be economically distributed to countries around the world and aras where clean water is in short supply.

In order to make water, the engineers used a special material called a metal-organic framework, or MOF, from UC Berkeley.

In collaboration with MIT's Device Research Laboratory - run by Dr. Evelyn Wang, the inventor of MOF - Omar Yaghi, a scientist at the Lawrence Berkeley National Laboratory, synthesized a zirconium-based material that binds water vapor and transforms it into a water-collecting system. But such water-saturated air is only common in very limited regions.

A report during the last year in Science Advances had found that nearly four billion residents, almost half in India as well as in China, face "severe water scarcity at least during one month of the year". "In taking the invention out of the lab and demonstrating the device in real-world conditions, we have shown that the MOF works and the device that it is contained within can operate and deliver water by trapping water from dry air". The device described in the new paper is tailored for a 20 percent humidity level, but other MOF designs may work best at 50 percent or higher. Their latest prototype uses a popular but unusual new material and requires little energy, even in some of the driest places on Earth. It could also be configured to work more effectively under different humidity conditions, Yaghi said. At the present, there are about 20,000 types of MOFs out there, each with their own unique properties and uses, but the particular MOFs in the new water harvester are capable of binding to water. Parts of the world which have scarce water resources will benefit from this advanced technology to improve the living conditions of people living in barren locations. The key to their success is a family of crystalline powders called metal organic frameworks, or MOFs. Since then, he and others have developed several types of applications for them, including membranes that absorb and later release methane, acting as a carbon tank for cars. To get the device ready for commercialization, he is now working on new MOFs that could hold more water by weight, while Wang is trying to increase the device efficiency and output. Their prototype can harvest 300 ml of water per kilogram of MOF, said researcher Eugene Kapustin from the University of California, Berkeley, but they only used 1.5 grams of the stuff. This drips into a collector and, presto, usable water from air.

Though that may not sound like much, its designers say the current device is just a prototype. The MOF has a porous structure that makes it ideal for holding water, similar to a sponge.

"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", he added.

Obviously scaling up to eventual commercialization comes next."We did some estimates, and anticipate if you had a 30 liter unit, say the size of a carry-on suitcase, that's equivalent to 5 kg of MOF or so", said Wang.

At $150/kg, zirconium is too expensive to use for a mass-produced product meant to be distributed to people living in arid environments, but Yaghi proposes further work that would swap in aluminum, which costs 1% of the cost of zirconium.