Water Harvester

Solar Powered Device Can Now Supply ‘Personalised’ Water

It is now possible to extract water from the air using a new device that uses sunlight to suck in water vapor even when humidity levels are relatively low. The device, which resembles a sponge, can produce nearly 3 litres of water per day for every kilo of absorbent material it contains. Future versions will be able to extract even more water from the air, including in desert-like conditions. Inhabitants of such areas might soon have a solar-powered appliance capable of providing them with all their water requirements

There are an estimated 13 trillion litres of water floating in the Earth’s atmosphere which is equivalent to 10% of the planet’s freshwater reserves. Earlier attempts to extract some water have included using fine nets used in foggy conditions and humidifiers. Both methods are inefficient as one requires a great deal of humidity to extract any significant quantity of water while the other consumes a large amount of electricity, making it very expensive.

Omar Yaghi, a chemist at the University of California, made a new breakthrough using metal organic frameworks or MOFs which he developed himself more than 20 years ago. Since then, chemists have synthesized more than 20,000 MOFs, each with distinctive and different molecule-grabbing properties.  These are porous crystalline powders that form continuous 3D networks. Chemists can manipulate the properties of each MOF by controlling the gases that bind them and how strongly they hold on.

In 2014 Yaghi and his team synthesized a MOF from zirconium with exceptional water absorption capability. Yaghi collaborated with Evelyn Wang, a mechanical engineer with the Massachusetts Institute of Technology, with whom he had worked earlier. Wang and her team designed a system that soaked up water vapor from the air at night and used the sun’s heat to release the water vapor as liquid during the day. It was constructed with MOFs which were pressed into a thin sheet of copper metal. The copper metal sheet was then positioned between a solar absorber and a condenser plate. The sheet has extraordinary properties, capable of producing 2.8 litres of water in 12 hours. It also can work in dry environments where the humidity levels are as low as 20%.

The new technology has the potential to provide enormous benefit and give access to clean water to over a billion people worldwide. It can supply the daily recommended water requirements of an individual (330 ml a day) within an hour. Furthermore, people living or stranded in the desert will have the capability of accessing water without needing a public supply connection or a well.

Over the long term, this can translate into off-grid water supplies with solar-powered devices delivering sufficient water to meet the needs of a household according to Professor Yaghi. He calls it ‘personalised water’.  Yaghi has stated that the technology will become both cheaper and better in the near future and is working on replacing the zirconium MOF with an aluminum-based one. Zirconium costs $150 per kilogram making water-harvesting devices an impractical proposition commercially. Aluminium is 100 times cheaper which will make future water harvesters much more affordable.