If working with solar thermal power, the design also incorporates a hot water tank that acts as a thermal battery, allowing it to run even when the sun goes down. The new design can now use a variety of heat sources, including solar thermal panels, biomass burners, or industrial waste heat. To create Uravu’s 1,000-L-per-day machine, the company will couple six absorbers with a single desorber unit. Each absorber unit is capable of collecting as much as 200 L per day. This creates air so humid it’s almost like steam, which then passes to a low-power, air-cooled condenser that turns it into liquid water.ĭecoupling the absorber and desorber leads to significant scaling efficiencies, says Shrivastav, since each desorber can serve several of the less complicated absorbers. After it absorbs moisture from the air, the desiccant is pumped to a separate desorber unit where the solution is heated to between 60 and 70 ☌ by a coiled pipe filled with hot water. In the absorber units the desiccant is sprinkled through a mesh to increase the surface area as air is drawn over it by a fan.
One key step involved swapping out the silica gel for a liquid desiccant-calcium chloride solution-which is pumped between dedicated absorber and desorber units. That’s why Uravu has now switched to a new design that decouples the key stages involved in harvesting water from air.
This could produce about 10 L of water a day, but because each unit required dedicated components like fans, valves, and pumps, the company found it got very little cost reductions when it tried to scale up, says Shrivastav. Initially, the company was working on a self-contained unit about 4 meters across that combined a solid desiccant called silica gel with a solar thermal panel, which uses the sun to warm up water that can then be used to heat the desiccant. Since then Uravu has raised US $2.5 million and completely revamped its design. The team started work on the idea in 2017 and made it to the finals of the Water Abundance XPrize, a two-year competition organized by XPrize to catalyze progress in atmospheric water-harvesting technology. This led Uravu to a solution that relies on water-loving materials called desiccants to absorb moisture from the air, which are then heated using renewable-energy sources to release the water again. “Our goal from day one was to not only be scalable and renewable but also be the most affordable,” he says. However, the approach requires huge amounts of electricity, says Shrivastav, and this makes these units expensive to run and unsustainable unless specifically powered by renewable energy.
Water pulls full#
The vast majority of companies working in this area rely on technology similar to that found in air-conditioning units-a coiled tube full of refrigerant is used to cool air until its moisture condenses on the surface as liquid water.
Uravu isn’t the only company working on this problem, but its approach is different from that of most of its competitors. By the end of the year the company hopes to scale that up to 10,000 L a day, says cofounder Swapnil Shrivastav. The device, the company says, will be capable of harvesting up to 1,000 liters of water a day when it goes online later this month, at its headquarters in the south Indian city of Bengaluru. Uravu is putting the finishing touches on its biggest unit to date. What comes out of the pipe, the company’s website says, is “100 percent renewable water”-renewably powered, harnessed from a vast and nearly inexhaustible source, and with no wastewater produced in the process. Indian startup Uravu Labs says its low-cost modular approach could provide a blueprint for more affordable and sustainable atmospheric water harvesting. BENGALURU, India-Technology that can pull water out of thin air could help solve the world’s growing water scarcity problem, but most solutions are expensive and difficult to scale.
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