Saudi Arabian summers may be dry and scorching hot, but in June last year, some 50 miles north of Jeddah, 57 seeds sprouted into healthy, seven-inch-tall water spinach leaves by harvesting water out of thin air.
Like all conventional crops, spinach needs water to grow. But, in this case, the spinach sprouted thanks to a solar-powered system that pulled vapor from the air and condensed it into two liters of water. Now published in the journal Cell Reports Physical Science, the results of the experiment suggest that small farms in remote, arid regions can grow their own crops without a water supply.
“If you have river water or lake water, you probably don’t need the system, but in places where you don’t have a conventional water system, it’s important,” says Peng Wang, a professor of environmental science and engineering at the King Abdullah University of Science and Technology (KAUST) and a senior author of the study.
The prototype used during the experiment consists of three main components: a small-scale photovoltaic panel, a composite material made of hydrogel (a high-tech version of the hydrogel used in bandages to re-hydrate wounds), calcium chloride (the kind of salt we use to de-ice roads), plus a metal container that acts as a condensation chamber. Like most conventional solar panels, 10-20% of the solar energy they absorb is converted to electricity. The remaining 80-90% is converted to heat. The hydrogel material—think of it as a layer of jelly attached to the backside of the solar panel—plays a dual role. First, it can cool the solar panel so it doesn’t overheat. Second, it can absorb water vapor from the air because of the calcium chloride, which can absorb more than its weight in moisture. The hydrogel itself swells and locks that moisture into the material so it doesn’t spill.
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