Close to the theoretical optimum
As tests of the new device under real-world conditions on the roof of an ETH building in Zurich showed, the new technology can produce at least twice as much water per area per day as the best current passive technologies based on foils: the small pilot system with a pane diameter of 10 centimetres delivered 4.6 millilitres of water per day under real-world conditions. Larger devices with larger panes would produce more water accordingly. The scientists were able to show that, under ideal conditions, they could harvest up to 0.53 decilitres of water per square metre of pane surface per hour. “This is close to the theoretical maximum value of 0.6 decilitres per hour, which is physically impossible to exceed,” says Iwan Hächler. He is a doctoral student in the group of Dimos Poulikakos, Professor of Thermodynamics at ETH Zurich.
Other technologies usually require the condensed water to be wiped from a surface, which requires energy. Without this step, a significant portion of the condensed water would cling to the surface and remain unusable while hindering further condensation. The ETH Zurich researchers applied a novel superhydrophobic (extremely water-repellent) coating to the underside of the pane in their water condenser. This causes the condensed water to bead up and run or jump off on its own accord. “In contrast to other technologies, ours can really function without any additional energy, which is a key advantage,” Hächler said.
The researchers’ goal was to develop a technology for countries with water scarcity and, in particular, for developing and emerging countries. Now, they say, other scientists have the opportunity to further develop this technology or combine it with other methods, such as water desalination, to increase their yield. The production of the coated panes is relatively simple and building water condensers that are larger than the current pilot system ought to be possible. Similar to the way solar cells feature several modules set up next to each other, several water condensers could also be positioned side by side to piece together a large-scale system.