Machines that harness the power of evaporating water have been created by scientists in the US.

Researchers at Columbia University in New York have built a miniature car that draws on the process to propel itself along, as well as an evaporation-driven generator that powers a flashing LED lamp.

The inventions pave the way for a new generation of renewable devices that extract energy from natural evaporation and transform it into something useful. Ozgur Sahin, who led the research, said the machines were cheap and could draw energy from water as it evaporates continuously from the surfaces of lakes and oceans.

“Water wants to evaporate. It has a desire to evaporate. If you make a surface wet, it will dry up, that’s the natural course,” Sahin said. “What we did was find a way to channel that desire into doing some useful work.”



Scientists at Columbia University in New York have created machines powered by evaporating water.

Credit: ExtremeBio

The machines build on Sahin’s discovery last year that spores of common soil bacteria swell when they absorb water in humid environments and shrink when they release the water in drier air. The change in spore size can be used to push and pull objects.



To make one of the machines, a floating piston engine, Sahin and his colleagues glued a line of spores to each side of a thin, plastic tape. The spores were spaced out and arranged so that those on one side overlapped with the gaps between spores on the other.



When the tape is exposed to dry air, the spores shrink and the tape retracts like a spring. In moist air, the tape extends as the contraction is released. The result is an artificial muscle powered by differences in moisture. The scientists call them hygroscopically driven artificial muscles, or hydra.



Using dozens of hydra, the scientists went on to build a rudimentary piston engine. The hydra are put inside a plastic case that has little shutters overhead. When placed on water, evaporating moisture makes the hydra elongate and open the shutters above them. This allows the moisture in the case to escape, causing the hydra to contract and the shutters to close again. The cycle then repeats.



In tests, the scientist found th engine generated enough electricity to make an LED bulb flash on and off.



The machine could be used to power small floating lights, or sensors on the bottom of the sea, the scientists believe. Details are published in the journal Nature Communications.



The scientists call their second invention a moisture mill. The machine has a plastic wheel covered with plastic tapes that are coated with spores on one side. Half the wheel is kept in dry air, which causes the tabs to curl up, while the other half is in more humid air, which causes the tabs to straighten out. Left to its own devices, the wheel spins around, and was powerful enough to drive a small toy car.

