Scientists Make Electricity From Evaporating Water

Columbia University researchers pioneer two devices powered by evaporation.

Scientists working at Columbia University have devised a way to convert energy expended by bacterial spores during the evaporation of water to usable electricity. In order to perform this somewhat strange task, the team constructed two devices for the conversion of mechanical energy to electricity.

Under humidity changes, bacterial spores push and pull objects.

Previous research by Columbia University associate professor Ozgur Sahin had revealed that bacterial spores in water shrink and swell with humidity changes, pulling objects hard in the process. When the air is dry, the spores shrink. When the humidity increases, the spores swell up. The team behind the evaporation energy-harvesting mechanism made use of this finding to create a sort of artificial muscle controlled by changes in humidity.

How do the energy-harnessing mechanisms work?

In order to build the evaporating water engine, the scientists’ first step was to glue bacterial spores to both sides of a thin plastic tape, forming a dashed line of spores on each side. In the places where one side of the film has spores, the other side has gaps, so that the “dashes” on one side touch gaps in spores on the other side. That way, when air is arid, the spores shrink and make the dashes curve, curling the tape. With one or both sides of the tape attached to something, the curving of the tape causes a tug on the taped side(s). Then, when dank air is introduced, the spores swell, the tape extends, and the force is thus released.

Evaporating water energy system acts like water-powered muscle.

Ozgur Sahin and postdoctoral fellow Xi Chen took dozens of tapes like the one above and place them side-by-side in a floating plastic case with shutters on top. Within the case, evaporating water humidifies the air. The humidity causes the spores to grow and the “muscle” to elongate, which opened the shutters and let the humid air out. Once the moisture got out, the spores shrank, making the muscle contract, which in turn closed the shutters. With the shutters now closed, the spores grow, the muscle extends again, and the cycle is repeated. The muscle was then free to move on its own, acting not unlike a piston driven by evaporating water. With the piston hooked up to a generator, enough energy could be produced to power a small light. The other evaporation-engine-powered device the researchers ran was a small toy car they built themselves. They used what they call the “Moisture Mill,” a plastic wheel featuring tabs of tape with spores on one side, driven by the same principles as the evaporation piston.


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