A new means of generating electricity, one that utilizes bacteria to harness the energy of evaporating water, has been created by researchers from the Wyss Institute of Biologically Inspired Engineering at Harvard University.
The completely new means of generating electricity could potentially be used to capture the energy released by ponds, harbors, and other bodies of water when the Sun warms them (causing evaporation), according to the researchers.
The newly created prototype generators work by harnessing the movement of a sheet of rubber that’s coated on one side with bacterial spores. As the sheet dries out, it bends, and as the humidity rises, it straightens out — the energy of these movements is then captured and used to drive a generator.
“If this technology is developed fully, it has a very promising endgame,” stated lead researcher Ozgur Sahin, PhD. “Water evaporation is the largest power source in nature. Sunlight hits the ocean, heats it up, and energy has to leave the ocean through evaporation. If you think about all the ice on top of Mt. Everest — who took this huge amount of material up there? There’s energy in evaporation, but it’s so subtle (that) we don’t see it.”
Despite the enormous potential, until now, no one has really found an effective way to tap this energy. The breakthrough came during previous research on bacterial films when Sahin observed the inherent energy potential in such films.
The Wyss Institute for Biologically Inspired Engineering at Harvard provides more:
A soil bacterium called Bacillus subtilis wrinkles as it dries out like a grape becoming a raisin, forming a tough, dormant spore. Unlike raisins, which cannot re-form into grapes, spores can take on water and almost immediately restore themselves to their original shape. Sahin realized that since they shrink reversibly, they had to be storing energy.
When Sahin first set out to measure the energy of the spores, he was taken by surprise. He put a solution thick with spores on a tiny, flexible silicon plank, expecting to measure the humidity-driven force in a customized atomic force microscope. But before he could insert the plank, he saw it curving and straightening with his naked eye. His inhaling and exhaling had changed the humidity subtly, and the spores had responded.
In fact, simply increasing the humidity from that of a dry, sunny day to a humid, misty one enabled the flexible, spore-coated plank to generate 1000 times as much force as human muscle, and at least 10 times as much as other materials engineers currently use to build actuators, Sahin discovered. In fact, moistening a pound of dry spores would generate enough force to lift a car one meter off the ground.
With this knowledge, Sahin then devised a very basic humidity-driven generator “out of Legos™, a miniature fan, a magnet and a spore-coated cantilever,” Wyss Institute notes. “As the cantilever flips back and forth in response to moisture, it drives a rotating magnet that produces electricity.”
While this prototype itself captures only a very small percentage of the energy released during evaporation, there is a great deal of room for improvement. In particular, the researchers note the potential improvements available through genetic engineering.
While the technology is certainly interesting, and the potential energy is certainly there, it remains to be seen if an approach to electricity generation such as this can be economical.
The new research was just published in the journal Nature Nanotechnology.