Bioengineers from Columbia University have developed a cheap evaporation engine that could power devices with clean energy source. The engine, which only costs $5 to build, only needs bacterial spores and evaporating water to work.

In their study published in the journal Nature Communications on June 16, Ozgur Sahin, from Columbia University, and colleagues presented devices powered by bacterial spores that harvest energy from evaporating water.

Sahin and colleagues used bacterial spores that swell when they absorb water and contract when lose water.  The researchers glued billions of these spores on several plastic tapes and tapped on the movement to produce energy that powered an engine capable of running LED light and drive a miniature car weighing 0.1 kilograms. They were able to demonstrate that this miniature car could move forward as the water in it evaporated.

"Using these engines, we demonstrate an electricity generator that rests on water while harvesting its evaporation to power a light source, and a miniature car (weighing 0.1 kg) that moves forward as the water in the car evaporates." The researchers wrote.

Although it can only power small devices at the moment, the researchers are convinced that they are only beginning to tap the technology's energy potentials. They said that such technology could have applications in providing power to robotic systems, sensors and other machineries that work in the natural environment.

"People before us had shown that the spores change shape in response to humidity," Sahin said. "They shrink when they're dry and expand when exposed to moisture. But in our studies, we found them to be surprisingly rigid. That told us that this shape change must come with a lot of energy.

What makes the technology a good alternative compared to solar energy is that the engine is cheap. It only costs $5 to build. Sahin also said that theoretically, the spores could produce more energy per square foot compared with wind farms and for a much lower cost albeit this has not yet been shown in a real device.

"This is not the first time that evaporation energy has been captured, but it is the first time that it has been done a scale where objects could be moved," said Peter Fratzl, from Max Planck Institute of Colloids and Interfaces. "The work pushes a great idea all the way into a practical demonstration of the potential".

Sahin said that while their devices may seem to be like toys there are actually a number of big technologies that started out this way. 

Photo:  Xi Chen/Columbia University 

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