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Could humidity power join the list of renewable energy sources?


January 27, 2014

The humidity-driven flexing of a spore-covered piece of latex rubber (right) drives the mo...

The humidity-driven flexing of a spore-covered piece of latex rubber (right) drives the movement of a magnet, which produces electricity (Photo: Xi Chen/Columbia University)

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Ozgur Sahin, Ph.D., believes that water evaporation is the largest power source in nature. In an effort to demonstrate the potential of this untapped resource, Sahin and his fellow researchers have created prototype electrical generators with rubber sheets that move in response to changes in humidity thanks to a coating of bacterial spores.

In a 2012 study published in the Journal of the Royal Society Interface, Sahin, along with Wyss Institute Core Faculty member L. Mahadevan, Ph.D., and Adam Driks,Ph.D., a professor of microbiology and immunology at Loyola University Chicago Stritch School of Medicine, detailed how a soil bacterium called Bacillus subtilis dries up to become a tough, wrinkled, dormant spore. These spores can then be almost immediately restored to their original shape when taking on water.

As Bacilli bacteria dry out and form spores (shown here), they wrinkle, and as they rehydr...

With their ability to shrink reversibly, the researchers realized the spores must be storing energy. In an effort to measure the energy of the spores, Sahin coated a tiny, flexible silicon plank in a solution containing the spores with the assumption he would be able to measure the humidity-driven force in a customized atomic force microscope. To his surprise, before he could even get it under the microscope, Sahin could see with the naked eye the plank curving and straightening in response to the subtle humidity changes from his breath.

"I realized then that this was extremely powerful," said Sahin.

Powerful indeed. Sahin discovered that the flexible, spore-coated plank could generate 1,000 times as much force as human muscle when the humidity was increased from that of a dry, sunny day to a humid, misty day – this is 10 times greater than materials currently used to build actuators. Sahin also calculated that moistening 1 lb (0.45 kg) of dry spores would generate enough force to lift a car 3.2 ft (1 m) off the ground.

After testing silicon, rubber, plastic, and adhesive tape, Sahin settled upon rubber as the most promising material for a spore-coated actuator. Using Legos, a miniature fan, a magnet and a spore-coated cantilever, he constructed a simple humidity-driven generator that produces electricity via the rotation of the magnet that is driven by the cantilever flipping back and forth in response to changing humidity levels.

Although the prototype only captures a small percentage of the energy released by evaporation, Sahin says efficiency could be improved by genetically engineering the spores to be stiffer and more elastic. In fact, in early experiments a mutant strain provided by Driks has already been shown to store twice as much energy as normal strains. The researchers believe the technology will one day make it possible to have electrical generators driven by changes in humidity from sun-warmed ponds and harbors.

"Solar and wind energy fluctuate dramatically when the sun doesn't shine or the wind doesn't blow, and we have no good way of storing enough of it to supply the grid for long," said Wyss Institute Founding Director Don Ingber, M.D., Ph.D. "If changes in humidity could be harnessed to generate electricity night and day using a scaled up version of this new generator, it could provide the world with a desperately needed new source of renewable energy."

The team, which also included Xi Chen, a postdoctoral research associate at Columbia University, has had their study published in the journal Nature Nanotechnology.

A spore-covered piece of latex is shown moving in response to changes in humidity in the following video.

Source: Wyss Institute

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick

The science seems fine...but where is such a regular, rhythmic, change in humidity to be found apart from day-night variations? Perhaps in Metro stations with a sudden rush of air as trains arrive? Does anyone have any more ideas?

28th January, 2014 @ 04:30 am PST

Nature finds a way

Brian M. J. Novak
28th January, 2014 @ 06:17 am PST

I guess 2 fans, one blowing low humidity air across the sensor and one blowing high humidity air across it. Just switch each fan on in turn. Shouldn't take too much of the energy produced to keep it going.

28th January, 2014 @ 07:24 am PST

Perhaps a mister could provide a humid punch to an airstream. Overcoming mechanical losses may be a challenge, but a solar chimney might eliminate the need for a fan.

Bruce H. Anderson
28th January, 2014 @ 08:12 am PST

There are lots of things that change with humidity or moisture. The forces involved can be enough to crack foundations, for example. That's why people water their yard around the foundation.

I guess the trick is to find something that responds at about the frequency of the humidity change cycle.

Victor Engel
28th January, 2014 @ 08:29 am PST


wasting water to make power

wasting most of the evaporation energy

sounds like it;s about .001% as good as anything available, plus the bonus danger of mutant bacteria

Larry English
28th January, 2014 @ 08:33 am PST

There may be a lot of power here, but it would be pretty darned diffuse. There are lots of great sources of diffuse power but harvesting any of them on a meaningful scale has always remained elusive. This is entertaining, but I can't imagine it ever being more than a parlor trick. Maybe David Copperfield would pay something for this kind of mechanism to use in one of his acts.

28th January, 2014 @ 12:36 pm PST

"Solar and wind energy fluctuate dramatically when the sun doesn't shine or the wind doesn't blow, and we have no good way of storing enough of it to supply the grid for long," said Wyss Institute Founding Director Don Ingber, M.D., Ph.D

Once again, a person who ought to know better, assumes that solar power must be limited to collection and conversion on the planetary surface, when only a few thousand miles over their head, the sun shines continuously, without interruption…

Why do even scientists who know better, assume that all problems must be solved using only those things inside the box we call Earth?

We are NOT limited to resources on or in the Earth. We have access to the entire Solar System, and near infinite energy flows by just above our heads. Not only that, but we have the tech to recover it easily!

The Earth and all it's resources are but a minute grain of dust when compared with what the Solar System holds.

To stop thinking inside the box, quit making boxes before you solve the problems!

There is no 'box' until you create it.

Charles Barnard
28th January, 2014 @ 12:41 pm PST

coastal valleys have variable humidity sometimes on a scale of minutes. Dry places where fog comes in , like Peru/Chile, Australia, and the African & mediterranean coasts, could also use this to power desalinization. Imagine a bank of spore driven pistons that pressurize reverse osmosis.

28th January, 2014 @ 01:12 pm PST

SuperFool: Costal mist is desalinated. It can be collected easily, no energy needed. But now it can be used to fuel a generator thanks to Wyss Institute.

Don Duncan
28th January, 2014 @ 06:13 pm PST

Isn't this basically the plot of The Matrix but with bacteria instead of people???

28th January, 2014 @ 10:14 pm PST

How does this compare to horse hair which was used to drive the dial on early humidity gauges???

29th January, 2014 @ 07:42 am PST

Don Duncan: yes the mist is mostly desalinated already, but the collection process for drinking and irrigation is relatively inefficient. I was referring to using it for desalinating seawater.

29th January, 2014 @ 02:47 pm PST

"Sahin also calculated that moistening 1 lb (0.45 kg) of dry spores would generate enough force to lift a car 3.2 ft (1 m) off the ground."

Question - what has the force got to do with the distance lifted?? The force is the weight of the car, which is not stated. The product of force and distance lifted is the "work done", which has units of Joules. This is what we're interested in (energy)!

Mark Windsor
31st January, 2014 @ 05:14 am PST
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