Renewable energy from evaporating water (w/ Video)

June 16, 2015, Columbia University
The "moisture mill" is a new kind of turbine engine that turns continuously as water evaporates from the wet paper lining the walls of the engine. Credit: Joe Turner Lin

An immensely powerful yet invisible force pulls water from the earth to the top of the tallest redwood and delivers snow to the tops of the Himalayas. Yet despite the power of evaporating water, its potential to propel self-sufficient devices or produce electricity has remained largely untapped—until now.

In the June 16 online issue of Nature Communications, Columbia University scientists report the development of two novel devices that derive power directly from - a floating, piston-driven engine that generates causing a light to flash, and a rotary engine that drives a miniature car.

When evaporation energy is scaled up, the researchers predict, it could one day produce electricity from giant floating power generators that sit on bays or reservoirs, or from huge rotating machines akin to wind turbines that sit above water, said Ozgur Sahin, Ph.D., an associate professor of biological sciences and physics at Columbia University and the paper's lead author.

"Evaporation is a fundamental force of nature," Sahin said. "It's everywhere, and it's more powerful than other forces like wind and waves."

Last year, Sahin found that when bacterial shrink and swell with changing humidity, they can push and pull other objects forcefully. They pack more energy, pound for pound, than other materials used in engineering for moving objects, he reported in a paper published in Nature Nanotechnology, which was based on work Sahin had started as a Scholar in Residence at the Wyss Institute for Biologically Inspired Engineering at Harvard University.

Building on last year's findings, Sahin and his Columbia colleagues sought to build actual devices that could be powered by such energy.

Renewable Energy from Evaporating Water. Credit: ExtremeBio

To build a floating, piston-driven engine, the researchers first glued spores to both sides of a thin, double-sided plastic tape akin to that in cassette tapes, creating a dashed line of spores. They did the same on the opposite side of the tape, but offset the line so dashes on one side overlapped with gaps on the other.

When dry air shrinks the spores, the spore-covered dashes curve. This transforms the tape from straight to wavy, shortening the tape. If one or both ends of the tape are anchored, the tape tugs on whatever it's attached to. Conversely, when the air is moist, the tape extends, releasing the force. The result is a new type of artificial muscle that is controlled by changing humidity.

The devices are put together piece by piece by hand. Shown here is the rotating part of the moisture mill. Credit: Joe Turner Lin

Sahin and Xi Chen, a postdoctoral fellow in his lab, then placed dozens of these tapes side by side, creating a stronger artificial muscle that they then placed inside a floating plastic case topped with shutters. Inside the case, evaporating water made the air humid. The humidity caused the muscle to elongate, opening the shutters and allowing the air to dry out. When the humidity escaped, the spores shrunk and the tapes contracted, pulling the shutters closed and allowing humidity to build again. A self-sustaining cycle of motion was born.

"When we placed water beneath the device, it suddenly came to life, moving on its own," Chen said.

The spore-covered artificial muscles function as an evaporation-driven piston. Coupling that piston to a generator produced enough electricity to cause a small light to flash.

The oscillatory engine. Credit: Chen et al.
"We turned evaporation from a pool of water into light," Sahin said.

With its current power output, the floating evaporation engine could supply small floating lights or sensors at the ocean floor that monitor the environment, Chen said, speculating that an improved version with stickier plastic tape and more spores could potentially generate even more power per unit area than a wind farm.

The Columbia team's other new evaporation-driven engine - the Moisture Mill - contains a plastic wheel with protruding tabs of tape covered on one side with spores. Half of the wheel sits in dry air, causing the tabs to curve, and the other half sits in humid environment, where the tabs straighten. As a result, the wheel rotates continuously, effectively acting as a rotary engine.

A miniature car driven by evaporation Credit: Chen et al.

The researchers next built a small toy car, powering it with the Moisture Mill and were successful in getting the car to roll on its own, powered only by evaporation. In the future, Sahin said, it may be possible to design engines that use the mechanical energy stored in spores to propel a full-sized vehicle. Such an engine, if achieved, would require neither fuel to burn nor an electrical battery.

A larger version of the Moisture Mill could also produce electricity, Sahin said, suggesting a wheel that sits above a large body of water and evaporates saltwater, causing the wheel to rotate and generate electricity. This development would steadily produce as much electricity as a wind turbine, Sahin said.

Explore further: Getting a charge from changes in humidity

More information: Nature Communications,

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3.2 / 5 (5) Jun 16, 2015
When I was a child I was fascinated by the duck that would bob it's head into water and then return to the upright position in what appeared to be perpetual motion. I am glad to see that they are making "Progress" after 50 years and are now producing miliwatts. Next if sufficient grant money is available perhaps they can harness the immense power or radiometers.
2.3 / 5 (3) Jun 16, 2015
"Next if sufficient grant money is available perhaps they can harness the immense power or radiometers."

Ok that should read "Next if sufficient grant money is available perhaps they can harness the immense power of radiometers."


2.3 / 5 (3) Jun 16, 2015
Who will send a lb of spores?
Just a joke; Not for Some, though!
2.3 / 5 (3) Jun 16, 2015
Terrific mind-boggling result!

I love the smell of fresh science in the morning!
4 / 5 (4) Jun 16, 2015
I am glad to see that they are making "Progress" after 50 years and are now producing miliwatts. Next if sufficient grant money is available perhaps they can harness the immense power or radiometers.

The potential available in evaporating water is about 600 Watt per liter per hour.

The drinking duck was actually a heat engine that operated on the fact that the evaporating water cooled the beak. Nothing to do with this case.
3 / 5 (2) Jun 16, 2015
I was thinking the opposite direction.
A huge amount of energy goes into water to cause it to evaporate. Then when water condenses back into rain that energy MUST be released. Normally it is released as heat energy into the atmosphere. If we could capture that energy it would be a huge resource. I will hazard to say that it would also reduce global warming since the heat is no longer going directly into the atmosphere. And if we could trigger the release of that energy, force the clouds to release the energy they have stored, then that would also trigger rain when and where we need it.
4.3 / 5 (3) Jun 16, 2015
adam hasn't looked into price/payoff systems before :(...
yes, lets somehow take some heat out of the atmosphere. that's not a totally rediculous way of harvesting energy, nor is it impossible to do on a large scale, but would probably cause the burning of equivalent fossil fuels to create the infrastructure.. etc.etc.etc. solar roadways all over again.

this is similarly problematic- The input vs the output is insanely low. Sure, there's plenty of energy in there, but how much energy do you put in to cause the evaporation, how much to transport the water. Wouldn't it work better with ethanol?, What's the mW per cm^3? weight? transportability...
sounds like one of those "we need something to justify our budget" stories to me.

not scalable, Extremely delecate, intermittant with temperature- dollar for dollar and inch for inch worse than solar, for even crappy commercial panels, or wind for locales where that's possible.
5 / 5 (1) Jun 16, 2015
in a real way most of our power generation is done by using the volume expansion with the evaporation of water.
all [industrial- tower based] solar systems are powered by heating water and the steam spins a turbine to do work- just like coal and nuclear. The largest chunk of our power not generated by steam is hydroelectric.
so you could say that essentially all of our power is generated through 4 ways-
Steam,gravity, temperature gradients (wind), and photovoltaics.

trying to eliminate the need for a fuel will reduce this to an oddity of physics- Great if you have very little outside energy and tons and tons of time, but worthless to us beings living in today.
not rated yet Jun 16, 2015
Well, I guess it would work okay in dry climates. However, in midst of summer humidity, I have doubts that it would be all that effective. I also have to wonder how this works as temperatures approach freezing.

Just like every other such energy source: It works best when you don't need it to.
1 / 5 (3) Jun 16, 2015
It is QUITE UNFORTUNATE & DUMB that They cannot make something, Some Artificial Substance similar to those Spores that could provide Far better Energy!
It is so sad that no one is broaching that. Why? The World is so Wide and Population is so Dense, I thought.
2 / 5 (4) Jun 16, 2015
So, What traits are we looking for?
That Absorbs most moisture?
That Evaporates most of it OR The Fastest Evaporator of All?
If We could get all Evaporated Energy from the Entire Ocean on one fine day in some distant future, Who will then lift the Moisture up into the Clouds? Will Water Fall Back into the Ocean right then & there without moving up? Then, No Rains on the Land at all? WoW!
not rated yet Jun 17, 2015
Yup I like Betterexists point of view.

Messing with the water cycle for the planet, doesn't sound any better than burning fossil fuels!!!
not rated yet Jun 17, 2015
Human water use is sucking dry around a third of the world's largest underground water basins at an alarming rate, with potentially risky consequences for farmers and other consumers.
5 / 5 (2) Jun 17, 2015
So, What traits are we looking for?
That Absorbs most moisture?
That Evaporates most of it OR The Fastest Evaporator of All?

Messing with the water cycle for the planet, doesn't sound any better than burning fossil fuels

Human water use is sucking dry around a third of the world's largest underground water basins at an alarming rate, with potentially risky consequences for farmers and other consumers.

I think you might have missed the significant points in this that it's not the absorption or evaporation per se that is important but the change of size in the spores when that process occurs, and that the water is not necessarily in fluid form but rather as a humid atmosphere, and the moisture is not "used up" but simply evaporates into the wider atmosphere to later precipitate out somewhere else as rain or snow or whatever. This seems to me an ingenious, very useful and environmentally friendly alternative way to generate electricity.
not rated yet Jun 21, 2015
How many contractions and expansions such device can take before being worn out ?
not rated yet Jun 21, 2015
Scaled up to container size this engine would not pull skin off a rice pudding.
not rated yet Jun 22, 2015
This is a neat experiment, but I just do not think it is a viable energy source. The idea behind it - using the spores to react to moisture and create motion as an artificial muscle - Is pretty cool. If we can create biological muscles, maybe even that repair themselves, it would be better than our old machines that wear out. Great Science though!

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