These Tiny, Living ‘Evaporation Engines’ Could Power 70% Of America

Image via Virginia State Parks/Flickr.

Imagine sitting by a lake sometime in the near future. It’s a bright, sunny summer day. There are swimmers, paddleboarders, and, a little ways away, a flotilla of strange-looking devices. A couple thousand of them float on the surface of the lake, bobbing slowly up and down as a boat passes by. Strange little shutters on top open and close with soft noises, like the sound of rain on leaves. You sit back and relax. These strange devices aren’t anything to worry about. In fact, they’re what’s powering your entire neighborhood.

When we talk about renewable energy, the first thing that comes to mind is likely solar or wind. But researchers now think that in the future, another natural cycle could be harnessed — evaporation. In a new paper published in Nature Communications, researchers at Columbia University calculated that by harnessing the natural evaporation of lake and river water, tiny half-biological “evaporation engines” could power a significant swath of the United States.

These HYDRAs are artificial muscles that move as humidity changes and power the evaporation engine. Image via Ozgur Sahin and Xi Chen, used with permission.

Wait, what’s an evaporation engine? And did you say “half-biological”?

These small devices, about the size of a paperback book, each contain strips of a special material that looks a bit like a packet of ramen noodles and functions like a cross between a sponge and a rubber band.

When the air around the material is dry, the strips tighten and bunch up. When the air is humid, the strips absorb water from the air and relax.

[quote position="left" is_quote="true"]The secret behind the material’s springiness is that it’s partly alive.[/quote]

In normal conditions, water naturally starts to evaporate over time, so by placing the device over a puddle of water — and with the help of special shutters that open and close to control humidity — the researchers can create a heartbeat-like rhythm of push and pull that powers a tiny electric generator.

The secret behind the material’s springiness is that it’s partly alive: Each strip is painted with dormant, harmless bacterial spores that naturally absorb water from the air.

Each individual device isn’t that powerful, but together, evaporation engines have the potential to generate some serious juice. According to the senior author of the study, Ozgur Sahin, a flotilla the size of a football field could theoretically power between five and 50 houses.

Scaled up, if the researchers covered all major American rivers and lakes (excluding the Great Lakes), Sahin’s team has calculated that we could potentially produce a whopping 325 gigawatts of power — about 70% of what the United States currently produces.

No way. How is that possible?

When Sahin and his colleagues first unveiled their idea back in 2015, they started small, like any researcher testing out a new idea, powering powering little LED lights and toy cars. But now that they’ve done the math, Sahin says there’s a reason they’re thinking much, much bigger.

"We have the technology to harness energy from wind, water and the sun, but evaporation is just as powerful," said Sahin in a press release. "We can now put a number on its potential."

These engines would potentially be affected by weather or time of day, like solar or wind power is, but the exact impact would be different. While direct sunlight does energize evaporation (which means sunnier states like Arizona would get more of a punch out of each of their engines), evaporation also happens at night as well. This means it could potentially be more reliable than solar or wind, Sahin said.

Furthermore, since the devices capture evaporation, they could help drier states reduce water loss.

Sahin and his team are still working to improve the engine’s energy efficiency in the lab, so it’s hard to say when they’d start generating power, but Sahin says it might be as little as five years before we see a pilot study.

So we’re probably not going to see these on our lakes and rivers any time soon. But they present an interesting solution to our energy problem.

As we’ve moved beyond fossil fuels, humanity has turned to a wide array of renewable energy sources — from the sun and wind to the waves and tides to geothermal and hydroelectric. If Sahin and his team are right, one day we might add evaporation to that mix.