What a wild idea, right? I mean, humans have been harvesting energy from falling moisture for centuries. Rain drops fall and form streams and rivers, which we then dam up and use for hydroelectric power — but up until now, nobody has really figured out a way to gather energy from water that’s traveling back up into the air.

So how exactly do you capture energy from evaporating water? Well, in order to understand how the engine works, you first need to understand the material inside of it. To make the engine possible, doctor Ozgur Sahin invented a new material he calls HYDRAs (short for hygroscopy-driven artificial muscles). They’re basically thin plastic bands that are strategically imbued with bacteria spores, so they expand when exposed to tiny amounts of moisture, and contract when they dry out — sort of like an artificial muscle that runs on water vapor.

To translate this motion into usable energy, Sahin and his team have built a number of engines. The first (and most illustrative) is basically just a set of HYDRA coils placed inside a small enclosure. When water is introduced beneath the engine, surface molecules naturally begin to evaporate and cause the enclosure to become slightly more humid. The HYDRA strips soak up this tiny amount of moisture and begin to expand — in the process collectively pulling on a small cord which in turn spins a small electromagnetic generator.

While they expand, the coils also pull open a set of shutters located above themselves which releases the humidity inside the enclosure, causing the coils to contract. This contraction returns the shutters to a closed position, thereby starting the entire process over again, ad infinitum, until the evaporation stops.

The engine only produces about 50 microwatts of energy on each stroke, but huge power output isn’t really the point here. The amazing and potentially revolutionary thing about this engine is that it’s capable of gathering energy from a puddle of water that’s not really doing anything but sitting there and existing at room temperature. With 60-degree water, the engine will open and close its shutters once every 40 seconds. At 70 degrees, it does so every 20 seconds. At 90 degrees, it’s every 10. That’s enough power to light up a small LED, or even send out a quick burst of radio waves. And to top it all off, Sahin says the entire engine — HYDRAs included — should cost less than $5 to build.

Don’t toss your solar panels in the trash quite yet though. While the technology looks quite promising, it’s definitely more of a proof-of-concept at this point. In order to become a viable source of alternative energy, the evaporation engine would need to be refined, improved, and scaled up in a big way. Keep your fingers crossed and who knows? You might be able to power your house with your swimming pool by 2025.

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