Scientists have long known how to use precipitation as a source of renewable energy. Now, it seems as though a team of researchers at Columbia University has figured out how to harness evaporation, too.
Xi Chen and his colleagues noticed that spores of the bacterium Bacillus subtilis expand when they’re exposed to humidity and contract when they’re dry, behaving much like a muscle. When lined up on a piece of tape, the expanding and contracting spores were able to straighten and curl the strips of tape as the humidity of their environment changed. Their research is detailed in a paper published in the journal Nature Communications.
This discovery suggests that evaporation may be eventually be used as a source of power. During the study, the team observed that two strips of spores could make the tape scrunch, instead of curl, and several of them acting together could contract with enough force to lift small weights of 0.2 lbs to 0.7 lbs. This may not seem like much, but is in fact 50 times the weight of the strips themselves. They wondered if harnessing the collective force of these contractions could propel a device.
They tested that idea by building an "engine." The researchers stretched these so-called HYDRA strips horizontally over a small container of water covered with shutters. As the water evaporated, the strips expanded, causing the shutters to open. Once the water had been released, the humidity dropped, the spores contracted, and the shutters closed, allowing the process to begin again. By collecting, storing, and releasing the evaporation in a controlled, cyclic fashion, the researchers created a continuous power source.
Chen and his team built another generator, resembling a spore Ferris wheel, which they dubbed the "Moisture Mill." They placed half of the wheel in a moist environment, and the other half in a less-humid space. The tiny imbalance created by the expansion of the spores in the humid environment caused the wheel to continuously tip forward, creating a rotation. This wheel was then affixed to a tiny toy car—thus creating the first evaporation-powered vehicle.
The possibilities for this newfound source of energy have yet to be fully explored, but researchers speculate that evaporation could someday be put to work in batteries, smart sportswear, and robotic limbs.