Amid the quest for self-cleaning windows, MIT scientists found a brand new source of green energy

See the power plant?
See the power plant?
Image: AP Photo / Michael Probst
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In the future, if you need to charge your iPhone, you might just be able to snatch some energy from the air. Or more specifically, the carbon-free electricity that is generated when charged water droplets repel each other, say scientists at the Massachusetts Institute of Technology.

A team of researchers led by Nenad Miljkovic, a postdoctoral associate at the school’s NanoEngineering Group,  was investigating how water droplets interact with superhydrophobic surfaces—basically glass, metal or other materials treated with coatings that repel water—in an effort to create potential new products. (Think self-cleaning windows.)

But after reviewing high-speed video, researchers found, under certain conditions, water droplets don’t just slide off those surfaces. They sometimes leap into the air and repel each other. And when that happens, the droplets create a small electrical charge. The upshot? According to Miljkovic, it may be possible to generate electricity by merely collecting condensation from the ambient air.

Here’s how it would work: Two extremely water-repellent metal plates are placed outside. Water droplets jump from one plate to the other, generating an electrical charge along the way. “You just need a cold surface in a moist environment,” Miljkovic said in a statement.

“The power generated could be used anywhere,” Miljkovic told Quartz in an email. “You could run a steady load, or you could charge a plate like a capacitor (like a battery). A simple embodiment is charging your phone out in the wilderness or something.”

But don’t expect to see superhydrophobic power plants anytime soon. Leaping water droplets don’t seem to create anywhere near as much power as, say, a major utility operator would need to run a plant that powers a city.  “At this point, I can’t give you a quantifiable number, however I can tell you that it will be a relatively low power density,” Miljkovic said.

Even so, Miljkovic said his team is currently working on a prototype to demonstrate that electricity can be produced from such charged droplets. They expect to have a working model in the laboratory next year.