Environment

It's Not the Heat, It's the Humidity: Electricity From Air

Science Not FictionBy Eric WolffAug 30, 2010 8:00 AM

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Who needs Mr. Fusion if you can draw energy straight out of the air? A team of scientists from the University of Campinas in Brazil worked out a way to draw charge from air in high humidity, going some distance to explaining the origins of lightning, and offering the promise of renewable power for San Francisco and New England, where humidity is abundant and sunshine, not so much. The study authors, Telma R. D. Ducati, Luis H. Simoes and Fernando Galembeck, found that tubes of aluminum, stainless steel, or chromium acquired electric charge in high relative humidity, and that the charge rose as the humidity went up.

Those metals are key, because none of them rust in swampy air, the paper said. Instead they develop a metal oxide coating that absorbs ions from surrounding water droplets. Whether the ion is OH- or H+, the other half of the water molecule ricochets off into the atmosphere, allowing the metal tube to acquire a charge. I'm rather taken with the simplicity of Ducati et. al.'s experiment: They made a sandwich of several sheets of filter paper, a sheet of aluminum and a sheet of stainless steel. They mounted this capacitor in an aluminum box, and then put the box in a Faraday Cage. They could easily generate a charge simply by adding humidity to the space in the box, and drain it with a short circuit. Whether this is the first step to a new kind of renewable power will take a long time to figure out, but it seems to offer a new opportunity to humid parts of the country that can't easily benefit from wind or solar power. The scientists have decided to call it hygroelectricity, which means "humid electricity." I recommend the paper itself to anyone with even a modest recall of high school chemistry, or a semester of college chemistry. In most respects it's a model of clarity not often seen in published scientific studies.

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