Harvesting electrical power from vibrations or other mechanical stress is pretty easy. Turns out all it really takes is a bit of crystal or ceramic material and a couple of wires and, there you go, piezoelectricity. As stress is applied to the material, charge accumulates, which can then be shuttled away to do useful work. The classic example is an electric lighter, in which a spring-loaded hammer smacks a crystal, producing a spark. We're surrounded by this sort of ambient energy. The whole universe is just a big mess of force and stress. The tapping of my fingers on the keyboard now could theoretically be used to generate voltage. In fact, the idea is already under patent: a battery-charging keyboard cover. But the idea scales way up too: Imagine the sway of a skyscraper or the trembling of an entire forest in the wind.

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