A Stirling Engine is one of the world’s oldest, having been conceived in 1816 as a rival to the steam engine. It uses differences in temperature to drive a piston back and forth, turning a flywheel in the process. It’s this engine, albeit a tiny one, that sits inside the onE Puck you see above, and which allows you to charge your USB-connected device using nothing but the heat of your coffee cup. Or the cold of your iced tea. Just place any sufficiently cold or hot object on top of the onE Puck, and the Stirling engine will kick to life, driving a tiny generator. Obviously the hotter (or colder) the object, the more efficient the onE Puck becomes, but it’s designed to generate 5W of power at a combination of 1,000mA and 5Vdc. That’s standard for a phone charger, but these are clearly ideal conditions. It might generate this much at peak performance, when you’ve placed a piping hot drink, and then slowly lose its charging power. There’s an internal battery which accumulates charge, and delivers it in batches to your connected device, so it may appear as though it’s not charging at times, but it’ll kick in eventually.
It’s slow and steady, rather than fast and efficient, and is more of a novelty than anything else. But as a Kickstarter project, it’s been successful enough to raise $125,000 with 23 days to spare. If you want yours, you’ll have to pledge $115 and expect delivery in one year.