It's an alarmingly simple concept that claims to be the world's first application: Netherlands-based company Natuurcafé La Port installed a power generator into a revolving door. Fantastic, but it took us this long?
The door is the entrance to the Driebergen-Zeist railway station, where it's predicted to generate 4600 kwh of energy a year—or somewhere around what the average house needs annually, depending who you talk to. Not bad at all. Sure, it's probably not enough to power all of those train lines, but it's essentially free energy. And heck, it's a lot more practical than this idea. [Boon Edam via Inhabitat]