I worked in the offices of a power company this past summer (Progress Energy in Raleigh, NC) and they had revolving doors in front. And there were big signs encouraging you to use the revolving doors. I put two and two together and kinda guessed that they were using those to generate electricity, seeing as how they're saving themselves money directly. I guess I could've been wrong, but I kinda thought it was common sense.
12/10/08