Most of The Physics of the Death Star is pretty much Greek to me (art degree!) but long story short, the amount of energy the Death Star needs just to blow stuff up:
It’s a solid week of the sun’s entire power output. Dumping it in about a single second, as required to blow up Alderaan, is a very, very impressive feat. Doubly so when you take into account the fact that the binding energy is just enough to dissociate the planet into a diffuse cloud. If you want to actually blow the thing up into pieces flying out at many times escape velocity, you need much more energy.
So how much would it take to move that thing around? Even in zero gravity? How about the lights? Interior gravity? Refreshers? Mouse-droid charging stations? On second thought… I don’t want to know. (via)