Power generation using the potential energy stored in our tanks?

[FitoPharmer]

I thought these type of Stirling engine energy recovery systems were neat for saving some money. Just have to figure out if you can use them for a reef tank. Maybe run water cooled halide shades then run it through one of these

http://www.greenoptimistic.com/2010/...irling-engine/

There are even versions that can take the energy left over from hot showers, dish washing, laundery, ect....