[praptak]

This looks like the opposite of a low hanging fruit. That fruit is hanging very high and on top of that it is very small and hard to get to the edible part.

Solar, wind, hydro, biofuel, geothermal, maybe even day-night temperature cycles - all of these look much more promising in the "free" energy department. Actually it's hard to think about a worse energy source. Earthquakes maybe? :-)