The fact that Geothermal energy is considered to be a depletable energy source got me interested. How many years would you expect to get from a power plant and would the fact that you draw heat from the earth give any side effects that we are not aware of.
More info on Geothermal energy can be found at:
https://secure.wikimedia.org/wikiped...thermal_energy
It has a depletion section:
https://secure.wikimedia.org/wikiped...ergy#Depletion
Doesn't seem like it's a huge problem.