I'm surprised of how little potential geothermal has as a sustainable energy source. The total heat flow from the earth is 42 TW, and wikipedia says world energy consumption in 2008 averaged at 15 TW. We'd need a better then 30% global efficiency to use geothermal exclusively long term. This pretty much makes geothermal non-renewable...

Solar energy on the other hand clocks at 173 petawatts (of which 30% is reflected, so that makes it 120). http://en.wikipedia.org/wiki/Earths_energy_budget#Incoming_e...