The progress that has been made over the last few years in developing “closed loop” geothermal resources (i.e., re-injecting recovered water back into the circuit), and employing dual cycle systems to operate at relatively low temperatures is very impressive. Add to that the fact that many of the recent advances in the natural gas industry that has led to a dramatic increase in provable, recoverable gas resources (e.g., horizontal drilling, artificial site stimulation, coatings and composites necessary to withstand highly corrosive environments) are at least theoretically applicable to geothermal applications as well. That's the good news. The bad news is that, as far as I know, the ability to identify productive sites with a high likelihood of success is still in its infancy. That is partially counter-acted by the fact that the oil and gas industries have provided enough information over the years to render many thus far un-tapped sites more or less no-brainers — particularly in places like CA, NV, ID, UT, and AZ. So there's an obvious trajectory available for production, not to mention further research, at a reasonable cost. Nonetheless, drilling into those fields is still risky — drilling a well is always an expensive proposition, and if it comes up dry, well, it's money down the drain (so to speak). And of course there's the possibility that stimulating a site will cause tectonic instability. But to my mind, if all it takes is stimulating a well-head to cause an earthquake, that earthquake was going to happen in relatively short order anyway. Think of the stresses involved as a constantly expanding balloon: the balloon will pop eventually, whether or not a pin (i.e., a stimulated well-head) is inserted in it beforehand. The difference, of course, is that the “pin” has a considerable amount of political fall-out associated it, lol!

At any rate, my impression is that it's still too early to tell how much of a contribution hot rock geothermal could make to the overall energy picture. It could be huge or it could be a niche. But either way, IMO, it's worth spending a reasonable amount of money to find out. I think Steven Chu has it exactly right.

Now consider an underground building (whose temperature the Earth moderates) with geothermal temperature control (heating and climate control system) added. That's real geothermal living!

In this case, though, it's simply a pair of pipes, one intake and one exhaust, going through a heat exchanger, for 95% heat recovery. Take a look at the poster (PDF) for more detail. Very clever:
http://www.ecofuturesbuilding.com/files/active/…

http://www.ecofuturesbuilding.com/taxonomy_menu…

No great implications to this story; just an interesting tidbit from out here in the pacific.

These problems are shared as well by wind (which, also, is intermittent, another defect) and hydro.

Check your units. That's 100,000 MW of capacity, not generation. The U.S. consumes about 3.6 trillion kWh according to EIA. 100,000 MW of capacity running at 95% capacity factor would generate ~ 832.2 billion kWh, or roughly 20% of US consumption. That's roughly the current share of nuclear power, which operates a little over 100,000 MW of capacity in the US.

The US currently consumes about 4 Trillion watts as of 2008. So even if this hypothetical value does get reached by 2050 and our consumption stays the same, your looking at an answer to 2.5% of our power needs. Geothermal is clean, and it certainly should be used where it can be, but overall it is not an answer to our needs. There just aren't enough locations to provide enough energy to make it one. The same can be said of tidal energy. Both solutions are side dishes to the clean energy problem, not the main course.