[NicknamedBob]

"I think I'll start a Renewable Energy Ping list."

Geothermal Energy is not renewable. It's simply inexhaustible.

But ... at least there is that -- "no exhaust."

[Eric in the Ozarks]

As we were planning our Missouri retirement house, we looked at several high-tech heating/cooling systems and even a solar electric (off the grid) system. We settled on the Waterfurnace because the company had a good track record and we got to interview others in this area who used our installer. A bonus is that the unit also produces heat for the thermal floor in the lower level which we covered with tile.
I don't think this system would work very well in a northern climate like Minnesota but since our heating demands are moderate, it manages our needs without constantly running (like our gas furnace did in the Twin Cities.) A good amount of blown-in cellulose insulation and high quality Andersen windows have made this place very comfortable.

[Michael.SF.]

t's simply inexhaustible.

On a world wide basis yes, the statement is true. But on a case by case basis, the answer is not as definitive. Large geothermal plants, which tap geothermal brine, bring it to the surface as a heat-exchanger fluid and then re-inject it into the ground, can have a limited life. The Geysers is a perfect example of depletion over time at a specific site.