Also note that geothermal energy is not formally "renewable" because eventually the local temperature is pulled down. Iceland and New Zealand have to continually manage this problem as older heat supplies fail. The Geysers site near San Francisco used to provide 2000 MW, but it's cooled off...
http://www.sciam.com/article.cfm?articleID=00011EB0-E249-1CF4-93F6809EC5880000
However, I think that's more a problem with close-to-surface natural hot-water aquifiers, if they are over-used; not with deep shafts where rock heats the water. (In hot dry-rock (HDR) shafts, water supplied from the surface.) On the other hand, the German potential in the estimate I linked includes deep hot aquifiers, so the sustainable part might be 'only' 300 times the present German demand. *Lunatic*, n. One whose delusions are out of fashion.
