Saw this interesting article. What I thought was fascinating is that the yields of the underground crops were so extensive, and that the article in effect refers to the possibility of using TDP to turn the crop waste into fuel to power the electricity. Also that the crops are in effect organic, since they don't need pesticides in the caves. So in a peaked world where people are trying to produce more food locally they could use caves for agriculture.
I guess what we need now is a lot of caves!!
I guess the main issue is where would the soil come from, and as we know, fertilizers would be increasingly expernsive.
http://wired.com/news/medtech/0%2C1286% ... _tophead_2