SBP017 The Role of New Technologies in a Sustainable Energy Economy is a very interesting podcast about what will be required to keep up the standard of living currently enjoyed in the U.S.A. It's a recording of a lecture held at MIT in late 2006.. the scientist talking is a "solar energy guy" and one of the aspects he presented is the energy requirements for society in 2050. If you project forward current growth rates of people and energy use, it will mean global society will require 30 terawatts of energy (equating all the energy into one unit. the Watt).
Ignore global warming.. ignore peak oil.. ignore illegal wars in the middle east. Current energy use is 12 terawatts, in 2050 it will be 30 terawatts by current growth rates. An increase of 18 terawatts is required.
He went through a laundry list of ways that global society could get there. For example adding 8 terawatts of nuclear power would mean building one new nuke plant every 1.6 days. He went through a longish list..
He made a few assumptions I think are incorrect. For example he said "Gross Domestic Product (GDP) scales 1:1 with energy use". To increase GDP, he claims, has to increase energy use. I disagree. I think there is a lot of inefficient machines around us, and that we could do more with less energy input. But I think he's generally right, and that increasing efficiency isn't a cure-all. He even said something similar, he just called it 'conservation'. Hurm..
A solution direction he's pointing in is a form of solar energy deriving from plants. Plants are themselves solar energy systems. And he thinks there's a lot of potential to fine tuned plants who can directly produce useful materials for energy production. He gave one figure about if you take all available land and turn it into producing biomass for energy production .. we wouldn't have food to eat .. it would account for 2 terawatts of energy. Clearly not enough. But he also said currently known plants are about 1% efficient at converting sunlight to energy. Bioengineered plants could easily do a better job.