These are good articles to read:
(1) Energy Transitions Past and Future
June 7th 2010
http://www.theoildrum.com/node/6561
(2) 21st century, some sobering thoughts
.
5 challenges:
(a) Scale of shift
(b) Lower energy density of replacement fuels (energy content in unit of fuel)
Crude oil: 42 MJ/kg
Air dry crop residue: 12-15 MJ/kg
(c) Substantially lower power density of renewable energy extraction
Hydrocarbons: 100-1,000 W/m2
Biomass: 1 W/m2
Water & wind: 10 W/m2
Photovoltaic: 20 W/m2
US corn ethanol: 0.22 W/m2
(d) Intermittency of renewable flows
Coal fired power plant: >75% load factor
Wind: 20-25% load factor
(e) Uneven distribution of renewable energy resources
Many major load centres far away from available sources
by Vaclav Smil, University of Manitoba
http://www.vaclavsmil.com/wp-content/uploads/docs/smil-article-2006-oecd-observer.pdf
