Engineer Poet has some posts up exploring alternative energy:
faq (on alternatives)
Question #1: Do solar panels ever pay back the energy needed to make them?
Answer: Yes. As of the late 1990's, systems based on crystalline silicon PV panels returned their energy of manufacture in less than 4 years (about 3 years for the module and frame), and systems based on thin-film panels in a bit over two years (2 years for the module and frame); advances were expected to reduce the system figures to about 2 years and 1 year, respectively.
This caught my interest -- I need to survey solar technologies again. I know that about a year ago my Dad priced out a "complete" home solar system, including deep cycle batteries and in no way did a complete system pay for itself in 4 years -- more like 15. That includes profit for the solar company and installation, of course. However, I can readily believe that the cost of the solar panels themselves are dropping in terms of energy cost -- although for the average buyer, prices are high because solar is booming right now.
A Lever and a Place to Stand
It appears that a process which uses biomass to produce carbon which is then used to drive a zinc cycle for zinc-air fuel cells could replace all petroleum-based motor fuel used in the USA, and all of the natural gas burned for electric generation as well. No process for turning biomass into ethanol could accomplish anywhere near as much for the same inputs, and no alcohol process can use wind power to generate the same product. Even allowing for rather poor efficiency of zinc-air fuel cells, the zinc route gets much better leverage out of limited inputs.
Read the whole post -- in the sense that this conclusion relies on something akin to a life-cycle analysis, note that various input variables greatly affect energy output levels. More simply, we don't have the specific energy infrastructure in place to do this on the scale suggested. This infrastructure is but one variable.
As peak oil sets in, projects to rethink and redo how we aquire energy will become extremely difficult.
Chopping down trees for firewood will remain tragically easy.