"Renewable energy sounds so much more natural and believable than a perpetual-motion machine, but there's one big problem: Unless you're planning to live without electricity and motorized transportation, you need more than just wind, water, sunlight, and plants for energy. You need raw materials, real estate, and other things that will run out one day. You need stuff that has to be mined, drilled, transported, and bulldozed -- not simply harvested or farmed."
As these costs change with new technologies, constant re-assessment and balancing of pro and cons needs to be standard procedure.
And, of course, reduced and more efficient energy use is always a wise option.