Meanwhile, the source of energy has also evolved from wood to coal, to petroleum, natural gas and nuclear sources of electric power. (pppl.gov)
While there is neither a population increase nor a standard of living change, over there, just an attempt to replace fossils and nuclear sources with renewables... (realclimate.org)
Energy produced from hydro, wind, solar, and other renewables sources is expected to exceed that from natural gas and double that from nuclear sources by 2016 — becoming the second most important energy source behind coal. (scientificamerican.com)