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According to Vaclav Smil, anything below 5% of global total primary energy supply (TPES) can be considered a marginal energy source.  Using this marker, today we have the following energy sources that can be considered non-marginal: Oil Coal Natural Gas Hydro Nuclear  Oil Price widget to work Currently, wind is at 1.24% and solar  at 0.25% of global TPES, thus both are deep into marginal territory. Energy transitions take time and the number of years required to reach penetration thresholds tend to increase with each newer energy source.* The reasons are mainly these: The larger the overall energy market, the bigger the absolute amounts of energy the new source needs to supply. The advantages of subsequent energy sources keep diminishing. In particular: coal is much better than wood. Oil is better than coal in transportation uses. Natural gas is only better than oil in say, stationary uses like space heating, industri...