Why Renewable Energy Cannot Replace Fossil Fuels
In 2013, the world used 533 exajoule of commercial primary energy, of which 87% was from fossil fuels. Renewable energy (RE) accounted for just under 9% [BP 2014] (http://www.bp.com/content/dam/bp/pdf/Energy-economics/statistical-review-2014/BP-statistical-review-of-world-energy-2014-full-report.pdf). Because of global fossil fuel depletion and climate change, fossil fuel use must fall in the coming decades. Nuclear energy faces an uncertain future, with output stagnating over the past decade.
RE promises to ease reliance on fossil fuels, reduce energy imports, and cut CO2 emissions. Resources appear more than adequate to replace fossil fuels as the dominant source. But the two most abundant sources, solar and wind, are intermittent; conversely, the non-intermittent sources such as hydro and geothermal for electricity production, are limited. Bioenergy faces competing uses: food, forest products, animal forage. Already, RE has a much lower energy return on energy invested than fossil fuels. If RE is to provide all our energy, conversion and storage of intermittent energy will be needed, further lowering the energy return.
The world will eventually have to rely on RE sources, but we’ll never again have the high-energy society of the fossil fuel era. Instead, the we’ll have to make do with a lot less energy.