John Morgan questions whether wind and solar are viable energy sources when one considers energy returned on energy invested (EROEI).
There is a minimum EROEI, greater than 1, that is required for an energy source to be able to run society. An energy system must produce a surplus large enough to sustain things like food production, hospitals, and universities to train the engineers to build the plant, transport, construction, and all the elements of the civilization in which it is embedded. For countries like the US and Germany, Weißbach et al. estimate this minimum viable EROEI to be about 7……
The fossil fuel power sources we’re most accustomed to have a high EROEI of about 30, well above the minimum requirement. Wind power at 16, and concentrating solar power (CSP, or solar thermal power) at 19, are lower, but the energy surplus is still sufficient, in principle, to sustain a developed industrial society. Biomass, and solar photovoltaic (at least in Germany), however, cannot. With an EROEI of only 3.9 and 3.5 respectively, these power sources cannot support with their energy alone both their own fabrication and the societal services we use energy for in a first world country.
Energy Returned on Invested, from Weißbach et al.,1 with and without energy storage (buffering). CCGT is closed-cycle gas turbine. PWR is a Pressurized Water (conventional nuclear) Reactor. Energy sources must exceed the “economic threshold”, of about 7, to yield the surplus energy required to support an OECD level society.
These EROEI values are for energy directly delivered (the “unbuffered” values in the figure). But things change if we need to store energy. If we were to store energy in, say, batteries, we must invest energy in mining the materials and manufacturing those batteries. So a larger energy investment is required, and the EROEI consequently drops…[to the buffered level].