EROI - Energy Return on (energy) Invested

It takes energy to make energy available.
Hopefully, over the lifetime of a large wind turbine, the cost in dollars (and the amount of energy it took to make it)...

is less than

the money it generates (and the amount of electric energy it generates).

Energy return on energy invested

EROI or EROeI: This was originally a concept used by anthropologists and biologists to look at the energy that humans and other animals expend (invest) compared to the energy of the food they eat or harvest (the return on the investment). $$\text{EROI}=\frac{\text{energy gained from food}}{\text{energy used by eater}}$$

In order for an animal to survive, this ratio had better be....?

Another low-energy food strategy, favored by some humans...

In a 2006 FAQ from Sandia National labs the authors point out that in one hour, more sunlight hits Earth than all humanity consumed in the year 2001. But we want to leave some for other species too...

For our purposes.. $$\text{EROI}=\frac{\text{usable energy ("at the pump")}}{\text{energy expended in production}}$$

  • The EROI number is dimensionless--it's a ratio.
  • Does not include carbon emissions impact.
  • Does not generally include any environmental impact.
  • Does not take into account the energy density. (Gasoline, with high energy density, is great for transportation).
  • Does not take into account land needed for production.
  • Does not take into account government subsidies.
  • Should it take into account things like decommissioning of plants?

Oil production

Ever heard about "peak oil"? What is that?

Oil rig

More recently...EIA data 1860-present.

Are we experiencing a dire crisis in oil availability right now?

Extracting oil from shale: "Fracking"

EROI of different energy sources

Here is my graph of EROI by energy sources based on a paper by Gupta and Hall (2011): [spreadsheet]

Note the logarithmic scale!

Scientific American article, "The True Cost of Fossil Fuels" by Mason Inman: page 58-59, page 60-61, notes & sources.

Image credits

Jim Culp, Keith Williams, Gord McKenna LM Wind Power Southlake Mormons