James Conca at Fortune looks at Energy Returned on Investment or EROI. EROI was an early concept that easily demonstrated the advantages, as well as the investment needed, to exploit these new energy sources (The Encyclopedia of Earth). Also referred to as Energy Returned on Energy Invested (EROEI), EROI is the ratio of energy returned to energy invested in that energy source, along its entire life-cycle.* When the number is large, energy from that source is easy to get and cheap. However, when the number is small, the energy from that source is difficult to get and expensive.
When the number is one, there is no return on the energy invested, and the entire investment has been wasted. The break-even number for fueling our modern society is about 7.
"Energy Returned on Investment, or EROI, with and without energy storage (buffering or load following). CCGT is combined-cycle natural gas turbine. Nuclear is conventional Pressurized Water Reactors, fast reactors are several times higher. Solar CSP is concentrated solar ('a la Ivanpah), solar PV is photovoltaic solar cells like on rooftop solar. Energy sources must exceed the economic threshold of about 7 (blue line) in order to yield the surplus energy required to support a modern society. EROI is similar to Energy Returned on Energy Invested (EROEI). After Weissbach (2013)"
