The Changing Meaning of Energy Return on Investment and the Implications for the Prospects of Post-fossil Civilization

Abstract

Energy return on investment (EROI) is a useful physical metric to compare the utility of energy production processes and their development over time. The concept has been extended from its physical, process-based origin to one that describes the societal metabolism. As such, EROI has been used to speculate about the prospects of humanity in a late-fossil and post-fossil civilization. Often, the narrative to emerge around EROI is that in the (near) future, prosperity will be compromised. Here, we take a fresh look at EROI, with a distinction between a physical EROI, which is useful at energy project level, and a societal, or economic, EROI—appropriate at the level of the whole economy. This distinction leads us to conclude that a renewable future is possible. Such a future is essentially unconstrained by the physical EROI and will have an acceptable economic EROI—not much different from that of the past century.