Energy return on investment: toward a consistent framework

Numerous technologies have been proposed as partial solutions to our declining fossil energy stocks. There is a significant need for consistent metrics to compare the desirability of different technologies. The ratio of energy produced to energy consumed by an energy production technology-known as the energy return on investment (EROI)-is an important first indicator of the potential benefits to society. However, EROI analysis lacks a consistent framework and has therefore yielded apparently conflicting results. In this article, we establish a theoretical framework for EROI analysis that encompasses the various methodologies extant in the literature. We establish variations of EROI analysis in two different dimensions based on the costs they include and their handling of nonenergy resources. We close by showing the implications of the different measures of EROI upon estimating the desirability of a technology as well as for estimating its ultimate net energy capacity.