Energy Return on Energy Investment, an Important Figure-of-Merit for Assessing Energy Alternatives

Abstract

Energy Return On Energy Investment (EROEI usually abbreviated as EROI and also referred as net energy analysis or energy payback ratio) is an important figure of merit for assessing the viability of energy alternatives. EROI analyses of geothermal energy are either out of date, of uncertain methodology, or presented online with little supporting documentation. Too often comparisons of energy systems are made ambiguous by inappropriately using a metric based on “efficiency” when EROI would be more appropriate. For geothermal electric power generation, EROI is determined by the energy delivered to the consumer compared to the energy consumed to build, operate, and decommission the facility. Thus, EROI compares high quality input energies, e.g. the diesel fuel used to run the drill rig to another high quality energy, the electricity produced.

The methodology (Input/Output Analysis) and results of past geothermal EROI are reviewed and issues or problems conducting and interpreting EROI analyses are discussed. The validity of past geothermal EROI estimates is investigated by spot checking come of the major energy inputs into constructing geothermal wells using process analysis rather than economic data. Preliminary updates of past geothermal power production EROI are estimated and applied to understanding the future of geothermal development.