What is the Minimum EROI that a Sustainable Society Must Have?

Abstract

Economic production and, more generally, most global societies, are overwhelmingly dependant upon depleting supplies of fossil fuels. There is considerable concern amongst resource scientists, if not most economists, as to whether market signals or cost benefit analysis based on today's prices are sufficient to guide our decisions about our energy future. These suspicions and concerns were escalated during the oil price increase from 2005 -2008 and the subsequent but probably related market collapse of 2008. We believe that Energy Return On Investment (EROI) analysis provides a useful approach for examining disadvantages and advantages of different fuels and also offers the possibility to look into the future in ways that markets seem unable to do. The goal of this paper is to review the application of EROI theory to both natural and economic realms, and to assess preliminarily the minimum EROI that a society must attain from its energy exploitation to support continued economic activity and social function. In doing so we calculate herein a basic first attempt at the minimum EROI for current society and some of the consequences when that minimum is approached. The theory of the minimum EROI discussed here, which describes the somewhat obvious but nonetheless important idea that for any being or system to survive or grow it must gain substantially more energy than it uses in obtaining that energy, may be especially important. Thus any particular being or system must abide by a "Law of Minimum EROI", which we calculate for both oil and corn-based ethanol as about 3:1 at the mine-mouth/farm-gate. Since most biofuels have EROI's of less than 3:1 they must be subsidized by fossil fuels to be useful.

A Review of the Past and Current State of EROI Data

“…More recently as energy prices have again been increasing the interest in EROI has again increased (e.g., Heinberg [8], many web sites). Additionally many papers on energy and emerging economic fields discuss this ratio and what it means to current and future economies (e.g., Hall and Klitgaard [9], Hall [10], Mearns [11], Day et al [12], Hall et al [13], Hall and Day [14], Murphy and Hall [15]). However, given the number of decades the concept of EROI has been around, only a small, although growing, body of work is available on the subject [15].…”

Implications of Energy Return on Energy Invested on Future Total Energy Demand

“…Estimates [19] for the EROEI of several primary energy sources and fuels currently used or being considered for the future are listed in Table 1. We can apply these results to the generation of electrical energy by considering the relative EROEI for coal and natural gas (which currently dominate electricity production worldwide) and new electrical energy sources such as nuclear, solar PV, hydropower or wind.…”

Methods of energy extraction from microalgal biomass: a review

“…An EROI of 3 has been suggested as the minimum that is viable to 'support continued economic activity' Hall et al 2009). …”