On the Second-Law inconsistency of Emergy Analysis

The paper argues against the claim made by Emergy Analysts that emergy is an exergy-based procedure. Both Emergy- and Exergy Analysis employ space- and time integrated energy input/output models to quantitatively assess the resource consumption of physical systems: the issue at stake is whether Emergy is embodied energy or embodied exergy. Although the compatibility of Exergy- and Emergy accounting procedures, the significance of the peculiar Emergy Algebra, and some cost-allocation issues have been studied in detail, a final agreement could not be reached, so that some doubt exists about the degree of compatibility of the two methods. The present paper shows that the definitions and the procedures employed in Emergy Analysis are in fact First Law-based, and that they neglect or misrepresent Second Law issues. This conclusion is reached by carefully reviewing and critically analyzing a series of general and specific procedures contained in the original Odum books and in some of the most representative publications by Emergy analysts.The conclusions are that Emergy Analysis is a cumulative energy cost accounting method, and that therefore the claim that “emergy is embodied exergy” is not congruent with the methods adopted by Emergy Analysts in their studies, because the subsumed theory does not contain any consistent feature that allows it to treat fluxes with exergy factors different than unity.It is recommended therefore that Emergy Analysis be not used to assess the global resource consumption caused by anthropic activities, because its results are misleading when it comes to estimate the exergy destruction enacted by real industrial transformations. For this kind of analyses, genuinely Second Law-based methods are the only ones to date that lead to a correct assessment of the real exergy resource use “embodied” in a commodity. It must be stressed that the arguments put forth in this paper do not deny the validity of Emergy Analysis per se: they simply disprove the claim that Emergy is a “Second Law-based method”.