Strategy for sustainable energy matrix conversion based on exergy life cycle analysis: a case study

Scientists and policymakers are searching for alternatives for the current energy transformation systems to address the problems of environmental pollution and resource scarcity and depletion. The questions are: how environmentally friendly and sustainable are the available alternatives and which of them will ensure a major improvement in environmental quality at lowest economic cost? To answer some of these questions, the present work proposes a method where a sustainability indicator based on exergy life cycle data complemented with concepts from classical monetary investment assessment. This approach allows for the determination of an investment hierarchy by comparing alternative energy conversion routes in terms of their concerned environmental contribution and their natural resource indirect cost. The aim of this work is to highlight the convenience of a quite different exergy indicator, based on indirect exergetic cost and environmental exergetic cost. Four approaches are at the base of this
investigation: the cumulative exergy consumption (CExC) from Szargut [1] and its implementation as a Life Cycle Assessment (LCIA) on the Ecoinvent database; the zero-exergy emission approach from Cornelissen [2] also used by Sciubba's Extended Exergy Accounting [3]; the renewability concept from Dewulf [4-5] and Ocaña [6]; and the indirect exergy concept, defined as the additional exergy needed from the technosphere to drive a transformation energy route as proposed by Wall [7]. Important concepts that were followed in this paper are the concept of energy route or energy path, and the philosophy behind a System Perturbation Analysis from Bram [8]. A case study is presented using data from the Ecoinvent database (v2.01 2007) to investigate the alternatives for petrol driven cars. The alternative energy routes assessed were methanol from biomass synthetic gas and biogas. All three energy routes for personal transport were compared to find out the most sustainable route with the lowest indirect exergy cost.