Exergy replacement cost of fossil fuels: Closing the carbon cycle

Abstract

The Exergy Replacement Cost (ERC) is an indicator that is used to ascertain the sustainability of non-renewable resource depletion. Specifically, it measures the amount of exergy society would have to expend if it were forced to re-capture and re-concentrate dispersed minerals back into a manmade usable deposit. Due to an assumption regarding the non-substitutability of fossil fuels, the original method failed to properly account for them. In fact, it sub-estimated their exergy replacement cost forty-seven-fold, on average, when considering solar radiation to fuel, and by approximately fivefold when going from crop to fuel. This new method, via the cumulative exergy consumption (CExC), calculates the exergy replacement cost of photosynthesis and bio-energy production, as together they form the best available technology when it comes to closing the carbon cycle. This approach ties together the "cradle to grave" to the "grave to cradle", standardises the ERC calculations and enables comparisons between fuel and non-fuel mineral consumption. It also opens a discussion as to the role of the ERC in sustainability debates and whether resource depletion should be a matter of geological patrimony or material/energy services.