With the supply of conventional energy resources depleting at their fastest rates and the environmental and societal impacts of their use better understood, there is an increasing desire to use alternative resources and technologies that lessen our dependence on conventional resources and reduce environmental and societal impacts. In order to determine which alternative energy resources and technologies to pursue, the potential technologies need to be compared based on an energetic, economic, and environmental basis. Currently, there are a number of well established methods for quantifying an energy technology’s energetic and economic performance. However, there are no comparable, fundamentally sound methods available for measuring overall environmental performance. The objective of this research is to fill this gap by developing an analytical method for quantifying the environmental performance of energy technologies based on fundamental scientific principles, namely thermodynamics.
The production of transportation fuels will be used as a test case in developing this method. However, the method will be general enough to be applied to any set of energy technologies. Transportation fuels provide an excellent test case because of the number of potential feedstocks (crude oil, tar sands, biomass, natural gas, coal, water) and production pathways (refining, reforming, Fischer-Tropsch synthesis, fermentation) available for making a range of commercial transportation fuels (gasoline, diesel, ethanol, methanol, hydrogen). The environmental performance of a pathway (from feedstock extraction to final commercial fuel) includes two parts: (1) the environmental impact caused by the effluents of a pathway, and (2) the environmental services required to support a pathway, specifically the production of the feedstock. In order to quantify these parts, and therefore the overall environmental performance, this research will utilize the underlying, ecology-based concept of embodied energy (emergy) in conjunction with the thermodynamic-based definition of free energy (exergy).
Separating the environmental performance into its upstream and downstream parts allows for each part to be quantified and analyzed separately. Each part can be used individually as an environmental performance metric or combined to form a single metric since both are based on free energy. Another advantage of the proposed method is that the environmental performance of a technology is quantified independently from its energetic and economic performance.
In many ways, this work provides the final piece needed for developing a comprehensive multi-criteria analysis technique for measuring economic, energetic, and environmental performance. With such a multi-criteria technique, complex energy options, such as alternative fuel production pathways, can be compared based on quantitative, independent metrics – energy efficiency, cost, and environmental performance.