Driving toward sustainable algal fuels: A harmonization of techno-economic and life cycle assessments
Jesse Cruce, Audrey Beattie, Peter Chen, David Quiroz, Michael D. Somers, Samuel Compton, Katherine DeRose, Braden Dale Beckstrom, Jason C. Quinn
Abstract
Research efforts have investigated a range of system designs for algae growth and conversion into biofuels. The economic feasibility and environmental impact of these systems are frequently evaluated through techno-economic analyses (TEA) and life-cycle assessment (LCA), which typically determine the levelized cost of fuel production in gallons of gasoline equivalent (MFSP, in $-gge−1), global warming potential (GWP, in g CO2-eq-MJfuel−1), and net energy ratio (NER, unitless). While the outputs from these models seem comparable, the results often conceal the impact of a large number of assumptions inherent to the modeling, limiting direct comparisons. As such, a direct comparison of the modeling results as published can be misleading due to differences in critical assumptions and/or foundational methodology. This work applies harmonization methodology to several sustainability assessment studies found in the literature with the goal of enhancing comparability through implementation of a standard set of assumptions. For the economic evaluation, two harmonization efforts were performed: the first focused on harmonizing productivity, economic assumptions, and cost year for the entire growth to product process; the second compared only downstream fuel conversion technologies by fixing the biomass cost, thereby removing the uncertainty of upstream-growth assumptions. For LCA, harmonization focused on productivity and system boundary. The results of these efforts show a decrease of 43% in the range of reported fuel prices and minimal redcution in the range of LCA results. Both TEA and LCA harmonization efforts then investigated the impact of productivity by simulating a range of biomass productivity values (12.5, 25, and 50 g-m−2 day−1). The work reveals limitations to both the economic and environmental benefits of productivity improvements past approximately 35 g-m−2 day−1. Results highlight the need to redirect research efforts not only to increase productivities, but also to other areas where investments can make a greater impact in terms of economic viability and environmental impact.