Implications of CO2 Sourcing on the Life-Cycle Greenhouse Gas Emissions and Costs of Algae Biofuels

Abstract

Production of algal biomass and its conversion to biofuels are important technological platforms within the larger umbrella of CO₂ capture and utilization. This analysis incorporates a life-cycle assessment (LCA) with respect to global warming potential and techno-economic assessment (TEA) of algae biofuels, focusing on the sourcing and delivery of CO₂. This analysis evolves past work in this area to include high-purity biogenic CO₂, industrial fossil fuel use, fossil power plants, and direct air capture, and uses a Sherwood plot approach to estimate the CO₂ capture energy penalty. We also show that allocation or displacement facilitates a more intuitive distinction between biogenic and fossil sources of carbon. Thus, the LCA better reflects the influence of coproduct handling strategies as compared to previous works. The TEA is also strongly influenced by the CO₂ concentration in the flue gas. Currently, when CO₂ is sourced from large-point sources, the price of biofuels ($4.5-6.5/GGE) may become comparable to fossil diesel. However, as DAC systems become more economical, they may deliver competitive CO₂ sources for biofuels in 2050 with a total cost of <$7/GGE. Based on the net emissions and costs, algae biofuels with CO₂ sourced from biogenic sources are consistent with a decarbonized economy as of now, with substantial potential for DAC with decreasing costs.