Sun-to-Fuel Assessment of Routes for Fixing CO₂ as Liquid Fuel

Abstract

This study presents a systems approach for comparing alternative routes for converting CO 2 to liquid fuel using solar energy based on a novel metric of sun-to-fuel (STF) efficiency. The metric refers to the fraction of incident solar energy that is recovered in the liquid fuel. The STF efficiency analysis identifies energy and land use efficient routes that require immediate research and development effort to speed up their progress toward long-term cost-effectiveness. The analysis' unique insights are particularly relevant for densely populated regions, having scarce per capita land availability relative to the per capita energy demands. With atmospheric CO 2 as the renewable carbon source, we present a detailed case study comparing the currently known photosynthetic routes with a theoretical route based on direct extraction of CO 2 from air and its subsequent thermochemical conversion to liquid fuel. The findings indicate that the latter route could be potentially more energy and thereby land use efficient than any of the currently known photosynthetic routes, therefore, warranting its inclusion in any transportation fuels research portfolio. An interesting finding of our study is that for the interim period while CO 2 extraction is still uneconomical and CO 2 sourced from power plants is instead used, the relative energy efficiency of different routes remains unchanged. This suggests that the results in general are independent of the concentration of the CO 2 source.

Isothermal reverse water gas shift chemical looping on La0.75Sr0.25Co(1−)Fe O3 perovskite-type oxides

“…Recently, Mallapragada et al [6] performed a technoeconomic analysis on the conversion of CO 2 to fuels by different approaches including using algae, photosynthesis and the reverse water gas shift reaction (RWGS). The study determined the RWGS process, operated at 976 • C and 30 atm, as the method with the highest estimated current and future efficiency.…”

Limiting and achievable efficiencies for solar thermal hydrogen production

“…From Eqs. (8) and (9), this suggests that the process will require increased work input and lower heat input compared to the U hte , loss ¼ 0 case. The solar conversion efficiency to produce electrical energy is much lower than the efficiency at which heat is recovered at 1223 K. Therefore, the STH 2 efficiency of HT electrolysis processes operating with a non-zero value of U hte , loss will be lower than 32.7%.…”

“…Towards this end, the conversion of solar energy into chemical energy in the form of a fuel derived from the raw materials of air, water and soil, is critical for energy storage in a solar economy. For the known approaches of converting sunlight to fuel [3e7], a metric of interest is the process sun-to-fuel (STF) efficiency [3,8]. It refers to the fraction of incident solar energy recovered as the lower heating value (LHV) of the produced fuel.…”

“…It refers to the fraction of incident solar energy recovered as the lower heating value (LHV) of the produced fuel. The STF efficiency metric is useful for comparing the relative land area requirements of different processes to meet a given fuel demand using solar energy [8]. In addition, it also provides an indirect measure of the overall cost of harnessing solar energy using a particular STF process.…”

Continuous baseload renewable power using chemical refrigeration cycles

“…In addition to the available infrastructure and technologies for their utilization, carbon fuels, such as methane and methanol, are dense energy carriers which makes them attractive candidates for energy storage. However, synthesizing these carbon fuels in a carbon neutral manner require renewable carbon sources such as biomass and/or atmospheric carbon dioxide (Agrawal et al, 2007;Graves et al, 2011;Rihko-Struckmann et al, 2010;Mallapragada et al 2013). The use of renewable carbon for energy storage in an open loop system (i.e.…”