A general framework for the assessment of solar fuel technologies

Abstract

The conversion of carbon dioxide and water into fuels in a solar refinery presents a potential solution for reducing greenhouse gas emissions, while providing a sustainable source of fuels and chemicals. Towards realizing such a solar refinery, there are many technological advances that must be met in terms of capturing and sourcing the feedstocks (namely CO₂, H₂O, and solar energy) and in catalytically converting CO₂ and H₂O. In the first part of this paper, we review the state-of-the-art in solar energy collection and conversion to solar utilities (heat, electricity, and as a photon source for photo-chemical reactions), CO₂ capture and separation technology, and non-biological methods for converting CO₂ and H₂O to fuels. The two principal methods for CO₂ conversion include (1) catalytic conversion using solar-derived hydrogen and (2) direct reduction of CO₂ using H₂O and solar energy. Both hydrogen production and direct CO₂ reduction can be performed electro-catalytically, photo-electrochemically, photo-catalytically, and thermochemically. All four of these methods are discussed. In the second part of this paper, we utilize process modeling to assess the energy efficiency and economic feasibility of a generic solar refinery. The analysis demonstrates that the realization of a solar refinery is contingent upon significant technological improvements in all areas described above (solar energy capture and conversion, CO₂ capture, and catalytic conversion processes).