An integrated concentrated solar fuel generator utilizing a tubular solid oxide electrolysis cell as solar absorber

We numerically assessed the potential of a solar reactor concept for efficient fuel processing under concentrated solar irradiation. This design integrates a cavity receiver, a tubular solid oxide electrolyzer, and the concentrated photovoltaic cells into a single reactor. The tubular electrolyzer simultaneously acts as the solar absorber (for reactant heating) and as the electrochemical device (for water and carbon dioxide splitting). A multi-physics axisymmetric model was developed, considering charge transfer in the membrane-electrolyte assembly, electrochemical and thermochemical reactions at the electrodes' reaction sites, species and fluid flow in the fluid channels and electrodes, and heat transfer for the whole reactor. A high solar-to-fuel efficiency was predicted (18.6% and 12.3% for indirectly and directly connected approaches, respectively, both at CPV = 385 and Cap = 1273). For synthesis gas production, the upper current density threshold to avoid carbon deposition was found to be 8725 A/m2 at reference conditions. A continuous range of H2/CO molar ratios of the synthesis gas was achieved by varying the inlet H2O/CO2 ratio, the irradiation concentration, and the operation current density. Efficiency-optimized operating conditions and design guidelines are presented. Our novel and integrated solar reactor concept for the solar-driven high-temperature electrolysis of H2O and CO2 has the potential to provide a simple, high solar-to-fuel efficiency reactor at reduced cost, all given by the reduced transmission losses of the integrated reactor design.