4.18 Solar Fuels

Concentrated solar power (CSP) can be employed as the only energy source for the renewable production of hydrogen and/or syngas from water/carbon dioxide. Such a route has in principle the potential to culminate essentially to the synthesis of liquid hydrocarbon fuels using only renewable/recyclable resources: solar energy, water, and captured/recycled CO2. The chapter presents the evolution and current development status of such CSP-aided hydrogen and/or syngas production via redox-pair-based, water/carbon dioxide splitting (WS/CDS) thermochemical cycles. The various options and routes with respect both to redox oxide materials chemistry as well as to solar reactor concepts employed to render the WS/CDS scheme solar-powered are critically reviewed. Based on the results of relevant work up to date, the prevailing current and near-future trends are presented with emphasis on technologies having reached pilot-plant demonstration level. The lessons learned so far from the operation of such reactors and the particular issues to be addressed in the near future to induce industrial-scale implementation of the technology are identified and discussed