Dynamic simulation and optimal heat management policy of a coupled solar reforming-heat storage process

This work is a first simplified approach on the exploitation of “direct” solar heat during on-sun operation, and stored solar-heat through thermochemical energy storage involving redox pair cycles during off-sun operation, for the production of solar hydrogen using concentrated solar energy. The coupling of the processes in a compact solar reforming-thermochemical heat storage system is conducted in terms of a lumped dynamic model; for the determination of the syngas composition in the reforming unit, thermodynamic equilibrium is assumed, while the required heat to facilitate the endothermic reforming reactions is provided by either solar heat (on-sun operation), or a combination of stored energy and an optimal linear profile of external heat provision (off-sun operation). The optimal heat management policy for the reduction or the oxidation step (during the solar heat storage and release process) ensures a steady H2 molar fraction for most of the operating time. It is revealed that the coupled scheme suggested is an in-principle viable option for sustainable H2 production, since reforming needs are entirely complemented by solar heat also supplying the required energy input for the storage unit, which in turn may provide almost 25% of the overall reforming energy needs under off-sun operation.