Thermal design of a solar hydrogen plant with a copper–chlorine cycle and molten salt energy storage

In this paper, the operating temperature ranges of various solar thermal energy technologies are analyzed, with respect to their compatibility with solar hydrogen production via thermochemical cycles. It is found that the maximum temperature of 530 °C required by the oxygen production step in the Cu–Cl cycle can be supplied by current solar thermal technologies. The heat requirements are examined for the Cu–Cl cycle and it is found that the heat source must be sufficiently high and above the maximum temperature requirement of the Cu–Cl cycle, in order to match the heat requirements of the cycle. The quantity of molten salt and solar plant dimensions for capturing and storing solar heat for an industrial hydrogen production scale are also estimated for 24 h operation per day. The flow characteristics and heat losses of molten salt transport in pipelines are studied while considering the influences of pipeline diameter, heat load and weather conditions. The heat loss from a solar salt storage tank is also calculated based on various tank diameters and heights. The intermediate product of molten salt produced in the oxygen production step gives the Cu–Cl cycle a significant advantage of linkage with current high temperature solar thermal technologies. This allows flexibility for integration of the Cu–Cl cycle and solar thermal plant. Using a thermal network analysis of the Cu–Cl cycle, the layout options for the integration of a Cu–Cl cycle with various solar thermal technologies are presented and discussed in this paper.