Double-walled reactor tubes containing thermal storage materials based on the molten carbonate salts-100 wt% Na2CO3 molten salt, 90 wt% Na2CO3/10 wt% MgO and 80 wt% Na2CO3/20 wt% MgO composite materials were studied for the performances of the reactor during the heat charging mode, while those of methane reforming with steam during heat discharging mode for solar steam reforming. The variations in the temperatures of the catalyst and storage material, methane conversion, duration of reforming for obtaining high levels of methane conversion (> 90%), higher heating value (HHV) power of reformed gas and efficiency of the reactor tubes were evaluated for the double-walled reactor tubes and a single-wall reactor tube without the thermal storage. The results for the heat charging mode indicated that the composite thermal storage could successfully store the heat transferred from the exterior wall of the reactor in comparison to the pure molten-salt. The double-walled reactor tubes with the 90 wt% Na2CO3/10 wt% MgO composite material was the most desirable for steam reforming of methane to realize large HHV amounts of reformed gas and higher efficiencies during heat-discharging mode. (C) 2014 Elsevier Ltd. All rights reserved.