A special setup, electrically heated, enabling the simulation of the process conditions encountered in a solar chemical reactor, is described. The setup allows us to study the thermal and chemical processes in different solid (powder or granules) reactant layers from the beginning of the heating until the reaction is completed, in a heating condition typical for indirectly, externally heated solar reactors. The particular case of the ZnO carboreduction process is analyzed in this paper as an example. Tests were executed using different powder mixtures of ZnO–C to demonstrate the layer-wise nature of the process. The results show that the reactivity and the behavior of mixtures strongly depend on their components structures, impurities, and stoichiometry. This method can be generally applied for studying endothermic chemical reactions involving other solid reactants.