The large-scale use of renewable energy, in particular solar energy, requires the development of energy storage technologies to compensate for the intermittent availability of solar radiation. Among all storage methods, the thermochemical storage of energy appears to be particularly interesting due to its high storage density and its potential ability to avoid energy losses. A charge reaction stores the solar energy whereas the reverse discharge reaction gives back this energy whenever it is needed the most. Among the different reactors allowing one to do this for Concentrated Solar Power (CSP), Solar Rotary Kilns (SRK) appear to be particularly promising as they can potentially allow the continuous and uninterrupted storage of energy unlike batch and semi-batch reactors. There are, however, two main aspects that need to be further explored. On the one hand, the modelling of solar rotary kilns is still at its infancy and a realistic understanding of the interaction between granular flow, heat transfer and chemical kinetics has yet to be reached. On the other hand, the construction of a directly irradiated SRK with the possibility of adjusting the solid flow rate to the fluctuating radiance of the sun would be highly beneficial. The purpose of the project MULTITHERMO will be to develop a realistic and physically and chemically sound multiphysics model describing all aspects of heat storage in a rotary kiln and to validate it based on the data from a new prototype of SRK and from an already existing electrical rotary kiln and an already existing rotary drum. It will be mainly based on the reduction of BaO2(s) as a promising heat-storing reaction. This reaction will be also studied during the projetc in order to master its chemical kinetics.