Solar sulphuric acid cracking is a key step of the hybrid sulphur cycle (HyS) for thermochemical water splitting producing hydrogen free of CO2 emissions. In the European projects HYTHEC and HycycleS the concept of a receiver-reactor was developed by DLR and tested in its solar furnace in Cologne, Germany. A model of the high temperature chamber for SO3 decomposition is presented and validated with experimental results of the HycycleS test reactor. In a scaling analysis, this model is integrated into a previously published flowsheet of a solar HyS process predicting the performance of the system at industrial size. Applying stationary and dynamic simulation, an optimum reactor length of 1 m can be identified. The results of the simulation are now used in the European project SOL2HY2 to develop and operate a demonstration plant for sulphuric acid cracking on DLR's solar tower in Juelich, Germany. (C) 2015 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.