Thermochemical cycles for water splitting are considered as a promising example of
emission-free routes for large-scale hydrogen production e with potentially higher
efficiencies and lower costs compared to low temperature electrolysis of water. The hybrid
esulfur cycle was chosen as one of the most promising cycles from the ‘sulfur family’ of
processes. A process model has been established to study the main parameters influencing
efficiency with specific attention paid to dynamic effects when coupled to solar heat. The
process is separated into two sections e one at steady-state, and the other one fictively
imposed by transients. This allows a first analysis with respect to reasonable energy and
mass flow management, while considering concepts of coupling such a process to a
concentrating solar system in a later step. Process efficiencies are calculated based on
conservative assumptions, revealing the most important development tasks for the
future. The extensive usage of recoverable high temperature heat e including the heat
from the highly corrosive condensing phases e is a key factor to attain reasonable effi-
ciencies for industrial application. With idealised heat recovery rates e limited by thermodynamic
considerations, but excluding heat exchange between stationary and dynamic
sections e and for decomposer temperatures appropriate for volumetric solar receiver
operation, a thermal process efficiency close to 30% is predicted for stationary operation
based on the lower heating value of hydrogen. Subsequent investigations will derive
annual yields, taking into account the effect of coupling to solar energy.