Analysis and improvement of a high-efficiency solar cavity reactor design for a two-step thermochemical cycle for solar hydrogen production from water

• Analysis of key components for a thermochemical cycle for solar hydrogen production.
• Process analysis of this two-step thermo chemical cycle with an exergy analysis.
• Development, simulation and optimization of the secondary concentrator shape.
• Reactor design with thermal balancing of the reactor.

The present study is related to the European research project HYDROSOL 3D dealing with a two-step thermochemical cycle for water splitting based on the use of redox materials. The overall process of a plant with a power input of 1 MWth will be developed and analyzed. This includes the definition of core components, e.g. solar reactors, heat exchangers, compressors, hydrogen separation unit and the elaboration of the flow sheet of the process. By process simulation components exergy efficiencies and thus main sources for exergy losses are determined. The results were used to identify and suggest possible improvements. Since the solar receiver-reactor was identified as the pre-dominant source of exergy losses a new design for such reactor was developed as described in the second part of the study based on the experimental experiences with a reactor developed and tested in previous projects. The main objective of the improvement of the design was to increase the efficiency by minimizing the re-radiation losses. With the support of a raytracing tool a combination of a cavity design, a hemispherical absorber shape and a secondary concentrator was derived as the most suitable reactor design exhibiting at least 25 percentage points less thermal losses than the previous version which was realized and tested as part of a pilot plant.