SOLAR H₂ THERMOCHEMICAL PRODUCTION AND STORAGE SYSTEMS

Many significant features lead to consider hydrogen as an interesting energy carrier. However since molecular hydrogen doesn't practically exist on the earth it has to be produced by traditional or renewable energy sources.
CO2 free hydrogen production can be obtained by means of water splitting promoted using solar energy. One of the most promising thermochemical cycles to efficiently produce solar hydrogen is the Sulphur-Iodine (S-I) one. This cycle involves three subsequent reactions, the decomposition of sulphuric acid to SO₂, H₂O and O₂, the reduction of I₂ to HI and the oxidation of HI to H₂. The first process represents one of the main basic and technical challenges to scale up to industrial level the whole cycle.
Hydrogen and oxygen can be recombined in situ for power generation. Since solar energy shows discontinuous availability a storage system must be considered and included between the solar water splitting section and the downstream power plant.
In such a way temporal de-coupling between the solar production plant and the downstream power plant can be obtained.
This paper reports a summary of the results of our research about the aforementioned key points in hydrogen production technologies by thermochemical cycles. Some new thermodynamic and kinetic results about the decomposition of sulphuric acid are reported together with some preliminary experimental evidences about the effect of potential catalysts. Simulations concerning thermo-fluid-dynamics aspects for solar reactors based on different approaches have been successfully conducted by Computational Fluid Dynamics (CFD) methods. About the hydrogen storage various different possibilities have been analysed and, finally, a characteristic liquid storage system is briefly discussed.