Solar Hydrogen via Water Splitting in Advanced Monolithic Reactors for Future Solar Power Plants
Christos Agrafiotis;
PSA Contact: Antonio López;
Cooperative Project funded by the EC 6th Framework Programme. Total Budget: 4.230 k€. CIEMAT budget: 647 k€.
December 1, 2005 – September 30, 2009

Solar hydrogen production by the thermochemical route confronts the enormous challenge of achieving scale-up of the solar concentrating technologies and reactors able to operate at powers of several MW. At the present time, there are developments, many of them tested jointly by DLR and CIEMAT, at the PSA facilities, which enable operation with volumetric receivers at temperatures above 1000ºC. The reason for the Hydrosol-II Project is the confidence of being able to transfer the cumulative materials and system development experience with catalytic matrices using SiC with monolithic channels that were successfully validated during the SOLAIR Project. Impregnation of these ceramic matrices with mixed ferrites would make their use possible for hydrogen production. The possibility of using this monolithic reactor with ferrites fixed to a substrate facilitates the separation of oxygen and hydrogen in alternating charge/discharge stages.


The second stage of this project (Hydrosol-II) began in November 2005 and its purpose is to evaluate a 100-kW reactor at the Plataforma Solar de Almería using mixed Zn ferrites impregnated on ceramic SiC matrices. The novelty of this design is the use of a discontinuous charge/discharge operating mode. The endothermal stage is carried out with solar illumination in such a way that the focus of high solar radiation flux generated by the heliostat field moves alternately from some matrices to others to allow the following H2 discharge stage to take place.


The first tests were done in 2008 with HYDROSOL II installation (Fig. 1) in order to study the influence of such factors as preheat air flow, focusing and defocusing of heliostats, the temperature reached in the reactor and effectiveness of temperature control with regard to the requirements of the water splitting/regeneration cycle.

First thermal cycles demonstrated the operational reliability of all of the necessary peripheral systems installed (such as the PLC, electric panel, wiring, desk support, thermocouples, pressure sensors, data acquisition system and process control system) and led to the first basic recommendations concerning operating strategy, especially the way to accomplish fast changes in temperature.

HYDROSOL II in operation

Hydrogen concentration detected by GC

Test campaigns in 2009 demonstrated the feasibility of hydrogen production in the experimental reactor for two consecutive cycles. The monoliths used in the thermal tests were replaced by monoliths coated with zinc ferrite. At the beginning of the experiment the two reactors were heated up to operating conditions at 800ºC and in continuation, two cycles were performed (heating to 1200ºC and cooling to 800ºC) in both modules. Fig. 2 shows results found during testing with both modules. The concentration measured would correspond to 30% steam conversión.

Several test campaigns were performed in 2009 with different types of monolith coatings, observing that the material shows the same activity as in the cycles shown in Figure 2. This testing demonstrated the operating capacity of the HYDROSOL II reactor for semi-continuous hydrogen production in a power tower with a heliostats field.

APTL (GR), DLR (D), CIEMAT (E), STC (DK), Johnson Matthey (RU).