Concentrated solar energy can be transformed into electricity, heat or even solar fuels, such as hydrogen, via thermochemical routes with high exergetic efficiency. In this work, a specific methodology and experimental setup are described, developed to assess the production of hydrogen by water splitting making use of commercial cerium oxide, ceria (CeO₂), in a solarized reactor. A fixed bed reactor, directly irradiated by a 7 kWe high flux solar simulator (HFSS) was used. Released H₂ and sample temperature levels were continuously monitored. Three tests were carried out consisting of three consecutive redox cycles each, with irradiances in the range of 1017–2034 kWm⁻². It was necessary to achieve a compromise between sample temperatures (higher temperatures lead to higher reduction rates) and sample stability, since absorbed radiation can degrade a sample at lower temperature (1280–1480 °C) than in a conventional infrared oven (T > 2000 °C). Irradiating the surface of the sample with an irradiance of 2034 kWm⁻² (270 W of total radiation power) during 9.5 min eventually degraded the sample, resulting in a conversion into stoichiometrically reduced oxide (Ce₂O₃) of 11%. A similar conversion was achieved (9.7%) after 2 min of irradiation at 270 W (100% of radiation), but without irreversibly damaging the sample.

The main objective of the European Project SUN-to-LIQUID is the scale-up and experimental demonstration of the complete process chain to solar liquid fuels from H₂O and CO₂. This implies moving from a 4 kW laboratory setup to a pre-commercial plant including a heliostat field. The small power and high irradiance onto the focal spot is forcing the optical design to behave half way between a large solar furnace and an extremely small central receiver system. The customized heliostat field makes use of the most recent developments on small size heliostats and a tower with reduced optical height (15 m) to minimize visual impact. A heliostat field of 250kWth (500 m² reflective surface) has been built adjacent to IMDEA Energy premises at the Technology Park of Móstoles, Spain, and consists of 169 small size heliostats (1.9 m × 1.6 m). In spite of the small size and compactness of the field, when all heliostats are aligned, it is possible to fulfil the specified flux above 2500 kW/m² for at least 50 kW and an aperture of 16 cm, with a peak flux of 3000 kW/m².