The present work describes the study of a solar reactor for a two-step solar thermo-chemical water splitting cycle concerning the EU-project Hydrosol Plant, which aims to build a plant at the end of 2016 on a solar tower at the Plataforma Solar de Almeria with a thermal input power of 750 kW to produce 3 kg/week of hydrogen. The process applies nickel-ferrite as reactive species, which works optimally at 1100 degrees C for the water splitting step and at 1400 degrees C for the regeneration step. This material is provided in form of monoliths which are used in cars as catalytic converter. On the platform three reactors are placed to reach a volume of about 0.3 m(3) of active material inside the reactor chambers. During the operations two of these will be regenerated while one will work on water splitting, to reach a quasi-continuous hydrogen production. The design concept of the reactor is taken from the SOLREF reactor, which was originally developed by DLR for methane reforming at 900 degrees C and 10 bar. The scheme and the layout of the plant to feed the reactors have been studied, too. A thermodynamic model for the regeneration step has been also developed to check if the thermal power demand of the three reactors can be supplied by the defined thermal input power. The differences to the other HYDROSOL projects are: The Upscaling from 100 kW to 750 kW, the usage of monoliths completely made of nickel-ferrite and the control strategy with three reactors instead of two. (C) 2016 Elsevier Ltd. All rights reserved.