This paper presents a process analysis of ZnO/Zn, Fe3O4/FeO and FC2O3/Fe3O4 thermochemical cycles as potential high efficiency, large scale and environmentally attractive routes to produce hydrogen by concentrated solar energy. Mass and energy balances allowed estimation of the efficiency of solar thermal energy to hydrogen conversion for current process, data, accounting for chemical conversion limitations. Then, the process was optimized by taking into account possible improvements in chemical conversion and heat recoveries. Coupling of the thermochemical process with a solar tower plant providing concentrated solar energy was considered to scale up the system. An economic assessment gave a hydrogen production cost of 7.98$ kg(-1) and 14.75$ kg(-1) of H-2 for, respectively a 55 MWth and 11 MWth solar tower plant operating 40 years. (C) 2007 Elsevier Ltd. All rights reserved.