(473b) Solar-Thermal Water Splitting Process Development and Economics to Produce Renewable H2

Using concentrated solar energy from a heliostat field, metal ferrite materials (MFe2O4) can be reduced according to the reaction MFe2O4 = 1.2 FeO + 0.4Fe2O3 + MO + 0.3O2 at 1,400°C. The resulting solid solution is then used to split water at 1,000°C via an exothermic oxidation reaction 1.2FeO + 0.4Fe2O3 + MO + 0.6H2O = MFe2O4 + 0.6H2, producing high purity renewable hydrogen. Various metals are under investigation including M = Co, Ni, and Zn. This process has been designed and modeled using AspenPlus? to produced 100,000 kg H2/day with reduction conversions of 35%, 70%, and 100%. Once the base case AspenPlus? models were developed, the process was optimized to produce electricity by generating steam in the heat removal steps of the cycle. The models were then used to size and cost all capital equipment and the solar heliostat field to determine the total capital investment (TCI) of the process. The TCI and fixed/variable operating costs were then entered into the Department of Energy's (DOE) H2A economic analysis program to establish the allowable purchase price of metal ferrite for a given hydrogen selling price to meet the DOE cost targets through 2017. The results of this analysis are very promising with solar to receiver annual average efficiencies of 45% and thermal cycle efficiencies as high as 50%. The targeted hydrogen selling price of $4/kg was met with reasonable allowable ferrite capital costs. The economic analysis indicates that the development of solar-thermal water splitting processes using ferrite materials in a redox cycle is a potentially economical pathway to renewable hydrogen.