SUMMARY

Solar thermochemical energy storage is a promising pathway towards extending the utility of concentrated solar power technologies. With continued research and development, solar electricity production can be decoupled from intermittent solar conditions, leading to an economically competitive, on-demand energy resource. In this work, a two-step solar thermochemical cycle is proposed for energy storage based on the reduction/oxidation of metal oxides for direct integration into an air-Brayton cycle. The two steps encompass 1) the sensible heating and thermal reduction of metal oxides using concentrated solar irradiation, and 2) the extraction of stored sensible and chemical energy during re-oxidation of metal oxides for an air-Brayton cycle. A thermodynamic analysis is performed on the proposed cycle using Co3O4/CoO to assess the cycle potential and identify thermodynamic constraints. Thermogravimetric analysis is performed to extract thermal reduction kinetics of Co3O4 to evaluate operation in similar conditions to the solar thermochemical reactor for the proposed cycle. Next, to realize the proposed cycle a solar thermochemical reactor is optimized to achieve solar energy storage within directly irradiated dense, granular flows of reactive metal oxides. The reactor concept is first evaluated using a design-stage heat and mass transfer model of a 5 kWth laboratory scale reactor for Co3O4/CoO media. From this modeling, a 5 kWth reactor is designed and evaluated using detailed heat and mass transfer modeling for aluminum-doped calcium manganite media. Lastly, the reactor performance is evaluated during experimentation in a high-flux solar simulator with aluminum-doped calcium manganite media.