Solar electricity via an Air Brayton cycle with an integrated two-step thermochemical cycle for heat storage based on Co3O4/CoO redox reactions: Thermodynamic analysis

• Published in: Solar energy Vol. 118; no. C; pp. 485 - 495
• Main Authors: Schrader, Andrew J., Muroyama, Alexander P., Loutzenhiser, Peter G.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 01-08-2015; Elsevier
• Subjects: Cobalt oxide; Concentrated solar energy; Thermochemical energy storage; Thermodynamic analysis; Two-step thermochemical cycle; Cobalt oxide; Concentrated solar energy; Thermochemical energy storage; Thermodynamic analysis; Two-step thermochemical cycle
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/j.solener.2015.05.045

•Coupled Air Brayton cycle and solar two-step thermochemical cycle proposed.•Heat storage based on Co3O4/CoO redox reactions.•Thermodynamic and exergy analysis conducted.•Maximum cycle efficiency of 45% determined for re-oxidizing CoO at 30bar.•Dominant source of exergy destruction from incoming concentrated solar irradiation.
Solar electricity production is considered in an Air Brayton cycle with an integrated two-step thermochemical cycle for heat storage based on Co3O4/CoO redox reactions. The two steps of the heat storage cycle are encompassed by (1) the high-temperature thermolysis of Co3O4 to CoO and O2 under vacuum pressure utilizing concentrated solar irradiation for process heat; and (2) the highly exothermic re-oxidation of CoO with O2 at elevated pressures, resulting in Co3O4 and providing the heat input to the Air Brayton cycle. The two steps may be decoupled, enabling long-term storage of heat (i.e., thermochemical storage of sunlight). A thermodynamic analysis is applied to determine cycle efficiencies over a range of operating parameters, and an exergy analysis is used to identify the major sources of irreversibilities. A maximum cycle efficiency of 44% was determined for re-oxidizing the CoO at 30bar, with the maximum cycle efficiency reducing to 26% for a decrease in pressure to 5bar.