A unique phase change redox cycle using CuO/Cu2O for utility-scale energy storage

Abstract

Abstract In this article, a unique phase change redox (PCR) system capable of converting surplus electricity to sensible, latent, and thermochemical energy is proposed as an alternative technology for utility-scale energy storage. During the energy charging period, the system utilizes external heat to reduce and melt solid CuO into molten CuO/Cu2O at a high temperature in a reduction reactor. The external heat can be provided by Joule heating using the surplus electricity from the power grid or renewable energy plants (solar/wind). In this way, the surplus electricity is stored in the forms of sensible, latent, and thermochemical energy. A high value-added by-product, oxygen, can be produced simultaneously, which further enhances the economic competitiveness of the proposed system. During the energy discharging period, the molten CuO/Cu2O is oxidized and cooled in an oxidation reactor using air. In this step, the stored energy is released and transferred to the high-pressure and high-temperature air, which can be further converted into power via an air Brayton cycle coupled with a bottoming organic Rankine cycle. The simulation package, Aspen Plus v10, is used to develop a thermodynamic model of the PCR system, in which its technical performance and influential parameters are examined in details. The simulation study shows that the PCR process can achieve a round trip efficiency of about 50% with an energy storage density of up to 1600\u202fkJ/kg. The parametric analysis reveals that the round trip efficiency of the PCR system is greatly influenced by the compression ratio, while the energy storage density and oxygen production are affected by the temperature and oxygen partial pressure of the reduction reactor. Apart from the simulation study, thermogravimetric analyses on phase change redox cycles are also carried out. The experiment results are found to successfully validate the key energy storage mechanism behind the PCR process, namely the reduction, melting, solidification, and oxidation processes. The reversibility and stability of the PCR process over 10 cycles are found to be excellent with minor degradation and enthalpy changes.