Efficient direct solar-driven thermochemical energy storage of (AlMgFeMn) OxCaCO3 pellets in a fluidized bed reactor

Calcium looping (CaL) is one of the most promising thermochemical energy storage technologies for high-temperature applications such as next-generation concentrated solar power (CSP) systems. However, most previous investigations have mainly focused on optimizing Calcium-based materials to maintain their reactivity during cycling, while their behavior in reactors under direct solar irradiation has rarely been reported. In this paper, highly efficient and stable direct solar-driven thermochemical energy storage in fluidized reactors is demonstrated. (AlMgFeMn)OxCaCO3 pellets demonstrated excellent long-term stability with an energy storage density of more than 85% of the initial value after 100 cycles. The underlying mechanism can be attributed to the presence of poly-oxide (AlMgFeMn)Ox crystals, which prevent crystallite growth and sintering, as confirmed by in-situ X-ray diffraction analysis. Moreover, the solar-thermal conversion efficiency of (AlMgFeMn)OxCaCO3 pellets in fluidized bed reactors is significantly improved from 9% to 19% thanks to the considerably increased average solar absorptance and fast reaction kinetics over white (AlMg)OxCaCO3 pellets. The experimental analysis using an operando fluidized thermogravimetric analyzer (F-TGA) further revealed that the interparticle diffusion control limitation in traditional TGA or fixed bed and localized overheating due to Gaussian distri-bution of solar irradiation are successfully relieved in a fluidized bed. We further suggest that steam has a positive effect on enhancing reaction kinetics and stability by performing 10 energy storage/release cycles of (AlMgFeMn)OxCaCO3 pellets under direct irradiation of concentrated light due to the increase of surface area after rehydration and the higher OH reactivity toward CaO. This work paves the way for the application of solar-driven fluidized bed reactors for scalable thermochemical energy storage.