High Energy Storage Density, High Power Density and Highly Stable Calcium-Looping Solar Thermochemical Heat Storage Promoted by Binary Sulfate

Abstract

Calcium looping (CaL) solar thermochemical heat storage is a potential technology for future concentrated solar power (CSP) systems. However, conventional calcium carbonate (CaCO3) pellets face problems of poor cyclic stability, slow decomposition kinetics, and low optical absorptance. Here, for the first time, we successfully realized high power density and highly stable solar thermochemical energy storage/release by synergistically accelerating heat storage/release via binary sulfate and promoting cyclic stability, mechanical strength, and optical absorptance via Al-Mn-Fe oxides. The novel CaCO3-based pellets still have an energy storage density (ESD) of 1455 kJ/kg after 100 cycles, and the energy storage density decay rate is only 4.91%, much smaller than 69.9% of conventional CaCO3 pellets after 35 cycles. Compared with conventional CaCO3, the energy storage power density or decomposition rate is improved by 120% due to lower activation energy and promotion of Ca2+ diffusion by binary sulfate. The energy release power density or carbonation rate rises by 10% because of high O2- transport ability of molten binary sulfate. Benefiting from fast heat storage/release rate and high optical absorptance, thermochemical heat storage efficiency is enhanced by more than 50% under direct light irradiation. This work paves the way for industrial application of integrated CaL-CSP system via achieving fast energy storage/release rate, high ESD, outstanding cyclic stability, and high optical absorptance simultaneously.

Keywords: Solar thermochemical heat storage, calcium looping, binary sulfate, cyclic stability, energy power density.