Modified Ca-Looping materials for directly capturing solar energy and high-temperature storage

Abstract

The thermochemical energy storage based on Calcium looping (CaL) process shows great potential for the application in the 3rd generation Concentrated Solar Power (CSP) compared to other high-Temperature heat storage schemes. However, due to the inherent low solar absorptance of CaCO3, the surface heating mode is widely adopted in the conventional CaL-CSP system, which causes large thermal resistance and severe radiative heat loss. Herein, we propose achieving direct solar absorption in the CaL-CSP system through enhancing the CaCO3’s ability to capture thermal energy from the concentrated solar irradiation. Efforts are devoted to design and fabricate a modified CaL material by doping CaCO3 with some materials with high solar absorptance. In order to obtain a highly stable CaL, the cyclic performance of the composite material is investigated and optimized. The calcium gluconate ((Ca(C6H11O7)2)) was used as the precursor while fabricating the porous CaCO3, and the Mn–Fe oxides were doped into CaCO3 through two different doping processes. The experimental results indicate that the proposed material obtains the solar absorptance of ∼90%. The heat release efficiency (equal to carbonation activity) remains over 92% in 60 cycles, which is much higher than that of the commercial CaCO3 powder (20% after 60 cycles). The proposed calcium-based thermochemical energy storage material is expected to dramatically improve both the solar utilization efficiency and cyclic stability of the integrated CaL-CSP system.