Enhancing Photo-to-Thermal Energy Conversion Efficiency of the CaO/CaCO₃ Composite with Co and Mn Additives for Concentrated Solar Power Systems

CaO/CaCO3-based sorbent can be used as a thermochemical energy storage (TCES) material in concentrated solar power (CSP) systems due to its ability to convert thermal energy to chemical energy through repetitive carbonation-calcination cycles. Typically, a CSP system consists of a solar field, solar receiver, thermal energy storage (TES), and a power generation system. Recently, research has focused on technologies that eliminate the need for heat transfer media, allowing TCES materials to directly capture heat and convert it into chemical energy. Despite CaO/CaCO3’s relatively superior chemical energy storage capacity, its photo-to-thermal energy conversion efficiency under solar irradiation is low, limiting its application in such direct thermal energy capture technologies. This study focuses on methods to increase the photo-to-thermal energy conversion efficiency while maintaining the excellent thermal-to-chemical energy conversion characteristics of CaO/CaCO3. A CaO/CaCO3-based composite with cobalt (Co) and manganese (Mn) additives was synthesized using the sol–gel method, and its optical properties under solar irradiation were measured using a lab-built apparatus under conditions ranging from 1 sun to 148 suns. It was found that the CaCO3-based sorbent with added Co and Mn could reach temperatures of up to 650 °C under 148 sun conditions. Additionally, due to the structural stabilization effect of CaCO3 from the addition of Co and Mn, it demonstrated very stable CaO conversion efficiency over 20 repeated carbonation-calcination cycles. This indicates that the CaO/CaCO3-based composite with Co and Mn additives has the potential to directly capture solar irradiation while efficiently converting solar thermal energy into chemical energy repeatedly.