Enhancing\nPhoto-to-Thermal Energy Conversion Efficiency\nof the CaO/CaCO<sub>3</sub> Composite with Co and Mn Additives for\nConcentrated Solar Power Systems

CaO/CaCO<sub>3</sub>-based sorbent can be used as a thermochemical\nenergy storage (TCES) material in concentrated solar power (CSP) systems\ndue to its ability to convert thermal energy to chemical energy through\nrepetitive carbonation-calcination cycles. Typically, a CSP system\nconsists of a solar field, solar receiver, thermal energy storage\n(TES), and a power generation system. Recently, research has focused\non technologies that eliminate the need for heat transfer media, allowing\nTCES materials to directly capture heat and convert it into chemical\nenergy. Despite CaO/CaCO<sub>3</sub>’s relatively superior\nchemical energy storage capacity, its photo-to-thermal energy conversion\nefficiency under solar irradiation is low, limiting its application\nin such direct thermal energy capture technologies. This study focuses\non methods to increase the photo-to-thermal energy conversion efficiency\nwhile maintaining the excellent thermal-to-chemical energy conversion\ncharacteristics of CaO/CaCO<sub>3</sub>. A CaO/CaCO<sub>3</sub>-based\ncomposite with cobalt (Co) and manganese (Mn) additives was synthesized\nusing the sol–gel method, and its optical properties under\nsolar irradiation were measured using a lab-built apparatus under\nconditions ranging from 1 sun to 148 suns. It was found that the CaCO<sub>3</sub>-based sorbent with added Co and Mn could reach temperatures\nof up to 650 °C under 148 sun conditions. Additionally, due to\nthe structural stabilization effect of CaCO<sub>3</sub> from the addition\nof Co and Mn, it demonstrated very stable CaO conversion efficiency\nover 20 repeated carbonation-calcination cycles. This indicates that\nthe CaO/CaCO<sub>3</sub>-based composite with Co and Mn additives\nhas the potential to directly capture solar irradiation while efficiently\nconverting solar thermal energy into chemical energy repeatedly.