Investigation on an innovative resorption system for seasonal thermal energy storage

An innovative resorption system is established and investigated for seasonal thermal energy storage. Solar energy is stored in form of chemical potential in summer whereas the stored energy could be released in form of sorption heat in winter. Working pair of MnCl₂-CaCl₂-NH₃ is selected and composite sorbents are developed with expanded natural graphite treated with sulfuric acid as the matrix for heat and mass transfer intensification. It is indicated that the highest effective heat storage density, heat power density and system COP are able to reach 1047 kJ kg^-1, 402 W kg^-1 and 0.58 under the condition of 30 °C heat output temperature and 15 °C ambient temperature. Novel resorption thermal energy storage system verifies the feasibility for seasonal energy storage at high ambient temperature in winter, which reveals great potentials for solar energy utilization. Also worth noting that two possible solutions i.e. temperature upgrade mode and sorption-compression mode are analyzed and compared when ambient temperature is relatively low i.e. below 0 °C. Results demonstrate that heat could be supplied in term of -15 °C ambient temperature and 50 °C heat output temperature. Two methods could deal with the issues at low ambient temperature, which have their respective advantages for different applications.