Design and Test of a Three-Phase Absorption Thermal Storage System with High Energy Storage Density

Absorption thermal storage, as a type of thermal storage technology with a high energy storage density and long thermal storage period, is the key to storing solar thermal energy and solving the mismatch between solar thermal energy supply and demand during different seasons. Traditional absorption systems avoid crystallization by limiting the solution concentration, which assures reliability and safety but causes a limited energy storage density of the system. In this study, a closed three-phase absorption heat storage system is designed and tested. Through filtering and high-level inlet by the filters, crystal fusion by the heating rods, and flushing of the solution circulation lines, the system can operate normally after the solution crystallization, increase the concentration glide, and improve the energy storage density. Testing shows that the energy storage density of the system can reach 220 kW·h/m³ upon heat supply, which is an 114% increase compared to traditional two-phase absorption heat storage systems. Hence, the three-phase absorption heat storage technology with the utilization of crystallization is expected to realize high-density long-term solar energy thermal storage.