Experimental study on a double-stage absorption solar thermal storage system with enhanced energy storage density

The solar energy utilization has great significance regarding the ever-increasing environment pollution and energy shortage issues. To overcome the instability and intermittency of solar energy, various solar thermal storage technologies have been proposed, and absorption thermal storage is promising for its high energy storage density and long-term storage. However, past researches focused more on working pair and neglected the potential of cycle enhancement. In this paper, an absorption solar thermal storage system with enhanced energy storage density from double-stage output is studied experimentally. A prototype with water-LiBr working pair was designed, manufactured, and tested. The long-term heat storage and short-term heat/cold storage were both tested and evaluated for the double-stage and single-stage working modes. Hot water at 75-85 degrees C was used as heat source in the charging process to simulate the solar energy from non-concentrated collector, and the prototype was able to provide heating output/cooling output at 50/11 degrees C in discharging process. Energy storage density of 233 kJ/kg (103 kWh/m(3)) was achieved for heating output with temperature lift of 30-46 degrees C, which was 2.51 times higher than that of the single-stage system (93 kJ/kg). The proposed system with large temperature lift, multi-function output, and enhanced energy density has proved its effectiveness in solar thermal storage and conversion, which also provides a feasible option for the large-scale utilization of solar energy.