Dynamic characteristics and performance enhancement of two-stage absorption thermal battery for long-term renewable energy storage

Absorption thermal battery (ATB) has garnered significant attention in recent years due to its high energy storage density (ESD), low heat loss, and versatile output functionalities. However, reducing the charging temperature to improve the performance under low-grade renewable energy sources poses critical challenges for ATB applications. The two-stage ATB has been proposed for extremely low charging temperatures. To comprehensively and accurately investigate the performance of the two-stage ATB under different conditions, this work establishes an experimentally validated dynamic model. Then, the operation behaviors and cycle performance for cold and heat storage scenarios have been compared between the basic and two-stage cycles. Subsequently, the effects of solution distribution between the two solution tanks (i.e., the main storage tank and auxiliary tank) on cycle performance have been studied under various charging temperatures. Moreover, the advantages and suitability of the two-stage ATB for long-term storage have been analyzed. Results indicate that the two-stage ATB achieves a cold storage density of 115.8 kWh/m3 at 55 °C and a heat storage density of 59.7 kWh/m3 at 50 °C, both more than doubling those of the basic ATB (57.7 kWh/m3 and 27.5 kWh/m3). At low charging temperatures, different solution distribution in tanks show significant differences in ESD. The optimal distribution scheme for achieving the highest ESD tends to allocate more solutions to the main storage tank as the charging temperature rises. For long-term storage scenarios, the two-stage ATB shows advantages over the basic ATB, achieving higher concentration glides (i.e., higher ESD), especially under low charging temperatures.