Experimental study on a two-stage absorption thermal battery with absorption-enhanced generation for high storage density and extremely low charging temperature (∼50 °C)

Absorption thermal battery (ATB) is a promising solution to balance the timing or intensity mismatch between low-grade renewable energy sources and end users, which can significantly alleviate the growing energy and environmental issues. However, the performance of the basic ATB needs to be improved, and there is still a lack of experimental research on advanced ATBs. This study proposes a two-stage ATB with absorption-enhanced generation to achieve high energy storage density (ESD) and extremely low charging temperature. A prototype is designed and manufactured, including the single-stage and two-stage modes. The experimental results indicate that the single-stage ATB is fully charged under a charging temperature of 90 °C with an energy storage efficiency (ESE) of 0.62 and an ESD of 137.3 kWh/m3 (357.2 kJ/kg). Under a charging temperature of 70 °C, the ESD of the single-stage ATB is only 62.7 kWh/m3 (163.1 kJ/kg), which can be greatly enhanced to 100.0 kWh/m3 (260.1 kJ/kg) by the two-stage ATB. The lowest charging temperature of the single-stage ATB is 60 °C, with an ESE of 0.31 and an ESD of 22.1 kWh/m3, while the two-stage ATB improves the ESE and ESD by 9.7% and 190.5%, respectively. Even under 50 °C, the ESE (0.33) and ESD (29.4 kWh/m3) of the two-stage ATB are higher than those of the single-stage ATB under 60 °C. The experiment results prove that the two-stage ATB has the advantages of higher ESD and lower charging temperature than the conventional ATB, which provides a promising option for low-grade renewable energy utilization.