Type II absorption thermal battery for temperature upgrading: Energy storage heat transformer

Low grade and intermittence are the two main obstacles hindering the utilization of renewable/waste energy. The conventional thermal battery can address the intermittence issue by matching the timing between energy supply and energy demand, but it can never address the low-grade issue. To address this problem, a novel type II absorption thermal battery for temperature upgrading is proposed, which combines the functions of energy storage and heat transforming. Dynamic simulation is conducted based on an experimentally validated model to investigate the transient characteristics and cycle performance. Both the energy storage performance (i.e., energy storage efficiency and density) and the heat transformer ability (i.e., temperature lift) are comparatively analyzed. The maximum energy storage efficiency is between 0.42 and 0.44, while the maximum energy storage density varies from 195.6 kWh/m³ to 292.7 kWh/m³, with charging temperatures of 70–90 °C, temperature lifts of 10–55 °C, and a cooling water temperature of 32 °C. There is a trade-off between the energy storage performance and the heat transformer ability. Besides, a higher charging temperature or a lower cooling water temperature can enhance the energy storage performance and the heat transformer ability. Compared to the existing thermal batteries, the novel type II absorption thermal battery shows a unique advantage of temperature upgrading whilst yielding a high energy storage density and a high exergy efficiency. This study aims to provide theoretical references and suggestions for the development of the type II absorption thermal battery.