Large-temperature-lift energy storage heat transformer for deep thermal energy utilization

The features of low grade and instability hinder the extensive utilization of renewable energy. Energy upgrading technology is needed to turn unusable renewable energy into usable energy, and energy storage systems are also required to solve the mismatch problem between energy sources and end users. Therefore, the energy storage heat transformer (ESHT) based on the desorption-absorption cycle has been proposed and regarded as a promising solution. To further reduce the heat input temperature and improve the cycle performance for deep utilization of renewable energy, a novel two-stage ESHT cycle is proposed and investigated. Preliminary experiments are conducted and used to validate the established dynamic model. Then, the performance under different working conditions are compared between the basic and two-stage ESHT cycles. Results show that one of the two solution tanks in the two-stage ESHT achieves a higher concentration compared to basic ESHT, increasing from 55.7 % to 65 % with the same temperature lift of 30 °C. The energy storage density (ESD) is significantly improved from 51.0 kWh/m³ to 96.1 kWh/m³ with similar energy storage efficiency (ESE) and exergy efficiency (EXE). A maximum temperature lift of 50 °C is reached under an input temperature of 60 °C. A minimum heat input temperature of 55 °C is achieved with a temperature lift of 35 °C. This work aims to provide references and suggestions for the improvement of absorption-based ESHT. © 2025 Elsevier Ltd.