Thermodynamic analysis of a novel versatile thermochemical heat storage system containing dissolutive endothermic salts

Closed salt hydrate-based thermochemical heat storage (TCHS) systems have attracted widespread attention due to its high energy density, environmental friendliness, high safety and flexible discharge of evaporative cold energy and/or reactive thermal energy, but they always suffer the inferior low-temperature adaptability due to the freezing point (0 °C) limitation of water. Here, we propose a modified closed salt hydrate-based TCHS system containing a dissolutive endothermic salt, which enables to improve the low-temperature adaptability by yielding the salt solution with a low freezing point (<0 °C) and meanwhile further boosts the system flexibility by temporally decoupling the cold and heat output. Such a system is highly versatile and can be operated in multiple modes to regulate the intermittent solar thermal for on-demand heating and cooling. Using five commonly used salt hydrates as storage mediums paired with a selected dissolutive endothermic salt (KSCN), the system’s thermodynamic performance is systematically evaluated for three typical operating modes and scenarios, including daily cold storage with cooling in daytime (Mode 1), daily thermal storage with cooling in daytime (Mode 2), and seasonal thermal storage with cooling in summer (Mode 3). Results show that a system coefficient of performance (COP) of 0.7 and cold storage density of 495.8 kJ kg⁻¹ can be achieved by using CaCl₂ in Mode 1; Mode 2 yields a system COP exceeding 1.0 and a thermal energy storage density of 603.6 kJ kg⁻¹ based on SrBr₂; and the system operated in Mode 3 exhibits excellent low-temperature environmental adaptability. This work provides a potential solution for daily and seasonal solar energy management based on the versatile TCHS systems.