State of the art on salt hydrate thermochemical energy storage systems for use in building applications

Thermal energy storage (TES) for storing low-grade energy is a promising approach to achieving higher energy security and minimizing greenhouse gas emissions. TES is shifting towards using thermochemical materials (TCM) since there are several advantages when compared to sensible or phase change materials. However, thermochemical energy storage (TCES) is more complex and thus has not yet been developed commercially. To further develop this technology and bring it closer to commercialization, there needs to be a merging of research from both material and system design viewpoints. At a material level, salt hydrates are considered the most suitable materials for residential applications due to their high energy density (400-870 kWh m−3) and low turning temperature (<150 °C). From an engineering point of view, different system configurations have been designed and tested for salt hydrates. However, there are several technical challenges to the design of an efficient and stable system which need to be addressed before commercialization. This paper aims to provide a comprehensive review of the advancements of the long-term energy storage technology using salt hydrates at a material and system level. Furthermore, it covers the criteria for system design and the prototypes which have been designed and tested, as well as the technical challenges associated with TCES.