Material research on salt hydrates for seasonal heat storage application in a residential environment

Water vapor sorption in salt hydrates is a promisi ng method to realize seasonal solar heat storage in the residential sector. Several materials already showed promising performance for this application. However, the stab ility of these materials needs to be improved for long term (30 ye ar) application in seasonal solar heat storages. Th e purpose of this article is to identify the influence of the materia l properties of the salt hydrates on the performanc e and the reaction kinetics of the sorption process. The experimental investiga tion presented in this article shows that the two s alt hydrates Li 2SO 4·H 2O and CuSO 4·5H 2O can store and release heat under the operating co nditions of a seasonal solar heat storage in a full y reversible way. However, these two materials show differences in terms of energy density and reaction kinetics. Li 2SO 4·H 2O can release heat with an energy density of around 0.80 GJ/m 3 within 4 hours of rehydration at 25°C, while CuSO 4· 5H 2O needs around 130 hours at the same temperature to be fully rehydrated and reaches an energy density of 1.85 GJ/m 3 . Since the two salts are dehydrated and hydrated u nder the same conditions, this difference in behavi or is directly related to the intrinsic properties of the materials.