With an innovative concept for the storage of thermal energy at low and constant temperature levels, solar thermal energy can be used effectively in transition and winter periods. Furthermore, the solar energy can be stored to increase the efficiency of heat pumps. A latent heat storage system based on salt hydrates is introduced, where the salt hydrate has a melting point of 15 degrees C and is in direct contact with an immiscible heat transfer fluid generating a high charging and discharging capacity. Initial experimental results and application examples are presented and discussed.