New highly efficient regeneration process for thermochemical energy storage

Thermochemical energy storage is a key technology to realize highly efficient thermal energy storages for various applications such as solar thermal systems or cogeneration systems. As thermal storage material zeolite and composite materials of zeolite and e.g. salts are the subject of intensive research at present. These materials meet the combined requirements of high energy storage density and good heat transfer rates. However, in order to obtain a high energy storage density, comparatively high temperatures of in excess of 180 °C are needed during the regeneration process. This is a drawback especially when used as storage material in solar thermal systems. In this paper, a new regeneration strategy is proposed for an open sorption process. The new regeneration strategy allows regeneration of the storage material at significantly lower temperatures without reducing the energy storage density of the material. For the example of a solar thermal combisystem with thermochemical energy storage, a concept for integrating this new regeneration strategy into an overall system will be presented. For an energetic assessment, annual system simulations have been performed with the dynamic simulation software TRNSYS. A comparison of the system design with a “conventional” regeneration strategy (regeneration temperature of 180 °C) and with the new regeneration strategy (regeneration temperature of 130 °C) has been made. The results of the simulation study show that with the new regeneration strategy the fractional energy saving as a measure of the thermal performance of the system can be maintained or even increased. These promising results demonstrate that this process design may be a breakthrough in realizing thermochemical energy storages for solar thermal applications based on high performance zeolite or zeolite composite materials.