Thermochemical Heat Storage – from Reaction Storage Density to System Storage Density

Long-term and compact storage of solar energy is crucial for the eventual transition to a 100% renewable energy economy. For this, thermochemical materials provide a promising solution. The compactness of a long-term storage system is determined by the thermochemical reaction, operating conditions, and system implementation with the necessary additional system components. Within the MERITS project a thermochemical storage (TCS) system is being demonstrated using evacuated, closed TCS modules containing Na2S as active material. The present modules are expected to reach a heat storage density of 0.18GJ/m3. In this paper, we discuss the different factors leading to this storage density, and argue that by further optimization of the selected reaction and architecture, the result may be improved to approximately 1GJ/m3, which would be a practical value for seasonal heat storage in buildings.