EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Storing thermal energy in the summer and re-using it in the winter could be a game-changer for reducing energy consumption. In the EU, 3.6 EJ/year are used for heating, 28 GJ per-capita. The source of this energy comprises 47% natural gas, 16% oil products, 9% biofuel/waste, 3% coal. Saving even a small fraction of this energy would provide an enormous reduction in fuel consumption.
Seasonal thermochemical heat storage is based on the idea that heat can be stored seasonally by using a reversible endothermic/exothermic reaction. In particular, among the best is the hydration/dehydration of MgSO4 or CaCl2. However, to full exploit the thermal potential of the salt, and to guarantee stability after several cycles, the salt must be dispersed homogeneously in a highly porous material. In the literature, materials like zeolites or silica are suggested, but their cost is too high for a real application of this technology. Other porous materials, like vermiculite, are cheaper but they have problems of stability and cyclability.
Here we propose a very widespread and cheap material, cement, as the porous matrix for MgSO4 or CaCl2. Pure cement hydrated at high water-to-cement ratio is in itself a heat storage material, however its performance is rather scarce. But it is a perfect matrix for salts.
We produced cement-salt composites either by infiltrating the porous cement or by a novel one-step approach, by making the cement hydration reaction happen in an almost saturated solution of the salt. The obtained materials were characterized in terms of their physical and thermal properties. The energy density in particular was estimated by a self-built calorimetric analysis. The performance of the composites was compared with literature values, showing that the material cost lies close to 1 €/kWh, significantly lower than literature values for pure zeolite or zeolite/salt.