Experimental assessment of calcium L-lactate as thermochemical heat storage material

ThermoChemical heat Storage (TCS) technology based on salt hydrates offers a viable path in the transition towards more sustainable energy systems. However, the materials explored so far, within the class of inorganic salts, suffer severe drawbacks due to the deliquescence phenomenon. We aim to progress here by proposing an organic salt hydrate, namely calcium L-lactate pentahydrate (CaLP), which is able to combine a low water solubility, that is, more resistance to deliquescence, with the coordination to a high number of water molecules and stability under operating conditions. The thermochemical behavior for thermochemical energy storage applications of this salt has been experimentally assessed for the first time. It was demonstrated that CaLP reversibly dehydrates/hydrates within an operating temperature range suitable for low-temperature thermochemical heat storage. Additionally, the material showed good thermal and chemical stability. Morphological and structural investigations conducted in situ were carried out while dehydrating/hydrating. Furthermore, water vapor pressure (pH2O) and temperature boundary conditions were identified to define the operating conditions required for this salt for its future use as thermochemical heat storage material. The heat storage capacity was estimated to be 1127 kJ kg−1 (or 1696 MJ m−3), thus ranking this organic salt among the most competitive inorganic counterparts. As further advantages, calcium L-lactate is inexpensive, non-toxic, largely available, and shows no deliquescence-related issues, making it suitable for realistic large-scale apparatus.