Thermodynamic modeling of nitrate materials for hybrid thermal energy storage: Using latent and sensible mechanisms

Applications for thermal energy storage (TES) are often found in nitrate salts which show high specific heat and high thermal stability over a wide temperature range, such as in the case of solar salt (NaNO3-KNO3). However, the combination of both sensible and latent heat capacity is desired since it increases the energy storage performance over the value of each of the mechanisms apart. We use CALPHAD thermodynamic modeling to study the role of this hybrid storage capacity in temary nitrates composed by the solar salt and either CsNO3 or LiNO3 along certain compositional lines. For most cases, the highest amount of stored energy is for the pure sensible mechanisms; however, at NaNO3 and LiNO3 rich conditions for the NaNO3-KNO3-CsNO3 and NaNO3-KNO3-LiNO3 systems, respectively, we obtain that latent mechanisms increases up to 3% the value of the pure sensible mechanism. This estimation can shed light into novel procedures to find more effective materials for energy storage, and we expect new experimental measurements will be conducted to validate these criteria. (C) 2017 Elsevier Ltd. All rights reserved.