Efficiency Evaluation of Double Hydrate Salt Mixtures as Low Temperature Thermo Chemical Heat Storage Materials

Abstract

Recently, thermo chemical heat storage (TES) has gained important attentions,
since it offers a high storage capacity with low temperature ensured by thermochemical
heat storage materials (TcSM) 1. The hydrates salt can react, store and release heat during a
Charge/Discharge cycle based on hydration/dehydration reactions over different
temperature range. Due to their good energy storage density, hydrates salts have been
widely developed on different researchs to be used in solar energy storage2.Blödite,
Konyaite and Löweite are double salt with a good behavior as TcSM thanks to their
significant reaction enthalpy. However, theirapplications still limited by the problems of
reversibility, complexity and the high charging temperature which is supposed to be
provided by solar domestic collectors applications. Moreover, it is complicated to predict
the purity and the structural stability of these salts during the dehydration and hydration
reaction, which affects the storage density and the efficiency of TcSM. In this work,
Konyaite-Blödite (MDHS1) and Löweite-Blödite (MDHS2) were synthesized and
characterized. Quantitative XRD analysis of mixtures was performed adopting the
Reference Ratio Intensity (RIR) method 3. In addition, an evaluation of (MDHS) is
developed taking into account many parameters such as charge temperature, storage
density, reversibility and storage performance in order to identify the most promising
candidate for domesticheat storage systems. FTIR results confirm good reversibility of
hygroscopic behavior at temperature up to 200 °C. Thesemixtures show agood stability
behavior, but only MDHS2 offers a good net storage density of 370.8 KWh.m-3 and an
excellent efficiency of 38%.