Salt hydrates in renewable energy systems: A thorough review

This paper aims to review recent advancements in the utilization, storage, and integration of salt hydrates (SHs) in renewable energy (RE) systems. Initially, the latest review articles on applications of SHs in the energy sector are discussed. Then, various categories of SHs are extensively studied, emphasizing their thermochemical and thermophysical properties. SHs utilized in RE technologies across different temperature ranges alongside limitations like toxicity, corrosion, and cost are reviewed, and the most effective SHs in terms of chemical energy density, and cost-effectiveness at various temperatures are identified. Eventually, challenges, research gaps, and potential future work regarding these SHs are discussed. The study concludes that the most frequently used salts in sustainable energy systems include, but are not limited to, LiOH (0→-1) for temperatures above 150 °C, LiNO₂ (1  →  0) for 80 °C to 150 °C, LiOH (1  →  0) for 40 °C to 80 °C, LiCl (2  →  1) for 10 °C to 40 °C, and LiBr (2  →  1) for temperatures below 10 °C. Moreover, the study highlights a significant group of SHs with diverse operating temperatures and high energy densities that have not yet been sufficiently investigated. Economically, the most promising salts are identified as Na₂CO₃, MgCl₂,MgSO₄ and Ca(OH)₂ due to their low cost per unit of chemical energy.