Thermal energy storage (TES) plays a crucial role in improving the efficiency and reliability of solar thermal systems, particularly when low-cost and readily available materials are desired. This study experimentally investigates the performance of a water–salt thermal energy storage system using sodium chloride (NaCl) at different concentrations in a simple solar collector setup. Experiments were conducted using a laboratory-scale solar thermal energy system under controlled conditions, with water serving as the heat transfer fluid and a fixed flow rate of 15 L/h. The storage medium consisted of water mixed with salt, which was obtained from the Dead Sea before any treatment. In its raw form, this type of salt contains impurities, mainly sand, at a fixed concentration of approximately 1% by weight. The effects of salt concentration on storage temperature, system efficiency, and effective heat capacity were analyzed. The results show that moderate NaCl concentrations improved the average storage temperature by up to 12–18%, increased thermal storage efficiency by approximately 1%, and enhanced the effective specific heat capacity compared to pure water. In contrast, higher salt concentrations resulted in a performance reduction of up to 8–12% due to increased thermal resistance and reduced heat transfer effectiveness. An optimal salt concentration range was identified at which maximum storage efficiency and heat capacity were achieved. These findings demonstrate that common sodium chloride can serve as an effective and economical enhancement material for thermal energy storage when properly optimized. The study provides quantitative evidence and practical insights for the development of low-cost, salt-based thermal energy storage systems for solar thermal applications. This study highlights the importance of concentration optimization and provides practical insights for the development of low-cost, salt-based thermal storage systems for solar energy applications.
Abdelhafez et al. (Sat,) studied this question.