Techno-economic assessment of salt hydrate-based solar water heating systems under different climate scenarios

Large energy storage capacity and low cost of salt hydrates make them ideal candidates for integration into solar water heating systems. In this work, the phase-change performance and system reliability of the sodium acetate trihydrate–acetamide-based system and the sodium acetate trihydrate-based system were experimentally compared. The former system achieved a 5.6% higher efficiency. The system performance was further investigated numerically under varying setpoints and climate conditions to determine the optimal operating conditions for each material. Due to its more efficient use of latent heat, the sodium acetate trihydrate–acetamide-based system achieves a reduction of approximately 3.0% in annual cost compared to the sodium acetate trihydrate-based system at a setpoint of 40 °C in Hong Kong. However, the former system shows a longer payback period of approximately 4.9% in Denmark, and both phase-change materials showed negative net present values in France. The sodium acetate trihydrate–acetamide-based system exhibited lower energy use and operating expenditure under solar radiation of around 350–700 W/m 2 in Hong Kong. Nevertheless, after accounting for degradation, the higher replacement cost offset its operational savings, leading to a slightly higher lifecycle cost than the sodium acetate trihydrate-based system. This study highlights the importance of climate-specific material selection to balance energy performance and cost-effectiveness.