Optimized thermal energy storage in conical solar stills: enhancing water productivity with flint stone-based heat retention

Abstract The efficiency of solar desalination systems is often hindered by the intermittent nature of solar radiation, leading to thermal fluctuations and reduced freshwater yield. This study investigates the integration of flint stones as a low-cost and effective thermal energy storage (TES) medium to enhance the productivity and efficiency of conical solar stills. A series of experimental analyses were conducted using flint stones of varying diameters (1, 1.5, 2, and 2.5 cm) to determine their impact on thermal regulation, evaporation rates, and freshwater production. The findings revealed that 2 cm flint stones exhibited the highest thermal storage capacity and energy retention, leading to a 40.18% increase in water yield (7.85 L/m2/day) compared to the conventional system (5.6 L/m2/day). Additionally, the system with 2 cm flint stones demonstrated a 119.62% improvement in overall efficiency, 135% enhancement in exergy efficiency, and 195% increase in the exergy production factor over the baseline system. The integration of flint stones provided thermal stability by reducing heat loss, maintaining consistent basin water temperatures, and extending the evaporation process beyond peak sunlight hours. This improved the overall stability and continuity of distillation performance throughout the day. Quantitatively, the economic analysis indicated a shortened payback period of 19 days for the optimized system, compared to 27 days for the conventional system, making it a cost-effective and sustainable solution for water-scarce regions. This study is the first to optimize the size of natural flint stones as TES materials in conical solar stills, demonstrating their superior heat retention capacity and significant performance improvement in freshwater production and energy utilization. The results validate the synergy between optimized TES and conical geometry as a promising design strategy for sustainable and affordable solar desalination systems. These findings pave the way for more efficient, economically viable, and environmentally sustainable solar desalination systems to combat global water scarcity.