Experimental Performance Enhancement of a Single-Slope Solar Distiller Using Date Pits and Walnut Shells as Sensible Thermal Energy Storage Media for Freshwater-Scarcity Mitigation

Freshwater scarcity is a pressing global challenge, particularly in arid and semi-arid regions, necessitating sustainable and cost-effective desalination solutions. This study experimentally investigates the performance enhancement of a single-slope solar distiller using date pits and walnut shells as low-cost sensible thermal-energy-storage media. Two experimental cases were conducted under nearly identical weather conditions: a conventional distiller versus a date-pits-modified distiller, and a conventional distiller versus a walnut-shells-modified distiller. The incorporation of both storage media enhanced thermal performance by increasing the temperature difference between the basin water and glass cover and sustaining heat release during periods of declining solar radiation. Cumulative daily productivity improved by 18.32% for date pits and 17.14% for walnut shells, reaching 2637.5 mL/m2 and 2562.5 mL/m2, respectively. Energy efficiency increased by 17.96% and 16.93%, while exergy efficiency improved by 27.34% and 25.60% for date pits and walnut shells, respectively. Economic analysis revealed cost reductions of 14.92% and 14.06%. Date pits exhibited slightly higher overall performance, consistent with their higher reported thermal conductivity and specific heat capacity. The results demonstrate the potential of agricultural waste materials as sustainable sensible thermal-energy-storage media for improving the thermal and energetic performance of solar-desalination systems.