Sustainable desalination using agricultural waste: 4E performance assessment of solar stills with palm shells as thermal energy storage

This study experimentally evaluates the performance of double-slope solar stills integrated with palm shell waste as a sensible heat storage material. Four configurations were tested: a conventional still and three variants containing 3 kg of palm shells with different mesh sizes (1, 2, and 5 mesh). A comprehensive 4E analysis (Energy, Exergy, Economic, Environmental) was conducted. The results demonstrate that incorporating palm shells significantly enhances freshwater productivity by up to 37.49 %, with corresponding increases in energy efficiency of 38 % and exergy efficiency of 10–58 % compared to the conventional still. The lowest cost of freshwater production was achieved with 5-mesh palm shells, at 0.039 $/L, representing a 26.41 % cost reduction. Environmentally, palm shell integration reduced lifetime CO₂ emissions by 43 %, while also accelerating the energy payback period from 1.08 years to 0.52 years. Among the tested sizes, 5-mesh palm shells consistently delivered the highest overall performance. These findings highlight palm shells as a sustainable, low-cost, and high-impact material for improving solar desalination, particularly in regions with abundant palm oil waste.