Enhancing the thermal efficiency of hemispherical solar still using waste aluminium cans filled with beeswax as thermal energy storage

• Beeswax PCM enables heat storage and nighttime freshwater production. • Nanoparticle-coated cans reduce heat loss and enhance evaporation. • Freshwater yield increased by 51 distillation. • Thermal efficiency improved from 29 coupling. • Low-cost and eco-friendly system for solar-driven seawater desalination. Increasing global freshwater scarcity has intensified the need for sustainable and low-cost desalination technologies, particularly for remote and arid regions. Solar stills represent an environmentally friendly solution; however, their practical application is limited by low productivity and poor heat retention, especially during off-sunshine hours. This paper is focused on the addition of encapsulated PCMs in the form of recycled aluminum cans to a Hemispherical Solar Still (HSS) and how it can augment freshwater yield as well as thermal efficiency. The augmentations in freshwater production will validate the hypothesis put forth in this research. Beeswax, a biodegradable Phase Change Material (PCM) with a latent heat of fusion of 180 kJ/kg, was encapsulated in coated black aluminum cans along with iron oxide (Fe 2 O 3 ) nanoparticles to maximize solar energy capture and retention. Different configurations were tested based on three different principles: HSS with no PCM (baseline), HSS with uncoated PCM-filled aluminum cans, and HSS with nanoparticle-coated PCM-filled cans. The results came along with impressive outputs. For example, the uncoated PCM system achieved a peak of 0.86 kg/m 2 (51% higher than baseline) and unbeatable nocturnal production (0.17 kg/m 2 at 21:00 Hrs). The uncoated average daily thermal efficiency also surged from 29.2%, marking it the best baseline system up to 45.8%, while coated PCM systems reached 60%. Due to the enhanced heat-transfer capabilities and reduced interfacial thermal resistance introduced by the nanoparticle coating, latent heat capture during non-solar hours increased. Economic analysis revealed a reduced levelized cost of water of 0.01679 USD/L and a payback period of 2.11 years for the coated system. Water quality analysis confirmed that the distilled water met the WHO drinking water standards. The results demonstrate that combining low-cost PCM encapsulation, recycled materials, and nanoparticle-enhanced coatings provides an effective and economically viable approach to improving solar still performance. Furthermore, using beeswax provided an environmental benefit compared to traditional synthetic and inorganic PCMs. Solving water scarcity issues through solar desalination, especially in remote and resource-poor areas, is made easier by combining low-cost PCM encapsulation, nanoparticle-enhanced coatings, and sustainable materials, as this study emphasizes.