Performance Enhancement of Single and Double-Slope Solar Stills by Integrating Energy Storage Material: Energetic and Exergetic Approach

Abstract

Access to safe freshwater remains a challenge, particularly in arid and water-scarce areas. Growing freshwater scarcity due to rapid climate change, industrialization, and population growth has increased the demand for sustainable and decentralized desalination technologies. Solar radiation distillation offers a simple, low-cost, and environmentally friendly solution, but its low productivity limits large-scale adoption. This experimental study investigates performance improvements in a single-slope and double-slope solar still incorporating a eutectic phase change material (EPCM) at a fixed basin water depth of 10 mm under winter (December) and summer (May) conditions. A eutectic mixture of stearic acid with palmitic acid at a melting temperature around 55 °C was used as latent heat storage to stabilize basin temperature and extend distillation during off-sunshine hours. The study analyzed four configurations: a conventional single slope solar still (CSSS), a single slope solar still with eutectic phase change material (SSEPCM), a conventional double slope solar still (CDSSS), and a double slope solar still with eutectic phase change material (DSSSEPCM. December freshwater yields were 1575, 2350, 2000, and 2785 ml, respectively, and increased in May to 1835, 2605, 2355 and 3130 ml. Phase change material (PCM) integration improved night distillation with yields of 580-750 ml in December and 610-810 ml in May for SSSEPCM and DSSSEPCM, which resulted in longer operational periods. The highest energy efficiency was 42.65% in December and 49.3% in May, and the highest exergy efficiency for DSSSEPCM was 17.1% and 18.6%. The proposed Eutectic phase change material-integrated solar stills provide a sustainable and decentralised solution for freshwater production in arid and water-scarce regions, where abundant solar energy is often accompanied by freshwater scarcity.