High-efficiency desalination of hemispherical solar still incorporating dish collector, hanging wick, nanofluids, back reflector, and external condenser: A 4E perspective

Water scarcity and the high energy demand of conventional desalination systems motivate the development of low-cost, low-carbon freshwater production technologies. Solar stills are attractive for remote and arid regions, but their productivity and efficiency are typically low. This work experimentally investigates a modified hemispherical solar still (MHSS) that integrates a parabolic dish collector, a hanging wick, a copper oxide nanofluid, a back reflector, and an external condenser. It evaluates its performance from a comprehensive 4E perspective (energy, exergy, economic, and environmental). Two identical hemispherical stills were constructed and tested under the climate of Kafr El-Sheikh, Egypt: a conventional hemispherical solar still (CHSS) and four MHSS configurations. The cases considered were: (1) dish-fed HSS with hanging wick, (2) case 1 plus CuO nanofluid, (3) case 2 plus back reflector, and (4) case 3 plus external condenser. Results show that the fully integrated system (case 4) increases daily freshwater productivity from 3.36 to 11.03 L/m² compared with the CHSS, while the cumulative energy efficiency rises from about 31% to 66.35% and the exergy efficiency from about 1.8% to 5.92%. The annual freshwater yield increases from 1130 to 3752 L/year, reducing the specific water production cost from 0.0148 to 0.0099 $/L relative to the conventional still. From an environmental standpoint, the modified system avoids approximately 3.96 tons of CO₂ emissions over its lifetime compared with the CHSS. Overall, the proposed configuration substantially enhances thermal performance, water productivity, and economic and environmental indicators, demonstrating its potential as a sustainable option for solar desalination.