Efficient passive solar desalination using cooling tower integration and thermal insulation

Freshwater scarcity remains a critical global issue, particularly in arid regions with inadequate infrastructure. In this study, a passive, solar-powered desalination system was designed and evaluated for continuous freshwater production without reliance on fossil fuels or external electricity sources. The system integrates a solar water heater, a thermally insulated evaporation chamber, and a spiral condenser coil linked to a water-based cooling tower, enhancing daytime and nighttime water recovery. This innovation achieves higher efficiency with minimal operational cost, demonstrating significant potential for deployment in water-stressed regions. Field tests conducted in Tehran, Iran, during August and September 2023 showed a substantial increase in daily water output following the integration of the cooling tower-from 3018 to 6978 mL in August and from 2409 to 7016 mL in September-representing gains of 286.82 and 231.21%, respectively (p < 0.0001). The device also sustained overnight water production due to effective thermal insulation, yielding 1936 ± 51.55 mL of distilled water after sunset. Water quality analysis confirmed the removal of toxic elements while retaining essential minerals within safe limits. The system's embodied carbon footprint was estimated at 0.139 kg CO₂ per liter of water produced, with zero operational emissions. Economic analysis indicated a cost of 0.526 USD/L in the first year, decreasing to 0.105 USD/L over five years, with an internal rate of return (IRR) of 26.50%. The proposed integration of a cooling tower and thermal insulation significantly enhances water yield and operational efficiency, outperforming conventional passive desalination systems in both distillate output and energy conservation. This positions the system as a superior, scalable, and sustainable solution for decentralized freshwater generation in off-grid and water-stressed regions.