Researchers in Tehran, Iran, have unveiled a groundbreaking passive solar desalination system that dramatically boosts freshwater production by integrating a water-based cooling tower and advanced thermal insulation. Field tests conducted in August and September 2023 demonstrated an unprecedented increase in daily water output, offering a sustainable and economically viable solution for water-stressed regions without reliance on fossil fuels or external electricity.

The innovative system, developed at the Chemistry Research Institute, combines a solar water heater, a thermally insulated evaporation chamber, and a spiral condenser coil linked to a water-based cooling tower. This design significantly enhances both daytime and nighttime water recovery. During August 2023, the system’s daily output surged from 3018 milliliters (mL) to 6978 mL following cooling tower integration, representing a 286.82% gain. Similarly, in September, output increased from 2409 mL to 7016 mL, a 231.21% rise (p < 0.0001). Crucially, the effective thermal insulation enabled sustained overnight production, yielding 1936 ± 51.55 mL of distilled water after sunset, a critical advantage over traditional solar stills.

Conventional thermal desalination methods, such as multi-stage flash (MSF) and multi-effect distillation (MED), are highly energy-intensive and predominantly dependent on fossil fuels, contributing significantly to greenhouse gas emissions. While solar still distillation (SSD) systems offer a low-cost, solar-powered alternative, their typical daily yields of 2–3 liters per square meter have limited their broader application to small-scale uses. Previous solar-assisted hybrid systems often lacked thermal storage, resulting in limited nighttime productivity.

This new system addresses these limitations directly. Its fully passive operation eliminates the need for photovoltaic input or grid electricity, making it ideal for off-grid deployments. Water quality analysis confirmed the effective removal of toxic elements while retaining essential minerals within safe limits, ensuring the produced water is potable. The system’s embodied carbon footprint was estimated at a remarkably low 0.139 kg CO2 per liter of water produced, with zero operational emissions, aligning with global decarbonization efforts.

From an economic perspective, the system presents compelling figures. The cost of water production was calculated at 0.526 USD per liter in the first year, projected to decrease significantly to 0.105 USD per liter over five years. The internal rate of return (IRR) stands at a robust 26.50%, indicating strong financial viability for investors and project developers. This performance positions the integrated passive solar desalination system as a superior, scalable, and sustainable alternative, outperforming existing conventional and passive desalination technologies in both distillate output and energy conservation.