Architectural and real-time monitoring design of multi-stage solar still for solar water purification

Multi-stage solar still with separated photothermal/evaporation interfaces have high energy utilization and water collection efficiency compared to widely reported single-stage upward solar interfacial evaporation. Despite progress, it still faces a “black box” issue regarding internal conditions like evaporation and salt accumulation due to its enclosed design. Herein, we developed a real-time operating status monitoring system for multi-stage solar stills with separated photothermal/evaporation interfaces. Firstly, we designed an optimal 5-stage solar still architecture with two-way water supply to achieve rapid water collection rate (1.72 L m⁻² h⁻¹ under 2.0 kW m⁻²) and desalination effects. Secondly, the optimal operating status (12 h of solar irradiation + 12 h of dark rinsing) was achieved through verification of different salinities and operating conditions. Finally, the resistance and temperature monitoring strategies applied to determine the operating status of multi-stage solar stills were explored: The water supply status, irradiation intensity, and salinity can be monitored by resistance change at the water supply inlet; and the salt precipitation status in the evaporation dead zone can be monitored by the temperature change at evaporation layer. This study holds significant value for implementing and optimizing multi-stage solar stills in solar desalination, offering insights into intelligent, automated operation and monitoring systems for enhanced sustainability.