Photonic Structures to Achieve High-Performance Dew-Harvesting in a 24-h Day-Night Cycle

TL;DR

This paper develops a theoretical framework and photonic design for 24-hour dew-harvesting, overcoming daytime challenges and achieving significant water collection, nearly 70% of the theoretical maximum, with practical layout optimization.

Contribution

It introduces a novel theoretical framework and photonic design for continuous dew-harvesting across day and night, addressing daytime challenges and optimizing condenser layout.

Findings

Achieves a water production rate of 313 g/m2-day with 40% from daytime.

Requires a minimum average solar reflectivity of 0.92 for effective daytime dew-harvesting.

Design reaches approximately 70% of the theoretical maximum water collection.

Abstract

Although most prior research on the dew-harvesting technology has focused on nocturnal operations, achieving round-the-clock freshwater harvesting remains crucial. However, daytime dew-harvesting faces two key challenges as compared to its nighttime counterpart: the high solar irradiance and the large contrast between the ambient temperature and the dewpoint. To address these challenges and guide the photonic design, we develop a theoretical framework to analyze dew-harvesting in a 24-h day-night cycle. Using Nanjing as an example, our analyses reveal that, in the solar regime, a minimum average solar reflectivity of 0.92 is required; in the infrared regime, a 10% reduction in absorptivity outside the 8-13 um transparency window is equivalent to a 5.9% enhancement in emissivity within the window. Guided by these findings, we propose a photonic design, which, in a synthetic experiment with measured meteorological datasets, achieves a water production rate of 313 g/m2-day, in which nearly 40% is contributed by daytime. This performance reaches approximately 70% of the theoretical maximum predicted using the ideal spectrum. We end by optimizing the layout of condensers in practical applications.