Advanced Fog Harvesting Techniques

Abstract

Water scarcity is one of the most urgent global challenges, affecting a substantial portion of the world's population and expected to worsen with the advancing impacts of climate change. Although the Earth is predominantly covered by water, only a small fraction is freshwater, and an even smaller portion is accessible for human use. Most freshwater is either frozen in glaciers or stored deep underground, with only a minimal amount available in rivers, lakes, and other surface sources. Traditional water sourcing methods—such as groundwater extraction, rainwater harvesting, desalination, and surface water diversion—often rely on significant infrastructure or existing water bodies.

Atmospheric water harvesting (AWH) has emerged as a promising and adaptable alternative that bypasses many of these limitations. By tapping into the water vapor naturally present in the atmosphere, AWH offers a decentralized and potentially low-cost means of supplementing freshwater supplies. Unlike conventional methods, it can operate independently of geographic constraints and large-scale infrastructure. The primary AWH techniques include fog harvesting, dew condensation, and sorbent-based water vapor capture, each offering unique advantages for addressing water scarcity across a range of environmental conditions.

Chapter 2 proposes the development of large-scale, high-tension Fog Harps as a solution to the limitations of existing fog harvesting systems. While Fog Harps have been shown to collect significantly more water than traditional mesh-based harvesters, previous large-scale versions have relied on low-tension, hand-wound assemblies that are prone to elastocapillary wire tangling. To overcome these challenges, this chapter introduces manufacturable and anti-tangling Fog Harps that maintain the record fog harvesting efficiency (~17%) achieved by optimized scale-model designs, while enabling practical deployment. Manufacturability was realized by repurposing an existing industrial process used to fabricate harp screens for solid-material filtration. Furthermore, the critical wire tension needed to suppress tangling was quantified using an improved elastocapillary model, offering key design insights for scalable implementation.

Chapter 3 explores the real-world performance of mesh and Fog Harp harvesters—two of the leading technologies for scalable fog harvesting—through field testing in Monterey Bay, California. Although laboratory studies have shown that anti-clogging Fog Harps can outperform standard Raschel meshes by a factor of 3–7×, such results were limited to scale-model devices exposed to artificially dense fog. Recognizing that fog harvesting is inherently dependent on environmental conditions and system scale, this chapter presents a comprehensive comparison of scaled-up Fog Harps and Raschel meshes under natural fog events. The findings reveal that the performance advantage of Fog Harps is highly sensitive to fog intensity: while they performed best during light fog, their benefit diminished during moderate fog events, with the large laboratory multipliers never naturally replicated. Interestingly, a greater enhancement in water collection was achieved simply by increasing the size and elevation of a Raschel mesh, underscoring that environmental factors and harvester positioning may have a greater impact than device architecture alone.

Chapter 4 presents the design and development of 3D-printed mesh-harp hybrid fog harvesters as a practical solution to the limitations of existing technologies. While mesh-based harvesters are prone to clogging and Fog Harps suffer from elastocapillary tangling that reduces collection efficiency, this chapter introduces a hybrid approach that effectively mitigates both issues. By integrating sparse cross-supports into a vertically aligned mesh framework, the hybrid structure maintains open airflow while preventing wire bundling. Field and lab tests demonstrate that these hybrids improve water harvesting efficiency by a factor of 2–6 compared to traditional mesh or Fog Harp systems alone. Additionally, an elastocapillary model is developed to determine the optimal spacing of the cross-supports required to suppress tangling without the need for high wire tension, enabling a scalable and manufacturable design. Future work will leverage the polar nature of water droplets and utilize electrostatic forces to enhance water capture in metal-based harvesters.