Abstract
Solar-based water sanitation is an environmentally friendly process for obtaining clean water that requires efficient light-to-heat-to-vapour generation. Solar-driven interfacial evaporation has potential, but the inability to control interfacial evaporators for solar tracking limits efficiency at large solar zenith angles and when using optical concentration. Furthermore, clogging affects the efficiency of the device. Here, we create a super-wicking and super-light-absorbing (SWSA) aluminium surface for efficient solar-based water sanitation. The measured evaporation rate exceeds that of an ideal device operating at 100% efficiency, which we hypothesize resulted from a reduced enthalpy of vaporization within the microcapillaries. Limited solar absorber–water contact for water transport minimizes heat losses to bulk water and maximizes heat localization at the SWSA surface. The device can be mounted at any angle on a floating platform to optimize incident solar irradiance and can readily be integrated with commercial solar-thermal systems. With a design that is analogous to bifacial photovoltaic solar panels, we show a 150% increase in efficiency compared with a single-sided SWSA. Given the open capillary channels, the device surface can be easily cleaned and reused. Using the SWSA surface to purify contaminated water, we show a decrease in the level of contaminants to well below the WHO and EPA standards for drinkable water.
Highlights
Solar-based water sanitation is an environmentally friendly process for obtaining clean water that requires efficient light-to-heat-to-vapour generation
The demonstrated device has the potential to be used as part of the solution to the global water crisis due to its simplicity, durability, reusability, efficiency and compatibility with solar-thermal technology
Al electrodes at the back of silicon PV cells can be treated to become super-wicking and super-light-absorbing (SWSA), which can increase the PV efficiency by cooling it, while simultaneously generating clean water[19,33]
Summary
Single-sided versus double-sided SWSA sheets (Extended Data Fig. 6) mounted in the vertical plane. Note that the dark-condition water-evaporation rate changes as a function of the incidence angle, Θ, as the water transport properties and the effective surface area at the water–air interface have orientation-angle dependence (Supplementary Fig. 20). Note that the difference in the average solar irradiance that is available at flat and tilted surfaces of the same area is minimum in the month of June at Rochester, NY (Extended Data Fig. 7d) leading to the small difference in water-evaporation rates between the two panels. Similar to a photovoltaic (PV) solar panel, our SWSA panel can be mounted at a fixed angle over a given season and the angle of tilt can be manually changed from season to season to optimize incident solar flux This strategy would both minimize the complexity that is associated with a live solar-tracking system and sanitize more water. Owing to the open-capillary architecture of SWSA surface, the contaminants that remain on the SWSA surface after several cycles of operation (Fig. 5f, top) can be cleaned by applying pressurized water (Fig. 5f, bottom; Extended Data Fig. 10) to its surface, which substantially reduces the maintenance cost for commercial and personal solar-based water sanitation systems (Supplementary Video 4)
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