Water may be produced from atmospheric humidity anywhere on Earth; however, current approaches are energy intensive and costly, thus limiting the deployment of atmospheric water harvesting (AWH) technologies.  We present a system-level thermodynamic analysis of several pathways for solar-driven atmospheric water harvesting as a first step in demonstrating the feasibility of these technologies.  In this analysis we identify the minimum energy required to actively produce a cubic meter of fresh water from atmospheric humidity, and then estimate the cost of doing so with a system powered solely by solar electricity supplied by photovoltaic modules and operating without energy storage.  To accomplish this, expressions for the minimum specific energy consumption (SEC) of several AWH approaches are first derived and then compared under realistic operating conditions.  Our results show that fresh water may be produced from humid air via processes driven solely by solar electricity in an arid climate with an energy input between 158 kWh~e~/m^3^ and 1021 kWh~e~/m^3^ depending on atmospheric conditions and processing configuration. We show that AWH processes utilizing desiccants, such as chloride salts, to remove water from the air in a multi-step temperature swing reaction sequence can do so with an SEC about 50% lower than the next best approach.  We then present a more detailed study of the thermodynamic considerations associated with the internal recovery of both latent and sensible energy in the context of the design of a novel, desiccant-based AWH approach. In this system the latent heat of vaporization is internally recovered resulting in a significant reduction in energy requirements relative to the state of the art.  Finally, a parametric optimization model of a desiccant-based AWH system is developed and used to estimate the minimum levelized cost of water (LCOW) via solar-driven AWH at 6.5 \$/m^3^ when both latent and sensible energy is recovered internally.  This model is based on an annual performance simulation utilizing Typical Meteorological Year Data (TMY) as input and treating certain system parameters, such as desiccant regeneration temperature, as design variables.  Random sampling of these design variables within specific constraints is used to generate an exhaustive solution set of SEC and LCOW values for thousands of possible system design configurations.  The configuration demonstrating the minimum LCOW is selected from these.   This approach has the advantage of providing a comprehensive view of the AWH design space, and allows AWH systems to be designed for optimal performance in a specific location having unique meteorological conditions. 


A Techno-Economic Analysis of Solar-Driven Atmospheric Water Harvesting

Division / Sponsor:
Advanced Energy Systems Division (AESD) & Solar Energy Division (SED)

Paper Proceedings: https://asmedigitalcollection.asme.org/ES/ES2020/volume/83631

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