Issue 10, 2022

Thermodynamic limits of atmospheric water harvesting

Abstract

Atmospheric water harvesting (AWH) is a rapidly emerging approach for decentralized water production, but current technology is limited by trade-offs between energy consumption and yield. The field lacks a common basis to compare different AWH technologies and a robust understanding of the performance impacts of water recovery, desorption humidity (for sorbent systems), and realistic component-level efficiencies. By devising a set of unifying assumptions and consistent parameters across technologies, we provide the first fair thermodynamic comparison over a broad range of environmental conditions. Using 2nd law analysis, or least work, we study the maximum efficiency for common open system AWH methods – fog nets, dew plates, membrane-systems, and sorption processes – to identify the process performance limits. We find that the thermodynamic minimum for any AWH process is anywhere from 0× (relative humidity (RH) ≥ 100%) to upwards of 250× (RH < 10%) the minimum energy requirement of seawater desalination. Sorbents have a particular niche in colder (T < 310 K), arid regions (<6 g kg−1). Membrane-systems are best at low relative humidity and the region of applicability is strongly affected by vacuum pumping efficiency. Dew harvesting is best at higher humidity (RH > 40%) and fog harvesting is optimal when super-saturated conditions exist. Increasing efficiency at the component-level, particularly for vacuum pumps and condensers, may be the most promising avenue for improvement. Enabled by peta-scale computing, our findings use geographical and parametric mapping to provide a framework for technology deployment and energy-optimization.

Graphical abstract: Thermodynamic limits of atmospheric water harvesting

Supplementary files

Article information

Article type
Perspective
Submitted
01 Apr 2022
Accepted
18 Jul 2022
First published
13 Sep 2022

Energy Environ. Sci., 2022,15, 4025-4037

Thermodynamic limits of atmospheric water harvesting

A. K. Rao, A. J. Fix, Y. C. Yang and D. M. Warsinger, Energy Environ. Sci., 2022, 15, 4025 DOI: 10.1039/D2EE01071B

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