Addressing global water stress using desalination and atmospheric water harvesting: a thermodynamic and technoeconomic perspective

Freshwater is a critical resource but excessive withdrawal of natural reserves and inefficient water management, as well as climate change and pollution have resulted in global water stress that is projected to impact 4 billion people by 2030. Methods of artificially producing freshwater include desalination, which is a well-established process in which water is extracted from a saline source (typically seawater). Atmospheric water harvesting (AWH) is an alternate emerging process in which water vapor is extracted from ambient air and condensed into freshwater. Although AWH has attracted attention for decentralized water production using different materials and technologies (e.g., sorbents, active or passive cooling), the energy consumption and costs associated with practical systems that have meaningful yields to address water stress has not been reported. Herein we present a thermodynamic and technoeconomic framework to evaluate different AWH systems on the basis of these performance metrics (kW h m-3 and $ per m3), and we compare it to desalination at the coast with clean water transport inland (distributed). These results are weighted by the population and water risk across all global locations to identify regions where each process may be viable. We find that AWH is more energy intensive for 84% of the global population even if it operates reversibly (impractical system) when compared to distributed seawater desalination. Furthermore, a practical AWH system has a minimum levelized cost of water (LCOW) of $10 per m3, which is significantly higher than seawater desalination even after accounting for water transport costs. The analysis reveals a niche where AWH can be the lowest cost option, i.e., water harvesting in arid locations far from the coast (e.g., Sahara Desert) using sorbents, although this represents only a small fraction of the water-stressed population. Ultimately, this analysis framework informs material and system design targets for AWH research and development to maximize global impact. A thermodynamic and technoeconomic analysis reveals that desalination can produce freshwater at a lower energy footprint and levelized cost compared to atmospheric water harvesting.