Comparative meta-analysis of desalination and atmospheric water harvesting technologies based on the minimum energy of separation

Desalination and atmospheric water harvesting technologies are highly desirable to produce freshwater for daily life activities and alleviate the global water crisis. Efforts to improve these have mostly been based on better engineering or materials design, but a comparison of their energy performance over a theoretical optimum is not well consolidated. This research conducts a meta-analysis that comparatively assesses existing atmospheric water harvesting and desalination technologies by evaluating the energy optimality in terms of the Gibbs free energy principle derived theoretical limit. After a review of the various existing technologies in these two classes, energy optimality, defined as the theoretical minimum specific energy consumption divided by the specific exergy consumption, is used as the metric to make a comprehensive and fair comparison of the various desalination and atmospheric water harvesting technologies. Results show that the vapor compression cycle and hybrid technologies-based atmospheric water harvesters have higher energy optimality of 12%, whereas others have much poorer performances of under 3%. For desalination, reverse osmosis yielded the highest energy optimality of 67.43%. Furthermore, the ideal energy optimality needed by atmospheric water harvesting to become comparable to desalination is at least 89.9%, which is almost impossible to practically achieve.