Nighttime Atmospheric Water Harvesting Enabled by Solar Prestorage Using a Phase‐Change Thermal Storage System

Abstract Atmospheric water harvesting (AWH) offers a promising solution for achieving household water independence in arid regions. However, its efficiency is constrained by the reliance on daylight, limiting daily water yields. To address this challenge, a “nighttime AWH” system that operates without external energy input is proposed. The system leverages a thermal battery composed of composite phase‐change materials (CPCMs) with high energy density and photothermal conversion efficiency. During daylight hours, solar energy is stored within the thermal battery, and at night, a sorption layer utilizing MOF‐303 is activated for water production. The integrated system, referred to as the water generation unit (WGU), demonstrates rapid desorption due to efficient heat transfer between components. The adsorption‐saturated MOF‐303 layer releases ≈78% of its adsorbed water within 30 min, resulting in a theoretical nighttime water release as high as 3.8 g (water) g (MOF) −1 day −1 . Thermal imaging and heat‐transfer simulations are used to analyze the desorption mechanism and evaluate key operational parameters. This thermal energy storage‐integrated AWH system efficiently converts, stores, and releases solar energy, offering a sustainable and reliable solution for nighttime water harvesting in water‐scarce regions.