Significance Traditionally, the cooling for passive vapor condensation is mainly provided by convection and conduction. However, these mechanisms do not work when the vapor temperature is near the ambient air temperature. At such temperatures, radiative condensation remains effective. However, existing radiative vapor condensers must operate during the nighttime. Here, a novel radiative-cooling technique is applied to extend radiative condensation to both daytime and nighttime. The technique uses engineered thermal radiators that do not require lithography or other costly fabrication techniques and can be manufactured to cover large areas. When combined with traditional convective and conductive condensers, this passive technology can potentially double the water production rate for passive water technologies.

Vapor condensation with daytime radiative cooling