A gradient atmospheric model reveals enhanced radiative cooling potential and demonstrates the advantages of broadband emitters (2406.00572v3)

Abstract: Passive radiative cooling toward the sky is a developing technology for adaptation in hot climates. Previous calculations of cooling performance have generally used uniform atmospheric models that assume a single sky temperature and atmospheric transmittance spectrum. Here, we introduce a gradient atmospheric model that accounts for altitude-dependent temperature and gas composition, revealing that uniform models underestimate cooling power by 10 - 40%. Using our improved model, we systematically compared broadband emitters (BEs) and wavelength-selective emitters (SEs) for sky-facing radiative cooling at various locations on Earth. We find that the differences in cooling power between the two types of emitters in the sub-ambient temperature range are generally small, even under ideal conditions. Furthermore, in practice, BEs actually have superior performance than realistic SEs, because they have fewer design degrees of freedom and thus can be engineered to have lower solar absorption. Our analysis suggests that large-scale deployment of sky-facing passive radiative cooling technologies should prioritize the development of scalable, low-cost surfaces with minimal solar absorption, rather than focusing on achieving selective thermal emission.