Transparent conductors as solar energy materials: A panoramic review

Radiative cooling: A review of fundamentals, materials, applications, and prospects

Radiative sky cooling cools an object on the earth by emitting thermal infrared radiation to the cold universe through the atmospheric window (8–13 μm). It consumes no electricity and has great potential to be explored for cooling of buildings, vehicles, solar cells, and even thermal power plants. Radiative sky cooling has been explored in the past few decades but limited to nighttime use only. Very recently, owing to the progress in nanophotonics and metamaterials, daytime radiative sky cooling to achieve subambient temperatures under direct sunlight has been experimentally demonstrated. More excitingly, the manufacturing of the daytime radiative sky cooling material by the roll-to-roll process makes large-scale deployment of the technology possible. This work reviews the fundamental principles of radiative sky cooling as well as the recent advances, from both materials and systems point of view. Potential applications in different scenarios are reviewed with special attention to technology viability and benefits. As the energy situation and environmental issues become more and more severe in the 21st century, radiative sky cooling can be explored for energy saving in buildings and vehicles, mitigating the urban heat island effect, resolving water and environmental issues, achieving more efficient power generation, and even fighting against the global warming problem.

Radiative sky cooling: Fundamental principles, materials, and applications

Nanoparticles that have narrow absorption bands that lie entirely within the atmosphere’s transparent window from 7.9 to 13 μm can be used to radiatively cool to temperatures that are well below ambient. Heating from incoming atmospheric radiation in the remainder of the Planck radiation spectrum, where the atmosphere is nearly “black”, is reduced if the particles are dopants in infrared transmitting polymers, or in transmitting coatings on low emittance substrates. Crystalline SiC nanoparticles stand out with a surface phonon resonance from 10.5 to 13 μm clear of the atmospheric ozone band. Resonant SiO2 nanoparticles are complementary, absorbing from 8 to 10 μm, which includes atmospheric ozone emissions. Their spectral location has made SiC nanoparticles in space dust a feature in ground-based IR astronomy. Optical properties are presented and subambient cooling performance analyzed for doped polyethylene on aluminum. A mixture of SiC and SiO2 nanoparticles yields high performance cooling at low cost w...

Radiative Heat Pumping from the Earth Using Surface Phonon Resonant Nanoparticles

Nanoparticle embedded double-layer coating for daytime radiative cooling

Spectrophotometric measurements are reported for NH3 gas layers, and the potential use of this substance in radiative cooling devices is evaluated. The basic cooling parameters and the radiated power versus temperature drop are computed: the cooling power at near‐ambient temperature can be exceptionally large. The radiative properties are discussed from the configuration of the NH3 molecule. Typically a 2‐cm‐thick NH3 gas slab can provide 26 Wm−2 useful cooling power at 15 °C below ambient temperature in a device with a moderate nonradiative loss (heat transfer coefficient of 1 Wm−2 K−1).

E. M. Lushiku

Papers

Radiative cooling with selectively infrared‐emitting ammonia gas

Radiative cooling to low temperatures with selectively infrared-emitting gases