Polymer solar filter for enabling direct daytime radiative cooling

• Published in: Solar energy materials and solar cells 2020-03, Vol.206 (C), p.110319, Article 110319
• Main Authors: Torgerson, Erik, Hellhake, Josh
• Format: Article
• Language: English
• Subjects: Cooling; Daytime; Irradiance; Low cost; LWIR transparent; Passive cooling; Photons; Polyethylene; Polyethylenes; Polymers; Radiative cooling; Solar filter; Temperature
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2019.110319

Passive radiative daytime cooling is a low-cost solution to improve human comfort and reduce the energy demands of cooling on a global scale. We present the first demonstration of direct full-sun daytime radiative cooling using an all-polymer filter that blocks solar irradiance while maintaining high transmittance in the long-wave infrared (LWIR). Warm objects and surfaces radiatively transfer heat through the polymer solar filter to the cold sink of space, decreasing temperatures up to 10 °C during day and night. The polyethylene (PE) filter exploits scattering by size-controlled air pores to maximize reflection of solar photons, while preserving the LWIR transparency inherent to PE. We demonstrated cooling power of over 110 W/m2 for an emissive surface placed beneath the solar filter. Scalable, low-cost manufacturing of a radiative cooling polymer solar filter allows direct full-sun daytime cooling of heat-emitting surfaces in a variety of settings. •Cooling power of over 110 W/m2 from a 100% polymer film.•Direct radiative cooling of any emissive surface.•Tents, canopies, and sunshades with integrated passive cooling.•Optimal performance in hot, dry climates to match growing global need.•Potential for carbon offsets of 1000 metric tons of CO2 per acre.