Fabrication Methods, Structures, and Uses for Passive Radiative Cooling

Abstract

Passive radiative cooling structures and apparatus manufactured with such cooling structures conserve energy needs. A flexible film transparent to visible light incorporates particles at a volume percentage larger than 25% so as to absorb and emit infrared radiation at wavelengths where Earth's atmosphere is transparent. Another film transparent to visible light is thin and flexible and configured to absorb and emit infrared radiation at wavelengths where Earth's atmosphere is transparent, wherein etchings or depositions are present on one or both surfaces. A high efficiency cooling structure has an emissive layer sandwiched between a waveguide layer and a thermal conductive layer. A solar cell panel is covered by a transparent passive radiative cooling film. A container housing an active cooling unit incorporates passive radiative cooling structures on one or more exterior surfaces.

What is claimed is: 
     
         1 . A passive radiative cooling structure comprising:
 a flexible film, transparent to visible light, and incorporating a first material at a volume percentage larger than 25% so as to absorb and emit infrared radiation at wavelengths where Earth's atmosphere is transparent;   wherein the flexible film includes a first surface parallel to a second surface, and an inner region between the first surface and the second surface.   
     
     
         2 . A passive radiative cooling structure according to  claim 1  wherein the flexible film comprises a flexible sheet of a second material that incorporates the first material as embedded particles having an average per particle volume greater than 14,200 μm 3 . 
     
     
         3 . A passive radiative cooling structure according to  claim 2  wherein the embedded particles are spherical particles. 
     
     
         4 . A passive radiative cooling structure according to  claim 3 , wherein the spherical particles are polished or flash heated to minimize surface roughness. 
     
     
         5 . A passive radiative cooling structure according to  claim 2  wherein the embedded particles are curved-sidewall structures, each curved sidewall structure comprising a first circular area bounded by a first circular area circumference and a second circular area bounded by a second circular area circumference wherein the first circular area circumference and the second circular area circumference are connected by a concave surface, enclosing an inner volume connecting the first circular area and the second circular area; and wherein the first circular area is oriented parallel with the first surface and the second circular region is oriented parallel with the second surface. 
     
     
         6 . A passive radiative cooling structure of  claim 1 , positioned in proximity to a surface of a panel so as to cool solar cells in the panel sufficiently to increase the efficiency of the conversion of light to electrical energy. 
     
     
         7 . A passive radiative cooling structure according to  claim 2 , the embedded particles occupying a volume percentage of the flexible film that is less than 73%. 
     
     
         8 . A passive radiative cooling structure according to  claim 1 , further comprising a reflective backlayer in contact with the flexible film. 
     
     
         9 . A passive radiative cooling structure according to  claim 1 , further comprising a window that is transparent to the wavelengths where the Earth's atmosphere is transparent, wherein the window is fitted over the flexible film. 
     
     
         10 . A passive radiative cooling structure comprising:
 a flexible film, transparent to visible light, configured to absorb and emit infrared radiation at wavelengths where Earth's atmosphere is transparent;   wherein the flexible film includes a first surface parallel to a second surface, and an inner region between the first surface and the second surface;   wherein the flexible film comprises a thin sheet of a first material, and wherein etchings are present on one or both of the first surface and the second surface.   
     
     
         11 . A passive radiative cooling structure of  claim 10 , positioned in proximity to a surface of a panel so as to cool solar cells in the panel sufficiently to increase the efficiency of the conversion of light to electrical energy. 
     
     
         12 . A passive radiative cooling structure of  claim 10 , wherein one or both of the first surface and the second surface are polished or flash heated to minimize surface roughness of the flexible film. 
     
     
         13 . A passive radiative cooling structure of  claim 10 , further comprising a conforming material layer deposited on one or both of the first surface and second surface. 
     
     
         14 . A passive radiative cooling structure of  claim 10 , further comprising a reflective backlayer in contact with the flexible film. 
     
     
         15 . A passive radiative cooling structure according to  claim 10 , further comprising a window that is transparent to the wavelengths where the Earth's atmosphere is transparent, wherein the window is fitted over the flexible film. 
     
     
         16 . A passive radiative cooling structure comprising:
 one or more cooling stacks;   wherein each cooling stack is configured with a first waveguide layer, a first emissive layer and a thermal conductive layer, wherein the first emissive layer is sandwiched between the first waveguide layer and the thermal conductive layer;   wherein the first emissive layer is configured to absorb and emit infrared radiation at wavelengths where Earth's atmosphere is transparent;   wherein the thermally conductive layer has a proximal end and a distal end; and   wherein the thermally conductive layer is substantially perpendicular to and in thermal contact at its proximal end with a source of heat to be cooled.   
     
     
         17 . A passive radiative cooling structure according to  claim 16 , wherein each cooling stack further comprises a second waveguide layer, and a second emissive layer;
 wherein the second emissive layer is sandwiched between the second waveguide layer and the thermal conductive layer;   wherein the thermal conductive layer is sandwiched between the first emissive layer and the second emissive layer;   wherein the second emissive layer is configured to absorb and emit infrared radiation at wavelengths where Earth's atmosphere is transparent.   
     
     
         18 . A passive radiative cooling structure according to  claim 16 , wherein the first waveguide layer comprises one or more sub-layers to redirect thermal wavelengths of electromagnetic radiation towards the sky. 
     
     
         19 . A passive radiative cooling structure according to  claim 16 , further comprising a window fitted over the radiative structure that is transparent to the wavelengths where the Earth's atmosphere is transparent.