Simultaneous sub-ambient daytime radiative cooling and photovoltaic power generation from the same area

Abstract

Embodiments relate to apparatuses, methods, and systems configured to provide simultaneous cooling and power generation. In particular, embodiments relate to a radiative cooling device having a radiative cooler and a solar cell that provide simultaneous sub-ambient daytime radiative cooling and photovoltaic power generation. In a first aspect, a radiative cooling device can be provided. The radiative cooling device can include a first member. The first member can be visibly transparent. The radiative cooling device can include a solar cell. The solar cell can be underlying and spaced apart from the first member. The radiative cooling device can include a second member. The second member can be positioned intermediate the first member and the solar cell. The second member can be visibly transparent and infrared radiation (IR)-opaque. The first and second members can be configured to pass sunlight to the solar cell such that the solar cell can generate photovoltaic power.

Description

SIMULTANEOUS SUB-AMBIENT DAYTIME RADIATIVE COOLING ANDPHOTOVOLTAIC POWER GENERATION FROM THE SAME AREACROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is related to and claims the benefit of priority of U.S. Provisional Application 63 / 564,807, filed on March 13, 2024, the entire contents of which is incorporated by reference.FIELD

[0002] Embodiments relate to apparatuses, methods, and systems configured to provide simultaneous cooling and power generation. In particular, embodiments relate to a radiative cooling device having a radiative cooler and a solar cell that provide simultaneous sub-ambient daytime radiative cooling and photovoltaic power generation.BACKGROUND

[0003] Radiative cooling has attracted great interest as it exploits the cold universe as a new renewable resource for applications ranging from passive cooling (e.g., of buildings, textiles, solar cells, and electronics) to power generation. Radiative cooling operates by sending thermal radiation, through a transparency window of the Earth’s atmosphere at 8-13 μm wavelengths, to the cold universe. At 8-13 pm, the available thermal radiation power of a 300K blackbody emitter is 148 W / m2. Thus, to passively cool to below the ambient air temperature during the daytime when the peak cooling load occurs, a radiative cooler must have negligible sunlight absorption. Existing approaches for achieving sub-ambient daytime radiative cooling require reflecting almost all the sunlight (typically >88%) by using structures including multilayers,metamaterials, porous structures, and paints. Thus, existing sub-ambient daytime radiative coolers are incompatible with solar energy harvesting.SUMMARY

[0004] The sun and the cold universe are two major scalable renewable resources and it is highly desirable to co-harvest the sun and the cold universe for producing electricity and sub-ambient cooling at the same time and from the same area. Utilizing both the cold universe and the sun may point to an untapped opportunity for harvesting renewable energy at a level that is not possible by using either resource alone. Simultaneous radiative cooling and solar heating has been achieved by placing an infrared transparent solar absorber on top of a radiative cooler, or a vertically-oriented radiative cooler between tilted selective solar absorbers. While such heat can be used for heating applications, converting such low-grade heat to electricity is challenging due to the low energy conversion efficiency associated with material constraint. Radiative cooling and solar energy harvesting have also been achieved in a same device asynchronously. A dual- mode radiative cooling and solar heating device was demonstrated by actuating between a radiative cooling surface at summer, and a solar absorbing surface at winter, for overall energy savings throughout the year. Solar cells were used to achieve nighttime radiative cooling while producing photovoltaic electricity during daytime. However, at one single time (summer or winter, nocturnal or diurnal), only radiative cooling or solar energy harvesting functions. Thus, it is believed that simultaneous sub-ambient passive radiative cooling and photovoltaic electricity generation have not been achieved.

[0005] We have developed a system for achieving simultaneous sub-ambient daytime radiative cooling and photovoltaic electricity generation from the same area. The system consists of a visibly-transparent radiative cooler over a photovoltaic cell, with a visibly-transparent infrared-opaque layer in between. The radiative cooler may function by strongly emitting thermal radiation at 8-13 μm wavelengths, negligibly absorbing sunlight, while having no direct radiative heat exchange with the photovoltaic cell. Sunlight irradiates the photovoltaic cell by passing through the radiative cooler.

[0006] Our system notably demonstrates simultaneous sub-ambient daytime radiative cooling and substantial electrical power output. By providing separate photovoltaic power output, the system contrasts with many existing studies on simultaneous sub-ambient radiative cooling and solar heating. We have surprisingly found that the total electricity savings of simultaneous radiative cooling and photovoltaic power generation can surpass the electricity savings of a bare solar panel by as much as 30%. Our system therefore highlights the significant opportunity of simultaneously harvesting both the sun and the cold universe for renewable energy, at a level that can exceed the performance of using either resource alone.

[0007] In a first aspect, a radiative cooling device can be provided. The radiative cooling device can include a first member. The first member can be visibly transparent (e.g. transparent, translucent, clear, etc.). The radiative cooling device can include a solar cell. The solar cell can be underlying and spaced apart from the first member. The radiative cooling device can include a second member. The second member can be positioned intermediate the first member and the solar cell. The second member can be visibly transparent and infrared radiation (IR)-opaque. The first and second members can be configured to pass sunlight to the solar cell such that the solar cell can generate photovoltaic power. The first member can be configured to emit IR such that the first member can provide a radiating cooling effect.

[0008] In some embodiments, the first member can be a material configured to absorb no greater than 10% of sunlight.

[0009] In some embodiments, the first member can be further configured to have an average IR emissivity of 0.83 at wavelengths in a range 8 to 13 micrometers (gm).

[0010] In some embodiments, the first member can include a visibly-transparent thermally- emissive material. The visibly-transparent thermally-emissive material can include at least one compound from a group including SiCh, Na2O , CaO, MgO, AI2O3, K2O, and Fe2CO3.

[0011] In some embodiments, the visibly-transparent thermally-emissive material can include less than 0.1% ofFe2C>3

[0012] In some embodiments, the first member can be a thickness within a range of 0.1 to 10 millimeters (mm).

[0013] In some embodiments, a radiative cooling structure can include the radiative cooling device. The radiative cooling structure can further include a first chamber suspended within a second chamber. The first chamber can include the first member. The first chamber can also include the second member. The first chamber can include at least one insulative member. The at least one insulative member can separate the first member from the second member such that the at least one insulative member, the first member, and the second member can define a cavity. The solar cell can be positioned beneath and spaced apart from the second member. The solar cell can also be positioned below the first chamber.

[0014] In some embodiments, the first chamber can further include a first support structure. The first chamber can further include a second support structure. The second support structure can extend from the second chamber. The first support structure and the second support structure can be configured to suspend the first chamber within the second chamber.

[0015] In some embodiments, a surface of the second chamber can be positioned above and spaced apart from the first member and can include an aperture.

[0016] In some embodiments, the radiative cooling structure can include a third member. The third member can overlay and extend across the aperture. The third member can be visibly transparent.

[0017] In some embodiments, the third member can be configured to prevent ambient air from entering into the radiative cooling structure via the aperture.

[0018] In some embodiments, the radiative cooling device can include at least one heat exchange element. The at least one heat exchange element can include a heat transfer fluid. The heat transfer fluid can be configured to exchange heat with the first member, such that the heat transfer fluid can be cooled via the radiative cooling effect. In some embodiments, the heat transfer fluid can be water, a solution, a refrigerant, or other type of heat transfer fluid.

[0019] In some embodiments, the at least one heat exchange element can be at least one tubular conduit.

[0020] In some embodiments, the at least one tubular conduit can be visibly transparent and configured to pass sunlight.

[0021] In some embodiments, the first member can include at least one channel defined within the first member. A heat transfer fluid can be configured to flow through the at least one channel such that the heat transfer fluid can be cooled via the radiative cooling effect.

[0022] In some embodiments, the radiative cooling device can further include at least one heat exchange element including the heat transfer fluid. The at least one heat exchange element can be positioned within the at least one channel of the first member.

[0023] In some embodiments, the at least one channel can further include at least one baffle.

[0024] In a second aspect, a radiative cooling device is provided. The radiative cooling device can include a first member. The first member can be configured to emit infrared radiation (IR)such that the first member can provide a radiative cooling effect. The radiative cooling device can include a solar cell. The solar cell can be underlying the first member. The radiative cooling device can include at least one IR-reflective member. The at least one IR-reflective member can be positioned adjacent the first member and overlay the solar cell. The at least one IR-reflective member can be visibly transparent. The at least one IR-reflective member can be configured to pass sunlight to the solar cell such that the solar cell can generate photovoltaic power.

[0025] In some embodiments, the first member can include at least one heat exchange element. The at least one heat exchange element can include a heat transfer fluid. The heat transfer fluid can be configured to exchange heat with the first member such that the heat transfer fluid can be cooled via the radiative cooling effect. In some embodiments, the heat transfer fluid can include water, be water, include a refrigerant, or be another type of heat transfer fluid.

[0026] In some embodiments, the at least one heat exchange element can be at least one tubular conduit.

[0027] In some embodiments, the first member can include at least one channel defined within the first member. A heat transfer fluid can be configured to flow through the at least one channel such that the heat transfer fluid can be cooled via the radiative cooling effect.

[0028] In some embodiments, the radiative cooling device can further include at least one heat exchange element including the heat transfer fluid. The at least one heat exchange element can be positioned within the at least one channel of the first member.

[0029] In some embodiments, the at least one channel can further include at least one baffle.

[0030] In some embodiments, the at least one IR-reflective member can include a visibly transparent low-emissivity coating.

[0031] In some embodiments, the first member can be configured to reflect at least a portion ofsunlight.

[0032] In some embodiments, the solar cell can be positioned in a horizontal orientation. The first member can be positioned in a vertical orientation such that the first member can be positioned perpendicularly relative to the solar cell (e.g. the length or height of the first member can extend in a direction that is perpendicular to a direction at which the upper surface of the solar cell can extend along its width or length, etc.).

[0033] In some embodiments, the at least one IR-reflective member can be positioned angularly relative to the first member and the solar cell. The at least one IR-reflective member can be configured to reflect at least a portion of IR emitted from the first member in a skyward direction, (e.g. the length or height of the first member can extend in a direction that is at a pre- selected angle relative to a direction at which the upper surface of the solar cell can extend along its width or length. The pre-selected angle can be about 45°, between 5° and 75° or between 10° and 60°, etc.).

[0034] In a third aspect, a method for concurrently cooling fluid and generating photovoltaic power is provided. The method can include providing a radiative cooling device. The radiative cooling device can include a first member. The first member can be visibly transparent and thermally emissive. The radiative cooling device can further include a solar cell. The solar cell can be underlying and spaced apart from the first member. The radiative cooling device can further include a second member. The second member can be positioned intermediate the first member and the solar cell. The second member can be visibly transparent. The second member can be IR-opaque. The method can further include passing fluid through at least one heat exchange element configured to exchange heat with the first member. The first member can provide a radiative cooling effect. The fluid can be configured to exchange heat with the firstmember such that the fluid is cooled by the radiative cooling effect. The first and second members can be configured to pass sunlight to the solar cell such that the solar cell can generate photovoltaic power.

[0035] In some embodiments, the first member can include at least one channel defined within the first member. The at least one heat exchange element can be positioned within the at least one channel of the first member.

[0036] In some embodiments, the at least one heat exchange element can be at least one tubular conduit.

[0037] In some embodiments, the at least one tubular conduit can be visibly transparent and configured to pass sunlight.

[0038] In a fourth aspect, a method for concurrently cooling fluid and generating photovoltaic power is provided. The method can include providing a radiative cooling device. The radiative cooling device can include a first member. The first member can be thermally emissive. The radiative cooling device can further include a solar cell. The solar cell can be underlying the first member. The radiative cooling device can further include at least one IR-reflective member. The at least one IR-reflective member can be positioned adjacent the first member and overlaying the solar cell. The at least one IR-reflective member can be visibly transparent. The method can further include passing fluid through at least one heat exchange element configured to exchange heat with the first member. The first member can provide a radiative cooling effect. The fluid can be configured to exchange heat with the first member such that the fluid is cooled by the radiative cooling effect. The at least one IR-reflective member can be configured to pass sunlight to the solar cell such that the solar cell can generate photovoltaic power.

[0039] In some embodiments, the first member can include at least one channel defined withinthe first member. The at least one heat exchange element can be positioned within the at least one channel of the first member.

[0040] In some embodiments, the at least one heat exchange element can be at least one tubular conduit.

[0041] In some embodiments, the first member can be further configured to reflect at least a portion of sunlight.

[0042] In some embodiments, the solar cell can be positioned in a horizontal orientation. The first member can be positioned in a vertical orientation such that the first member can be positioned perpendicularly relative to the solar cell.

[0043] In some embodiments, the at least one IR-reflective member can be positioned angularly relative to the first member and the solar cell. The at least one IR-reflective member can be configured to reflect at least a portion of IR emitted from the first member in a skyward direction.

[0044] These and other embodiments shall be described in more detail herein and in the drawings that show exemplary embodiments. Therefore, other details, objects, and advantages will become apparent as the following description of certain present preferred embodiments thereof and certain present preferred methods of practicing the same proceeds.BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The above and other objects, aspects, features, advantages and possible applications of the present innovation will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings. Like reference numbers used in the drawings may identify like components.

[0046] FIG. 1 shows a schematic representation of an exemplary embodiment of a radiativecooling device.

[0047] FIG. 2 shows a schematic representation of an exemplary embodiment of a radiative cooling structure including the radiative cooling device.

[0048] FIG. 3A shows a schematic representation of a cross-sectional view of an exemplary first member of the radiative cooling device.

[0049] FIG. 3B shows a schematic representation of a top perspective view of an exemplary first member of the radiative cooling device.

[0050] FIG. 4 shows a schematic representation of an exemplary embodiment of a radiative cooling device.

[0051] FIG. 5 is a flow diagram of an exemplary method for concurrently cooling fluid and generating photovoltaic power.

[0052] FIG. 6 is a flow diagram of an exemplary method for concurrently cooling fluid and generating photovoltaic power.

[0053] FIG. 7 is a schematic illustration of an exemplary radiative cooling device.

[0054] FIG. 8 is a schematic illustration of a cross-sectional view of an experimental setup of a radiative cooling device.

[0055] FIGS. 9A-C show images of an experimental setup of a radiative cooling device. FIG. 9A is an image of the entire setup, in which a transparent radiative cooler is installed inside a chamber, and a solar cell is mounted below the chamber. FIG. 9B is a top-view photograph of the setup. FIG. 9C is a bottom-view photograph of the setup.

[0056] FIG. 10 is a graph showing measured absorptivity (a cooler) and transmissivity (T cooler) of radiative cooler and absorptivity (aPV) of PV solar cell at 8° angle of incidence at ultraviolet- visible-near IR wavelengths. Normalized AMI.5 solar spectrum is also shown.

[0057] FIG. 11 is a graph showing measured emissivity of transparent radiative cooler at near normal angle over mid-infrared wavelengths averaged over both polarizations. The emissivity of silica and atmospheric transmittance are also shown.

[0058] FIGS. 12A is a graph showing measured temperature of the transparent radiative cooler over 4 hours around solar noon. At the beginning, a metal cover is removed from the chamber and the solar cell is completely lit by the sun. The measured solar irradiance is also shown.

[0059] FIG. 12B is a graph showing temperature difference between the radiative cooler and the ambient air.

[0060] FIG. 13 A is a graph showing current versus voltage curves of the solar cell at three times.

[0061] FIG. 13B is a graph showing solar cell performance for a 2-hour period around solar noon when the solar cell is completely lit by the sun.

[0062] FIG. 14A is a graph showing temperature difference between the cooler and the ambient as a function of time, with stepwise heating on a night with clear sky. Each colored shade indicates a heating level exerted over 20 minutes. The temperature difference reaches zero when 87.0 W / mA2 heating is applied.

[0063] FIG. 14B is a graph showing applied heating as a function of the difference between the steady-state temperature of the cooler and the ambient air temperature. A linear fit is also included.

[0064] FIG. 15 is a graph showing electricity saving of the system and a bare solar cell over 24 hours. Here, the electricity saving for radiative cooler is the electricity saved from operating an air conditioner with a COP of 2.8.

[0065] FIG. 16 is a graph showing electricity saving from passive radiative cooling and photovoltaics modeled for seventeen cities from different climate zones of U.S. The calculationis based on a roof area of 3135 m2and the roof is assumed to be covered with the dual system of radiative cooling and photovoltaic power generation. The existing cooling system in the building is assumed to have a coefficient of performance of 2.8. Radiative cooling power is considered only when the ambient air temperature exceeds the target indoor temperature of 24 °C.

[0066] FIG. 17 is a graphical representation of annual electricity saving from radiative cooling simulated across the U.S. The calculation is based on a roof area of 3135 m2and the roof is assumed to be covered with the dual system of radiative cooling and photovoltaic power generation. The existing cooling system in the building is assumed to have a coefficient of performance of 2.8. Radiative cooling power is considered only when the ambient air temperature exceeds the target indoor temperature of 24 °C.

[0067] FIG. 18 is a graphical representation of annual electricity saving from photovoltaics simulated across the U.S. The calculation is based on a roof area of 3135 m2and the roof is assumed to be covered with the dual system of radiative cooling and photovoltaic power generation. The existing cooling system in the building is assumed to have a coefficient of performance of 2.8. Radiative cooling power is considered only when the ambient air temperature exceeds the target indoor temperature of 24 °C.

[0068] FIGS. 19A-19B show images of measured spectral, angular emissivity for low-iron glass over the mid infrared wavelengths for P-polarization and S-polarization.

[0069] FIG. 20 shows a graphical representation of emissivity averaged over the mid infrared wavelengths (5μm - 25 pm) of low-iron glass and polyimide as a function of angles.

[0070] FIGS. 21A-C show images of a 25cm x 25cm polyimide film insulated heater instrumented on a 2mm thick 1ft x 1ft aluminum heat spreading layer.

[0071] FIG. 22 is a graphical representation of experiments comparing a bare solar cell and the solar cell of an exemplary embodiment of the radiative cooling device.

[0072] FIG. 23 is a graphical representation of experiments comparing a bare solar cell and the solar cell of an exemplary embodiment of the radiative cooling device.

[0073] FIG. 24 is a graphical representation of experiments comparing a bare solar cell and the solar cell of an exemplary embodiment of the radiative cooling device.

[0074] FIG. 25 is a graphical representation of experiments comparing a bare solar cell and the solar cell of an exemplary embodiment of the radiative cooling device.

[0075] FIG. 26 is a graphical representation of experiments comparing a bare solar cell and the solar cell of an exemplary embodiment of the radiative cooling device.

[0076] FIG. 27 is a graphical representation of experiments comparing a bare solar cell and the solar cell of an exemplary embodiment of the radiative cooling device.

[0077] FIG. 28 illustrates a schematic for integration of the radiative cooling device with an external cooling system.

[0078] FIG. 29 illustrates a schematic for integration of the radiative cooling device with an external cooling system using liquid fluid cooling.

[0079] FIG. 30 illustrates a graphical representation of modeled absorptivity at the solar spectrum for 50 μm of water between two SiO? layers.

[0080] FIG. 31 is a graph showing electricity saving from passive radiative cooling and photovoltaics modeled for seventeen cities from different climate zones of U.S. Radiative cooling power is considered irrespective of ambient air pressure.

[0081] FIG. 32 is a graphical representation of annual electricity saving from radiative cooling simulated across the U.S. Radiative cooling power is considered irrespective of ambient air pressure.

[0082] FIG. 33 is a graphical representation of annual electricity saving from photovoltaics simulated across the U.S.DETAILED DESCRIPTION

[0083] The following description is of exemplary embodiments that are presently contemplated for carrying out the present invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles and features of the present invention. The scope of the present invention is not limited by this description.

[0084] Embodiments generally relate to apparatuses, methods, and systems configured to provide simultaneous radiative cooling and photovoltaic power generation. In particular, a radiative cooling device can be configured to provide such simultaneous cooling and power generation and can include a first visibly transparent member over a solar cell, with a second visibly transparent, infrared-opaque member positioned intermediate the first member and the solar cell.

[0085] Referring to FIG. 1, a radiative cooling device 100 includes a first member 102. The first member 102 can be visibly transparent and have low or negligible sunlight absorption, such that at least a portion of sunlight may pass through the first member 102. For example, the first member 102 may be configured to pass at least a portion of sunlight such that the sunlight may be received by an underlying solar cell 104. The first member 102 can further be thermally emissive and be configured to emit thermal (e.g., infrared) radiation. Specifically, the first member 102 can be configured to emit thermal radiation through a specific atmospheric windowwhere the Earth's atmosphere is transparent, such that the first member 102 can cool down passively and provide a cooling effect without using electricity. For example, the first member 102 can be a radiative cooler.

[0086] As used herein, the terms infrared, IR, and mid-IR can be used interchangeably. In particular, the term mid-IR can refer to infrared wavelengths greater than 4 μm and less than 25 pm. Further, the term sunlight as used herein can include visible sunlight, near-IR sunlight (e.g., sunlight at IR wavelengths between 0.7 μm and 4 pm) and / or ultraviolet sunlight.

[0087] The first member 102 can be a material configured to be both visibly transparent (e.g. clear, transparent, translucent, etc.) and also thermally emissive. In some embodiment, the first member 102 can be configured to absorb no greater than 10% of sunlight and transmit, or pass, at least 80% of sunlight. In some embodiments, the first member 102 can be configured to absorb no greater than 0.9% of sunlight and transmit, or pass, at least 90% of sunlight. The material of the first member 102 can be configured to have an average IR emissivity of 0.92 at wavelengths in a range of 5 to 25 pm. In some embodiments, the material can be configured to have an average IR emissivity of at least 0.7 at IR wavelengths in a range of 8 to 13 pm. For example, in some embodiments, the material can be configured to have an average IR emissivity of 0.83 at IR wavelengths in a range of 8 to 13 pm.

[0088] In some embodiments, the first member 102 can be a material that has enhanced IR emissivity at the 8 to 13 μm atmospheric transparency window. For example, the first member 102 can be a visibly transparent material made primarily of oxides and / or polymers, such as glass, that has enhanced IR emissivity.

[0089] In some embodiments, the first member 102 can be a visibly transparent material. For example, the first member 102 can be low-iron glass. In some embodiments, the first member102 can include a material composition including at least one of SiO2,Na2O, CaO, MgO, AI2O3. K2O, or Fe2C>3, or mixtures thereof. In some embodiments, the material composition can include each of SiC>2, Na2O, CaO, MgO, AI2O3, K2O, and Fe2O3. In some embodiments, the material composition can include a weight ratio of Fe2O? no greater than 0.1% (e.g. be a type of low iron content glass). It should be further understood that the above compounds are merely exemplary, and that the material composition can include any suitable visibly transparent oxides and / or polymers.

[0090] The IR emissivity of SiCh at the atmospheric transparency window can be enhanced by using multilayers, patterning, anti -refl ection coatings, and / or metamaterials consisting of microspheres and polymer. In some embodiments, the first member 102 can include transparent polymers, such as polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS), and / or polypropylene (PP).

[0091] In some embodiments, the first member 102 can include an anti -reflection coating and / or film to reduce the reflection of sunlight as it passes through the first member 102. It is understood that the above materials are merely exemplary, and that the first member 102 can include any suitable visibly transparent material(s) with high transmittance at photon energies above the bandgap of the solar cell 104, high emissivity at 8-13 μm wavelengths, and negligible absorptance over the entire solar band, such that sub-ambient radiative cooling under direct sunlight can be achieved.

[0092] In some embodiments, the first member 102 can have a thickness of 2.88 mm. It should be understood that the above thickness is merely an exemplary thickness, and that the thickness of the first member 102 can be any suitable thickness that has low solar absorptivity and high IR emissivity, such that the first member 102 can provide a radiative cooling effect andpass sunlight to the solar cell 104. For example, in some embodiments, the first member 102 can have a thickness in a range of 0.1 mm to 10 mm.

[0093] In some embodiments, the first member 102 can be a configured to cool to 5.1°C below ambient air temperature under 1000 W / m2of light, for example, sunlight.

[0094] The radiative cooling device 100 further includes a solar cell 104. The solar cell 104 can be any solar cell suitable for generating photovoltaic power. For example, the solar cell 104 can be at least one of a monocrystalline silicon solar cell, a polycrystalline silicon solar cell, a thin- film solar cell, a perovskite solar cell, an organic photovoltaic cell, or a concentrated photovoltaic cell.

[0095] As previously described, the solar cell 104 may be positioned beneath the first member 102 such that light may pass through the first member 102 and irradiate the solar cell 104.

[0096] The radiative cooling device 100 further includes a second member 106 positioned between the first member 102 and the solar cell 104. The second member 106 can be visibly transparent such that at least a portion of sunlight may pass through the first member 102 and the second member 106. For example, the first member 102 and the second member 106 can each be configured to pass at least a portion of sunlight to the underlying solar cell 104, The second member 106 can further be IR-opaque such that the second member 106 does not pass IR radiation, or passes small amounts of IR radiation. Accordingly, there may be little to no direct radiative heat exchange between the first member 102 and the solar cell 104.

[0097] In some embodiments, the second member 106 can be a visibly transparent glass material (e.g., standard soda-lime glass, low-emissivity glass, etc.), polycarbonate, and / or acrylic. In some embodiments, the second member 106 can be a visibly transparent material having an IR- opaque film and / or coating. In some embodiments, the second member 106 can be the samematerial as the first member 102. In other embodiments, the second member 106 can be comprised of a material that is different than the material of the first member 102.

[0098] In some embodiments, the second member 106 can be configured to absorb IR at wavelengths between 5 and 25 pm. In some embodiments, the second member 106 can be configured to reflect IR at wavelengths between 5 and 25 pm. It should be understood that the above materials are merely exemplary, and that any suitable material, film, and / or coating that is visibly transparent and IR-opaque. In some embodiments, the second member 106 can include an anti -refl ection coating and / or film to reduce the reflection of sunlight as it passes through the first member 106.

[0099] Referring to FIG. 2, in an exemplary embodiment, the radiative cooling device 100 can be part of a radiative cooling structure 108. The radiative cooling structure 108 can include a first chamber 110 suspended within a second chamber 112.

[0100] The first chamber 110 can include the first member 102, the second member 106, and at least one insulative member 114 separating the first member 102 and the second member 106. The insulative member(s) 114, the first member 102, and the second member 106 may together define a cavity of the first chamber 110.

[0101] The insulative member(s) 114 can be configured to suppress heat conduction of the first member 102. The insulative member(s) 114 may be formed of any insulative material. In some embodiments, the insulative material may be an insulative foam (e.g., Styrofoam, a type of closed-cell extruded polystyrene foam (XPS), etc ).

[0102] The first chamber 110 can include a first support structure 116 and a second support structure 118 extending from the second chamber 112, and the first support structure 116 and the second support structure 118 can be configured to support and suspend the first chamber110 within the second chamber 1 12. In some embodiments, the first and second support structures 116, 118 may extend from a top wall of the second chamber 112. In some embodiments, the first and second support structures 116, 118 may extend from side wall(s) of the second chamber 112. In some embodiments, the first and second support structures 116, 118 may be spaced apart and define an aperture 120, such that the second member 106 may overlay and extend across the first aperture 120.

[0103] In some embodiments, the first and second support structures 116, 118, can be a visibly transparent material (e.g., acrylic, clear plastic, clear glass, etc.) to pass sunlight to the solar cell 104 and / or to reduce solar heating of the first chamber 110.

[0104] The solar cell 104 can be positioned within the second chamber 112 and beneath the first chamber 110 (e g. beneath and spaced apart from the second member 106).

[0105] In some embodiments, a top wall of the second chamber 112 may include an aperture 122 positioned above and spaced apart from the first member 102. The radiative cooling structure 108 can include a third member 124 overlaying and extending across the aperture 122. The third member 124 can be configured to prevent ambient air from entering the radiative cooling structure 108 via the aperture 122 and / or protect against environmental conditions, such as wind.

[0106] In some embodiments, the third member 124 can be a visibly transparent material, such as polyethylene or other type of transparent material (e.g. glass, etc.) that can permit sunlight and IR to pass through the member. In some embodiments, the third member 124 can include an anti-reflection coating and / or film to reduce the reflection of sunlight as it passes through the third member 124.

[0107] The radiative cooling device 100 can further include a heat transfer fluid configured to exchange heat with the first member 102. For example, the heat transfer fluid can be water or another type of fluid that can exchange heat with the first member 102 such that the heat transfer fluid can be cooled via the radiative cooling effect. The heat transfer fluid can be a gas, such as air or nitrogen or can be a liquid, such as water, or a refrigerant, etc.

[0108] Referring to FIGS. 3 A and 3B, a radiative cooling device 100 can further include at least one heat exchange element 126 configured to convey the heat transfer fluid. The heat exchange element(s) 126 can be positioned within the first member 102 such that heat transfer fluid flowing through the heat exchange element(s) 126 can be configured to exchange heat with the first member 102. Alternatively, or additionally, the heat exchange element(s) 126 can be disposed on a surface of the first member 102, such as an outer surface, such that heat transfer fluid flowing through the heat exchange element(s) 126 can be configured to exchange heat with the first member 102.

[0109] In some embodiments, the at least one heat exchange element 126 can be at least one conduit configured to convey the heat transfer fluid. The conduit(s) can be a visibly transparent material (e.g., plastic, glass, etc.) and can be configured to pass sunlight.

[0110] In some embodiments, the first member 102 may include at least one channel 127 positioned within the first member 102, such that the heat transfer fluid may flow through the channel(s) 127 and exchange heat with the first member 102. For example, the channel(s) may include an inlet at one end of the first member 102 and an outlet at an opposite end of the first member 102, and the channel(s) may extend from the inlet to the outlet. In other embodiments, the heat exchange element(s) 126 can be positioned in the channel such that the heat transferfluid may flow through the heat exchange element(s) 126 and exchange heat with the first member 102.

[0111] In some embodiments, the first member 102 can include first and second layers and the channel(s) 127 can be defined intermediate the first and second layers.

[0112] In some embodiments, the channel(s) 127 may include one or more baffles. The baffles may be configured to increase the turbulence of flow of the fluid and / or to enhance the exchange of heat between the fluid and the first member 102. For example, in some embodiments, the at channel(s) 127 may form a saw-tooth pattern extending from an inlet at one end of the first member 102 and an outlet at an opposite end of the first member 102.

[0113] Referring to FIGS. 17 and 18A, in some embodiments, the radiative cooling device 100 can be in fluid communication and / or electrical communication with an external cooling system. For example, the radiative cooling device 100 can be in fluid communication with an external air conditioning system via an inlet conduit and / or an outlet conduit. The external air conditioning system can be configured to cycle gaseous fluid, such as air, from an area (e.g., an indoor area) through the radiative cooling device 100 to cool the air, and the cooled air can be recirculated back into the area to cool the area. The external air conditioning system can include a fan configured to transport air from the area into the radiative cooling device 100, such as via the inlet conduit in fluid communication with the at least one heat exchange element 126. The air can exchange heat with the first member 102 such that the air cools to a sub- ambient temperature.

[0114] In some embodiments, the radiative cooling device 100 can be in electrical communication, e.g., via electrical conduits, cables, etc., with one or more electrical components of the external air conditioning system, such that the one or more components can receiveelectric energy from the photovoltaic power generated by the solar cell 104. For example, the photovoltaic power generated by the solar cell 104 can be converted to AC or DC power, and can be utilized to power one or more components of the air conditioning system, such as a DC fan.

[0115] In some embodiments, the external air conditioning system can include a refrigerant heat exchanger in fluid communication with the radiative cooling device 100. The refrigerant heat exchanger can be in fluid communication with a pump configured to pump a second heat transfer fluid into the radiative cooling device 100, such as via the least one heat exchange element 126 or via a channel 127 of the first member 102. The second heat transfer fluid can exchange heat with the first member 102 such that the second heat transfer fluid can be cooled to a sub-ambient temperature.

[0116] The external air conditioning system can further include a refrigeration cycle including, in sequence, an expansion valve, an evaporator, a compressor, and a condenser in fluid communication with the refrigerant heat exchanger. The refrigerant heat exchanger can be configured to exchange heat between the second heat transfer fluid cooled by the radiative cooling device 100 and a working fluid (e.g., refrigerant, such as R-22, R-140A, etc.) flowing through the refrigeration cycle.

[0117] Referring to FIG. 4, a radiative cooling device 200 can include a first member 202, a solar cell 204 underlying the first member 202, and at least one IR-reflective member (e.g., members 206, 208) positioned adjacent the first member 202 and above the solar cell 204 (e.g. overlaying the solar cell 204).

[0118] The radiative cooling device 200 may be similar to the radiative cooling device 100 such that features shared between like elements may not be described in detail. For example, first member 102 and first member 202 are like elements such that features related to both thefirst member 102 and the first member 202 may not be repeated in the interest of brevity, solar cell 104 and solar cell 204 are like elements such that features related to both the solar cell 104 and the solar cell 204 may not be repeated in the interest of brevity, etc.

[0119] In some embodiments, the first member 202 can be reflective such that the first member 202 can reflect sunlight. For example, the first member 202 can be configured to reflect at least 88% of sunlight. In other embodiments, the first member 202 can be visibly transparent, such that at least a portion of sunlight may pass through the first member 202. The first member 202 can further be thermally emissive and be configured to emit thermal (e.g., infrared) radiation through a specific atmospheric window where the Earth's atmosphere is transparent, such that the first member 202 can provide a radiative cooling effect to cool to sub-ambient temperatures.

[0120] The radiative cooling device 200 can include at least one IR-reflective member. In some embodiments, the radiative cooling device 200 includes one IR-reflective member. In some embodiments, the radiative cooling device 200 includes a plurality of IR-reflective members.The IR-reflective member(s) can be visibly transparent and configured to pass sunlight to the solar cell 204. The IR-reflective member(s) 206, 208 can be a visibly transparent material, such as glass, plastic, etc., and can include an IR-reflective coating. For example, the IR-reflective coating can be a low-emissivity coating having an emissivity of less than 10%. In some embodiments, the IR-reflective coating can be multilayer dielectric coating, such as one or more layer(s) of metal (e.g., silver, etc.) disposed between two or more dielectric layers, such as aluminum oxide, silicon oxide, etc. In some embodiments, the IR-reflective coating can be a doped metal oxide coating, such as indium tin oxide, gallium zinc oxide, aluminum zinc oxide, etc. It should be understood that the above materials and coatings are merely exemplary, andthat the IR-reflective member(s) can include any materials and / or coatings suitable for reflectingIR, or thermal radiation, and passing sunlight.

[0121] In some embodiments, the radiative cooling device 200 can include at least one ZR-reflective member 206 positioned on one side of and adjacent to the first member 202 and at least one IR-reflective member 208 positioned on an opposite side of and adjacent to the first member 202.

[0122] In some embodiments, the IR-reflective member(s) can be positioned adjacent the first member 202 and overlay the solar cell 204 while also being spaced apart from the solar cell 204, and can be configured to reflect IR, or thermal radiation, emitted from the first member 202 in an upward (e.g., skyward) direction. For example, the IR-reflective member(s) can be angularly positioned relative to the first member 202 and / or the solar cell 204.

[0123] In an exemplary embodiment, as seen in FIG. 4, the first member 202 can be positioned overlaying the solar cell 204. The solar cell 204 can be positioned in a horizontal orientation and the first member 202 can be positioned in a vertical orientation, such that the first member 202 is perpendicularly oriented relative to the solar cell 204, and such that the first member 202 is positioned overlaying a minimal amount of the total surface area of a surface of the solar cell 204. For example, the solar cell 204 can have a first surface 212a and a second surface 212b opposite the first surface 212a. The first surface 212a can be a sunlight-absorbing surface of the solar cell 204. The solar cell 204 can be positioned in a horizontal orientation such that the first surface 212a and the second surface 212b extend parallel relative to the X-axis shown in FIG. 4. The X-axis at which the first and second surface extend can be a width direction or length direction of the solar cell 204 in some configurations. The first member 202 can have a first surface 210a and a second surface 210b opposite the first surface 210a. The firstmember 202 can be positioned in a vertical orientation such that the first surface 210a and the second surface 210b extend parallel relative to the Y-axis shown in FIG. 4. The first surface 210a and the second surface 210b can be considered to extend along the Y-axis in a height direction or length direction of the first member 202. In other words, the first member 202 can be positioned such that the first surface 210a and the second surface 210b extend along the length or height of the first member 202 perpendicularly relative to the first surface 212a and the second surface 212b of the solar cell 204 may extend along the length or width of the solar cell 204.

[0124] The first and second TR-reflective members 206, 208 can be positioned adjacent the first member 202 and overlaying the solar cell 204, and can be configured to reflect IR, or thermal radiation, emitted from the first member 202 in a skyward direction. For example, the first and second IR-reflective members 206, 208 can be angularly positioned relative to the first member 202 and / or the solar cell 204. For example, the IR-reflective member 206 can have a first surface 214a and a second surface 214b opposite the first surface 214a and the IR-reflective member 208 can have a first surface 216a and a second surface 216b opposite the first surface 216a. The IR-reflective member(s) 206 and / or 208 can be oriented such that the first and second surfaces 214a and 214b and / or 216a and 216b can extend at an angle (depicted in FIG. 4 as angle(s) 9aand / or 0b) in a range from 0° to 90°, the range not including 0°, relative to surfaces 210a and 210b and / or 212a and 212b. For example, the IR-reflective member(s) 206 and / or 208 can be angularly positioned such that the first and second surfaces 214a, 214b and / or 216a, 216b extend at an angle (e.g., 0aand / or 0b) of 45° relative to first and second surfaces 210a, 210b and / or relative to the first and second surfaces 212a, 212b. The exemplary angles 9aand / or 0b can include any suitable angle, or range of angles, such that the IR-reflective member(s) 206and / or 208 reflect IR in a skyward direction and pass sunlight to the solar cell 204. For example, the range of angles can include angles from 15° to 75°, 30° to 60°, etc.

[0125] It should be understood that the above physical arrangement and / or positioning of the first member 202, the solar cell 204, and the first and second IR-reflective members 206, 208, is merely exemplary, and that each of the first member 202, the solar cell 204, and the first and second IR-reflective members 206, 208, can be arranged and / or positioned in any suitable way, such that the first member 202 provides a radiative cooling effect and sunlight is passed to the solar cell 204 to generate photovoltaic power. Additionally, it should be understood that the radiative cooling device 200, and / or any individual element thereof (e.g., first member 202, solar cell 204, first and second IR-reflective members 206, 208) can be positioned in any suitable orientation and / or angle such that IR is reflected by the IR-reflective members 206, 208, sunlight is passed to the solar cell 204 such that the solar cell generates photovoltaic power, and / or sunlight is reflected by the first member 202.

[0126] The radiative cooling device 200 can further include a heat transfer fluid configured to exchange heat with the first member 202. For example, the heat transfer fluid is configured to exchange heat with the first member 202 such that the heat transfer fluid is cooled via the radiative cooling effect. As noted above, the heat transfer fluid can be a gas, such as air or can be a liquid, such as water, a refrigerant, etc.

[0127] The radiative cooling device 200 can further include at least one heat exchange element 226 configured to convey the heat exchange fluid. The heat exchange element(s) 226 can be positioned within the first member 202 such that heat transfer fluid flowing through the heat exchange element(s) 226 can be configured to exchange heat with the first member 202. Alternatively, or additionally, the heat exchange element(s) 226 can be disposed on a surface ofthe first member 202, such as an outer surface, such that heat transfer fluid flowing through the heat exchange element(s) 226 can be configured to exchange heat with the first member 202.

[0128] In some embodiments, the at least one heat exchange element 226 can be at least one conduit configured to convey the heat exchange fluid. The conduit(s) can be a visibly transparent material (e.g., plastic, glass, etc.) and can be configured to pass sunlight. In some embodiments, the conduit(s) can be visibly opaque (e.g., colored plastic, metal, etc.)

[0129] In some embodiments, the first member 202 may include at least one channel positioned within the first member 202, such that the heat transfer fluid may flow through the channel(s) and exchange heat with the first member 202. For example, the channel(s) may include an inlet at one end of the first member 202 and an outlet at an opposite end of the first member 202, and the channel(s) may extend from the inlet to the outlet. In other embodiments, the heat exchange element(s) 226 can be positioned in the channel such that the heat transfer fluid may flow through the heat exchange element(s) 226 and exchange heat with the first member 202.

[0130] In some embodiments, the channel(s) may include one or more baffles. The baffles may be configured to increase the turbulence of flow of the fluid and / or to enhance the exchange of heat between the fluid and the first member 202.

[0131] In some embodiments, the radiative cooling device 200 can include at least one heat exchange element 226 and can be in fluid and / or electrical communication with an external cooling system, as described above in relation to radiative cooling device 100, the details of which can equally apply to the radiative cooling device 200 and will not be repeated here in the interest of brevity.

[0132] Referring to FIG. 5, an exemplary method 300 for concurrently cooling fluid and generating photovoltaic power is provided. The method 300 can utilize any of the above- described embodiments and / or elements of the radiative cooling device 100 for concurrently cooling fluid and generating photovoltaic power, the details of which are not repeated here in the interest of brevity. The method 300 can include a first step 302, providing a radiative cooling device. The radiative cooling device can include a first member that is visibly transparent, a solar cell underlying and spaced apart from the first member, and a second member that is visibly transparent and IR-opaque and positioned intermediate the first member and solar cell. The method 300 can include second step 304, passing fluid through at least one heat exchange element configured to exchange heat with the first member. The first member can provide a radiative cooling effect and the fluid can be configured to exchange heat with the first member such that the fluid is cooled by the radiative cooling effect, and the first and second members can be configured to pass sunlight to the solar cell such that the solar cell generates photovoltaic power. The fluid can be a gaseous fluid and / or or a liquid fluid.

[0133] Referring to FIG. 6, an exemplary method 400 for concurrently cooling fluid and generating photovoltaic power is provided. The method 400 can utilize any of the above- described embodiments and / or elements of the radiative cooling device 200 for concurrently cooling fluid and generating photovoltaic power, the details of which are not repeated here in the interest of brevity. The method 400 can include a first step 402, providing a radiative cooling device. The radiative cooling device can include a first member, a solar cell underlying the first member, and at least one IR-reflective member that is visibly transparent positioned adjacent the first member and overlaying the solar cell. The method 400 can include second step 404, passing fluid through at least one heat exchange element configured to exchange heat with the firstmember, the first member can provide a radiative cooling effect, and the fluid can be configured to exchange heat with the first member such that the fluid is cooled by the radiative cooling effect, and the at least one IR-reflective member can be configured to pass sunlight to the solar cell such that the solar cell generates photovoltaic power. The fluid can be a gaseous fluid and / or a liquid fluid.

[0134] Embodiments can be configured to include at least one device, such as a plurality of devices and / or an array of devices. In embodiments including a plurality of devices, each device may operate independently such that each device may independently provide cooling and power generation effects.

[0135] In application, device(s) may be positioned such that he device(s) may receive sunlight. In some embodiments, device(s) may be positioned and / or angled to more optimally receive sunlight.

[0136] The device(s) may be positioned on a building (e.g., on a roof of a building), in a field, or anywhere that enables the device(s) to receive sunlight. In embodiments in which the device(s) are positioned on a building, it is contemplated that the device(s) may be configured to provide simultaneous cooling and power to the building.

[0137] The following disclosure discusses exemplary implementations, methods, and test data related to the same.EXAMPLES

[0138] FIG. 7 illustrates the working principle of our dual -harvesting system. A transparent radiative cooler emits thermal radiation towards the sky. At the same time, the transparent radiative cooler allows sunlight to pass through it, enabling power generation from the underlying solar cell.

[0139] The net cooling power Pcoonngof a transparent radiative cooler at temperature T per unit area can be written as:Here, Pradis the power of thermal radiation emitted by the cooler towards the sky,Jo where 9 is the angle of incidence, X is the wavelength, s the spectralradiance of a blackbody at temperature T, and e(X, 0) is the spectral, angular emissivity of the cooler. Patmis the power of downward atmospheric thermal radiation that is absorbed by the cooler,where eatm(X, 0) is the spectral, angular emissivity of the atmosphere. Here, Kirchhoffs law of thermal radiation has been applied. Pbot(T, Tamb) is the net radiative heat transfer power from the bottom cover to the cooler,where 6 / ,ot(A, 0) denotes the spectral, angular emissivity of the bottom cover. The bottom cover is considered to be at ambient temperature, which agrees with our experimental measurement. PSoiar is the solar absorption power of the cooler,where is the AMI.5 solar irradiance spectrum. PnOn-rad is non-radiative parasitic heatgain due to conduction and convection,where hnOn-rad is the effective non-radiative heat exchange coefficient which combines convective and conductive heat exchange between the cooler and its surroundings.

[0140] Experiment Design

[0141] From the energy balance in Equation (1), achieving net cooling requires controlling optical properties across a broad spectrum from ultraviolet to far infrared, and suppressing conductive and convective heat exchange.

[0142] A radiative cooler with 2.8 mm thickness and 1 ft x 1 ft area, was mounted inside a chamber to suppress non-radiative heat exchange, FIG. 8. The radiative cooler was supported by Styrofoam blocks at four corners to suppress heat conduction between the cooler and the chamber. The was is covered with a transparent polyethylene film on the top and a transparent glass layer at the bottom to minimize the influence of wind. To reduce solar heating, the wall of the chamber was made of acrylic, FIG. 9C. Side covers were further installed to reduce solar heating of the chamber at the walls, FIG. 9A. A solar cell was instrumented below the chamber to harvest sunlight, FIG. 9B. During the experiment, the setup was tilted by 22.5° towards the south to ensure that the sunlight near normally irradiated on the setup at solar noon. The solar irradiance was measured using a pyranometer.

[0143] Spectral Characterization Of Radiative Cooler And Solar Cell

[0144] We used low-iron glass as the radiative cooler since low-iron glass is highly transparent across the whole solar wavelength range and has high emissivity at mid infrared. We purchased low-iron glass Optiwhite S from Pilkington. For the solar cell, we used a commercial Si photovoltaic cell with an area of 125 mm X 125 mm (Maxeon, SunPower). A spectroscopic measurement showed that the radiative cooler only absorbs 0.9% of sunlight, while transmits 91% of sunlight, FIG. 10. In comparison, the state-of-the-art solar-reflective radiative coolers absorb from 1.9%, 3%, to 4% of sunlight. Therefore, at 1000 VF / m2solar irradiance, our transparent radiative cooler had 10 IV / m2to 31 VF / m2less solar absorption compared with the best achieved solar-reflective radiative coolers. A UV-Vis-NIR spectroscopic measurementshowed that the solar cell strongly absorbs light at wavelengths shorter than 1100 nm wavelength, FIG. 10.

[0145] At mid infrared wavelengths, spectroscopic measurement showed that the transparent radiative cooler has high emissivity with an averaged emissivity of 0.92, FIG. 11. In particular, at 8-13 μm atmospheric transparency window, the averaged emissivity is 0.83. SiO2is a typical material used in radiative coolers owing to its phonon polariton at 9 μm which can contribute to thermal emission. However, for a thick SiCh layer, its emissivity suffers from a large dip at 8-13 pm, and a small dip at 20-25 pm, due to high impedance mismatch between SiO2and air, FIG. 11. Various photonic approaches have been used to enhance the emissivity of SiO2at the 8-13 pm atmospheric transparency window, such as by using multilayers, patterning, anti -refl ection coating, and metamaterial consisting of microspheres and polymer. Here, we used low-iron glass (Optiwhite S, Pilkington) as an effective metamaterial in the infrared. The low- iron glass consisted of by weight 72.7% of SiOs, 13% of Na2O, 8.8% of CaO, 4.3% of MgO, 0.6% of AI2O3, 0.4% of K2O, and 0.02% Fe2O3. The mixing of multiple compositions broadened the frequency response of phonon polaritons of SiCE at 8-13 pm, leading to reduced reflection and enhanced emissivity. The low solar absorptivity and high infrared emissivity made low-iron glass suitable for achieving sub-ambient radiative cooling under direct sunlight.

[0146] Experimental Results

[0147] We performed an outdoor testing near solar noon facing the setup towards a clear sky in State College, Pennsylvania. Before starting the experiment, we covered the setup with an aluminized mylar fdm to block the access to the sky and the sun. At the start of the experiment about 11 :30 AM Eastern Time (E.T.), we removed the aluminized mylar cover and thus exposed the cooler to the sky when the solar cell is completely lit by the sunlight. We measured thetemperature of the cooler and the ambient air using thermocouples. The temperature of the cooler dropped to about 5.1°C below the ambient air temperature within 15 minutes due to passive radiative cooling. FIG. 12A shows the measured temperature of the cooler and ambient air temperature for over three hours when the solar irradiance exceeded 900 I / F / m2. When solar irradiance was near the peak value from 923 W / m2to 1089 W / m2between 12:00 pm to 3:00 pm E.T., the radiative cooler was on average 5.1°C below the ambient air temperature, FIG. 12B.

[0148] We simultaneously measured electric power generation from the solar cell using a source measure unit. FIG. 13A shows current vs voltage curves of the solar cell at three different times. The maximum power generation rate at each time was determined by maximizing minus the product of current and voltage. FIG. 13B shows the measured maximum power generation rate as a function of time. When characterizing the solar cell performance, the solar cell needed to be completely lit by the sunlight. In our experiment, the solar cell was completely lit between 11 :30 am to 1 :30 pm E.T. During this duration, the solar cell generated electric power between 147.2 W / m2to 159.9 W / m2, FIG. 13B. By normalizing the measured electricity generation rate and the measured solar irradiance, the average power conversion efficiency of the solar cell was 14.5%. Our experiment for the first time showed that sub-ambient daytime radiative cooling and photovoltaic power generation can be achieved simultaneously, and from the same area.

[0149] Cooling power, another important figure of merit for quantifying the performance of radiative cooling, was also carefully measured. We experimentally determined the cooling power that can be extracted from the radiative cooler. The cooling power in Equation (1) can be approximated as:Here, PCOoiing,amb is the cooling power that can be extracted from the radiative cooler when the radiative cooler is at the same temperature as the ambient air. htotaiis the total heat exchange coefficient between radiative cooler and surroundings, including radiative, convective, and conductive heat exchange. Each data point for the cooler temperature represents a steady state, where PCOoiing(T, Tamb) = 0. Using Equation 7, one then can determine the ambient cooling power Pcooling,ambh-total (Tamb T~).

[0150] To experimentally determine the total heat exchange coefficient and daytime ambient cooling power, we performed an experiment at nighttime. We mounted a radiative cooler onto a 2 -mm thick, 1ft X 1ft aluminum heat spreading layer using epoxy and instrument a 25cm x 25cm polyimide film insulated heater to the back of the aluminum layer.

[0151] At nighttime, when there is no heating applied, the radiative cooler reached 7 °C below the ambient air temperature, FIG. 14A. We then supply four levels of stepwise Joule heating power to the heater, including 21.6 W / m2, 44.5 W / m2, 65. 1 W / m2, and 87.0 W / m2, respectively. After an increased heating load is applied, the temperature of the radiative cooler rises. FIG. 14B shows the relation between the heating power of the heater and the steady-state temperature of the radiative cooler. When there was a heating power of 87.0 W / mf the radiative cooler stabilized to the temperature of the ambient air. As the heating power balances the ambient cooling power when the cooler stabilizes to ambient air temperature, the nighttime ambient cooling power was determined to be 87.0 W / m2.

[0152] From the slope of a linear fit between heating power and temperature reduction (FIG. 14B), the nighttime total heat exchange coefficient was determined to be htotal night& 12.1 W / (m2K)' . The total heat exchange coefficient htotaiat nighttime was different from that at daytime, as the backside of the radiative cooler was polyimide in nighttime experiment butwas low-iron glass in daytime experiment (see FIG. 20). By accounting for a slight difference between the emissivity of low-iron glass and the emissivity of polyimide, we determined the daytime total heat exchange coefficient was htotai12.5 I / F / (m2 / <). Using the experimentally determined total heat transfer coefficient htotaiand the achieved temperature reduction at daytime, we determined the daytime cooling power of the radiative cooler at ambient air temperature as 12.5 W / (m2 / Q x 5.1 K = 63.8 M7 / m2.

[0153] Further, we compared the electricity saving of the dual-harvesting system, and the electricity saving of a solar cell without radiative cooler (hereafter referred to as bare solar cell), FIG. 15. The electricity saving of a bare solar cell equaled the photovoltaic electricity generation rate, with a measured power conversion efficiency TJbar e=17.5% (see FIGS. 22-27). The electricity saving of the dual system included both the electricity produced by the solar cell, and the electricity saved from cooling systems by using radiative cooling. The solar cell in the dual system had a measured apparent power conversion efficiency of 77=14.5%. In FIG. 15, radiative cooling power was set to 63.8 W / m2when the solar irradiance exceeds 100 W / m2, and 87.0 I / F / m2otherwise. We assumed air conditioning would otherwise be used as cooling system, and had a coefficient of performance (COP) of 2.8. FIG. 15 showed that the bare solar cell produced more electricity than the solar cell in the dual system. The reduced performance of the solar cell in the dual system was largely due to the reflection loss at the glass layers and the polyethylene cover. After accounting for the electricity saving from radiative cooling, the dual system had higher combined electricity saving rate than the bare solar cell, when the solar irradiance was below 750 VF / m2including night.

[0154] The total electricity saving of the dual harvesting system integrated over 24 hours can be evaluated using:where Pcooiis the radiative cooling power, COP= 2.8, and Isoiar(t) was solar irradiance measured over 24 hours on March 20, 2023. The total electricity saving of the dual-harvesting system over 24 hours is evaluated as 1.80 kWh / m2. The electricity saving of the bare solar cell can be evaluated using:which amounts to 1.38 kWh / m2. Therefore, the dual-harvesting system saves as much as 30% more electricity than the bare solar cell for the same area through day-night cycles.

[0155] Energy Saving Potential Of The Device For Different Geographical AndClimate Regions

[0156] We estimated the potential energy savings from simultaneous sub-ambient radiative cooling and photovoltaic power generation for different geographical and climate regions. In the simulation, we considered a four-story midrise apartment with roof area of 3135 m2. We assumed the roof is covered by the dual system of radiative cooling and photovoltaic cell. When ambient air temperature exceeds a target indoor temperature of 24 °C, we assumed that the cold produced by radiative cooling was transferred by a physical mechanism to reduce the electricity usage for running an air conditioning system. The air conditioning system was considered to have a coefficient of performance (COP) as 2.8. For the solar cell, we considered an energy conversion efficiency of 14.5%. According to American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHR.AE) and American National Standards Institute (ANSI) standard 169-2020, there are seventeen different climate zonesthroughout the U.S., based on eight temperature zones ( 1 (hottest) to 8 (coldest)) and three regimes based on moisture (A (Humid), B (Dry ) and C (Marine)).

[0157] We used one representative city from each of the seventeen climate zones including Albuquerque (NM), Atlanta (GA), Baltimore (AID), Bremerton (WA), Chicago (H.). Denver (CO), Duluth (MN), Fairbanks (AK >. Helena (MT), Houston (TX). Las Cruces (NM), Las Vegas (NV). Los Angeles (CA), Miami (FL), Minneapolis (MN), Phoenix (AZ), and San Francisco (CA). For different cities, we used the Typical Meteorological Data (TMY3) to determine the ambient temperature, dew point, and solar irradiance By analyzing the energy savings for these cities, we made estimations for the whole U.S. We model the ambient cooling power using Equation (1), using measured polarization-dependent, angular, spectral emissivity (see FIGS. 19A-B) of the radiative cooler, dew point dependent atmospheric transmittance from MODTRAN, ambient temperature, and solar irradiance.

[0158] FIG 12A shows both annual electricity saved by radiative cooling and solar cells in the dual system. Cities with hot and dry climate such as Phoenix (3.61 x 105kWh), Las Vegas (3.14 x 105kWh), Las Cruces (2 06 x 10skWh), and Albuquerque (0,97 x 105kWh) exhibited high electricity saving by radiative cooling. The map in FIG, 12B shows the same feature. The lower humidity in dry climate led to higher atmospheric transparency and accordingly enhanced radiative cooling performance. Also, cities with hot and humid climate such as Miami (2.21 * 10° kWh) and Houston (1.21 * 10' kWh) showed significant electricity saving by radiative cooling. In cities with hot and humid climate, though the high humidity reduced the performance of radiative cooling, owing to high ambient temperature and thus high cooling demand, the electricity saving from radiative cooling was significant.

[0159] FinaHy, in cold climate, there was reduced cooling demand for space cooling in buildings and thus small potential benefit of radiative cooling. In FIGS. 16-18, we considered radiative cooling benefit, only when the ambient air temperature exceeds the target indoor temperature 24 °C. As the average hourly temperature throughout the year in certain cities (such as Los Angeles and San Francisco) doesn’t exceed 24 °C due to TMY3 data, the electricity saving of radiative cooling for these cities was assessed as zero in FIGS. 16-8. However, in scenarios such as data centers, manufacturing, and refrigeration systems, radiative cooling can be useful even in cold climate. By accounting for radiative cooling power at all ambient temperatures, the electricity saving from radiative cooling can have similar magnitude as electricity generation from photovoltaics (see FIGS. 19A-C).

[0160] Photovoltaic electricity generation majorly depends on solar irradiance. FIG. 12C shows that places with lower altitude like Phoenix (9.37 x 105kWh), Las Cruces (9.26 * 105kWh), Las Vegas (9.10 * 103kWh), Albuquerque (8.87 * 103kWh), Los .Angeles (8 17 * 105kWh), and Miami (7.85 * 105kWh) can produce more electricity from photovoltaics than places at higher altitude. Thus, dry and hot places, such as Phoenix and Las Vegas, can benefit most by simultaneous radiative cooling and photovoltaic power generation. The substantial potential electricity saving from radiative cooling and photovoltaics highlighted the great opportunity of simultaneously harvesting the cold universe and the sun for renewable energy.

[0161] Discussion

[0162] We demonstrated simultaneous sub-ambient daytime radiative cooling at 5.1 °C temperature reduction under solar irradiance about 1000 l¥ / m2and solar power generation up to159.9 VK / m2from the same area. We experimentally achieved ambient cooling power of 63.8W / m2under peak sunlight, and ambient cooling power of 87.0 W / m2at nighttime. In thefollowing, we briefly compare the overall performance of the dual system with existing sub- ambient daytime radiative coolers. Assuming that the generated photovoltaic electricity were to be used to drive a cooling system with coefficient of performance of 2.8, under peak sunlight, the total cooling power from our system due to radiative cooling and photovoltaics would be 511.5 PV / m2, which is >5 times bigger than the daytime cooling power achieved in solar-reflective radiative coolers (40-100 W / m2) and >1.8 times bigger than the daytime cooling power achieved in double-sided radiative cooler (273.3 W / m2). Further, the electricity saving of the dual system exceeds that of a bare solar cell by 30% through day-night cycles. Our results highlight new opportunities of simultaneously harnessing both the cold universe and the sun for renewable energy.

[0163] One potential application of the dual-harvesting system is to integrate it with buildings to reduce the overall energy consumption. The photovoltaic electricity generated in the dual system can be used for energy storage or be converted to AC current by using an inverter. The coldness achieved on the transparent radiative cooler can be used to cool air or liquid, which can be driven by fan or pump, respectively, to interface with thermal systems for energy saving (see FIG. 28 and FIG. 29). In our proof-of-concept demonstration, the achieved photovoltaic conversion efficiency was affected by reflections taking place at multiple interfaces. The photovoltaic conversion efficiency could be improved by adding anti-reflection coatings to the radiative cooler, polyethylene, and the chamber bottom cover. FIG. 30 shows a graph of the modeled absorptivity at the solar spectrum for 50 μm liquid water between two SiCh layers.

[0164] There is room for further improving the transparent radiative cooler, including reducing visible reflection and enhancing infrared emissivity. Materials for transparent radiative cooler need meet stringent requirements, including high transmittance at photon energies abovethe bandgap of the solar cell, high emissivity at 8-13 μm wavelengths, and negligible absorptance over the whole solar band. Transparent radiative cooler may involve transparent polymers such as polymethyl methacrylate (PMMA), polydimethyl siloxane (PDMS), and polypropylene (PP).

[0165] Also, the performance of the dual-harvesting system can depend on multiple environmental parameters such as the ambient temperature, solar irradiance, and atmospheric transmittance which is influenced by dew point and cloud cover. At fixed solar irradiance and atmospheric transmittance, the ambient cooling power increases with the ambient temperature, as radiative heat exchange becomes more significant at higher temperature. The photovoltaic power output decreases with the ambient temperature, as solar cells typically have negative temperature coefficient for the conversion efficiency. As the ambient cooling power and the photovoltaic power output have opposite coefficients with respect to the ambient temperature, the sign of the temperature coefficient of the total electricity saving of the dual-harvesting system will depend on the details of the environmental parameters including solar irradiance, atmospheric transmittance, and ambient temperature. Finally, the time duration when the solar cell is lit by the sun is limited by the aspect ratio of the setup in the demonstration of concept, which could be solved by scaling up the transversal size of the setup.

[0166] It should be understood that the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points. It should also be appreciated that some components, features, and / or configurations may be described in connection with only one particular embodiment, but these same components, features, and / or configurations can be applied or used with many other embodiments and should be considered applicable to the other embodiments, unless stated otherwise or unless such a component, feature, and / or configurationis technically impossible to use with the other embodiment. Thus, the components, features, and / or configurations of the various embodiments can be combined together in any manner and such combinations are expressly contemplated and disclosed by this statement.

[0167] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible considering the above teachings of the disclosure. The disclosed examples and embodiments are presented for purpose of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof.

[0168] It should be understood that modifications to the embodiments disclosed herein can be made to meet a particular set of design criteria. Therefore, while certain exemplary embodiments of the compositions, materials, apparatuses, and methods of using and making the same disclosed herein have been discussed and illustrated, it is to be distinctly understood that the invention is not limited thereto but may otherwise be variously embodied and practiced within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A radiative cooling device comprising: a first member, wherein the first member is visibly transparent and thermally emissive; a solar cell underlying and spaced apart from the first member; a second member positioned intermediate the first member and the solar cell, wherein the second member is visibly transparent and infrared radiation (IR)-opaque, wherein the first and second members are configured to pass sunlight to the solar cell such that the solar cell generates photovoltaic power, and wherein the first member is configured to emit IR such that the first member provides a radiating cooling effect.

2. The radiative cooling device of claim 1, wherein the first member comprises a material configured to absorb no greater than 10% of sunlight.

3. The radiative cooling device of claim 2, wherein the material is configured to have an average IR emissivity of 0.83 at IR wavelengths in a range of 8 to 13 micrometers.

4. The radiative cooling device of claim 1, wherein the first member comprises a visibly- transparent thermally-emissive material comprising at least one compound from the group consisting of: SiCh, Na2O, CaO, MgO, AI2O3, K2O, and Fe2C>3.

5. The radiative cooling device of claim 4, wherein the visibly transparent and thermally emissive material comprises less than 0.1% of Fe2O3.

6. The radiative cooling device of claim 1, wherein the first member comprises a thickness within a range of 0.1 to 10 millimeters.

7. A radiative cooling structure comprising the radiative cooling device of claim 1, the radiative cooling structure further comprising: a first chamber suspended within a second chamber, wherein the first chamber comprises: the first member; the second member; and at least one insulative member separating the first member from the second member such that the at least one insulative member, the first member, and the second member define a cavity; wherein the solar cell is positioned beneath and spaced apart from the second member.

8. The radiative cooling structure of claim 7, wherein the first chamber further comprises: a first support structure and a second support structure extending from the second chamber, wherein the first support structure and the second support structure are configured to suspend the first chamber within the second chamber.

9. The radiative cooling structure of claim 7, wherein a surface of the second chamber positioned above and spaced apart from the first member comprises an aperture.

10. The radiative cooling structure of claim 9, wherein a third member overlies and extends across the aperture, wherein the third member is visibly transparent.

11. The radiative cooling structure of claim 10, wherein the third member is configured to prevent ambient air from entering the radiative cooling structure via the aperture.

12. The radiative cooling device of claim 1, further comprising at least one heat exchange element comprising a heat transfer fluid configured to exchange heat with the first member such that the heat transfer fluid is cooled via the radiative cooling effect.

13. The radiative cooling device of claim 12, wherein the at least one heat exchange element comprises at least one tubular conduit.

14. The radiative cooling device of claim 13, wherein the at least one tubular conduit is visibly transparent and configured to pass sunlight.

15. The radiative cooling device of claim 1, wherein the first member comprises at least one channel defined within the first member, and wherein a heat transfer fluid is configured to flow through the at least one channel such that the heat transfer fluid is cooled via the radiative cooling effect.

16. The radiative cooling device of claim 15, further comprising at least one heat exchange element comprising the heat transfer fluid, wherein the at least one heat exchange element is positioned within the at least one channel of the first member.

17. The radiative cooling device of claim 15, wherein the at least one channel further comprises at least one baffle.

18. A radiative cooling device comprising: a first member, wherein the first member is configured to emit infrared radiation (IR) such that the first member provides a radiative cooling effect; a solar cell underlying the first member; at least one IR-reflective member positioned adjacent the first member and overlaying the solar cell, wherein the at least one IR-reflective member is visibly transparent, wherein the at least one IR-reflective member is configured to pass sunlight to the solar cell such that the solar cell generates photovoltaic power.

19. The radiative cooling device of claim 18, further comprising at least one heat exchange element comprising a heat transfer fluid configured to exchange heat with the first member such that the heat transfer fluid is cooled via the radiative cooling effect.

20. The radiative cooling device of claim 19, wherein the at least one heat exchange element comprises at least one tubular conduit.21 . The radiative cooling device of claim 18, wherein the first member comprises at least one channel defined within the first member, and wherein a heat transfer fluid is configured to flow through the at least one channel such that the heat transfer fluid is cooled via the radiative cooling effect.

22. The radiative cooling device of claim 21, further comprising at least one heat exchange element comprising the heat transfer fluid, wherein the at least one heat exchange element is positioned within the at least one channel of the first member.

23. The radiative cooling device of claim 21, wherein the at least one channel further comprises at least one baffle.

24. The radiative cooling device of claim 18, wherein the at least one IR-reflective member comprises a visibly transparent low-emissivity coating.

25. The radiative cooling device of claim 18, wherein the first member is further configured to reflect at least a portion of sunlight.

26. The radiative cooling device of claim 18, wherein the solar cell is positioned in a horizontal orientation and wherein the first member is positioned in a vertical orientation, such that the first member is positioned perpendicularly relative to the solar cell.

27. The radiative cooling device of claim 26, wherein the at least one IR-reflective member is positioned angularly relative to the first member and the solar cell, such that the at least one IR- reflective member is configured to reflect at least a portion of IR emitted from the first member in a skyward direction.

28. A method for concurrently cooling fluid and generating photovoltaic power comprising: providing a radiative cooling device comprising: a first member, wherein the first member is visibly transparent and thermally emissive; a solar cell underlying and spaced apart from the first member; and a second member positioned intermediate the first member and the solar cell, wherein the second member is visibly transparent and infrared radiation (IR)-opaque; and passing fluid through at least one heat exchange element configured to exchange heat with the first member, wherein the first member provides a radiative cooling effect, wherein the fluid is configured to exchange heat with the first member such that the fluid is cooled by the radiative cooling effect, wherein the first and second members are configured to pass sunlight to the solar cell such that the solar cell generates photovoltaic power.

29. The method of claim 28, wherein the first member comprises at least one channel defined within the first member, and wherein the at least one heat exchange element is positioned within the at least one channel of the first member.

30. The method of claim 28, wherein the at least one heat exchange element comprises at least one tubular conduit.

31. The method of claim 30, wherein the at least one tubular conduit is transparent and configured to pass sunlight.

32. A method for concurrently cooling fluid and generating photovoltaic power comprising: providing a radiative cooling device comprising: a first member, wherein the first member thermally emissive; a solar cell underlying the first member; and at least one infrared radiation (IR)-reflective member positioned adjacent the first member and overlaying the solar cell, wherein the at least one IR-reflective member is visibly transparent; and passing fluid through at least one heat exchange element configured to exchange heat with the first member, wherein the first member provides a radiative cooling effect, wherein the fluid is configured to exchange heat with the first member such that the fluid is cooled by the radiative cooling effect, wherein the at least one IR-reflective member is configured to pass sunlight to the solar cell such that the solar cell generates photovoltaic power.

33. The method of claim 32, wherein the first member comprises at least one channel defined within the first member, and wherein the at least one heat exchange element is positioned within the at least one channel of the first member.

34. The method of claim 33, wherein the at least one heat exchange element comprises at least one tubular conduit.

35. The method of claim 32, wherein the at least one IR-reflective member comprises a visibly transparent low-emissivity coating.

36. The method of claim 32, wherein the first member is further configured to reflect at least a portion of sunlight.

37. The method of claim 32, wherein the solar cell is positioned in a horizontal orientation and wherein the first member is positioned in a vertical orientation, such that the first member is positioned perpendicularly relative to the solar cell.

38. The method of claim 37, wherein the at least one IR-reflective member is positioned angularly relative to the first member and the solar cell, such that the at least one IR-reflective member is configured to reflect at least a portion of IR emitted from the first member in a skyward direction.

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