Radiative sky cooling: fundamental physics, materials, structures, and applications

Sun, Xingshu; Sun, Yubo; Zhou, Zhiguang; Alam, Muhammad Ashraful; Bermel, Peter

doi:10.1515/nanoph-2017-0020

Cited by 180 publications

(102 citation statements)

References 98 publications

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“…2). Dependence on polar angle of the transmissivity is given by t atmos , λ ( θ ) = t atmos , λ ( θ = 0°) 1/ cosθ as in 5,12,25 . The heat load ( Q ) is calculated by simply subtracting the reflected flux and the electrical power output.where for the sake of limiting the number of variables, it is assumed that the panel does not transmit any radiation or that the transmitted part is included in the reflection term.…”

Section: Methodsmentioning

confidence: 99%

Pathways for mitigating thermal losses in solar photovoltaics

Vaillon

Dupré

Cal

et al. 2018

Sci Rep

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To improve the performance of solar photovoltaic devices one should mitigate three types of losses: optical, electrical and thermal. However, further reducing the optical and electrical losses in modern photovoltaic devices is becoming increasingly costly. Therefore, there is a rising interest in minimizing the thermal losses. These correspond to the reduction in electrical power output resultant of working at temperatures above 25 °C and the associated accelerated aging. Here, we quantify the impact of all possible strategies to mitigate thermal losses in the case of the mainstream crystalline silicon technology. Results indicate that ensuring a minimum level of conductive/convective cooling capabilities is essential. We show that sub-bandgap reflection and radiative cooling are strategies worth pursuing and recommend further field testing in real-time operating conditions. The general method we propose is suitable for every photovoltaic technology to guide the research focused on reducing thermal losses.

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Section: Methodsmentioning

confidence: 99%

Pathways for mitigating thermal losses in solar photovoltaics

Vaillon

Dupré

Cal

et al. 2018

Sci Rep

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“…In addition, for daytime cooling, high reflectivity in the entire solar spectral range (i.e., 300–4000 nm) is required to minimize heat generation from the absorbed solar power. Potential applications of these daytime coolers include temperature‐sensitive electronic/optoelectronic devices such as photovoltaics, thermophotovoltaics, rectennas, infrared detectors, and power electronics not limited to buildings and power plants.…”

mentioning

confidence: 99%

Colored, Daytime Radiative Coolers with Thin‐Film Resonators for Aesthetic Purposes

Lee

Kim

et al. 2018

Advanced Optical Materials

130

117

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sunlight. The features of an accurate radiative model, strong selective emission in the atmospheric transparency window, and broadband high reflectance to solar irradiation are each formulated individually and then configured collectively to accomplish this outcome. Because all of the successful examples of daytime radiative coolers possess high solar reflectivity, they are white or silver in color and are thus not visually appealing, [5][6][7]9] thereby restricting the possible installation locations and limiting their net cooling capacity. Although previous efforts have been paid to incorporate colors into the radiative cooler, [26] the research only dealt with theoretical calculations without experimental demonstrations, and structural optimization of colored radiative coolers has not been performed. Here, we present concepts and strategies for daytime radiative cooling systems that involve comparable attention to engineering design but with the goal of achieving systems that offer aesthetically desired colors and patterns and functional purposes, thus enabling more widespread installation. The experimental demonstration exhibits subambient cooling behaviors under a clear sky while preserving its color. The approaches reported here can address application concepts for wearable electronic devices whose operational temperature is lowered by radiative cooling. Figure 1a exhibits a schematic of a decorative colored passive radiative cooler (CPRC) for aesthetic purposes featuring areas with subtractive primary colors (i.e., cyan, magenta, and yellow) on a silvery background, where the latter area represents a conventional daytime radiative cooler. The CPRC consists of a SE comprising a bilayer of SiO 2 (650 nm) and Si 3 N 4 (910 nm), whose thicknesses are defined by extensive numerical optimization; and a metal reflector comprising an Ag film (100 nm) deposited on a silicon substrate (Figure 1b, left). Additional photonic nanostructures were inserted below the SE to generate vivid colors at specific desired areas (Figure 1b, right), which comprised a thin-film resonator composed of a metal-insulator-metal (MIM) structure. The MIM structure determined each color via interference in the 1D stacked layers, where the color generation was precisely controlled by tuning the thickness of the insulator layer (i.e., SiO 2 cavity) in the MIM.In this study, the MIM structure was chosen as the colorant structure because it provided minimal loss of solar reflectance and a narrow spectral width compared with other additive color filters such as metal gratings and 1D photonic crystals (1D PhC),Recently developed approaches in passive radiative cooling enable daytime cooling via engineered photonic structure layouts. However, the use of these daytime radiative coolers is restricted owing to their nonaesthetic appearance resulted from strong solar reflection. Therefore, this article introduces a colored passive radiative cooler (CPRC) capable of generating potential cooling power, based on a thin-film optical resonator embedded in ...

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“…A metamaterial, which only emits or absorbs the thermal radiation within the transparency window of the atmosphere (8-13 μm), is preferable for radiative sky cooling [49,53]. Various material structures have been proposed to match the spectrum of the atmospheric window, including planar multilayer structures [2,48], patterned meta-surface structures [47,50,51,54], and polymers doped with nanoparticles [45,52,55].…”

Section: A Target Metamaterialsmentioning

confidence: 99%

“…Another application that has recently attracted much attention, in response to concerns of global warming and energy crises, is radiative sky cooling that utilizes the untapped 3 K cold space as a heat sink. Previous designs on radiative cooling [2,[45][46][47][48][49][50][51][52][53][54][55] have focuses on simultaneously blocking solar energy (0.4-4 μm) while maximizing thermal radiation loss (>4 μm) to the surroundings. These designs have been experimentally demonstrated to be successful in dry and clear weather.…”

Section: Introductionmentioning

confidence: 99%

Designing metamaterials with quantum annealing and factorization machines

Kitai

Guo

et al. 2020

Phys. Rev. Research

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Automated materials design with machine learning is increasingly common in recent years. Theoretically, it is characterized as black-box optimization in the space of candidate materials. Since the difficulty of this problem grows exponentially in the number of variables, designing complex materials is often beyond the ability of classical algorithms. We show how quantum annealing can be incorporated into automated materials discovery and conduct a proof-of-principle study on designing complex thermofunctional metamaterials. Our algorithm consists of three parts: regression for a target property by factorization machine, selection of candidate metamaterial based on the regression results, and simulation of the metamaterial property. To accelerate the selection part, we rely on the D-Wave 2000Q quantum annealer. Our method is used to design complex structures of wavelength selective radiators showing much better concordance with the thermal atmospheric transparency window in comparison to existing human-designed alternatives.

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Radiative sky cooling: fundamental physics, materials, structures, and applications

Cited by 180 publications

References 98 publications

Pathways for mitigating thermal losses in solar photovoltaics

Pathways for mitigating thermal losses in solar photovoltaics

Colored, Daytime Radiative Coolers with Thin‐Film Resonators for Aesthetic Purposes

Designing metamaterials with quantum annealing and factorization machines

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