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In response to the development of the concepts of “carbon neutrality” and “carbon peak”, it is critical to developing materials with high near-infrared (NIR) solar reflectivity and high emissivity in the atmospheric transparency window (ATW; 8–13 μm) to advance zero energy consumption radiative cooling technology. To regulate emission and reflection properties, a series of high-entropy rare earth stannate ceramics (HE-RE2Sn2O7: (Y0.2La0.2Nd0.2Eu0.2Gd0.2)2Sn2O7, (Y0.2La0.2Sm0.2Eu0.2Lu0.2)2Sn2O7, and (Y0.2La0.2Gd0.2Yb0.2Lu0.2)2Sn2O7) with severe lattice distortion were prepared using a solid phase reaction followed by a pressureless sintering method for the first time. Lattice distortion is accomplished by introducing rare earth elements with different cation radii and mass. The as-synthesized HE-RE2Sn2O7 ceramics possess high ATW emissivity (91.38%–95.41%), high NIR solar reflectivity (92.74%–97.62%), low thermal conductivity (1.080–1.619 W·m−1·K−1), and excellent chemical stability. On the one hand, the lattice distortion intensifies the asymmetry of the structural unit to cause a notable alteration in the electric dipole moment, ultimately enlarging the ATW emissivity. On the other hand, by selecting difficult excitation elements, HE-RE2Sn2O7, which has a wide band gap (Eg), exhibits high NIR solar reflectivity. Hence, the multi-component design can effectively enhance radiative cooling ability of HE-RE2Sn2O7 and provide a novel strategy for developing radiative cooling materials.

Radiative cooling passively removes heat from objects via emission of thermal radiation to cold space. Suitable radiative cooling materials absorb infrared light while they avoid solar heating by either reflecting or transmitting solar radiation, depending on the application. Here, we demonstrate a reflective radiative cooler and a transparent radiative cooler solely based on cellulose derivatives manufactured via electrospinning and casting, respectively. By modifying the microstructure of cellulose materials, we control the solar light interaction from highly reflective (> 90%, porous structure) to highly transparent (≈ 90%, homogenous structure). Both cellulose materials show high thermal emissivity and minimal solar absorption, making them suitable for daytime radiative cooling. Used as coatings on silicon samples exposed to sun light at daytime, the reflective and transparent cellulose coolers could passively reduce sample temperatures by up to 15 °C and 5 °C, respectively. [ABSTRACT FROM AUTHOR]

• TRNSYS + MATLAB model can calculate energy saving of spectral-dependent super cool roof. • Radiative cooling roof can reduce more the energy use in a cooling-dominated climate. • When insulated, super cool roof has advantages but not in heating dominated climate. The implementation of radiative cooling materials can cool the substrate and the indoor air. It will generate energy saving for cooling in summer but increase the energy demand for heating in winter. In this study, a new method using TRNSYS integrated with MATLAB thermal model to calculate the energy saving for buildings with spectral-dependent radiative cooling roofs has been proposed. The energy-related strengths and weaknesses of applying such materials on the rooftop under various climatic and insulating conditions have been revealed, and three reference roofs have been analyzed as well. It is observed that radiative cooling roofs can reduce more annual energy use under cooling-dominated climates. Adding insulation with R-value equivalent to that of existing buildings can largely reduce the total energy consumption in all scenarios. Further increasing the thickness of the insulation layer to be equivalent to the requirement from the latest building code can only produce a tiny addition to the energy reduction. With insulation added, under cooling dominated climate or climate with mixed heating and cooling domination, the radiative cooling material still has advantages in reducing the overall energy consumption. Collectively, this study has provided reference and guidance for energy-oriented decision-making process for implementing radiative cooling roofs. It has highlighted that comprehensive analysis of local climate and building insulation condition is imperative. [ABSTRACT FROM AUTHOR]