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Graphical abstract Schematics of the PV/T system based on optical splitting film. Highlights: • Design and manufacture novel 2-axis tracking PV/T system with SiO 2 /TiO 2 thin film. • Design and fabricate SiO 2 /TiO 2 thin film with reflectance of 96.8% for PV bands. • Outdoor testing show PV cells with SiO 2 /TiO 2 thin film can decrease 3.0 K. • Power generation and efficiency of PV cells can be improved by 10% and 0.64%. • Energy and exergy efficiencies of PV/T can be improved by 4.94% and 1.03%. Abstract In a "thermally decoupled" PV/T system, photovoltaic and thermal absorbers are allowed to operate at different temperatures to utilize full-spectrum sunlight. In this study, a two-axis tracking PV/T system with a SiO 2 /TiO 2 interference thin film (irradiated by natural sunlight) was designed and fabricated initially. The SiO 2 /TiO 2 interference thin film designed by the authors achieved a high average reflectance (R ≥ 96.8%) for PV bands, with a high average transmittance (T ≥ 85%) at 1100–2500 nm. The photoelectric, photothermal, and overall efficiencies were tested and analyzed theoretically using the first and second laws of thermodynamics. Outdoor testing indicated that PV cells with SiO 2 /TiO 2 interference thin film can decrease by 3.0 K, and that the power generation and efficiency of the PV cells can be improved by 10% and 0.65%, respectively. The overall energy and exergy efficiency of the PV/T system based on SiO 2 /TiO 2 interference thin film can reach 22.72% and 18.81%, i.e., 4.94% and 1.03% higher than those without a SiO 2 /TiO 2 interference thin film, respectively. The calculated payback time was 17 years for this PV/T system. [ABSTRACT FROM AUTHOR]

Abstract This paper taken SiO 2 nanofluid spectral splitting PV/T system on as the object of the research, considering the effects of scattering, the Mie scattering theory combined with Monte Carlo Ray Tracing (Tracepro software) method was developed to study optical properties and solar energy conversion efficiency with SiO 2 nanofluid volume fraction and particle diameter. It is found that with the diameter of the nanoparticle is 5 nm, the spectral transmittance does not change with the increasing volume fraction, and the scattering effect of the nanofluid can be neglected, while the diameter of the nanoparticle is larger than 15 nm, the spectral transmittance change greatly, and the scattering needs to be considered; with the volume fraction and the diameter of SiO 2 nanofluids becoming larger, the total energy absorbed by the photothermal conversion of nanofluid increase slightly, so the scattering of SiO 2 nanofluid have minor effect on photothermal conversion of PV/T system, while the photoelectric conversion efficiency reduce because of the increasing scattering coefficient, which made total solar energy conversion efficiency reduced. [ABSTRACT FROM AUTHOR]

Semi-transparent solar-cell-based SBS PV/T system is promising. However, traditional semi-transparent solar cell-based SBS PV/T system can only produce low-grade thermal energy because the semi-transparent solar cell cannot concentrate long-wavelength sunlight. Even if a concentrating system is used, the semi-transparent solar cell must be able to withstand high temperatures, which increases the costs of the solar cell, and an additional bracket is required for installing the concentrator. In this study, the idea of using a single piece of photovoltaic (PV) to regulate the radiative transfer of the full solar spectrum for realizing the co-generation of electricity and high-grade thermal energy is proposed. A semi-transparent solar cell with a serrated groove structure at its bottom was fabricated. The solar cell can convert 400–800 nm wavelength photons to electricity, and focus 800–2500 nm wavelength photons on a small spot to produce high-temperature thermal energy. Therefore, the transmitted irradiance can be improved with a simple structure in a semi-transparent solar cell-based SBS PV/T system. [Display omitted] • Semi-transparent solar cell with serrated groove structure for SBS is proposed. • Idea of using a single piece of PV to regulate full solar spectrum is proposed. • Semi-transparent solar cell-based SBS PV/CST system is experimentally studied. • Feasibility of such novel system is validated by indoor and outdoor experiments. • The utilization efficiency of the full-spectrum solar energy can reach 77%. Semi-transparent solar cells can be used for spectral beam splitting (SBS) in which short-wavelength photons are converted to electricity and long-wavelength photons are transmitted to thermal absorbers. However, these thermal absorbers can only produce low-grade thermal energy because the semi-transparent solar cell cannot concentrate long-wavelength photons. In this study, based on the idea of regulating the radiation field to match the energy conversion on-demand, the strategy to use a single piece of photovoltaic (PV) to regulate the photon capture of the full solar spectrum for realizing the co-generation of electricity and high-grade thermal energy is proposed. A semi-transparent solar cell with a serrated groove structure at the bottom is designed and fabricated. The cell can convert 400–800 nm wavelength photons to electricity, and focus 800–2500 nm wavelength photons to a small spot to produce high-temperature thermal energy. A novel α-Si thin-film semi-transparent solar cell-based SBS hybrid photovoltaic/concentrated solar thermal system is established. The feasibility of the system is validated through indoor and outdoor experiments. The utilization efficiency of the full-spectrum solar energy can reach 77%. The high average concentrated irradiance of up to 4.31 KW/m2 transmitted through the semi-transparent solar cells is sufficient for high-temperature thermal utilization. [ABSTRACT FROM AUTHOR]

Daytime radiative cooling is an energy-free pathway to achieve cooling performance. Current radiative cooling materials with periodic photonic structures are facing a huge challenge in terms of scale expansion owing to complex preparation technology and high cost. Herein, we proposed the idea of using biomimetic wrinkle structure combined with optimized particles to achieve the efficient optical property regulation of both the solar band and "atmospheric window" band. On this basis, a large-scale radiative cooling coating with the biomimetic structure of human skin natural wrinkle, comprising high concentrations of BaSO 4 and SiO 2 particles, was demonstrated. The coating with a thickness of ~100 µm reflected ~95% of solar irradiance, and the emissivity in the "atmospheric window" band was ~96%. At noontime (11:00–13:00), in a populous area located at sea level, the average effective cooling power of ~89.6 W/m2 was recorded, and the maximum sub-ambient temperature drop can reach 8.1 °C. An outdoor-building test conducted over a year showed that the maximum average indoor air temperature of the building painted with the coating was reduced by 6.2 °C and the maximum power-saving rate of air-conditioning exceeded 50%. Our work provided a new idea for designing, fabrication, and application of high-performance radiative cooling materials. Inspired by the human skin wrinkle structure, the Bio-RC coating was designed, prepared, characterized and tested at outdoor actual buildings. [Display omitted] ● Idea of using biomimetic wrinkle structure to control optical property was proposed. ● The Bio-RC coating with biomimetic structure of human skin wrinkle was fabricated. ● The R ¯ solar = ~95% and ε ¯ atm = ~96% of Bio-RC coating were higher than that of planar coating. ● Achieved sub-ambient cooling of ~8.1 °C and average cooling power of ~89.6 W/m2. ● A year-round test of Bio-RC coating painted on an outdoor building was conducted. [ABSTRACT FROM AUTHOR]

Spectral beam splitting (SBS) hybrid PV/T system was a promising path for utilizing the full spectrum solar energy to cogenerate electricity and high-grade heat, with high conversion efficiency. To settle the balance between photoelectric and photothermal conversion performance for full spectrum solar energy utilization, the sunlight based on wavelength matching was divided into two or more parts at band-gap wavelength by a spectral beam splitter: sunlight with wavelength at and close to the band-gap of PV cell was directed to generate electricity, while the sunlight with rest wavelength was used for thermal output. SBS hybrid PV/T system can not only increase the overall efficiency, but can also decouple the photoelectric and photothermal conversion process in separated operation temperatures. The current state-of the-art review on the advancements of SBS hybrid PV/T system performed with the aid of nanofluids, nano-film and semitransparent PV cells was presented in this work, with emphasis on the latest developments during the last decade. Mechanisms of different SBS techniques, progress in system, thermodynamic and cost analyses of nanofluids, nano-film and semitransparent PV cell based SBS hybrid PV/T system were discussed in detail to give a comprehensive understanding of the nature of the full spectrum solar energy utilization and the factors impacting on the system efficiency. Though the cost increase can be offset by extra energy efficiency gain, the wavelength matching, optical losses and stability of SBS hybrid PV/T system needs to be solved for future industrial application. • Advancements of spectral beam splitting PV/T system was reviewed comprehensively. • Mechanisms of spectral beam splitting techniques was reviewed comprehensively. • Progress in system, thermodynamic and cost analyses were discussed in detail. • Problems of system needs to be solved for future application were discussed. [ABSTRACT FROM AUTHOR]

The mismatch between radiative intensity field and energy required for solar thermochemical reaction can cause serious heat waste and reduce energy conversion efficiency. To improve the energy conversion efficiency of solar to fuel, the radiative intensity regulation method to match energy conversion on demand in solar methane dry reforming is proposed in this study. The design of solar spots and biomimetic leaf hierarchical porous structures is investigated and optimized, which can realize a better radiative intensity field matching. The experimental and numerical studies show that, by using the method of regulating radiative intensity field to match energy conversion on-demand in solar thermochemical reactor, the methane conversion rate and solar thermochemical energy storage efficiency can be increased by 4.6% and 6.1%, respectively. The ideal synergy between real temperature field distribution and theoretical temperature requirement is perfectly achieved. [Display omitted] [ABSTRACT FROM AUTHOR]

Due the energy resource comes from solar energy, resulting in a high working temperature, radiation field has a significant influence on the energy storage efficiency of the high temperature solar thermochemistry. In order to promote the solar energy conversion efficiency of solar driven steam methane reforming (SMR), the idea of regulate the radiation field to be in accordance with the energy conversion on-demand is proposed and the biomimetic leaf-type hierarchical porous structure solar thermochemical reactor is introduced, which can regulate the spatial distribution of solar radiation intensity and optimize the temperature field. Combined with thermochemical kinetics and Finite Volume Method (FVM), the numerical calculation model of the SMR reaction in a biomimetic solar thermochemical reactor is established to optimize the temperature field. The effects of different reaction conditions and reactor parameters on steam methane reforming hydrogen production are analyzed. The results show that methane conversion in the biomimetic leaf-type solar thermochemical reactor is increased by 4.5%. [Display omitted] • Methane reforming in solar reactor with biomimetic leaf-type hierarchical porous is studied. • The idea of biomimetic hierarchical porous is proposed to regulate radiation field. • Biomimetic leaf-type hierarchical porous structure can increase methane conversion by 4.5%. • The best combination of structural parameters is d 1 = 1.0 mm, d 2 = 3.0 mm and L 1 = 0.02 m. [ABSTRACT FROM AUTHOR]

By exploiting the 3 K coldness of outer space as heat sink of terrestrial thermal radiation, passive daytime radiative cooling (PDRC) can achieve sub-ambient temperatures without any energy consumption, and thus exhibiting extraordinary application potentials. By pursuing the dual-band (solar and atmosphere window) optical properties to approach ideal 100 %, PDRC can maximize dissipating long wavelength infrared radiation to space and minimize absorbing sunlight simultaneously. PDRC technology can reach146 W/m2 theoretical cooling power and up to 120 W/m2 during application. This article focuses on the fundamental physics mechanism of radiative transfer and natural radiative cooling phenomena. Methodologies of infrared absorption functional group selection, optical band gap selection for solar reflection, photon and phonon enhanced resonance by micro-structure were discussed in detail to give a comprehensive instructing strategy of radiative cooling power improvement. Although PDRC technology can achieve sum-ambient temperature cooling without consuming any energy, its drawbacks such as single function of cooling and high whiteness requirement needed to hinder its large-scale application. This article also outlines the current primary applications of PDRC technology, along with summarizing the challenges and potential opportunities it encounters in practical implementation. This paper aims to provide a comprehensive overview on the fundamental physical mechanisms, methods for enhancing its power output, as well as the current state and future developments of PDRC applications, providing potential guidance for reducing greenhouse gas emissions and energy consumption. • Advancements of radiative cooling technology were reviewed comprehensively. • Fundamental physics of passive radiative cooling was reviewed comprehensively. • Material selection methodology and optical mechanism were discussed in detail. • The recent application of passive daytime radiative cooling was reviewed. • Some current challenges and potential applications were presented and discussed. [ABSTRACT FROM AUTHOR]

Abstract Radiative cooling, as a passive cooling method, is an effective way to save energy and reduce emissions by dissipating heat into space through the "sky window," without consuming any additional energy. The actual particles in the radiative-cooling coating constitute a particle cloud with non-uniform size distribution and the cooling effect is greatly affected by the spectral reflectance of the actual substrate. Herein, the radiative transfer of actual SiO 2 particles doped with a radiative-cooling coating was initially studied. Monte Carlo ray-tracing method, combined with Mie theory, was used to analyze the influence of particle size, volume fraction of particles, coating thickness, and different substrate reflectances on the spectral radiative characteristics of the radiative-cooling coating. The particles size distribution and spectral substrate reflectance were considered. The numerical results show that the maximum spectral reflectance difference between a coating with a uniform-size-distribution particle cloud and a coating with a non-uniform-size-distribution particle cloud can reach 27.3%. Furthermore, the influence of particle parameters and reflectance of the substrate on the radiative characteristics of the radiative-cooling coating is mainly concentrated in the 10–12 μm band. At 8–10 μm and 12–13 μm, the radiative-cooling coating emissivity varies little with the change of particle parameters and the reflectance of substrate, which is induced by the strong absorption of SiO 2 particles. [ABSTRACT FROM AUTHOR]

• Idea of using biomimetic structures to control solar irradiation was proposed. • The optical performance of energy-efficient glass was examined using FDTD method. • The τ e = ∼ 82 % and ρ N I R = ∼ 90 % of energy-efficient glass were higher than that of low-E glass. • Energy-efficient glass could save about 20% total electrical consumption per year. Solar irradiation is the main factor contributing to ultra-high energy demand in buildings, and windows are crucial elements with a significant effect on the energy demand in indoor spaces, affecting the cooling, heating, and artificial lighting requirements. Inspired by hercules beetle utilizing the refractive index difference of spongy multilayer structure for infrared reflection and moth-eye using the continuous refractive index change of microscopic convex structure for anti-reflection, this study proposes a visibly transparent and infrared-reflective energy-efficient glass using biomimetic structures to save energy in buildings, based on the idea of regulating the radiation to match the energy utilization on-demand. The selected materials for the proposed biomimetic energy-efficient (BE) glass are SiO 2 , Al 2 O 3 , and Ag based on the idea of using the difference in refractive index of multilayer media for radiation regulating. The transmissivity and reflectivity of BE glass are examined adopting the finite-difference time-domain (FDTD) method. The numerical analysis results demonstrate that BE glass covered with a cone-shaped biomimetic moth-eye structure and a biomimetic multilayer structure exhibits visible light transmissivity of 82.37%, in addition to an infrared light reflectivity of over 90%, which is higher than that of the currently employed low-E glasses. The proposed BE glass offers excellent energy-saving features in both hot and cold weather and the energy consumption analysis indicates that comparing with conventional common glass, it could save about 20% total electrical consumption (43.5 kWh/m2) per year [Display omitted] [ABSTRACT FROM AUTHOR]