Solar Transmittance Research Articles

Development of smart window with hydroxypropyl cellulose-acrylamide hydrogel: Effect of hydroxypropyl cellulose molecular weight on light scattering property

Reduction in the use of cooling systems can help in the reduction of CO2 emissions. Sunlight, particularly near-infrared light, entering through windows causes an increase in room temperature; therefore, a heat-shielding material that can automatically control the amount of sunlight without the use of electricity is required. Hydroxypropyl cellulose (HPC), a temperature-responsive polymer with a lower critical solution temperature (LCST), changes its optical properties in response to external temperature. This study aimed to prepare hydrogels with acrylamide (AAm) and HPC (HPC/AAm gel) and investigate the effect of HPC with different molecular weights on light transmittance and the state of HPC aggregation in hydrogels. The scattering mechanisms were discussed further. The solar transmittance of HPC/AAm gels below LCST exceeded 80%. Above LCST, the solar transmittance of HPC/AAm gels with large molecular weights decreased to 25%, whereas that with small molecular weight decreased to approximately 20%. The surface of HPC/AAm gels comprising HPC with large molecular weight exhibited numerous large pores following freeze-drying because the skeleton of the AAm and BIS inhibited the shrinkage of HPC above the LCST. In contrast, HPC/AAm gels comprising HPC with small molecular weight have a small number of pores owing to the easy shrinkage of HPC; they scatter sunlight by increasing the frequency of light collisions. Thus, the light transmittance decreases when using the HPC/AAm gels with small molecular weight.

Enhanced photochromic properties of 1D h-WO3 embedded in bio-degradable polymer for fabrication of smart windows

Fabrication of h-WO3, a photochromic material is capturing attention of the researchers as it has the ability to modulate solar light transmittance of different wavelengths automatically to adjust the indoor atmosphere. However, maintaining a balance between coloration and bleaching response of such windows have always been a great challenge. In the present paper, an attempt has been made to investigate the coloring/bleaching rates of self supporting, highly flexible h-WO3/Sg-St (Sago-Starch) nanocomposite films fabricated via solution casting technique. The samples were characterized using XRD, FESEM, TEM, Raman and FTIR spectroscopy. XRD reveal the hexagonal structure of WO3 while nano-rod morphology was ascertained using FESEM and TEM. The average diameter of nanorods calculated using TEM comes out to be 41.9 ± 1.6 nm. The capability of blocking UV region with fast UV irradiation response (<30 sec) and coloration efficiency makes these nanocomposite films a highly acceptable material for smart windows.

High-performance thermochromic YSZ/[formula omitted]/YSZ coatings for energy-saving smart windows

The reversible semiconductor-to-metal transition of vanadium dioxide (VO2) makes VO2-based coatings a promising candidate for thermochromic smart windows, reducing the energy consumption of buildings. We report on a scalable sputter deposition technique for fast preparation of strongly thermochromic YSZ/V0.986W0.014O2/YSZ coatings, where YSZ denotes Y-stabilized ZrO2, on conventional soda-lime glass at a relatively low substrate surface temperature (350 °C) and without any substrate bias voltage. The thermochromic V0.986W0.014O2 layers and the antireflection YSZ layers were deposited using a controlled high-power impulse magnetron sputtering of a single V–W and Zr–Y target, respectively. A coating design utilizing a second-order interference in the YSZ layers was applied to increase both the integral luminous transmittance (Tlum) and the modulation of the solar energy transmittance (ΔTsol). We present the phase composition (X-ray diffraction) and microstructure (high-resolution transmission electron microscopy) of the coatings and their optical properties (spectrophotometry and spectroscopic ellipsometry). The YSZ/V0.986W0.014O2/YSZ coatings exhibit a transition temperature of 33–35 °C with Tlum = 64.5% and ΔTsol = 7.8% for a V0.986W0.014O2 thickness of 37 nm, and Tlum = 46.1% and ΔTsol = 13.2% for a V0.986W0.014O2 thickness of 67 nm. The results constitute an important step to a cost-effective and high-rate preparation of large-area thermochromic VO2-based coatings for future smart-window applications.

Performance Signature of the Best Candidate-Graded Bandgap Materials for Solar Cells with Steady-State Conversion Efficiency

This is a comprehensive research endeavor focused on enhancing the efficiency of the proposed solar cell design. The integration of the simulation techniques, judicious material selection, and meticulous performance metrics showcase a methodical approach toward creating a solar cell capable of achieving high efficiency across a wide spectrum of light in the AM 1.5 G1 sun solar cell illumination spectrum. Having said this, many researchers are still working on the efficiency potential—based on external radiative efficiency (ERE), open-circuit voltage loss, and fill factor loss—of high-efficiency solar cells. The solar cell is built on aluminum-doped zinc oxide (ZnO) as a transparent conductive oxide layer; aluminum nitride (AlN) as the window layer (emitter); an SWCNT layer as the absorber layer; gallium phosphide (GaP) as the contact layer; and silicon as the substrate. The proposed solar cell transmission, reflection, and absorption relative to the variations in wavelength band spectrum are studied. The conduction and valence band energy diagrams of the solar cell design structure are simulated against the layer thickness variations for the suggested solar cell structure. Short-circuit current density and maximum power variations are clarified versus the bias voltage. Light current density is simulated versus the bias voltage (J/V characteristics curve) of the suggested solar cell design structure. The carrier generation–recombination rate is also simulated by the COMSOL simulation program versus the layer thickness of the suggested solar cell structure. The solar cell circuit design has a fill factor (FF) value of 74.31% and a power conversion efficiency value of 29.91%.

Transparent wood with heat shielding and high fire safety properties for energy saving applications

Improving the energy efficiency of buildings is critical to achieving net-zero and addressing the global energy and climate crises. By adopting simple spin-coating, a solar-blocking coating (Cs0.33WO3) was prepared on transparent wood (TW). Meanwhile, a liquid and transparent flame retardant (BPDP) was employed to enhance its fire safety. The chemical composition, physical morphology, the thermal stability, and the fire safety of the resulting heat-shielding TW were analyzed using FTIR, XRD, SEM, TGA, and Cone, respectively. Field tests and simulations were conducted to evaluate the solar-blocking capacity and energy-saving potential of the heat-shielding. The char yield (CY) of heat-shielding TW was increased from 7.3 % to 17.1 % due to the catalytic carbonization effect of BPDP and inorganic coating. The heat-shielding TW demonstrated significant solar-blocking capabilities, with a 46.63 % reduction in solar transmission compared to the original TW. The interior surface temperature (Ts) of the heat-shielding TW model was 10.2 °C lower than that of normal glass, indicating its remarkable heat shielding performance. Energy-saving simulations based on experimental findings revealed that such heat-shielding TW achieved energy savings of 9.6 %, 7.7 %, and 6.2 % in Hong Kong, Shanghai, and Singapore, respectively, when compared to traditional glazing glass. Overall, the prepared heat-shielding TW shows promise as a novel candidate for window applications, offering improved energy efficiency.

Ideal thermochromic smart window in a south-facing office room of China considering daylighting and energy performance

ABSTRACT Thermochromic (TC) smart window which allows modulating the transmission of solar heat energy and sunlight in response to environmental conditions has great potential for improving the building energy and daylighting performance simultaneously. In this study, the multi-objective optimization method is used to determine the ideal optical properties of TC windows. Parametric assessment is firstly conducted to investigate the influence of several crucial parameters. Multi-objective optimization is then carried out by applying Non-dominated Sort Genetic Algorithm-III, maximizing daylight availability and building energy efficiency. Finally, the decision-making of the Pareto frontier is performed to achieve the ideal TC windows in 32 representative cities in different climatic zones of China. Results demonstrate that increasing the luminous transmittance at low-temperature and decreasing luminous transmittance modulation ability are beneficial to daylighting and energy performance. Lower solar transmittance at low-temperature contributes to building energy savings in Beijing, Shanghai, Guangzhou and Kunming, except for Harbin. Higher solar transmittance modulation ability is desired for building energy efficiency. The optimum value for the transition temperature is in the range of 23.67–38.85°C. The building energy consumption can be reduced by 13.01%, and the desired daylighting hours can be improved by 8.90%, relative to the clear double-glazed windows.

Thermo-optical performance of building glass under salt sedimentation

The phenomenon of salt sedimentation on the building glass surface occurs in coastal salt-fog climates, leading to the changes in surface heat transfer characteristics and optical properties, which affects the indoor environment and gradually reduces building energy performance. Regrettably, there remains a paucity of research concerning the impact of salt sedimentation on the thermal and optical performances of building glass. This study investigated the salt sedimentation features of building glass using an indoor accelerated test, and explored the relationships between surface heat transfer coefficients, optical properties and salt sedimentation. As the spray duration grew, the sedimented salt stains appeared more dispersed and less dense, but their dimensions increased, exhibiting an exponential growth tendency. The salt sedimentation per unit area grew logarithmically with the spray duration, with the magnitudes being 14.4 to 40.0 mg/m2 and 15.6 to 44.3 mg/m2 under 5% and 10% brine concentration conditions, respectively. The convection heat transfer coefficient (CHTC) and radiative heat transfer coefficient (RHTC) showed a linear monotonic increase with the salt sedimentation, in contrast to the control condition, with the maximum growth rates reaching 178.7% and 97.2%, respectively. The extended CHTC model could be used to calculate the CHTC regarding the impact of salt sedimentation and wind speed. The entire solar spectral transmittance and reflectance was affected by salt sedimentation, and the visible light transmittance, reflectance, hemispherical emissivity, and shading coefficient of low-E and clear glasses all decreased linearly with the increase of salt sedimentation.

Building integrated concentrating photovoltaic window coupling luminescent solar concentrator and thermotropic material

Building integrated concentrating photovoltaic window (BICPVW) has been proven to be used in sustainable building transparent envelopes. Unfortunately, the balance between optical and electrical properties is difficult. This paper proposes a building integrated concentrating photovoltaic window coupling luminescent solar concentrator and thermotropic material (LT-BICPVW). The luminescent solar concentrator and thermotropic layer were fabricated by bulk polymerization and glass sandwich structure, respectively. Optical models are built based on the optical properties of optical waveguide and thermotropic layer, and optical simulations are performed with Monte Carlo ray tracing technology. Window prototypes are characterized under controlled indoor experimental conditions. The experiment found that as the temperature of the thermotropic film increased from 30 °C to 42 °C, the solar transmittance of LT-BICPVW decreased by 43.3%, and the maximum output power increased by 25%. Compared with, building integrated concentrating photovoltaic window coupled with thermotropic material (T-BICPVW), the power conversion efficiency was improved by 59% at the termination temperature. The LT-BICPVW system can effectively reduce solar heat gain and avoid glare hazards, while using renewable energy to significantly increase power output. A series of predictions are made using validated optical model and tracking technique to better guide the design of PV windows in actual buildings.

Double‐Sided Indium Tin Oxide Photonic Crystal Glazing for All‐In‐One Multifunctional Rigid and Flexible Windows

AbstractFuturistic and high‐performance windows are required to perform multiple functions, occasionally including photo‐ and electricity‐associated functions. For each function, suitable components must be added, but this might result in complicated window structures that can impede the basic window function: high visibility. Therefore, platform technology is necessary to simplify window structures with minimal components for basic functions while adding specific desirable functions. This study proposes non‐close‐packed indium tin oxide (ITO) photonic crystals coated on both sides of rigid and flexible windows. Their photonic bandgap frequencies (stopbands) are tunable through the modulation of the ITO thickness or lattice constant, thereby manipulating the window light transmittances. When the stopband lies in bluelight (400–500 nm), the window can simultaneously block the bluelight and exhibit high transmittance (antireflection function) at 500–1500 nm. The dual functions are enhanced with double‐sided photonic crystal windows: the optical contrasts in solar irradiance transmittances (ΔTsol) between 500–1500 and 280–500 nm are maximally 37.1% and 47.2% for the glass and polyimide windows, respectively. Additionally, the windows can have dual stopbands. Moreover, the window stopbands can enhance the photoluminescence intensities of quantum dot films. This simplistic window is applicable to houses/buildings, automobiles, electronics, displays, and energy industries.

Active and passive modulation of solar light transmittance in a uniquely multifunctional dual-band single molecule for smart window applications

Functional materials may change color by heat and electricity separately or simultaneously in smart windows. These materials have not only demonstrated remarkable potential in the modulation of solar radiation but are also leading to the development of indoor environments that are more comfortable and conducive to improving individuals' quality of life. Unfortunately, dual-responsive materials have not received ample research attention due to economic and technological challenges. As a consequence, the broader utilization of smart windows faces hindrances. To address this new generational multi-stimulus responsive chromic materials, our group has adopted a developmental strategy to create a poly(NIPAM)n-HV as a switchable material by anchoring active viologen (HV) onto a phase-changing poly(NIPAM)n-based smart material for better utility and activity. These constructed smart windows facilitate individualistic reversible switching, from a highly transparent state to an opaque state (thermochromic) and a red state (electrochromic), as well as facilitate a simultaneous dual-stimuli response reversible switching from a clear transparent state to a fully opaque (thermochromic) and orange (electrochromic) states. Absolute privacy can be attained in smart windows designed for exclusive settings by achieving zero transmittance. Each unique chromic mode operates independently and modulates visible and near-infrared (NIR) light in a distinct manner. Hence, these smart windows with thermal and electric dual-stimuli responsiveness demonstrate remarkable heat regulation capabilities, rendering them highly attractive for applications in building facades, energy harvesting, privacy protection, and color display.

Investigation of photochromic behavior of biodegradable MoO3/Sg-St nanocomposites

Now a days, the synthesis of α-MoO3 based photochromic materials are a subject of many investigations as they can modulate solar light transmittance automatically, according to wavelength, in response to UV irradiation and hence can adjust the indoor atmosphere to reduce the consumption of energy. In the present work, an attempt has been made to investigate the relation between coloring/bleaching rates of self-supporting, highly flexible α-MoO3/Sg-St (Sago-Starch) nanocomposites (NCs) fabricated via solution casting technique. The prepared samples were characterized using FESEM, XRD, FTIR, and UV–Vis–NIR spectroscopy. Nano-sheet morphology of the synthesized sample was ascertained using FESEM while XRD reveals the orthorhombic structure of MoO3 with an average crystallite size of 135 nm. The average thickness of nanosheets comes out to be 111.57 nm (using FESEM). FTIR spectroscopy depicts the strong interaction between α-MoO3 and Sg-St polymer confirming the successful incorporation of α-MoO3 in the Sg-St matrix. The value of Eg for virgin Sg-St comes out to be 4.56 ± 0.12 eV and decreases to 2.54 ± 0.07 eV for 10 wt% α-MoO3/Sg-St NC while the refractive index (n) increases from 1.53 for virgin Sg-St to 2.11 for 10 wt% α-MoO3/Sg-St NC at 450 nm wavelength. The value of tensile strength for virgin Sg-St is found to be 9.54 which increases to 17.07 after incorporation of 1 wt% of α-MoO3 suggesting the strong interfacial interaction of nanofiller with polymer matrix. The prepared NCs exhibited a fast response to UV exposure (<30 s) with high coloration efficiency; which makes them a highly acceptable material for photochromic smart windows. The maximum coloration efficiency ∼0.6071 and RDR (%) value of 75.29 corresponds to 1 wt% α-MoO3/Sg-St NC.

Detailed pathway for a fast low-temperature synthesis of strongly thermochromic W-doped VO2 films with a low transition temperature

We report the discharge characteristics, and population of chosen atomic neutral (V, O and Ar) and ionic (V+, V2+, O+ and Ar+) species in the discharge during low-temperature (350 °C) depositions of W-doped VO x films onto a 170 nm thick Y-stabilized ZrO2 layer on a 1 mm thick conventional soda-lime glass. The depositions were performed using reactive deep oscillation magnetron sputtering with a pulsed O2 flow control and to-substrate O2 injection into a high-density plasma in front of the sputter V-W target. The pre-selected critical values of the oxygen partial pressure were in the range from 82 mPa to 92 mPa. Optical emission spectroscopy proved a relatively high density of O atoms in front of the substrate, which is important for production of the W-doped VO2 films. It was found that setting of the amount of O2 in the gas mixture determines not only the elemental and phase composition of the films and their deposition rate but also the crystallinity of the thermochromic VO2 phase in them. The crystalline W-doped VO2 films with a low transition temperature of 28 °C exhibited a high modulation of the solar energy transmittance of 8.9%. The results are important for further improvement of this new scalable sputter deposition technique for a fast (53 nm min−1 at a target-substrate distance of 100 mm in this work) low-temperature synthesis of high-performance durable thermochromic VO2-based multilayer coatings designed for smart-window applications.

"Warm in Winter and Cool in Summer": Scalable Biochameleon Inspired Temperature-Adaptive Coating with Easy Preparation and Construction.

The highly reflective solar radiation of passive daytime radiative cooling (PDRC) increases heating energy consumption in the cold winter. Inspired by the temperature-adaptive skin color of chameleon, we efficiently combine temperature-adaptive solar absorption and PDRC technology to achieve "warm in winter and cool in summer". The temperature-adaptive radiative cooling coating (TARCC) with color variability is designed and fabricated, achieving 41% visible light regulation capability. Comprehensive seasonal outdoor tests confirm the reliability of the TARCC: in summer, the TARCC exhibits high solar reflectance (∼93%) and atmospheric transmission window emittance (∼94%), resulting in a 6.5 K subambient temperature. In the winter, the TARCC's dark color strongly absorbs solar radiation, resulting in a 4.3 K temperature rise. Compared with PDRC coatings, the TARCC can save up to 20% of annual energy in midlatitude regions and increase suitable human hours by 55%. With its low cost, easy preparation, and simple construction, the TARCC shows promise for achieving sustainable and comfortable indoor environments.

Assessment and ANN model development of natural light transmittance of light-transmitting concrete

This study aims to reveal the potential of Light-transmitting concrete (LTC) in transmitting natural light or sunlight, and to investigate the relationship between fibre diameter, fibre spacing, solar incidence angle, surface area, and light transmittance properties. The artificial neural network model as well as explicit equations from the model were developed to predict the light transmittance of LTC. The surface area was altered by varying LTC block arrangements from one to six. It was found that light incidence angle significantly affected the light transmittance of LTC. The highest light transmittance of LTC was achieved near solar noon, but it decreased drastically as soon as the solar incidence angle exceeded the acceptance angle. The effect of the LTC surface area and solar incidence angle on light transmittance diminished with a smaller fibre diameter or larger fibre spacing. The ANN model and explicit equations developed from the network provide good accuracy in predicting light transmittance of LTC.

Performance analysis of grey PV module with optical characteristics

Coloured PV modules improve the exterior design of normal PV modules and improve the aesthetics as well through various colour characteristics. In particular, for a BIPV system installed in place of conventional building envelope material, a coloured PV module can be efficiently utilized for harmonization with the building exterior materials, and to improve design. However, the electrical efficiency of coloured PV modules can decrease depending on the colour characteristics. In this study, the electrical performance characteristics of a coloured PV module with grey front glass (digital printing) were analysed through optical and outdoor performance tests and compared to those of a normal PV module with clear glass. Based on optical test results, the total solar transmission (S-Factor) of the grey glass was lower by approximately 15% compared to that of the clear glass. Similarly, electrical efficiency of the grey module was decreased due to its colourisation compared to the normal PV module. Outdoor experimental results showed that the temperature of the grey PV module was up to 3 °C lower than that of the normal PV module.

Simulating annual autoregulation of daylight by grating smart window with angular-selective transmission

As a basis for further development of the BPS computer software, a method for simulating the characteristics of buildings with grating smart windows is proposed. This novel smart technology provides annual autoregulation of light and solar transmission due to an optical filter with two thin-film gratings located on window surfaces to adapt to the Sun’s trajectory and achieve angular-selective transmission. The previously developed methods for calculating the filter parameters are modified and on their basis new equations for the BPS software are obtained, which differ from the existing ones, unsuitable for grating smart windows due to their distinctive properties. The fundamentals of BPS for a building with such smart windows are considered in detail in order to select the individual parameters of grating windows for all rooms where they are needed. Calculation methods are validated by numerical simulation of the transmittance, sDA, ASE, DGP and by illuminance measurements.

Preparation and Characterization of Low- emissivity AlN/Ag/AlN Films by Magnetron Cosputtering Method

AlN and Ag thin films were deposited independently on the Si(100) wafers and glass slides by sputtering techniqueat various times to find the optimum deposition times for coating AlN and Ag films layers. The results obtained fromglazing-incident X-ray diffraction (GIXRD), field-emission scanning electron microscopy (FE-SEM), and transmittancemeasurements showed that the optimum deposition time for coating AlN and Ag film layers were 40 min and 15 scorresponding to the film thickness of 46.7 and 19.6 nm, respectively. The optimum deposition times were used forcoating AlN and Ag films in the multilayer AlN/Ag/AlN film stack. Then, the multilayer AlN/Ag/AlN film stack wasdeposited on the glass slide for transmittance measurement and a test glass plate with a size of 10 cm x 10 cm for infraredprotection testing. The average solar transmittances in the visible range ( = 380-780 nm) and in the near infrared range( = 780-2,000 nm) were found to be 48.05 and 15.17%, respectively which are comparable with those of a commercialglass.

Influence of rejuvenating pruning on the potential productivity of the apple tree

The period of operation of intensive orchards is 15 years. At the age of 6-7 years, the quality of fruits decreases sharply and the frequency of fruiting increases. In order to extend the productive period of the orchard, an experiment was laid on the effect of rejuvenating pruning on the productivity of an apple tree, depending on the variety-rootstock combination. In the course of this scientific study, in the period from 2020 to 2022, results were obtained indicating the presence of the potential for productivity of apple varieties of the Kazakhstani selection Voskhod and Talgarskoe on the introduced forms B 7-35, Arm 18 and the rootstock of the Kazakhstani selection Zhetysu 5 in which the solar radiation transmittance was from 0.45% to 0.77%. On this basis, all the studied varieties are superior to the control variant. It also improved the light space inside the tree crown, which increased the number of young growth points and contributed to the awakening of reserve buds. Young growing fruits, located in the middle and central parts of the crown, are better supplied with nutrients after pruning than before pruning.

Using pretrained machine learning models to predict luminous and solar transmittance controllability of liquid crystal/polymer composites from microstructural images.

Polarized optical microscopy (POM) images of polymer network liquid crystals (PNLCs) were first analyzed using a pretrained machine learning model for feature extraction and hierarchical clustering. The analyses worked well in predicting and improving the thermoresponsive changes individually in direct luminous and hemispheric solar transmittance, both of which are crucial properties of energy-saving smart windows. The features of a 1280 × 1920-pixel color POM image were extracted by the latest pretrained algorithm, EfficientNet-B7, as a 2560-dimensional vector and then reduced into a two-dimensional space for clustering and visualization using the uniform manifold approximation and projection (UMAP) algorithm while efficiently preserving the global structures of the distance relationship in a high-dimensional space. The feature vectors in the UMAP space were correlated with the thermoresponsive transmittance and classified using hierarchical clustering analysis. The extracted features belonging to some clusters were also correlated with the fabrication parameters. The PNLCs here were produced from various raw materials under different fabrication conditions. These analyses and predictability are extensively applied to different PNLCs for stimuli-responsive optical devices, such as solar- and privacy-control windows.

Enhancing thermochromic properties of VO2 amorphous films on glass substrates by Sn-W co-doping

Co-doping is an effective method for VO2 films to meet the requirements of smart window applications. In this research, we prepared pure VO2, Sn-doped, and Sn-W co-doped amorphous films on glass substrates. Compared with pure and Sn-doped VO2 films, Sn-W co-doped samples showed better thermochromic properties. For the 4.8 % Sn-2.1 % W co-doped sample, the luminous transmittance (Tlum) reached 76 %, the metal-insulator transition (MIT) temperature (Tc) decreased to 46.7 °C, the solar transmittance modulation capacity (ΔTsol) was maintained at around 5.2 %, and the near-infrared modulation capacity (ΔTIR) was up to 13.5 %. These results show that co-doping Sn and W into VO2 is feasible for smart window applications.