Solar Conversion Research Articles

One-step fabrication of unique 3D/2D S, O-doped g-C3N4 S-scheme isotype heterojunction for boosting CO2 photoreduction

Solar irradiation-based CO2 conversion to energy-rich products is an efficient way to reduce excessive CO2 emissions and solve resource depletion. Unfortunately, achieving a cost-effective and dependable method for converting CO2 is still a significant challenge. Here, we introduce a hydrothermal approach followed by calcination to design a new-fashioned 3D S-doped g-C3N4/2D O-doped g-C3N4 (3D/2D SOCN) based step-scheme (S-scheme) heterojunction as an efficient photocatalysts for CO2 reduction. The adjusted sample demonstrated significantly greater CO2 photoreduction conversion rates compared to the blank control, including 3D S-doped g-C3N4 (3D SCN), 2D O-doped g-C3N4 (2D OCN), and bulk g-C3N4 (CN). The exceptional photocatalytic performance can be ascribed to multiple factors, including the S-Scheme isotype heterojunction that suppresses the recombination of photogenerated charge carriers, the material's high specific surface areas, which highly enhance the abundance of active sites, and the synergistic effect of the heteroatom as a dopant. The validity of the S-Scheme photogenerated charge transfer process is supported by measuring the work function and electron paramagnetic resonance (EPR). This research presents a practical method for fabricating multi non-metal-doped S-scheme isotype heterojunction photocatalysts that display remarkable efficiency for solar fuel conversion.

Intermediate Formation of Macrocycles for Efficient Crystallization of 2D Covalent Organic Frameworks with Enhanced Photocatalytic Hydrogen Evolution

AbstractCovalent organic frameworks (COFs) have gained significant attention as key photocatalysts for efficient solar light conversion into hydrogen production. Unfortunately, the harsh synthetic conditions and intricate growth process required to obtain highly crystalline COFs greatly hinder their practical application. Herein, we report a simple strategy for the efficient crystallization of 2D COFs based on the intermediate formation of hexagonal macrocycles. Mechanistic investigation suggests that the use of 2,4,6‐triformyl resorcinol (TFR) as the asymmetrical aldehyde build block allows the equilibration between irreversible enol‐to‐keto tautomerization and dynamic imine bonds to produce the hexagonal β‐ketoenamine‐linked macrocycles, the formation of which could provide COFs with high crystallinity in half hour. We show that COF‐935 with 3 wt % Pt as cocatalyst exhibit a high hydrogen evolution rate of 67.55 mmol g−1 h−1 for water splitting when exposed to visible light. More importantly, COF‐935 exhibits an average hydrogen evolution rate of 19.80 mmol g−1 h−1 even at a low loading of only 0.1 wt % Pt, which is a significant breakthrough in this field. This strategy would provide valuable insights into the design of highly crystalline COFs as efficient organic semiconductor photocatalysts.

Intermediate Formation of Macrocycles for Efficient Crystallization of 2D Covalent Organic Frameworks with Enhanced Photocatalytic Hydrogen Evolution.

Covalent organic frameworks (COFs) have gained significant attention as key photocatalysts for efficient solar light conversion into hydrogen production. Unfortunately, the harsh synthetic conditions and intricate growth process required to obtain highly crystalline COFs greatly hinder their practical application. Herein, we report a simple strategy for the efficient crystallization of 2D COFs based on the intermediate formation of hexagonal macrocycles. Mechanistic investigation suggests that the use of 2,4,6-triformyl resorcinol (TFR) as the asymmetrical aldehyde build block allows the equilibration between irreversible enol-to-keto tautomerization and dynamic imine bonds to produce the hexagonal β-ketoenamine-linked macrocycles, the formation of which could provide COFs with high crystallinity in half hour. We show that COF-935 with 3 wt % Pt as cocatalyst exhibit a high hydrogen evolution rate of 67.55 mmol g-1 h-1 for water splitting when exposed to visible light. More importantly, COF-935 exhibits an average hydrogen evolution rate of 19.80 mmol g-1 h-1 even at a low loading of only 0.1 wt % Pt, which is a significant breakthrough in this field. This strategy would provide valuable insights into the design of highly crystalline COFs as efficient organic semiconductor photocatalysts.

Novel anti-freeze and self-adhesive gellan gum/P3HT/LiCl based gel electrolyte for quasi solid dye sensitized solar cells

Gellan gum/poly(3-hexylthiophene)/lithium chloride gels with different ratios of LiCl containing I-/I3- liquid electrolyte were synthesized in one-pot reaction and used as gel electrolytes in the dye sensitized solar cells (DSSCs). Due to hygroscopic nature of LiCl, presence of 6 M LiCl was prevented shrinkage of gels by blocking water loss. In addition, by increasing LiCl amount in prepared gels, surface energy values increased that can cause good adhesive property. Furthermore, LiCl contained prepared gels were flexible at about − 20°C after being kept at − 60°C for 24 h. Anti-freezing and self-adhesive gel electrolytes can extend the usage of DSSCs at different conditions and cell architecture. Finally, with the usage of gel electrolytes, open circuit potentials of prepared DSSCs were increased above 1 V and high solar conversion efficiency was obtained at a 4.64% by using 6 M LiCl. The developed gel electrolyte can be a good alternative for solving the leakage and evaporation problems of liquid electrolytes used in DSSCs.

Janus film evaporator with improved light-trapping and gradient interfacial hydrophilicity toward sustainable solar-driven desalination and purification

Solar-driven desalination and purification offers a promising approach to water treatment, while the clean water yields under natural sunlight can be further increased by developing well-designed evaporators. Herein, a TiN/GO//GO Janus film was fabricated to realize the synergetic effect of effective photothermal conversion and water transportation. The top TiN/GO hybrid layer possesses high solar absorption and thermal conversion efficiency, while the bottom GO layer promotes expeditious water transport. Moreover, the film maintains gradient interfacial hydrophilicity due to the reservation of oxygen-functional groups, which facilitate the formation of thin liquid film at water-film interface and increase heat utilization efficiency. Therefore, the Janus film is demonstrated to possess high evaporation rate of 1.70 kg m−2 h−1 for various non-conventional water resources under 1 solar illumination, which is comparable or better than most of the film evaporators. The excellent durability is demonstrated in a wide acid–base range (pH 2–11) and salinity range (0–250‰) over 30 cycles. The outdoor device with Janus film exhibits daily water yield of 7.44 kg m−2, indicating a potential application in efficient solar-driven desalination and non-conventional water treatment.

Synergistic effect of electrochemically fabricated polyaniline nanofibers and silver for efficient solar steam generation

Solar steam generation (SSG) has been recognized as a promising and green technology to resolve the scarcity of drinking water in the near future. On the other hand, there are still several challenges associated with SSG system to its practical utilization. Design of suitable photothermal materials with high solar absorption and conversion efficiency is one of the challenges associated with the SSG technology. Herein, we demonstrated a strategy for the fabrication of bilayer structure of porous polyaniline (PANI) nanofibers and conducting silver (Ag) on a carbon cloth (PANI/Ag@CC) substrate using a facile electrochemical deposition approach. As prepared binder-free PANI/Ag@CC showed an excellent steam generation rate of 2.21 kg/m2h with superior evaporation efficiency of 98.0 % under 1 sun illumination when used for the SSG application. Furthermore, the bilayered PANI/Ag@CC exhibited excellent durability, effective seawater desalination and wastewater purification. The superior SSG performance is associated with the synergistic effect of surface plasmon resonance of Ag and porous PANI nanofibers. Therefore, practically simple fabrication, outstanding evaporation rate and water purification properties convince that the PANI/Ag@CC structure can be a promising candidate for SSG applications.

Insights into Perovskite Film Formation Using the Hybrid Evaporation/Spin-Coating Route: An In Situ XRD Study

The hybrid evaporation/spin-coating route has been widely used for fabrication of highly efficient fully textured perovskite silicon tandem solar cells and is a promising route for upscaling. Nevertheless, fundamental aspects of the fabrication process such as the kinetics of perovskite crystallization and the influence of the environmental conditions remain uncertain. In this work, we investigate the individual stages of tandem-relevant 1.66 eV bandgap perovskite formation and map the structural evolution from the precursor to the perovskite phase until the degradation phase. We find that the kinetics of these transitions can be tuned by varying the humidity or the temperature during the annealing treatment. Specifically, increasing the relative humidity up to 50% elevates the reaction rate and results in improved perovskite quality. This is directly reflected in the solar cell power conversion efficiency with a 3%abs increment on average. While high annealing temperatures are found to promote large grain size growth and enhanced crystallinity, we observe that above 150 °C the remnant PbI2 precursor compromises film quality. Furthermore, the perovskite formation kinetics is fitted using the Johnson–Mehl–Avrami–Kolmogorov model. The Avrami constant is found in the range 0.66–0.87, indicating a diffusion-controlled one-dimensional growth process with an associated activation energy of 54.49 kJ/mol. Using in situ XRD, this work gives insights on key process parameters to ensure reproducible synthesis of high-quality perovskite films.

Oxygen‐Induced Reversible Degradation of Perovskite Solar Cells

After remarkable progress over the past decades, perovskite solar cells (PSCs) currently exhibit efficient solar power conversion efficiency. However, the environmental instability of perovskite materials and devices is still a serious issue, impeding the future commercialization of this technology. Herein, why PSCs degrade in air is investigated and it is found that one of the critical reasons for the air‐induced PSC degradation is the doping of the 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobi‐fluorene (spiro‐OMeTAD) hole‐transport layer with oxygen. Photoelectron yield spectroscopy reveals that the hole‐transport level of the spiro‐OMeTAD layer becomes deeper by oxygen doping, increasing an energy barrier for hole extraction. In other words, decreased hole extraction at the perovskite/spiro‐OMeTAD interface induces the degradation of PSCs in air. However, this oxygen‐induced degradation of PSCs is reversible to some extent by storing PSCs in a vacuum to remove oxygen. In contrast, no detectable degradation of the perovskite light absorber is observed after ≈600 h of air exposure from the results of morphological and structural characterizations. These aspects provide a deeper understanding of PSCs degradation, giving insight into improving long‐term durability in air in the future.

Nonunit Protection of Parallel Lines Connecting Solar Photovoltaic Plants

Fault current control by solar plant converters introduces different fault characteristics compared to conventional synchronous generator-based systems resulting in numerous issues to the available protection methods. In this article, the issues with conventional distance relaying is analyzed while protecting parallel lines connecting solar plant to grid and a new protection method is proposed using local voltage and current data. The proposed nonunit protection method derives positive sequence reactive powers for both lines for different solar plant operating conditions and uses their difference to ensure correct zone-1 protection. For faults during single circuit operation, the method includes an additional scheme comprising of instantaneous zero-sequence overcurrent check and delayed distance relaying to derive correct protection decision. Performance of the proposed nonunit protection method is tested for parallel lines connecting the solar plant in a 39-bus test system for different situations using PSCAD/EMTDC simulated data and found to be accurate. Comparative assessment reveals the high reliability of the proposed method.

A Minimal Drift MPPT Technique for Solar Grid-Tied Multilevel Converter by Multiobjective Swarm

A new multi-objective minimal-drift maximum power point tracking (MOMD-MPPT) technique is introduced to harness maximum power from single photovoltaic (PV) array fed multilevel converter (MLC). A drift in voltage arises with conventional MPPT techniques, which is minimized in this work with a new multi-objective solution. A new swarm optimization algorithm (NSOA) is used for MPPT, which combines the concept of swarm intelligence and pressure gradient force. It provides a minimal drift phenomenon for the solar MLC. Acceleration factor of the swarm particles in NSOA relies on pressure difference and distance. It leads to smoother convergence towards the operating point without trapping in the local minima. The presented algorithm is compared with well-known MPPT algorithms. Simulated results analyze the performance of MOMD-MPPT considering upper and lower voltage drift for PV fed MLC. Later, this algorithm is experimentally validated for a single PV array fed grid-tied multilevel converter. Recorded results show that the algorithm has minimal drift and improves the system performance in dynamic solar conditions.

Strong photo-thermal coupling effect boosts CO2 reduction into CH4 in a concentrated solar reactor

This study is dedicated to solving the problems of low energy utilization and low yield in the conventional photocatalytic CO2 reduction process. Herein, we constructed a novel concentrated solar (light) reactor and enabled the titanium foam-based monolithic photocatalyst TF@TNT/0.4CoOx-0.1CuO to improve the solar energy utilization efficiency and CO2 conversion rate by concentrating light and its thermal effect. We found that the yield of CH4 increased up to 220 times (from 0.53 µmol/cm2 to 116.4 µmol/cm2) when the light intensity of the reactor was increased from 400 mW/cm2 to 4266 mW/cm2 (10.6 times). Meanwhile, the solar-to-fuel conversion efficiency was improved up to 0.35% in the concentrated solar (light) reactor. We further investigated the origin of the photothermal coupling effect with concentrated light through the electrochemical and photochemical measurements. It shows that the concentrated light can further lower the reaction barrier (from 41.62 to 31.51 kJ/mol) and the induced photothermal coupling effect could significantly increase the yield. This provides a valuable strategy for the efficient and environmentally friendly utilization of CO2 using solar energy.

Precise Tuning Near‐Infrared Photothermal Conversion of Ternary Cocrystals via Supramolecular Interactions

Effective utilization of solar energy through cocrystal strategy is still a considerable challenge. Herein, the ternary cocrystal strategy is subtly applied to broaden the absorption of cocrystals, resulting in an efficient solar photothermal conversion (PTC). Specifically, the donors of triphenylene (T) and perylene (P) and guest molecules anthracene (AT), pyrene (PY), and perylene (P) are self‐assembled with 7,7,8,8‐tetracyanoquinodimethane (TCNQ) to obtain five ternary cocrystals (AT‐T‐TCNQ, PY‐T‐T‐TCNQ, AT‐P‐TCNQ, PY‐P‐TCNQ, and P‐P‐TCNQ). The PTC of ternary cocrystals can be regulated by changing the number of benzene rings of donor and guest molecules, which may be attributed to the π–π and C–H···π intermolecular interactions. Femtosecond transient absorption and excited‐state theoretical calculations confirm that the intense π–π stacking interactions facilitate the light‐harvesting capability, while the weak C–H···π interactions are conducive to molecular stacking loosening and thus facilitate the rotation of C(C ≡ N)2, which promotes nonradiative transition to achieve the efficient PTC. As expected, the PTC efficiencies of AT‐T‐TCNQ, PY‐T‐TCNQ, AT‐P‐TCNQ, PY‐P‐TCNQ, and P‐P‐TCNQ are 59.62%, 63.07%, 81.72%, 79.06%, and 87.72%, respectively, under 808 nm irradiation. Due to the P‐P‐TCNQ having excellent near‐infrared PTC efficiency, it is applied in a solar‐driven interfacial heating evaporation system, gaining a decent evaporation efficiency (83.1%).

Scalable Bacterial Cellulose-Based Radiative Cooling Materials with Switchable Transparency for Thermal Management and Enhanced Solar Energy Harvesting.

Radiative cooling materials that can dynamically control solar transmittance and emit thermal radiation into cold outer space are critical for smart thermal management and sustainable energy-efficient buildings. This work reports the judicious design and scalable fabrication of biosynthetic bacterial cellulose (BC)-based radiative cooling (Bio-RC) materials with switchable solar transmittance, which are developed by entangling silica microspheres with continuously secreted cellulose nanofibers during in situ cultivation. Theresulting film shows a high solar reflection (95.3%) that can be facilely switched between an opaque state and a transparent state upon wetting. Interestingly, the Bio-RC film exhibits a high mid-infrared emissivity (93.4%) and an average sub-ambient temperature drop of ≈3.7 °C at noon. When integrating with a commercially available semi-transparent solar cell, the switchable solar transmittance of Bio-RC film enables an enhancement of solar power conversion efficiency (opaque state: 0.92%, transparent state: 0.57%, bare solar cell: 0.33%). As a proof-of-concept illustration, an energy-efficient model house with its roof built with Bio-RC-integrated semi-transparent solar cell is demonstrated. This research can shine new light on the design and emerging applications of advanced radiative cooling materials.

On the analysis of thermosolutal mixed convection in differentially heated and soluted geometries beyond rectangular

PurposeThis paper aims to study the impact of convexity and concavity of the vertical borders on double-diffusive mixed convection. In addition, the study of entropy generation is performed. This numerical study has been carried out for different patterns of wavy edges to reveal their effects on heat and mass transfer phenomena.Design/methodology/approachFour different flow features are treated by varying the directions of convexity and concavity of the vertical walls. A uniform temperature, as well as concentration distributions, are introduced to the left border while keeping a cold temperature and low concentration for the right border. The horizontal boundaries are in adiabatic condition. The upper border of the chamber is moving in the right direction with an equal speed. The governing Navies–Stokes equations are designed to describe energy and species transport phenomena, and these equations are solved by compact scheme.FindingsThe investigated results are analyzed for various parameters, namely, Prandtl number, Richardson number, thermal Grashof number, Lewis number, Buoyancy ratio and amplitude of the wavy walls. It is observed that the thermal and solutal transfer performance becomes effective with lower Richardson numbers. The results reveal that the concavity and convexity of the side borders of the cabinet can control the thermosolutal performance. It is also observed that among all wavy chambers, Case-4 records maximum thermosolutal transfer rate, while Case-3 attains minimum thermosolutal transfer rate.Originality/valueThis work is an example of solar thermal power conversion, power collection systems, systems of energy deficiency, etc.

Influence of heat enhancement technique on the thermal performance of solar water heater for sustainable built environment. Start-of-the-art review

Solar water heater (SWH) is important and low-cost technology for transforming solar radiation into heat energy that is utilized for commercial and industrial purposes. However, due to different advantages, this technology still suffers from poor thermal efficiency and thermal losses from the collector. The various reasons responsible for the poor heat transfer rate of SWH are heat losses from the system and different geometrical shapes of hindrance promoters. The researcher is working on various innovative methods to ameliorate the effectiveness of solar water heating systems (SWHS) by using various heat enhancement methods. The solar thermal conversion efficiency is found to be 70% as compared to solar electrical direct conversion system, which is around 17%. The different heat enhancement techniques, like twisted tape turbulator and their shape, etc., play a very remarkable role in ameliorating the effectiveness of SWHS. This review work abridges the previous research work with different heat enhancement techniques, including the coating effect of pipes, collector design, use of PCM, and different geometrical shapes of turbulence promoters. The twisted tape provides better η as compared to other heat enhancement techniques.

Model construction and electro-thermal-hydrogen co-generation performance for multi-section compound parabolic concentrator

Non-imaging solar concentrator has many applications in solar thermal conversion and photovoltaic power generation because of its performance characteristics such as no tracking, stable light concentration, compact structure and easy integration. For this purpose, this paper conducts a study on the non-imaging concentrator based on the optimized design of the concentrating surface structure for photovoltaic electric generation, thermal energy recovery and direct-drive hydrogen production. Firstly, a theoretical construction of a mathematical model of the solar Concentrating Photovoltaic and Photo-thermal (CPV/T) system with electricity-thermal-hydrogen co-generation and a numerical solution path for the Current and Voltage (I-V) characteristic curve is presented. Moreover, an integrated CPV/T system experimental setup is constructed outdoors and its power generation, heat collection and hydrogen production processes are measured. Finally, it is found that the average electrical efficiencies of the CPV/T system are 13.03 % and 13.29 % for theory and experiment, respectively. The theoretical and experimental average thermal efficiencies are 27.47 % and 27.24 %, respectively. The theoretical and experimental average hydrogen production rates based on Maximum Power Point Tracking (MPPT) control are 19.47 ml/min and 16.11 ml/min, respectively. The research results also show that the integrally constructed CPV/T system not only achieves effective conversion of solar energy into electrical and thermal energy, but also can directly convert electrical energy into clean, stable and easily stored hydrogen energy, which has potential application prospects.

Defect-enriched red phosphorus nanosheets as efficient and stable photothermal absorber material for interfacial solar desalination

The development of efficient photothermal materials has gained increasing attention for solar thermal-energy conversion. A good photothermal material has a strong light-absorption property, low thermal conductivity, high wettability, and high solar-to-thermal conversion efficiency. In this study, we prepared uniform, sub-micron, and defect-rich red phosphorus (RP) nanosheets via a simple ball-milling method to demonstrate their efficient and durable solar steam generation properties. Three RPs of different sizes were prepared by controlling the milling time (0 h: RP0, 30 h: RP30, and 60 h: RP60). Notably, RP60 exhibited the smallest particle (lateral) size, nanosheet morphology, and defect-rich surface. Furthermore, RP60 exhibited the distinctive properties of a small band gap (1.44 eV), low thermal conductivity (0.07 W/m·K), and low heat capacity (0.66 J/g·K) with exceptional wettability. With simulated sunlight illumination (100 mW/cm2, 1 sun), the RP60 photothermal absorber demonstrated a high water evaporation rate of 1.34 kg/m2·h with a stable solar steam generation efficiency of 74.1 % for over 10 h. A one-dimensional water path and porous polyurethane support facilitated the water supply, large contact area, heat localization, and steam escape. By employing plasmonic resonance-heating silver nanoparticles on the RP60, we achieved a significantly improved solar steam generation efficiency of over 96.0 % and a water evaporation rate of 1.75 kg/m2·h. This study highlights the critical role of morphology, particle size, and defects control in improving the photothermal properties for efficient and durable interfacial seawater desalination.

Erythritol/expanded graphite form-stable phase change materials with excellent thermophysical properties

Organic phase change materials possess the merits of high latent heat storage, small temperature changes, high chemical/thermal stability, low corrosion and reusability, and thus have attracted extensive attention in the research of low and medium-temperature energy storage media. However, pure phase change material has the deficiency of low thermal conductivity and easy leakiness, which seriously hinder their practical large-scale applications. In this work, the expanded graphite was used as the skeleton to encapsulate erythritol to form the composite phase change material. The composite had remarkably boosted thermal conductivity (5.97 ± 0.30 W/m·K compared with pure erythritol of 0.60 ± 0.03 W/m·K) and high melting latent heat (290.52 J/g) and solidification latent heat (239.52 J/g) at a loading rate of 95 wt%. The supercooling degree was reduced from 92.41 °C to 43.75 °C, facilitating the release of latent heat. The developed composite phase change material exhibits extraordinary heat transfer and storage characteristics, which has great application prospects in the fields of solar photothermal conversion utilization.

Yb3+ NIR emission enhancement in dichroic Cu-containing glass for solar spectral conversion

Ytterbium and copper co-doped phosphate glass containing plasmonic Cu particles showing dichroism was synthesized and the impact on Yb3+ near-infrared (NIR) emission evaluated. While the co-doped precursor glass exhibited ultraviolet to NIR luminescence down-shifting owing to copper(I), the dichroic glass displayed an enhanced NIR emission which is reported herein for the first time. It was found most favorable for Cu+ excitation around 360 nm. Scattering by Cu particles is suggested to produce the emission boost attractive for solar cell applications.

Performance Prediction Model Development for Solar Box Cooker Using Computational and Machine Learning Techniques

Abstract The development of prediction models for solar thermal systems has been a research interest for many years. The present study focuses on developing a prediction model for solar box cookers (SBCs) through computational and machine learning (ML) approaches. The prime objective is to forecast cooking load temperatures of SBC through ML techniques such as random forest (RF), k-nearest neighbor (k-NN), linear regression (LR), and decision tree (DT). ML is a commonly used form of artificial intelligence, and it continues to be popular and attractive as it finds new applications every day. A numerical model based on thermal balance is used to generate the dataset for the ML algorithm considering different locations across the world. Experiments on the SBC in Indian weather conditions are conducted from January through March 2022 to validate the numerical model. The temperatures for different components obtained through numerical modeling agree with experimental values with less than 7% maximum error. Although all the developed models can predict the temperature of cooking load, the RF model outperformed the other models. The root-mean-square error (RMSE), determination coefficient (R2), mean absolute error (MAE), and mean square error (MSE) for the RF model are 2.14 (°C), 0.992, 1.45 (°C), and 4.58 (°C), respectively. The regression coefficients indicate that the RF model can accurately predict the thermal parameters of SBCs with great precision. This study will inspire researchers to explore the possibilities of ML prediction models for solar thermal conversion applications.