Energy Conversion Efficiency Research Articles

Numerical study on solar photovoltaic/thermal system with tesla valve

In recent years, photovoltaic/thermal (PV/T) systems have played a crucial role in reducing energy consumption and environmental degradation, nonetheless, the low energy conversion efficiency presents a considerable obstacle for PV/T systems. Therefore, improving heat conversion efficiency is essential to enhance energy efficiency. In this paper, the PV/T system with the Tesla valve is proposed to solve this problem. Firstly, the cooling effect is simulated and analyzed in the system with four different flow channel structures: semicircle, rectangle, triangle and Tesla valve. The results indicate that the system with the Tesla valve exhibits superior cooling performance. Subsequently, several factors including angle, valve number, valve type, and pipe diameter ratio for the Tesla valve are further studied through numerical and simulation analysis. The results reveal that Tesla valves demonstrate optimal cooling performance when possessing the following structural parameters: complete symmetry, more valves, a 30-degree angle and a pipe diameter ratio of 1. Finally, four different types of fluid are selected to explore the Tesla valve. The conclusion shows that nanofluids with high density, low specific heat, and high thermal conductivity also improve the cooling performance. Thus, the PV/T system with the Tesla valve exhibits good heat dissipation and energy storage efficiency, electrical efficiency can reach 16.32% and thermal efficiency reach 59.65%.

Integration of Co Single Atoms and Ni Clusters on Defect-Rich ZrO2 for Strong Photothermal Coupling Boosts Photocatalytic CO2 Reduction.

We report a solvothermal method for the synthesis of an oxygen vacancy-enriched ZrO2 photocatalyst with Co single atoms and Ni clusters immobilized on the surface. This catalyst presents superior performance for the reduction of CO2 in H2O vapor, with a CO yield reaching 663.84 μmol g-1 h-1 and a selectivity of 99.52%. The total solar-to-chemical energy conversion efficiency is up to 0.372‰, which is among the highest reported values. The success, on one hand, depends on the Co single atoms and Ni clusters for both extended spectrum absorption and serving as dual-active centers for CO2 reduction and H2O dissociation, respectively; on the other hand, this is attributed to the enhanced photoelectric and thermal effect induced by concentrated solar irradiation. We demonstrate that an intermediate impurity state is formed by the hybridization of the d-orbital of single-atom Co with the molecular orbital of H2O, enabling visible-light-driven excitation over the catalyst. In addition, Ni clusters play a crucial role in altering the adsorption configuration of CO2, with the localized surface plasmon resonance effect enhancing the activation and dissociation of CO2 induced by visible-near-infrared light. This study provides valuable insights into the synergistic effect of the dual cocatalyst toward both efficient photothermal coupling and surface redox reactions for solar CO2 reduction.

Strain-Prompted Giant Flexo-Photovoltaic Effect in Two-Dimensional Violet Phosphorene Nanosheets.

As a second-order nonlinear optical phenomenon, the bulk photovoltaic (BPV) effect is expected to break through the Shockley-Queisser limit of thermodynamic photoelectron conversion and improve the energy conversion efficiency of photovoltaic cells. Here, we have successfully induced a strong flexo-photovoltaic (FPV) effect, a form of BPV effect, in strained violet phosphorene nanosheets (VPNS) by utilizing strain engineering at the h-BN nanoedge, which was first observed in nontransition metal dichalcogenide (TMD) systems. This BPV effect was found to originate from the disruption of inversion symmetry induced by uniaxial strain applied to VPNS at the h-BN nanoedge. We have revealed the intricate relationship between the bulk photovoltaic effect and strain gradients in VPNS through thickness-dependent photovoltaic response experiments. A bulk photovoltaic coefficient of up to 1.3 × 10-3 V-1 and a polarization extinction ratio of 21.6 have been achieved by systematically optimizing the height of the h-BN nanoedge and the thickness of VPNS, surpassing those of reported TMD materials (typically less than 3). Our results have revealed the fundamental relationship between the FPV effect and the strain gradients in low-dimensional materials and inspired further exploration of optoelectronic phenomena in strain-gradient engineered materials.

Dual-network fiber-hydrogel membrane for osmotic energy harvesting

Osmotic energy harvesting was a promising way to alleviate energy crisis with reverse electrodialysis (RED) membrane-based technology. Charged hydrogel combined with other materials was an effective strategy to overcome problems, including restricted functional groups and complicated fabrication, but the effect of the respective charges of the two materials combined on the membrane properties has rarely been studied in depth. Herein, a new method was proposed that charged hydrogel was equipped with charged filter paper to form dual network fiber-hydrogel membrane for osmotic energy harvesting, which had excellent ion selectivity (beyond 0.9 under high concentration gradient), high ion transference number and energy conversion efficiency (beyond 32.5% under wide range concentration gradient), good property of osmotic energy conversion (∼4.84 W/m2 under 50-fold KCl and ∼6.75 W/m2 under simulated sea water and river water). Moreover, the power density was attributed to the surface-space charge synergistic effect from large amounts overlapping of electric double layer (EDL), so that the transmembrane ion transport was enhanced. It might be a valid mode to extensively develop the osmotic energy harvesting.

Lianas in tropical dry seasonal forests have a high hydraulic efficiency but not always a higher embolism resistance than lianas in rainforests.

Lianas have higher relative abundance and biomass in drier seasonal forests than rainforests, but whether this difference is associated with their hydraulic strategies is unclear. Here, we investigate whether lianas of seasonally dry forests are safer and more efficient in water transport than rainforest ones, explaining liana abundance patterns. We measured hydraulic traits on five pairs of congeneric lianas of the tribe Bignonieae in two contrasting forest sites: the wet 'Dense Ombrophilous Forest' in the Central Amazonia (~ 2 dry months) and the drier 'Semideciduous Seasonal Forest' in the inland Atlantic Forest (~6 dry months). We also gathered a broader database, including 197 trees and 58 liana species from different tropical forests, to compare hydraulic safety between habits and forest types. Bignonieae lianas from both forests had high and similar hydraulic efficiency and exhibited variability in resistance to embolism across forest types when phylogenetic relationships are taken into account. Three genera had higher hydraulic safety in the seasonal forest than in the rainforest, but species across both forests had similar positive hydraulic safety margin despite lower predawn water potential values of seasonal forest' lianas. We did not find the safety-efficiency trade-off. Merging our results with previously published data evidenced a high variability of resistance to embolism in both trees and lianas, independent of forest types. The high hydraulic efficiency of lianas detected here probably favors their rapid growth across tropical forests, but differences in hydraulic safety highlight that some species are highly vulnerable and may rely on other mechanisms to cope with drought. Future research on the lethal dehydration threshold and the connection between hydraulic resistance strategies and liana abundance could offer further insights into tropical forest dynamics under climatic threats.

Relationships between diameter growth and functional wood anatomy in Eucalyptus globulus clones

Aim of study: We aimed to 1) analyze the variability of wood hydraulic anatomical traits in 10 clones of E. globulus Labill. with different growth rates, and 2) determine whether the magnitude of diameter growth affects the relationships between anatomical variables and diameter at breast height (DBH). Area of study: 25-year-old common garden trial in Balcarce, Buenos Aires, Argentina. Material and methods: We measured vessel diameter and number per unit area in transverse histological sections of stem wood, and calculated the proportion of vessel lumens, vessel composition (S), and theoretical specific hydraulic conductivity (Ks) of 10 E. globulus clones of high (HG) and low (LG) mean growth rates (measured as DBH) under field conditions. Main results: There was a difference in the range of variability in hydraulic anatomy between HG and LG clones, with LG clones showing a wider range. HG clones had wood with larger and fewer vessels and higher S compared to LG clones, with similar Ks between both growth groups. No clear or strong trends were observed between wood anatomy and DBH within the HG and LG groups, but across all clones a high correlation (Spearman coefficient r; p<0.001) was observed between vessel number ‒ DBH (r= -0.68), and S ‒ DBH (r= 0.74). These correlations were driven by contrasting mean values of both growth groups. Research highlights: Commercial E. globulus clones present a relatively large variation in anatomical and hydraulic strategies. However, in contrast to what is postulated for various woody species, there was no clear relationship between theoretical hydraulic efficiency and individual diameter growth rate in the genotypes studied.

Metal Sulfide‐Based Nanoarchitectures for Energetic and Environmental Applications

Despite their numerous excellent properties, metal sulfides are not particularly efficient at converting energy and purifying the environment, which limits their further applications. Fortunately, the energy conversion and environmental purification efficiencies of these materials have experienced notable advancements in recent years, accompanied by an improved understanding of their underlying mechanisms. Herein, progress in experimental researches in recent years on the engineering of single component metal sulfides by controlling morphology, construction of heterojunctions, and incorporating elements is reviewed. Methods to design and prepare metal sulfide‐based composites by building binary or ternary heterojunctions of metal sulfide/semiconductor/conductor are also discussed in detail. These materials are used in energy conversion and environmental purification systems, where they act as photocatalytic materials not only to split water, reduce carbon dioxide or nitrogen, but also to degrade pollutants (organic and inorganic) in water and gas. Finally, it is concluded by summarizing the research frontiers of metal sulfide nanomaterials in energy and environmental applications, as well as proposing potential challenges and future research directions. This work may contribute to a better understanding of metal sulfide nanocomposites and provide clues for the fabrication of more efficient metal sulfide‐based nanostructures for clean energy production and environmental remediation.

Integration of functional modules in a unified photoelectrochemical device for highly efficient solar-driven cathodic metal protection

The ever-increasing energy consumption stimulated the development of various solar energy conversion systems. Photocathodic protection (PCP), emerges as a promising photoelectrochemical technology to alleviate metal corrosion, but the centralization of all core reaction steps on one photoelectric-conversion-unit induces extremely low energy conversion efficiencies. Herein, a proof-of-concept modular PCP device incorporating electron transport layer (ETL), photoelectric conversion layer (PCL), hole transport layer (HTL) and hole consumption layer (HCL) is fabricated to delocalize the key reaction steps for the first time. Such a unified ETL/PCL/HTL/HCL architecture facilitates the efficient extraction of photoexcited electrons from the small-gap PCL to the protected metal through ETL, and holes to HCL for water oxidization through HTL. The directional “macroscopic” charge migration, prolonged charge lifetime and accelerated water oxidation lead to significantly improved PCP effectiveness in simulated seawater. Our findings provide a groundbreaking PCP design, allowing fine-tuning individual functional modules and inter-modular interfaces to vastly elevate performance.

Flexible Janus Black Silicon Photothermal Conversion Membranes for Highly Efficient Solar-Driven Interfacial Water Purification.

Photothermal conversion materials are critical in the development of solar-driven interfacial evaporation techniques; however, achieving a high energy conversion efficiency remains challenging owing to the high cost and instability of light-absorbing materials, in addition to the difficulties of simultaneously improving light absorption while suppressing heat loss. A black silicon (Si) powder with a porous structure was prepared by chemical etching of a low-cost commercial micron-sized Al-Si alloy, and a flexible Janus black Si photothermal conversion membrane was constructed. The partially broken spherical particles and porous structure obtained after etching enhanced the refraction of light from the Si powder, imparting the prepared membrane with an average light absorption rate of 95.95% over the solar spectrum. Evaporation from the membrane increased the intermediate water content and reduced the equivalent evaporation enthalpy. The thermal conduction loss was inhibited through a one-dimensional water transport structure, and the membrane achieved a water evaporation rate of 2.17 kg m-2 h-1 and a photothermal efficiency of 94.95% under 1 sun illumination. Benefiting from the broadband absorption and high photothermal efficiency of black Si powder, surface modification of hydrophobic polydimethylsiloxane, and directional salt-out structure design, the evaporation rate of the Janus black Si membrane-based system in a 10% NaCl solution was maintained >2.10 kg m-2 h-1 after 7 days of continuous evaporation cycles. The removal rate of metal ions from simulated seawater and from practical wastewater containing complex heavy metals reached >99.9%, indicating the promising potential of black Si membrane for application in solar-driven interfacial water purification.

Optimizing thin-film silicon solar cells with nanostructured TiO2 and a silver back reflector for enhanced energy conversion efficiency

This paper investigates the improvement of energy conversion efficiency in thin-film silicon solar cells by employing periodic nanostructures of TiO2 on the silicon active layer and a back reflector featuring periodic nanostructures of silver. The objective is to increase the optical path length, enhance absorption probability for longer wavelengths, and subsequently improve solar cell performance. Three silicon-based solar cell configurations are proposed and simulated using the finite difference time domain (FDTD) method to assess their performance. Electrical characteristics are obtained through the drift-diffusion method. The resulting short-circuit current density increased from 40.93 to 65.28 to 95.373mA/cm2 for the three cells, leading to significant improvements in conversion efficiency with observed values of 20.39%, 33.26%, and 47.28%, respectively, in the optimized structures. Furthermore, we compare the simulation results of the three structures with those of a reference structure and several structures previously proposed in the literature.

Efficiency of energy-generating tiles with different types of multipliers

Problem. With the urgent need for sustainable and renewable energy solutions, the integration of energy-harvesting technologies in urban infrastructure has become a focal point of innovation. Energy-generating tiles, transforming pedestrian movement into electricity, offer a viable path forward. Yet, their efficiency hinges on the internal design, particularly the type of multipliers used. Goal. This study aims to assess and compare the efficiency of energy-generating tiles equipped with helical and straight-cut gear multipliers, to identify the optimal design for maximizing energy conversion in urban environments. Methodology. An experimental setup was created to test prototypes of the energy-generating tiles under controlled foot traffic conditions. The study measured and analyzed the electrical output and efficiency of tiles with both types of gear multipliers, simulating real pedestrian traffic scenarios. Results. Energy-generating tiles featuring straight-cut gears outperformed those with helical gears in energy output and conversion efficiency. The research also illuminated the influence of pedestrian dynamics, like step force and frequency, on tile performance. Originality. This research advances renewable energy technology by offering a comprehensive analysis of energy-generating tile efficiency with different gear multipliers. It introduces an innovative method for evaluating tile performance, underscoring the significance of gear design in energy conversion. Practical value. The findings have considerable implications for sustainable urban development, suggesting that implementing energy-generating tiles in areas with high foot traffic could significantly enhance urban renewable energy sources. This study not only guides the design of more efficient energy-harvesting tiles but also encourages their broader adoption, supporting urban sustainability goals and the reduction of carbon emissions.

Analysis of Transient Thermoacoustic Characteristics and Performance in Carbon Nanotube Sponge Underwater Transducers

Recent advancements in marine technology have highlighted the urgent need for enhanced underwater acoustic applications, from sonar detection to communication and noise cancellation, driving the pursuit of innovative transducer technologies. In this paper, a new underwater thermoacoustic (TA) transducer made from carbon nanotube (CNT) sponge is designed to achieve wide bandwidth, high energy conversion efficiency, simple structure, good transient response, and stable sound response, utilizing the TA effect through electro-thermal modulation. The transducer has potential application in underwater acoustic communication. An electro-thermal-acoustic coupled simulation for the open model, sandwich model, and encapsulated model is presented to analyze the transient behaviors of CNT sponge TA transducers in liquid environments. The effects of key design parameters on the acoustic performances of both systems are revealed. The results demonstrate that a short pulse excitation with a low duty cycle could greatly improve the heat dissipation of the encapsulated transducer, especially when the thermoacoustic response time becomes comparable to thermal relaxation time.

To Get a Power Generation Using a Waste Heat Recovery from IC Engine

This Research paper aims to develop and design a low-temperature organic Rankine cycle (ORC) system, focusing on enhancing the performance of the expander and selecting optimal refrigerants and heat sources. The study begins with a comprehensive analysis of available expanders and refrigerants suitable for ORC applications. The research then progresses to the development and improvement of an expander utilizing a reverse scroll compressor configuration, a novel approach aimed at enhancing efficiency and performance. Dynamic tests are conducted to assess the performance of the scroll compressor in this new configuration, providing valuable data for further optimization. The same expander is then integrated into an ORC system to evaluate its performance within the overall setup. Various performance parameters of the scroll compressor and the ORC system are meticulously analyzed to gauge efficiency and identify areas for improvement. Furthermore, the research paper includes a detailed process of selecting the most appropriate refrigerant and heat source from the available options. This selection is critical in optimizing the ORC system's effectiveness and sustainability. Overall, this research contributes to advancing low-temperature ORC technology by improving expander design, optimizing component performance, and selecting suitable operating parameters for enhanced energy conversion efficiency.

How Components of Dye-sensitized Solar Cells Contribute to Efficient Solar Energy Capture

Herein, we reviewed the main components of dye-sensitized solar cells (DSSCs) which are an emerging cheap and environmentally benign alternative for solar energy capture and conversion to electricity. The role of individual parts such as the semiconductor electrode, counter electrode, photosensitizer, electrolyte, and substrate and their contribution to the overall efficiency (η) of DSSCs are discussed. In addition, parameters such as short circuit current, open circuit voltage, and fill factor used to quantify the efficiency of DSSCs are addressed. The highest solar-to-electric energy conversion efficiency of 13 % has been achieved using titanium dioxide as a semiconductor electrode, a triiodide system as a redox couple, and platinum counter electrodes. Semiconductors are made up of materials such as glass, carbon, conductive polymers and other metal oxides have lower efficiencies (< 8 %). In addition, synthetic photosensitizers especially ruthenium complexes have higher efficiencies (10-11 %) compared to natural dyes among which the highest efficiency (4.6 %) was achieved using chlorophyll. The performance of natural dyes based on efficiency of the DSSC is generally in the order: chlorophyll > anthocyanins > carotenoids that is highly attributed to their structure which not only dictates electron release and recombination but also attachment to other components. The DSSC performance is not fixed but rather tunable by variations in the components to achieve desired structural and electronic properties such as firm anchorage between the photosensitizer and the semiconductors, the reduction of the energy band gap by incorporation of other metal salts to extend the absorption range and use of additives that prevent electron recombination with the photosensitizer or any hindrances in the electrolyte redox reactions.

Thermodynamic analysis of liquid air energy storage system integrating LNG cold energy

Liquid air energy storage (LAES) presents a promising solution to effectively manage intermittent renewable energy and optimize power grid peaking. This paper introduces a LAES system integrating LNG cold energy to flexibly manage power peaking, including intermediate energy storage, power generation using organic Rankine cycle, multi-stage direct expansion, and solar energy for heating. Aiming to maximize the electrical round-trip efficiency, a genetic algorithm is employed to optimize the operational parameters of the proposed LAES system. The results indicate that the combined design of cold energy utilization, multi-stage direct expansion and solar heating for proposed LAES system significantly improve the power performance, achieving an energy capacity of 0.125 kWh/kgLNG and an electrical round-trip efficiency of 376.7 %. The exergy losses of heat exchange equipment are far larger than mechanical equipment in the LAES system, so the optimization design of heat exchange equipment is preferred to improve the exergy performance. The proposed system achieves both high efficiency and flexibility and hence contributes to the development of liquid air energy storage systems.

Experimental and numerical investigation on latent heat/cold stores for advanced pumped-thermal energy storage

Pumped-thermal energy storage plays a pivotal role in large-scale harvesting and utilization for renewable resource endowments with intrinsic properties such as intermittency and instability. Here, we conducted detailed experimental and numerical studies on latent heat/cold stores of Brayton-like pumped-thermal energy storage. A demonstration thermal energy storage system with rated power of 20 kW including phase change materials (PCMs) preparation and structural design of energy storage units is synergistically designed and built. In this paper, the operating mechanism behind the theoretical experiment and control groups that raises the intake temperature through an air heater is uncovered and compared. Moreover, an auxiliary numerical model for further energy and exergy analyses is established to perfect the system-wide assessment. In terms of the first law of thermodynamics, the speed of energy storage and efficiency increase with higher operational pressures. For instance, system properties like roundtrip efficiency can reach up to 0.37 at an operating pressure of 0.7 MPa. As for systematic exergy despite the total destruction of thermal energy storage units amounts to 12.25 kWh the maximum exergy efficiency could reach 0.61 simultaneously.

Boosting photocatalytic activity in ternary lamellar hierarchical structured ZnFe2O4/polymeric carbon nitride by constructing an electronic bridge

Photocatalytic technology is one of the ideal approaches for clean energy production and environmental pollution control in the future. However, the rapid recombination of photo-generated charge carriers is a bottleneck problem of low solar energy conversion efficiency. Herein, a magnetic ZnFe2O4/Pt/polymeric carbon nitride (PCN) semiconductor catalyst is designed and prepared for high-performance photocatalytic hydrogen production reaction and photocatalytic degradation rate of RhB. It exhibits 339.31 μmol·g−1·h−1 hydrogen production rate and 96.08 % photocatalytic degradation rate of RhB within 120 min under visible light. The introduction of Pt, constructing an electronic bridge, accelerated the transfer of photo-generated carriers, meanwhile, the smaller band gap of the ternary composites enabled the generation of more photo-generated electrons. The internal electric field accelerated the accumulation of electrons and holes in the conduction band of ZnFe2O4 and valence band of PCN, thus photocatalytic activity is greatly enhanced. The electron-hole separation is also improved and the transport of photo-generated electrons is facilitated by the special structure of the heterojunction and the unique morphology of PCN. In addition, the used catalyst can be recovered through magnetic fields, and this magnetic catalytic system has great application prospects in the fields of photocatalytic hydrogen production and pollutant degradation.

Electric Field Redistribution Triggered Surface Adsorption and Mass Transfer to Boost Electrocatalytic Glycerol Upgrading Coupled with Hydrogen Evolution

AbstractElectrocatalytic glycerol oxidation reaction (GOR) stands out as an economical and prospective technology to replace oxygen evolution reaction for co‐producing high‐valued chemicals and hydrogen (H2). Regulating the adsorption of glycerol (GLY) and hydroxyl (OH) species is of great significance for improving the GOR performance. Herein, a hierarchical p–n heterojunction by combining Co‐metal organic framework (MOF) nanosheets with CuO nanorod arrays (CuO@Co‐MOF) is developed to realize the optimization on GOR. Specifically, CuO@Co‐MOF electrode exhibits superior performance with a conversion of 98.4%, formic acid (FA) selectivity of 87.3%, and Faradaic efficiency (FE) of 98.9%. The flow‐cell system with the bifunctional CuO@Co‐MOF electrode for pairing GOR with the hydrogen evolution reaction (HER) reveals better energy conversion efficiency. Experimental results and theoretical calculations unravel the redistributed electric field by introducing Co‐containing species that contribute to the improved performance, which not only enhances the OH adsorption but also modulates the excessive GLY adsorption of CuO, thus reducing reaction energy barriers of FA desorption. Simultaneously, finite element analysis reveals that the novelty hierarchical structure can increase the concentration of OH− and facilitate the mass transfer of OH− in the solution.

Optimal declutching control of hinged multiple floating bodies

In deep seas, there is an increasing utilisation of multiple floating structures as devices for harnessing renewable energy, such as hybrid wind-wave energy systems and multi-body wave energy converters. The control strategies have a great influence on the motion characteristics and energy conversion efficiency of these systems. The control technology brings more benefits to the system's performance, yet also introduces more complex challenges. This paper aims to fill the research gap in the control of multiple floating bodies and to propose a novel optimal declutching control method. Declutching control enables discontinuous loading and releasing of the force from power take-off system between bodies. It was found that the feasibility of the proposed method is highly dependent on the choice of objective functions, iteration numbers, and wave frequencies. With appropriate parameters, the declutching control can achieve a variety of objectives for a hinged floating multibody system, such as reducing pitch motion, improving extracted wave power, increasing relative rotational speed, and enhancing power extraction. The control effects on the velocity and the force-velocity phase relationship and how they benefit the objectives are discussed. All objective functions show a better control effect (at least 7.76%) on their respective performance indices than others.

Graphene tunable dual-band nonreciprocal thermal emitter under TE polarization

Nonreciprocal thermal radiation is an emerging research direction, which can be achieved by adding anisotropic magneto-optical materials to some optical components. At present, most of the research focuses on nonreciprocal thermal radiation under TM polarization. In this paper, we propose a nonreciprocal emitter under TE polarization, which is a dual-band nonreciprocal emitter. There are twice guided mode resonances (GMRs) between 13 μm and 16 μm. It is a grating composed of a metal Ag and a magneto-optical material InAs. When the applied magnetic field is 3T, more than 90 % nonreciprocity is achieved at the incident wavelengths of 13.845 μm and 15.32 μm. In addition, we add a layer of graphene to the grating ridge to tune the peak position. It has a wide range of applications for the study of nonreciprocal thermal radiation, which can improve the energy conversion efficiency.