Theoretical Efficiency Research Articles

Tri-phase photonic crystal emitter for thermophotovoltaic systems

Thermophotovoltaics (TPVs) are devices that convert thermal radiation into electricity using a low-bandgap photovoltaic (PV) cell. While the theoretical efficiency can approach the Carnot limit, designing a TPV selective emitter that is spectrally matched with the PV cell's bandgap and is stable at high temperatures is critical for achieving high-efficiency systems. Photonic crystal (PhC) emitters can provide excellent spectral control, but prior experimental designs lack the thermal stability required for high-performance TPVs. In this study, a tri-phase PhC emitter design is proposed and optimized. The tri-phase design introduces an additional material in one of the alternating layers of an existing 1D PhC emitter, potentially stabilizing it at high temperatures. BaZrO3 is introduced in the CeO2 layers of a CeO2/MgO PhC emitter. Stanford Stratified Structure Solver (S4) is used to model the emittance of multiple tri-phase PhC variations. The parameter for optimization is the spectral efficiency of the emitter. The structure with the highest spectral efficiency is only 0.02% less efficient than the original design. The structure with the lowest spectral efficiency is only 0.28% less efficient. Therefore, any tri-phase variation can be applied to existing PhC emitters without compromising on their spectral efficiency. Without the need for manufacturing specific parameters, the tri-phase PhC can be an inexpensive emitter for real world applications that may improve thermal stability without compromising on the spectral efficiency, making the practical applications of TPVs feasible.

Evaluation of Empirical Separation Efficiency Theories for Uniflow Cyclones for Different Particle Types and Experimental Verification

Cyclones serve as essential devices in various industries for the removal of particulate matter from gases and liquids, contributing to improved equipment efficiency and longevity by mitigating the wear and damage caused by dust and small particles. Uniflow cyclones offer improved accessibility due to their predominantly horizontal orientation. This characteristic enhances the ease of maintenance and operation. This study focuses on investigating the collection efficiency of uniflow centrifugal cyclones for oil mist and fine dust particles ranging from 0.5µm to 29 µm in diameter. The investigation is based on the specific vane angles βv of a swirl inducer from 0∘ to 60∘ at a flow rate V˙ of 130 Ls−1. The measured collection efficiencies are compared with theoretical efficiencies calculated using six different empirical approaches. The different results for oil and fine dust particles are discussed. Comparison of the experimental results with the empirical models demonstrated that certain models closely matched the observed separation efficiencies for different aerosols and vane angles βv (respectively, their induced radial velocities V). Through a systematic examination, this research aims to provide more insight into the validity of empirical approaches for different particle types and compositions using a uniflow-cyclonic system.

MoSe2 Enhanced Raindrop Triboelectric Nanogenerators and Its Energy Conversion Analysis

AbstractTriboelectric nanogenerators (TENGs) are considered one of the most effective methods for harvesting irregular and low‐frequency raindrop energy. In this work, molybdenum selenide (MoSe2) nanosheets act as intermediate layers for improving droplet‐based TENG performance. Consequently, without surface etching process, the short‐circuit current (Isc) and open‐circuit voltage (Voc) of the TENG can reach as high as 1.2 mA and 120 V, respectively. Furthermore, precise energy analysis based on an optimization model for input energy calculation is carried out, allowing conversion efficiency to be calculated under diverse conditions. Finally, an all‐solid supercapacitor is fabricated for integration with the TENG. An intelligent wireless sensing system, powered by the integrated TENG and capacitor, is demonstrated for monitoring environmental information. This study provides new insights into intermediate‐layer materials' selection and action mechanisms. It fills a gap in the research on a precise model of theoretical energy conversion efficiency calculation. The integrated devices and sensing applications will provide strategies for creating smart cities.

Thioacetamide‐Assisted Crystallization of Lead‐Free Perovskite Solar Cells for Improved Efficiency and Stability

Perovskite solar cells (PSCs) have made great strides in recent years, operating inside the theoretical Scholkely–Quisser efficiency limit with a certified power conversion efficiency (PCE) of 26.1%. However, lead toxicity from Pb‐based PSCs can harm the environment. As a result, the search for nontoxic and environmentally friendly substances to replace Pb in perovskites is the need of the hour. Tin has emerged as the most viable choice to replace Pb, due to its favorable electronic properties and smaller bandgaps of Sn‐based perovskites between 1.1 and 1.4 eV, strong charge carrier mobility, and high theoretical efficiency of 32%. Sn vacancies and point defects, on the other hand, are easily produced in Sn perovskites, leading to nonradiative recombination. Furthermore, interfacial flaws and traps impede further performance improvement. In this research, to produce high‐quality Pb‐free perovskites for high‐performance PSCs, a Lewis‐base thioacetamide (TAA) is added to the simple FASnI3 perovskite solution. FASnI3 and TAA additive‐based films effectively control perovskite film crystallinity and grain size via Lewis acid–base reaction. The champion FASnI3 + TAA‐based PSC achieves a maximum PCE of 10.67% while paving a facile way for other compositional perovskite analogues to be integrated into highly efficient and operationally stable PSCs.

Insight into conduction band density of states at c-Si/TiO2 interface for efficient heterojunction solar cell

Carrier selective solar cell has become one of the hot spots in the area of Si solar cell. The proposed architecture FTO/TiO2/c-Si/i-a-Si:H/Cu2O/back contact studied through simulation demonstrates a power conversion efficiency of 20.03%. This study is the first to report detailed exploration of effect of the conduction band density of states on the efficiency of Si solar cell. Through optimization, the conduction band density of state (1017 cm-3) drastically increases the power conversion efficiency from 18% (at 1021 cm-3) to 21.25% (at 1017 cm-3) i.e., an improvement of 18% relatively. Along with this, the parameters like absorber layer thickness, absorber’s defect density, thickness of electron transport layer and interface defect density are also optimized. Moreover, the charge transport properties and the impact of the Schottky barrier height at c-Si/TiO2 interface on band alignment is studied. After optimization of various physical parameters such as thickness (100 μm), conduction band density of states (1017 cm-3) and defect concentration (1010 cm−3) of c-Si layer, thickness of TiO2 layer (20 nm) and interface defect density at c-Si/TiO2 junction (1010 cm−2), a short-circuit current of 38.11 mA cm−2, open-circuit voltage of 0.84 V, fill factor of 85.99% is obtained, leading to an enhanced theoretical power conversion efficiency of 27.77%.

Device modeling of all-inorganic CsPbI3 based perovskite solar cells: A numerical study

Lead-halide based perovskite solar cells (PSC’s) have proven to be efficient and have extraordinary stability. CsPbI3 is thought to be a potential light-absorbing material for use in all-inorganic PSCs due to its advantageous bandgap and thermal stability. In contrast to the organic-inorganic hybrid PSCs counterpart, the CsPbI3 has a high defect density resulting in a lower PCE and less stable structure. In this study, we performed a device modeling of all-inorganic CsPbI3 using SCAPS-1D to improve its performance. Here, we have shown how various electron and hole transport layers (ETL & HTL) affect the performance of the CsPbI3 device. For this, the effect of dopant concentration, the thickness of HTL, ETL, and absorber layer along with optimization of back contact metal work function have been numerically investigated. Under the optimum condition, the best theoretical conversion efficiency of ∼27.04% was achieved for FTO/SnO2/CsPbI3/CuSbS2/Pd configuration, which is the highest theoretical value reported among CsPbI3-based PSCs. Based on these results, we concluded that all-inorganic CsPbI3 PSCs under these optimized conditions might help researchers improve this material experimentally for renewable energy applications.

Analysis of a new adaptive time filter algorithm for the unsteady Stokes/Darcy model

In this article, we propose a new adaptive time filter algorithm for the unsteady Stokes/Darcy model. Firstly, we present a first order θ-scheme with variable time step which is one parameter family of Linear Multi-step method. Furthermore, using time filter scheme, the convergence order is increased to the second order without almost increasing the extra computation. Moreover, we construct decoupled and coupled adaptive algorithms to improve the computational efficiency. Theoretically, we analyze stability and the second-order accuracy of Linear Multi-step method plus time filter with non-increasing variable time step, respectively. Finally, numerical experiments are given to verify theoretical results, including effectiveness, convergence and efficiency.

A first‐principles investigation into the rational design of Sn‐halide perovskite materials as an alternative to Pb‐based perovskites

AbstractThe development of Pb‐free alternatives for perovskite‐based photovoltaics is extremely important due to the toxicity of Pb to the environment. Sn‐based organic inorganic hybrid halide perovskites are considered to be the most suitable alternative to Pb‐based ABX perovskites due to their similar optoelectronic properties. The selection of A site cation in ABX type perovskites is crucial for favorable structural and mechanical properties. Using first principle methods, we have designed and investigated Sn–I based hybrid halide perovskite materials with different organic cations mixed in equal proportions. Observed tolerance (TF) and octahedral factors () indicate the formation of stable three‐dimensional perovskite structure. Our studied materials also exhibit thermodynamic stability due to the negative value of their formation energies. Observed band gap values indicate the semiconducting nature of our studied perovskite materials. Calculated optical properties indicate that all of the compounds exhibit suitable dielectric functions and absorption coefficients in the visible range of the electromagnetic spectrum. The observed highest value of theoretical power conversion efficiency of MA‐AMSnI (11.24%) indicates its potential to be used in photovoltaics. Our investigation will be beneficial for researchers to develop less toxic and efficient perovskite materials for the fabrication of optoelectronic devices.

Synergistic Effect of Size-Tailored Structural Engineering and Postinterface Modification for Highly Efficient and Stable Dye-Sensitized Solar Cells.

Despite significant progress in device performance, dye-sensitized solar cells (DSSCs) continue to fall short of their theoretical potential. Moreover, research in recent years needs to pay more attention to improving the device fabrication process. To achieve the theoretical efficiency limit, it is crucial to optimize the interface between the dye and TiO2 nanoparticles in the entire device stack. Our study indicates that optimizing the structure or size of the coadsorbents and implementing a monolayer adsorption process can be an effective strategy to reduce charge recombination and enhance light-harvesting properties. Our research aims to develop a surface-coating adsorbent plan that controls the TiO2 nanoparticle interface to achieve the radiative limit of power conversion efficiency (PCE). Specifically, we utilized 2-thiophenecarboxylic acid (THCA) or chenodeoxycholic acid (CDCA) as postinterfacial surface-coating adsorbents. Our results demonstrate that this approach effectively achieves the desired PCE limit. Combined with the coadsorbent structure engineering and interface optimization, the device increased the packing area on the TiO2 nanoparticles' surface, reaching an improved PCE of over 13.17% under simulated sunlight (1.5G), which is the highest efficiency of a porphyrin single dye-based DSSC. In particular, this practical approach was also applied to a large-area DSSC with an area of 3 cm2, yielding a remarkable PCE of 9.04%. Furthermore, when applied to a polymer gel electrolyte, this novel approach recorded the highest PCE of 11.16% with a long-term operational stability of up to 1000 h for the quasi-solid-state DSSCs. Our research findings provide a promising avenue for achieving high-performance DSSCs with ease of access and demonstrate practical applications as alternatives to conventional power sources.

Numerical simulation study on the photovoltaic performance of tin-based perovskite solar cell using CuSCN as a hole transport layer giving 32% theoretical efficiency

Numerical simulation study on the photovoltaic performance of tin-based perovskite solar cell using CuSCN as a hole transport layer giving 32% theoretical efficiency

Intrinsic polarity inversion in III-nitride waveguides for efficient nonlinear interactions.

III-nitrides provide a versatile platform for nonlinear photonics. In this work, we explore a new promising configuration - composite waveguides containing GaN and AlN layers with inverted polarity, i.e., having opposite signs of the χ(2) nonlinear coefficient. This configuration allows us to address the limiting problem of the mode overlap for nonlinear interactions. Our modelling predicts a significant improvement in the conversion efficiency. We confirm our theoretical prediction with the experimental demonstration of second harmonic generation with an efficiency of 4%W-1cm-2 using a simple ridge waveguide. This efficiency is an order of magnitude higher compared to the previously reported results for III-nitride waveguides. Further improvement, reaching a theoretical efficiency of 30%W-1cm-2, can be achieved by reducing propagation losses.

Passivating contact-based tunnel junction Si solar cells using machine learning for tandem cell applications

Tandem solar cells are a key technology for exceeding the theoretical efficiency limit of single-junction cells. One of the most promising combinations is the silicon–perovskite tandem cells, considering their potential for high efficiency, fabrication on a large scale, and low cost. While most research focuses on improving each subcell, another key challenge lies in the tunnel junction that connects these subcells, significantly impacting the overall cell characteristics. Here, we demonstrate the first use of tunnel junctions using a stack of p+/n+ polysilicon passivating contacts deposited directly on the tunnel oxide to overcome the drawbacks of conventional metal oxide-based tunnel junctions, including low tunneling efficiency and sputter damage. Using Random Forest analysis, we achieved high implied open circuit voltages over 700 mV and low contact resistivities of 500 mΩ cm2, suggesting fill factor losses of less than 1% abs for the operating conditions of a tandem cell.

Self-excited wave stabilization in a linear detonation combustor

Detonative combustors, such as rotating detonation engines, have increasingly been viewed as next-generation propulsion and power generation systems because they offer higher theoretical thermal efficiencies than conventional constant-pressure combustors. In order for these systems to be realized in a practical context, the impacts of inflow and outlet conditions, reactant mixing, and interactions between counter-propagating waves must be better understood. To examine these phenomena in a simplified geometry, the present work considers a methane-oxygen reflective shuttling detonation combustor with an open-closed chamber configuration. High-fidelity simulations are conducted for two equivalence ratio conditions (lean and rich), and comparisons are made to complementary experiments. The results show that self-sustained steady-state wave behavior consists of minimally-reacting left-running waves and right-running detonation waves. The lean case is found to establish steady-state operation after a shorter time and exhibit detonation waves after a shorter distance from the closed end of the chamber. The simulations are able to predict the experimentally observed trends in the wave velocity in the direction of propagation. Wave-relative averaged flow fields show considerable reactant stratification and parasitic combustion ahead of the waves, likely contributing to their low speeds and pressures relative to ideal detonations. Conditional statistics ahead and behind the waves indicate that peaks in heat release occur at both lean and rich conditions near the open end of the chamber, and incomplete fuel oxidation in the primary detonation waves leads to delayed oxygen consumption and higher temperatures downstream.

Aviation fuel production pathways from lignocellulosic biomass via alcohol intermediates – A technical analysis

In order to achieve the goal of limiting global warming to 1.5 °C, also the growing aviation industry needs to take measures to reduce their greenhouse gas emissions. Various renewably sourced aviation fuels can significantly reduce greenhouse gas emissions and most of them, except for example liquid hydrogen or LNG, can be used in the existing infrastructure without airport or aircraft modifications. As most of these renewably sourced fuel types are not (yet) produced at commercial scale, many technological assessment parameter (e.g. carbon or energy efficiency) are uncertain. Thus, the goal of this study is to compare two different process routes, both being based on biochemical and thermochemical conversion steps. The processes evaluated against conversion efficiency of the available raw feedstock and process energy requirements. The evaluation uses theoretical and biochemical carbon efficiency as well as energy efficiency as indicators. A steady-state flowsheet simulation for two biogenic process paths via biogas and bioethanol as intermediate products is carried out on the basis of literature data. In addition, the optional use of solid residue from the biotechnological process step by combustion for direct heat supply cases are studied. In the ethanol-based route, about 23% of the carbon in the feed can be recovered as kerosene, whereas this is only about 19% in the biogas route. Simultaneously, the ethanol-based route without the combustion of the residue has an energy efficiency of 28%, while the biogas route has an efficiency of 24%.

Role of nanoscale compositional inhomogeneities in limiting the open circuit voltage in Cu(In,Ga)S2 solar cells

As Si-based solar cell technologies approach their theoretical efficiency limits, alternative photovoltaic systems, such as tandem solar cells, are gathering increased attention due to their potential to reach higher efficiencies by better use of the solar spectrum. Cu(In,Ga)S2 (CIGS) is a promising material for the top cell due to its large, tunable bandgap energy (Eg), stability, and already established high efficiencies. However, the deficit in open circuit voltage is still large; therefore, an improved understanding of the efficiency losses is required. Scanning electron microscopy cathodoluminescence was used to study the role of the polycrystalline nature for radiative recombination in CIGS samples of varying Cu-content. Considerable differences between neighboring grains were observed in the emission energy and the emission intensity, with significant drops in emission energy at the grain boundaries. Lateral homogeneity in the near band edge (NBE) energy was found to reduce for samples with Cu-poor compositions, with its standard deviation halving (σNBE ∼ 20 meV) compared to the more stoichiometric films (σNBE ∼ 50 meV), which corresponds to an open circuit voltage loss contribution that is nearly an order of magnitude lower. Such inhomogeneities can be attributed mainly to local variations of the Ga concentration. Hence, the differences between the samples could be explained by the different deposition times at elevated temperature allowing for different extents of homogeneity. Thus, Cu-poor films are not only favorable because of lower concentrations of deep defects but also because of reduced bandgap variations.

Design and development of modified high efficient high gain DC-DC converter for SPV standalone systems

<p class="MDPI17abstract"><span lang="EN-US">A conventional DC-DC converter is not viable for power conditioning in standalone solar photovoltaic applications. Switching losses are the primary reason for the poor performance of conventional DC-DC converters. To mitigate the issues in conventional DC-DC converters, a high efficient high gain (HEHG) DC-DC converter is designed and developed in this research work. Modified HEHG converter utilizes the passive components switched capacitors, coupled inductor, and resistor capacitor (RC) snubber circuit for minimizing the switching losses and improving the overall power conversion efficiency of the solar photovoltaic (SPV) system. In addition, a modified <br /> D-sweep maximum power point tracking (MPPT) algorithm is in-corporate into this system to improve the tracking efficiency of the SPV system. HEHG for a standalone system is designed using MATLAB/Simulink environment and developed the hard-ware prototype. As a part of the validation, real-time testing is carried out and compares the performance of the HEHG converter with a traditional DC-DC converter. The theoretical efficiency of the HEHG converter is 96.01%, and the real-time efficiency is 95.62%. Found that theoretical and practical values of performance parameters are closely tallying.</span></p>

Feasibility Study of Theoretical Efficiency Calculation for Flat Plate Collectors in Solar Water Heating Systems

Solar energy stands as a paramount clean, abundant, and renewable power source holding remarkable potential to address our escalating energy needs. Among its crucial utilization methods, solar water heating systems integrating flat plate collectors (FPCs) emerge as vital contributors in harnessing and converting solar energy into utilizable heat. This study delves into the realm of FPCs' theoretical efficiency assessment, employing mathematical models and factoring regional weather conditions to meticulously evaluate the efficiency of single-glaze and double-glaze collector variants. The outcomes spotlight the single glaze collector's efficiency at 0.669 and the double glaze collector at 0.713, underscoring the discernible performance gap. In a landscape where industries, hospitals, residences in Kandahar, and comparable settings extensively depend on hot water, often derived from fossil fuel-driven heating, this research's implications hold particular relevance. By transitioning towards solar water heating, this study not only underscores a concrete method to curtail carbon emissions but also to significantly reduce energy expenses linked with conventional heating techniques. The findings beckon a departure from the status quo, emphasizing that cleaner energy options are attainable, even for regions demanding hot water requirements. As society navigates complex decisions concerning energy sourcing, embracing solar water heating stands as an auspicious stride towards a sustainable future, beckoning us to collectively embark on a path of energy-conscious choices for the greater good of our planet and the generations that will inhabit it.

Improvement Efficiency of Solar Cells Using III-V Dual Junction: InGap/GaAs

Renewable energy is a very minor percentage of energy consumed in the world. Fossil fuels still dominate despite their drawbacks (degradation of the environment). Renewable energy is not yet cost competitive with fossil fuels. The conversion of energy from renewable sources, especially for inexhaustible and clean energy sources (solar cells), must be efficient to be viable for large scale use. Single junction cells (SJC) have a theoretical efficiency limit of 33.7%, called Shockley-Queisser limit (SQ). Because the cost of electricity produced from solar cells depends on their efficiency, improving their conversion efficiency is a key way to make them cost-competitive. The two most important efficiency losses in SJC are the inability to convert photons with energies below the band gap energy (Eg) into electricity and the thermalization of photon energies exceeding Eg. Dual Junction Solar Cells (DJSC) was proposed to avoid the efficiency losses and to overcome the SQ limit. Our simulation model, presented in a previous work, was used to calculate solar cells efficiency and to plot the current-voltage (I-V) characteristics and the power-voltage (P-V) characteristics curves. Our simulation results show that high conversion efficiencies can be achieved by DJSC, more than 43.5%.

(Invited) Recent Advances in Thermally Regenerative Batteries: A New Approach for Generating Electrical Power from Low-Grade Heat

Thermally regenerative flow batteries (TRBs) seek to tap into the unused terawatt-hours of low-grade heat that are currently being expelled from industrial plants and stationary power sources each year. Unlike typical flow batteries, TRBs can be recharged using thermal energy, therefore increasing grid efficiency by using an energy stream that is already widely available. This unique feature is accomplished through a thermally recoverable energy carrier that, when added or removed from an electrolyte, dramatically alters the standard electrode potential of an electrode reaction. To date, most TRBs use ammonia as the energy carrier, which lowers the standard electrode potential of their anode reaction by complexing with transition metal ions such as copper, silver, or zinc. Despite the early successes of TRBs relative to other emerging electrochemical technologies trying to harness low-grade thermal energy sources, they still lacked the energy efficiency and power densities needed to be economically viable. The first iterations of TRBs had peak power densities up to 3 mW cm-2 with competitive theoretical energy efficiencies (up to 1 %), but they suffered from extreme coulombic efficiency issues that limited realizable energy production values. Herein, we will discuss recent changes that have greatly improved the performance possible from these systems and discuss persistent challenges that remain to be solved. Coulombic inefficiencies were resolved by replacing unstable deposition-based reactions with all-aqueous alternatives that provided larger cell potentials and coulombic efficiencies for single metal and bimetallic-TRB systems. Electrolyte composition, operating temperature, and membrane transport all strongly influenced energy efficiency and power density limits from these new electrolyte chemistries. Peak power densities up to 100 mW cm-2 and theoretical energy efficiencies up to 12 % were identified through a preliminary survey of possible design choices. However, tradeoffs between attainable power density and energy efficiency limited cell performance values to a fraction of these values. Future work to better control diffusive transport without conductivity losses will be crucial for approaching theoretical battery performance limits.

(Invited) A Critical Review on the Expressions of Energy Efficiency Used in Low Temperature Water Electrolysis

The accurate knowledge of the energy efficiency coefficient of low temperature water electrolysis (Alkaline, PEM or AEM Electrolyzer) is a critical-point to estimate the total cost of electrolytic hydrogen production. After describing the fundamentals of these three processes and presenting the main data of water electro-dissociation under given temperature and pressure conditions, the energy efficiency coefficient can be calculated at the Laboratory scale by taking the ratio of the theoretical energy (ΔH) to decompose water under equilibrium conditions (no current) to the real energy used (ΔH + energy losses) to electrolyze water at a given current intensity. Different approximations of this coefficient are discussed and compared to data from literature. Conversely in the industry this coefficient can be calculated by taking the ratio of the total energy of hydrogen collected at the exhaust of the electrolyzer to the total energy (electricity + heat) supplied to the complete system. It is demonstrated that both definitions are consistent and similar if all the energy involved is taken into account. It is also shown that some approximations, in particular those neglecting the thermal energy in the denominator of this ratio, give efficiency coefficients larger than unity for cell voltages lower than the thermo-neutral voltage, which is a thermodynamic non-sense.The next figure shows the plot of the theoretical energy efficiency coefficient ε cell for p = 1 bar under the STP conditions (U0 tn = 1.48 V and U 0 rev = 1.23 V) up to Ucell = 2.0 V. There is a continuous decrease of ε cell,th vs. Ucell from 1.0 to 0.85 when Ucell = Utn = 1.48 V under STP conditions. Figure 1