Recently, rechargeable aqueous zinc-ion batteries (AZBs) have attracted extensive interest due to their safety, abundance, low cost, and low toxicity. However, aqueous electrolytes require a polymeric binder to prevent dissolution of the active material in addition to its binding properties. This study highlights binder-free, centimeter long, single-crystal, V2O5 nanofibers (BCS-VONF) on carbon cloth, as the cathode material for AZBs synthesized via a simple one-step hydrothermal process. BCS-VONF in 3.0 M Zn(OTf)2 exhibit promising electrochemical performance with excellent capacity retention. Even in the absence of a binder, BCS-VONF were found to be very stable in 3.0 M Zn(OTf)2. They will not yield to the dissolution and detachment of the active material on the current collector. The novel strategy described in this study is an essential step for the development of BCS-VONF on carbon cloth, as a promising cathode material for AZBs.

Frequency response analysis (FRA) is a popular method for assessing a transformer’s mechanical condition. The paper proposes a new method for interpreting the frequency response measurement results. The currently used numerical indices only give one value, which may be misleading in the analysis, while the proposed frequency response quality index (FRQI) tool analyses three separate features in the whole frequency range. The applied numerical calculations technique allows for estimations of not only the values of the average quality indices, but also locally for given frequency ranges of the analysed spectrum. It allows for determination of the problems that can be found in the active part of a transformer. The presented results come from three transformers, representing cases of typical faults. Two of them are from industry, while one was used for deformational tests in laboratory conditions. The proposed FRQI method showed its usefulness in FRA test results analysis and may be introd... [more]

This article is devoted to the development of the direct resistive heating of oxygen transport membranes technique. In this case, DC was selected to perform direct heating. The effect of DC on the oxygen fluxes and the microstructure of the membrane was studied. It is shown that in the short-term experiment with DC, a positive significant effect on the oxygen transport was found, while sample exposure under the influence of DC for a long period of time had a significant negative effect on the microstructure of the membrane.

For improving the performance of a doubly fed induction generator (DFIG) system under a harmonically distorted grid, this paper proposes a coordinated control strategy which is effective for grid inter-harmonics as well as grid integer harmonics. In order to suppress the negative impacts caused by grid harmonics, including inter-harmonics, this paper introduces an additional harmonics suppression controller, which contains a Chebyshev high-pass filter and a modified lead element considering the delay compensation. The proposed controller is employed in the rotor side converter (RSC) and grid side converter (GSC). Based on the proposed harmonics suppression controller, a coordinated control strategy between RSC and GSC is developed, in which the control targets, including the sinusoidal output current, constant power, or steady generator torque, can be achieved for DFIG, while GSC is responsible for maintaining the sinusoidal total current to guarantee the power quality of the grid conn... [more]

Western China has good conditions for constructing large-scale photovoltaic (PV) power stations; however, such power plants with large fluctuations and strong randomness suffer from the long-distance power transmission problem, which needs to be solved. For large-scale PV power stations that do not have the conditions for simultaneous hydropower and PV power, this study examined long-distance delivery mode and energy storage optimization. The objective was to realize the long-distance transmission of electrical energy and maximize the economic value of the energy storage and PV power storage. For a large-scale PV power station, the energy storage optimization was modelled under a given long-distance delivery mode, and the economic evaluation system quantified using the net present value (NPV) of the battery was based on the energy dispatch optimization model. By contrast, a lithium battery performance model was developed. Therefore, further analysis of the economics of the energy stora... [more]

This paper presents the Hybrid Renewable Energy System (HYRES), a powerful tool to contribute to the viability analysis of energy systems involving renewable generators. HYRES considers various input parameters related to climatic conditions, statistical reliability, and economic views; in addition to offering multi-objective optimizations using Genetic Algorithms (GAs) that have a better cost-benefit ratio than mono-objective optimization, which is the technique used in several commercial systems like HOMER, a worldwide leader in microgrid modeling. The use of intelligent techniques in HYRES allows optimal sizing of hybrid renewable systems with wind and solar energy generators adapted to different conditions and case studies. The elements that affect the system design like buying and selling energy from/to the grid and the use of storage units can be included in system configuration according to the need. Optimization approaches are selectable and include Initial Cost, Life Cycle Cos... [more]

Composite bucket foundations, which have been successfully transported, installed, and operated at the Qidong, Xiangshui, and Dafeng offshore wind farms in China, are economically advantageous due to the relatively simple transportation and installation process. The innovative one-step transportation and installation technology of foundation-tower-nacelle is the key phase in saving costs. In this paper, a “foundation lift ship” overall transport mode is proposed and introduced for the first time. Prototype data measurement, preliminary numerical simulation, and theoretical calculations were conducted to investigate whether the foundation-ship integrity, tower hoop stability, and various indexes of the nacelle met the requirements under the influences of various environmental factors. The multi-system coupling motion mechanism and analysis method of this new structure and transportation mode were expounded. Through the prototype observation data of the one-step overall transportation, t... [more]

The optimal planning of electric vehicle charging infrastructure has attracted extensive research interest in recent years. Most of the optimization problems were formulated by assuming that the configurations will be fixed at the optimal solution while overlooking the fact that the charging stations and the electric vehicles are “evolving” over time and have mutual impacts. On the other hand, little attention has been paid to evaluate the performance of the solutions in such a dynamic environment. Motivated by these gaps, this work develops a simulation model that captures the interactions between charging station configurations and electric vehicle population (and the preference of electric vehicles when choosing charging station). This modeling framework is then implemented to evaluate the performance of planned charging infrastructure in providing services to electric vehicles. Two indicators are calculated, i.e., usage rate and rejection rate. The former measures the “waste” due t... [more]

The Savonius-type hydraulic turbine, mainly known for its good self-starting properties and simple structure, not only has energy capturing characteristics but also has a certain effect on flow velocity reduction. Aside from ensuring energy capture efficiency, studying the effects of parameters on the flow velocity reduction capacity is of great significance for the protection of mariculture, as it can reduce the damage to cages and fishes. In this study, a computational fluid dynamics method was carried out to investigate the hydrodynamic characteristics and variations in the wake of a turbine. The accuracy of the simulation results was verified by experimental comparison. Firstly, the velocity contours and vectors were studied in detail to reveal the mechanism of the flow velocity reduction effect. Secondly, the velocity attenuation coefficient and relative attenuation length were formulated by the variation rule of the velocity field to evaluate the turbine reduction strength and ra... [more]

This study presents a simulation platform for a hybrid electric motorcycle with an engine, a driving motor, and an integrated starter generator (ISG) as three power sources. This platform also consists of the driving cycle, driver, lithium-ion battery, continuously variable transmission (CVT), motorcycle dynamics, and energy management system models. Two Arduino DUE microcontrollers integrated with the required circuit to process analog-to-digital signal conversion for input and output are utilized to carry out a hardware-in-the-loop (HIL) simulation. A driving cycle called worldwide motorcycle test cycle (WMTC) is used for evaluating the performance characteristics and response relationship among subsystems. Control strategies called rule-based control (RBC) and equivalent consumption minimization strategy (ECMS) are simulated and compared with the purely engine-driven operation. The results show that the improvement percentages for equivalent fuel consumption and energy consumption f... [more]

As a by-product of lignocellulosic depolymerization for furfural production, furfural residue (FR) is composed of residual cellulose, lignin, humic acid, and other small amounts of materials, which have high reuse value. However, due to the limitation of furfural production scale and production technology, the treatment of FR has many problems such as high yield, concentrated stacking, strong acidity, and difficult degradation. This leads to the limited treatment methods and high treatment cost of furfural residue. At present, most of the furfural enterprises can only be piled up at will, buried in soil, or directly burned. The air, soil, and rivers are polluted and the ecological balance is destroyed. Therefore, how to deal with furfural residue reasonably needs to be solved. In this review, value-added products for furfural residue conversion are described in detail in the fields of soil culture, catalytic hydrolysis, thermal decomposition, and porous adsorption. The future studies r... [more]

Water electrolysis with a fast change of polarity generates a high concentration of bulk nanobubbles containing H 2 and O 2 gases. When this concentration reaches a critical value, a microbubble pops up, which is terminated quickly in an explosion process. In this paper, we provide experimental information on the phenomenon concentrating on the dynamics of exploding microbubble observed from the top and from the side. An initial bubble with a size of 150 μ m expands to a maximum size of 1200 μ m for 150 μ s and then shrinks in the cavitation process. The sound produced by the event is coming from two sources separated in time: exploding bubble and cavitating bubble. The observed dynamics supports expansion of the bubble with steam but not with H 2 and O 2 mixture. A qualitative model of this puzzling phenomenon proposed earlier is refined. It is demonstrated that the pressure and temperature in the initial bubble can be evaluated... [more]

The paper presents a comprehensive study of the physicochemical and electrochemical properties of a new nano-microporous non-woven composite separation material for a lithium-ion battery based on nano- and microfibers of polyvinylidene fluoride (PVDF) and its copolymer with polytetrafluoroethylene (PTFE), obtained by capillary-less electrospinning. A technique for the synthesis of separation material was developed, and the composition of the polymeric solution and the electrospinning conditions were optimized to produce polymer nano-microfibers with the required physicochemical characteristics. The optimal synthesis conditions for the separation material were determined. Higher porosity of the separation material and increased wettability in the most common electrolyte compositions contribute to the higher conductivity of the obtained separation material in comparison with the widely used commercial separation materials based on polypropylene (PP). The working characteristics of the se... [more]

Power transmission (PT) projects are vital for the power sector. However, worldwide PT projects experience delay. There is an urgent need to understand the unique causes of delays in PT projects. This paper presents the first empirical study on causes of delays in PT projects via a comprehensive literature review. Based on this literature review, 63 potential delay factors are identified and divided into ten major groups. These include two new groups of delay attributes, comprising sector-specific factors (SSF) and general factors (GF), where SSF pertains solely to PT projects and GF contributes to minimizing the bias of project participants. A questionnaire survey of 311 PT stakeholders is conducted to determine the overall ranking of the delay factors using the relative importance index. The results indicate that SSF, GF, and external/unavoidable factors are the most critical groups of delay factors, with the top-ranked factors being right of way problems of transmission line (TL), f... [more]

Artificial Neural Networks (ANNs) have proven to be a powerful tool in many fields of knowledge. At the same time, evolutionary algorithms show a very efficient technique in optimization tasks. Historically, ANNs are used in the training process of supervising networks by decreasing the error between the output and the target. However, we propose another approach in order to improve these two techniques together. The ANN is trained with the points obtained during an optimization process by a genetic algorithm and a flower pollination algorithm. The performance of this ANN is used as a stop criterion for the optimization process. This new configuration aims to reduce the number of iterations executed by the genetic optimizer when learning the cost function by an ANN. As a first step, this approach is tested with eight benchmark functions. As a second step, the authors apply it to an air jet impingement design process, optimizing the surface temperature and the fan efficiency. Finally, a... [more]

The growing popularity of buildings with integrated sub-systems requires a review of methods to optimize the preheating of ventilation air. An integrated system permits using geothermal heat storage parallel to the direct outdoor air intake with additional treatment in the mechanical room as a part of building an automatic control system. The earth−air heat exchanger (EAHX) has many advantages but also has many unanswered questions. Some of the drawbacks are: A possible entry of radon gas, high humidity in the shoulder seasons, and the need for two different air intake sources with a choice that depends on the actual weather conditions. In winter the EAHX may be used continuously to ensure thermal comfort, while in other seasons its operation must be automatically controlled. To generate missing information about EAHX technology we examined two nearly identical EAHX systems, one placed in the ground next to a building and the other under the basement slab. In another project, we reinfo... [more]

This paper presents an analysis of a Total Energy Control System (TECS) introduced by Lambregts to control unmanned aerial vehicle (UAV) velocity and altitude by using the total energy distribution. Furthermore, an extended Kalman filter (EKF) approach was used to predict aircraft response in terms of angular rates and linear acceleration during a test flight campaign. From both approaches, state equations were obtained to model the aircraft using Matlab-Simulink. From an aerodynamic study, airplane characteristics were obtained in terms of non-dimensional derivatives and compared to those obtained from the experimental methods. It was determined that TECS approach was very accurate; however, disturbance errors could be decreased by adjusting some model parameters. On the other hand, it was difficult to obtain a real estimation from the EKF method due to the presence of turbulence during flight and the relatively low inertia of the scale model. Dynamic characteristics were validated us... [more]

The development of Short-Term Forecasting Techniques has a great importance for power system scheduling and managing. Therefore, many recent research papers have dealt with the proposal of new forecasting models searching for higher efficiency and accuracy. Several kinds of artificial intelligence (AI) techniques have provided good performance at predicting and their efficiency mainly depends on the characteristics of the time series data under study. Load forecasting has been widely studied in recent decades and models providing mean absolute percentage errors (MAPEs) below 5% have been proposed. On the other hand, short-term generation forecasting models for photovoltaic plants have been more recently developed and the MAPEs are in general still far from those achieved from load forecasting models. The aim of this paper is to propose a methodology that could help power systems or aggregators to make up for the lack of accuracy of the current forecasting methods when predicting renewa... [more]

South Africa’s energy consumption takes up about one-third of that in the whole African continent, ranking the first place in Africa. However, there are few researches on the prediction of energy consumption in South Africa. In this study, based on the data of South Africa’s energy consumption during 1998−2016, Autoregressive Integrated Moving Average (ARIMA) model, nonlinear grey model (NGM) and nonlinear grey model−autoregressive integrated moving average (NGM-ARIMA) model are adopted to predict South Africa’s energy consumption during 2017−2030. After using these NGM, ARIMA and NGM-ARIMA, the mean absolute percent errors (MAPE) are 2.827%, 2.655% and 1.772%, respectively, which indicates that the predicted result has very high reliability. The prediction results show that the energy consumption in South Africa will keep increasing with the growth rate of about 7.49% in the next 14 years. This research result will provide scientific basis for the policy adjustment of energy supply an... [more]

The social cost, as one of the factors determining sustainability of socio-economic development, is strongly dependent upon a number of casualties and mortality in road accidents. The condition of car tires appears to be one of the important factors determining the occurrence of accidents. The vast majority of vehicles are tested every year at vehicle inspection stations. One of the elements affecting the result of the technical condition test and basically the quality of vehicle braking is the technical condition of the tires. Their technical condition is a very important factor responsible for the quality of acceleration, braking, maintaining, or changing the direction of driving. As a consequence, it has a significant impact on road safety. The aim of the study is to examine the impact of tires on the results of tests performed at a vehicle inspection station. The study presents the results of bench measurements of the impact of selected features of tire condition of two vehicles du... [more]

The Philippines consists of 7100 islands, many of which still use fossil fuel diesel generators as the main source of electricity. This supply can be complemented by the use of renewable energy sources. This study uses a Philippine offshore island to optimize the capacity configuration of a hybrid energy system (HES). A thorough investigation was performed to understand the operating status of existing diesel generator sets, load power consumption, and collect the statistics of meteorological data and economic data. Using the Hybrid Optimization Models for Energy Resources (HOMER) software we simulate and analyze the techno-economics of different power supply systems containing stand-alone diesel systems, photovoltaic (PV)-diesel HES, wind-diesel HES, PV-wind-diesel HES, PV-diesel-storage HES, wind-diesel-storage HES, PV-wind-diesel-storage HES. In addition to the lowest cost of energy (COE), capital cost, fuel saving and occupied area, the study also uses entropy weight and the Techni... [more]

Medium and low-rank coal from the Zhunnan coalfield of Xinjiang in China was investigated for quantitatively characterizing its range of aperture structure. The pore parameters were determined by nitrogen adsorption at low temperature and mercury injection at high pressure, and the full aperture was determined. The FHH model, Menger model, Sierpinski model, and a thermodynamic model were used to calculate the comprehensive fractal dimension of the coal samples over the full range of aperture. The fractal characteristics of the pores of medium- and low-rank coal were quantitatively analyzed, which provided a reference for the overall characterization of pore structure heterogeneity in this coalfield. The results show that the FHH model and thermodynamic model more accurately calculate the fractal dimensions of less and greater than the joint pore position, respectively. The comprehensive fractal dimension of the low-rank coal pore is 2.8005−2.8811 and that of medium rank coal is 2.5710−... [more]

With the reform of the power system, the retail electricity market in China has gradually been liberalized. The mechanism of freely selling electricity have been set up. To grab market share and increase profits, electricity retail companies have introduced a series of retail electricity price packages. To evaluate the applicability of these retail electricity price packages, an adaptive evaluation index system that takes into account the interests of both the power company and the users is first established. Furthermore, an integrated evaluation model that combines data envelopment analysis (DEA) and the cloud model is proposed. In this model, DEA is used to process quantitative indicators and the cloud model is employed to quantify qualitative problems. A case study of Tianjin is conducted to verify the effectiveness of the proposed evaluation system and model. The empirical study shows that qualitative indicators can also affect the applicability of the retail electricity price pack... [more]

Alkanes are widely used as phase change materials (PCMs), especially for thermal energy storage (TES), due to their high thermal capacity, stability, availability, and non-corrosiveness. However, the drawbacks of alkanes are low heat conductivity and high cost. Our aim was to explore alternative organic PCMs for TES and to compare such compounds based on the relationship between their performance and cost. For this purpose, we analysed several commercially available products, including long chain alkanes, alcohols, monocarboxylic acid, amines, ethers and esters in high purities. Differential scanning calorimetry and thermogravimetry (DSC and TGA) were used to measure the melting point, melting enthalpy and thermal stability of these compounds. The materials were classified according to their melting temperature. In order to compare the compounds, we calculated from the measured enthalpies and the price list provided by producers a coefficient that represents factors in both the perform... [more]

Different alternatives are being studied nowadays in order to enhance the behavior of transcritical CO2 refrigeration plants. Among the most studied options, subcooling is one of the most analyzed methods in the last years, increasing cooling capacity and Coefficient Of Performance (COP), especially at high hot sink temperatures. A new cycle, called integrated mechanical subcooling cycle, has been developed, as a total-CO2 solution, to provide the subcooling in CO2 transcritical refrigeration cycles. It corresponds to a promising solution from the point of view of energy efficiency. The purpose of this work is to present, for the first time, thermodynamic analysis of a CO2 refrigeration cycle with integrated mechanical subcooling cycle from first and second law approaches. Using simplified models of the components, the optimum operating conditions, optimum gas-cooler pressure, and subcooling degree are determined in order to obtain the maximum COP. The main energy parameters of the sys... [more]