In order to obtain polyimide-based composite materials for energy storage applications, four synthetic methods towards a polyimide matrix with 2 wt.% pristine or acid-functionalized MWCNTs have been developed. The polyimide is derived from a nitrile aromatic diamine and a fluorene-containing dianhydride which allowed the formation of flexible free-standing nanocomposite films. The films were thoroughly characterized by means of structural identification, morphology, mechanical, thermal and dielectric behavior, as well as the charge storage performance. The obtained data indicated higher homogeneity of the composites loaded with acid-functionalized MWCNTs that enabled significantly increased dielectric properties compared to the matrix. To assess the electrical charge storage capability, cyclic voltammetry and galvanostatic charge−discharge measurements were employed in a three-electrode cell configuration. Due to the higher conductivity of pristine MWCNTs compared to acid-functionalize... [more]

The article presents studies on the impact of the significant process parameters of a paper machine with a Yankee cylinder on its production capacity and heat energy consumption for drying the paper web. Parameters such as machine speed, web moisture content before and after pressing, parameters of steam supplied to the cylinder and parameters of hot air flowing from the nozzles of the hood were analyzed. The study’s results were used to optimize production to improve the energy efficiency and performance of the machine. In order to use the possible methods of improving the production capacity and heat energy consumption, the parameters of the production process were measured and the basic indicators characterizing the operation of the machine were calculated in the Yankee cylinder−dryer hood system. The correct functioning of the machine components and the possibility of their modernization were also analyzed. Technological and construction changes introduced based on the research res... [more]

The paper provides an economic model for the assessment of hydrogen production at the site of an existing thermal power plant, which is then integrated into the existing gas grid. The model uses projections of electricity prices, natural gas prices, and CO2 prices, as well as estimates of the cost of building a power-to-gas system for a 25-year period. The objective of this research is to calculate the yellow hydrogen production price for each lifetime year of the Power-to-gas system to evaluate yellow hydrogen competitiveness compared to the fossil alternatives. We test if an incentive scheme is needed to make this technology economically viable. The research also provides several sensitivity scenarios of electricity, natural gas, and CO2 price changes. Our research results clearly prove that yellow hydrogen is not yet competitive with fossil alternatives and needs incentive mechanisms for the time being. At given natural gas and CO2 prices, the incentive for hydrogen production needs... [more]

In this article, the most important publications on the subject are compiled to highlight the progress in biodiesel production from tropical cultivars, including energy and environmental potential, raw materials, and the advantages and disadvantages of this biofuel. A critical and objective review of biodiesel production as an alternative fuel for power generation systems and its importance in the energy matrix was conducted. A survey of real applications, new computational and experimental trends, and proposals in internal combustion engines employing organic biofuel was performed. The main findings were as follows: (i) there is the possibility of integration and support in the energy matrix of different countries, as well as the competing with and complementing, energetically, other renewable energy sources, such as solar and wind; (ii) Jatropha curcas, sunflowers, soybean, Moringa oleifera, palm, cottonseed, castor, rubber seed, and coconut are tropical cultivars used to obtained oi... [more]

The operation of wireless battery chargers at multiple switching frequencies may lead to a noticeable suppression of conducted and radiated electromagnetic interference (EMI) at the cost of decreased efficiency (mainly at lower load resistances) and increased peak and root mean square values of currents of power components of the wireless battery charger. Moreover, the reduction in conducted EMI is only moderate (<8.3 dB). Therefore, a novel approach based on modified resonant circuits and a modified control technique to obtain better reduction in the conducted and radiated EMI without significantly compromising other performance characteristics of the wireless battery charger is proposed and validated by using simulations and experiments. It is shown in this paper that the wireless charger operating at multiple switching frequencies with the proposed approach for the performance improvement has a more effective implementation of the four-switching frequency spread-spectrum techniqu... [more]

Offshore photovoltaic installations are the future technology in solar energy since they enable the use of the large amount of maritime space, which is especially important when land space is not available. Various research groups are working to create viable installations. However, there are currently no tools available that an offshore system designer can use to quantify the effect of wave response motion on offshore photovoltaic installations. This research presents a new simulation tool termed the Offshore Solar Irradiance Calculator (OSIC) that is able to quantify this effect. Furthermore, a yearly parametric analysis is presented to show the effects of a characteristic wave equation on different offshore tracking systems; namely, horizontal single-axis tracking, vertical single-axis tracking and dual-axis tracking. Finally, another parametric analysis is presented to show the effects of varying wave amplitudes of oscillations on the incident irradiance received by these tracking... [more]

On board a satellite, there are different devices that operate from a common energy source called a power bus. Since there are many devices connected to the same power bus and they are in the close vicinity of each other, it is important that they are able to function adequately in the electromagnetic environment of the satellite without introducing intolerable electromagnetic interference to other devices. On-board devices often require voltage levels different from the bus voltage to function, and this is often produced by switching-mode power supplies (SMPS). Their switching-mode operation guarantees that there is less power loss during conversion; however, they also emit conducted and radiated noises into the direction of the power bus and the payloads. In the case of multiple SMPS powered by the same power bus, we can interleave their switching periods. Thus, their noises will cancel each other out on their common input. In this study, we are going to demonstrate the noise reducti... [more]

The article is devoted to solving the problem of charge equalization of multi-element batteries with rated voltage up to 1000 V, operating in dynamic modes with different charge and discharge depths. This article proposes a method of balancing the voltages of power battery elements. The essence of the proposed method is to form a reference signal equivalent to the reference voltage of the battery element for the current state of charge. The novelty of the method presented in this article, in comparison with relevant existing techniques, lies in active control over the balancing circuit proportional to real cell voltage deviation from the reference value. The proposed method can be used both for passive balancing techniques based on ballast resistors, and for circuits made on electromagnetic energy redistribution systems between galvanic cells. A number of Simulink models were developed to determine the electrical parameters of active and passive balancing circuits. Performance and accu... [more]

The increase in industrialization and development has tremendously diminished fossil fuel resources. Moreover, the excessive use of fossil fuels has resulted in the release of various toxic gases and an increase in global warming. Hence, necessitating the need to search for a renewable energy source. In this study, sesame waste biomass (SWB), which is abundantly available in Pakistan, has been used as feedstock for obtaining bio-oil using the pyrolysis technique. Pyrolysis was carried out using thermogravimetry and a pyrolysis chamber. Firstly, thermogravimetric analysis was performed on biomass with/without a laboratory synthesized catalyst Ni/Co/MCM-41 in nitrogen at different temperature programmed rates of 5, 10, 15, and 20 °C/min. A four-stage weight loss was observed that pointed toward the vaporization of water, and degradation of hemicelluloses, cellulose, and lignin. The kinetics parameters were determined using the Kissinger equation. The activation energy for the decompositi... [more]

Cyclic ethers (CEs) can be promising future biofuel candidates. Most CEs possess physico-chemical and combustion indicators comparable to conventional fuels, making them suitable for internal combustion engines. This work computationally investigates the kinetic behaviors of hydrogen abstraction from 2-methyl tetrahydrofuran (2MTHF), one of the promising CEs, by hydroxyl radicals under combustion and atmospheric relevant conditions. The various reaction pathways were explored using the CCSD(T)/cc-pVTZ//M06-2X/aug-cc-pVTZ level of theory. The Rice−Ramsperger−Kassel−Marcus-based master equation (RRKM-ME) rate model, including treatments for hindered internal rotation and tunneling, was employed to describe time-dependent species profiles and pressure and temperature-dependent rate coefficients. Our kinetic model revealed that the H-abstraction proceeds via an addition-elimination mechanism forming reaction complexes at both the entrance and exit channels. Eight different reaction channel... [more]

Recent R&D activities in nuclear fusion have identified the DEMO reactor as the ITER successor, aiming at demonstrating the technical feasibility of fusion plants, along with their commercial exploitation. However, the pulsed operation of the machine causes an “unconventional” operation of the system, posing unique challenges to the functional feasibility of the steam generator, for which it is necessary to define and qualify a reference configuration for DEMO. In order to facilitate the transitions between different operational regimes, the Once Through Steam Generator (OTSG) is considered to be a suitable choice for the DEMO primary heat transfer systems, being characterized by lower thermal inertia with respect to the most common U-tube steam generators. In this framework, the ENEA has undertaken construction of the STEAM facility at Brasimone R.C., aiming at characterizing the behavior of the DEMO OTSG and related water coolant systems in steady-state and transient conditions. A de... [more]

The accurate quantification of the performance loss rate of photovoltaic systems is critical for project economics. Following the current research activities in the photovoltaic performance and reliability field, this work presents a comparative assessment between common change point methods for performance loss rate estimation of fielded photovoltaic installations. An extensive testing campaign was thus performed to evaluate time series analysis approaches for performance loss rate evaluation of photovoltaic systems. Historical electrical data from eleven photovoltaic systems installed in Nicosia, Cyprus, and the locations’ meteorological measurements over a period of 8 years were used for this investigation. The application of change point detection algorithms on the constructed monthly photovoltaic performance ratio series revealed that the obtained trend might not always be linear. Specifically, thin film photovoltaic systems showed nonlinear behavior, while nonlinearities were als... [more]

Compared to fossil fuels, biodiesel is a clean fuel, does not pollute the environment, and can be produced from inexhaustible natural sources. The objectives of our research are to study how increasing doses of complex fertilizers, applied to rapeseed oil culture, affect the production of rapeseeds and oil; the comparative study between the quality parameters of refined rapeseed oil (RRO) and fatty acids (FA); and the analysis of the quality of the biodiesel obtained from them (BRO and BFA). The experimental field is set-up in a Latin rectangle format and is placed on a total area of 400 m2 divided into 16 parcels, randomized for uniformity with four replications and four fertilizer graduations (N0P0K0—Control, N160P160K160, N320P320K320, N480P480K480). To obtain biodiesel form oil (BRO) and fatty acids (BFA), the processes of esterification, transesterification, refining, washing, sedimentation, and drying were applied. A comparison between biodiesel quality parameters from RRO and FA... [more]

A simulation model based on Dymola modelling was developed to investigate the dynamic characteristics of automatic generation control (AGC) for variable-load thermal power units in this study. Specifically, a 300 MW unit from a power plant in northern China was used to verify the model’s validity in steady-state processes and to analyze the behavior of the main thermal parameters under different rates of load changes. The economic performance of the unit under different rates of load changes is also analyzed by combining the economic indexes of “two regulations” in the power grid. Results indicate that as the rate of load changes increases, boiler output, main steam temperature, reheat steam temperature, main steam pressure, and working temperatures of various equipment fluctuate more intensely. Specifically, at a rate of load reduction of 2.0% Pe MW/min, the maximum deviation of the main steam temperature can reach 7.6 °C, with the screen-type superheater experiencing the largest heat... [more]

The hybridization of PSO for the Optimal Coordination of Directional Overcurrent Protection Relays (DOPR) of the IEEE bus system proposes a new method for coordinating directional overcurrent protection relays in power systems. The method combines the hybrid particle swarm optimization (HPSO) algorithm and a heuristic PSO algorithm to find the minimum total operating time of the directional overcurrent protection relays with speed and accuracy. The proposed method is tested on the IEEE 4-bus, 6-bus, and 8-bus systems, and the results are compared with those obtained using traditional coordination methods. The collected findings suggest that the proposed method may produce better coordination and faster operation of DOPRs than the previous methods, with an increase of up to 74.9% above the traditional technique. The hybridization of the PSO algorithm and heuristic PSO algorithm offers a promising approach to optimize power system protection.

In this paper, a transcritical carbon dioxide power generation system based on a vortex tube is studied, which has the advantage of the self-condensation of carbon dioxide. The thermodynamic performance of the system was investigated by establishing a mathematical model. The results showed that under fundamental working conditions, the system could output a net power of 271.72 kW, and the thermal efficiency as well as the exergy efficiency of the system could reach 7.38% and 27.09%, respectively. Exergy analysis showed that the turbine had the greatest exergy loss among the system’s components, followed by the vortex tube, pump, heater and cooler. Parameter analysis showed that increasing the outlet pressure and inlet temperature of the vortex tube can improve the thermal efficiency and exergy efficiency of the system. In addition, the improvement in the turbine component’s efficiency is the most beneficial to the system’s performance, among which the turbine’s efficiency has the great... [more]

Phase change materials are used in passive solar house construction with light steel structure walls, which can overcome the problems of weak heat storage capacity and poor utilization of solar heat and effectively solve the thermal defects of light steel structure walls. Based on this, on the basis of preliminary experimental research, this study further carried out theoretical analysis and simulation research on the thermal performance of a light steel structure passive solar house (Trombe form) with PCM walls. Through the heat balance analysis of heat transfer in the heat collecting partition wall, the theoretical calculation formula of the phase change temperature of the PCM was obtained, and it verified theoretically that the phase change temperature value should be 1−3 °C higher than the target indoor air temperature. The evaluation index “accumulated daily indoor temperature offset value” was proposed for evaluating the effect of phase change materials on the indoor temperature... [more]

The aim of this study was to analyse specific greenhouse gas emissions savings for a variety of agricultural residues, industrial by-products, and municipal biowaste. One of the most viable alternatives to fossil fuels is bioenergy, particularly biogas produced by the anaerobic digestion of renewable feedstocks. The revised Renewable Energy Directive (D 2018/2001) recognizes that biogas production from agricultural residues, livestock production, and industrial by-products is an acknowledged greenhouse gas mitigation technology in cases where their use results in a certain level of specific greenhouse gas savings. This study delivered values for the maximum transport distance of agricultural residues and industrial by-products to achieve the greenhouse gas (GHG) emissions-saving requirement defined by Directive 2018/2001. It analysed the greenhouse gas emissions reduction for numerous feedstocks for which Directive 2018/2001 has not defined the default and typical values but which coul... [more]

As we move away from internal combustion engines to tackle climate change, the importance of hydrogen-powered vehicles and polymer electrolyte membrane fuel cell (PEMFC) technology has dramatically increased. In the present study, we aimed to determine the optimal configuration for the power output of a PEMFC system using computational fluid dynamics (CFD) modelling to analyse variations of the primary serpentine design of gas flow channels. This helps improve efficiency and save on valuable materials used, reducing potential carbon emissions from the production of hydrogen vehicles. Different numbers of serpentine gas channels were represented with various spacing between them, within the defined CFD model, to optimise the gas channel geometry. The results show that the optimum configuration was found to have 11 serpentine channels with a spacing of 3.25 mm. In this optimum configuration, the ratio between the channel width, channel spacing, and serpentine channel length was found to... [more]

Increasing interest in natural gas-fired gensets is motivated by District Heating (DH) network applications, especially in urban areas. Even if they represent customary solutions, when used in DH, duty regimes are driven by network thermal energy demands resulting in discontinuous operation, which affects their remaining useful life. As such, the attention on effective condition-based maintenance has gained momentum. In this paper, a novel unsupervised anomaly detection framework is proposed for gensets in DH networks based on Supervisory Control And Data Acquisition (SCADA) data. The framework relies on multivariate Machine-Learning (ML) regression models trained with a Leave-One-Out Cross-Validation method. Model residuals generated during the testing phase are then post-processed with a sliding threshold approach based on a rolling average. This methodology is tested against nine major failures that occurred on the gas genset installed in the Aosta DH plant in Italy. The results sho... [more]

Air contaminants can have detrimental effects on the performance and durability of proton exchange membrane (PEM) fuel cell vehicles. This research focuses on the experimental investigation of the effect of nitrogen monoxide (NO) in the cathode gas stream, which provokes a cell voltage decrease due to the partially reversible adsorption of NO on the platinum catalyst. The concentration and exposure time of NO in the cathode gas stream are varied at selected constant current densities and load ramps to assess the effects throughout the fuel cell system operating range. The results show the cell voltage loss in the presence of NO and reveal a near-catalyst saturation with increased injected NO mass. Additionally, several voltage recovery and mitigation strategies are introduced and discussed by presenting conclusions about the general effect of NO on a fuel cell system in operation. The most promising recovery strategy for fuel cell systems is identified, and the overall system degradati... [more]

With the wake effect between different wind turbines, a wind farm generally aims to achieve the maximum energy capture by implementing the optimal pitch angle and blade tip speed ratio under different wind speeds. During this process, the balance of fatigue load distribution is easily neglected because it is difficult to be considered, and, thus, a high maintenance cost results. Herein, a novel bi-objective optimal wind farm energy capture (OWFEC) is constructed via simultaneously taking the maximum power output and the balance of fatigue load distribution into account. To rapidly acquire the high-quality Pareto optimal solutions, the decomposition-based multi-classifier-assisted evolutionary algorithm is designed for the presented bi-objective OWFEC. In order to evaluate the effectiveness and performance of the proposed technique, the simulations are carried out with three different scales of wind farms, while five familiar Pareto-based meta-heuristic algorithms are introduced for per... [more]

This study discusses the influence of natural wind on the air flow of air-cooled condensers (ACCs) and then proposes a partition speed-regulation strategy for a fan group with enhanced generalized capability, which is of great practical significance for optimizing energy-saving operations. The stochastic time-varying features of natural wind are characterized by sine−Gaussian, Weibull, and composed winds. In a natural wind disturbance, using the Sugon Supercomputing Center, the transient numerical simulation of the dynamic evolution of the ACC flow field was found: the dynamic system of air flow is a typical time-varying nonlinear process. Cluster analysis was used to extract the nonlinear features of air flow, divide the fan group into four subregions with generalization capability, and implement a partitioned speed operation. It was found that giving priority to increasing the fan speed in the headwind partition can suppress the natural wind disturbance and improve the overall air fl... [more]

This article presents the results of an analysis of heat enhancement intensification using twisted tapes in linear absorbers for low-concentration parabolic trough collectors, a technology frequently considered as a supplementary energy source for industrial heat production. This contribution proposes a segmented application of different twisted tapes to intensify heat absorption. A 33.7 mm tubular absorber placed in the collector focal point with an aperture of 1.8 m was selected. The temperature range of the heat transfer fluid was chosen at 60−250 °C. The impact of inserts with twisted ratios of 1, 2 and 4 on system operation was analysed using the Ansys Fluent and mathematical model. The models used were validated based on experimental results from a parabolic trough collector with solar simulator test bench. The results indicated that for the range of mass flow between 0.15−0.3 kg/s, the most optimal is applying twisted ratio 1, except for the highest-temperature section. In this... [more]

This study proposes an optimal scheduling method for complex integrated energy systems. The proposed method employs a heuristic algorithm to maximize its energy, economy, and environment indices and optimize the system operation plan. It uses the k-means combined with box plots (Imk-means) to improve the convergence speed of the heuristic algorithm by forming its initial conditions. Thus, the optimization scheduling speed is enhanced. First of all, considering the system source and load factors, the Imk-means is presented to find the typical and extreme days in a historical optimization dataset. The output results for these typical and extreme days can represent common and abnormal optimization results, respectively. Thus, based on the representative historical data, a traditional heuristic algorithm with an initial solution set, such as the genetic algorithm, can be accelerated greatly. Secondly, the initial populations of the genetic algorithm are dispersed at the historical outputs... [more]