Natural gas is the primary source of energy, accounting for around 20% of the world’s energy production. It is also a key element in reducing CO2 emissions due to its key role in stabilizing renewable energy sources. At the same time, natural gas as a fossil fuel that emits CO2 should be limited. A natural candidate that can ensure the stabilization of RES and at the same time reduce the demand for fossil fuels is biogas. Successful use of biogas requires a thorough understanding of the potential, structure, and specifics of its sources and production technology. The presented study provides a perspective and a brief overview of the existing potential of biogas production. Poland was chosen as the case study and it was shown that almost 90% of the Polish biogas potential comes from sources with a capacity below 100 Nm3/h, which is the current minimum commercially available capacity of the biogas purification and liquefaction technologies. Consequently, full utilization of these sources... [more]

Residential coal combustion is a major source of air pollution in developing countries, including China. Indeed, precisely measuring the real-time emission of major air pollutants is often challenging and can hardly be repeated at a lab-scale. In this study, for the first time, two clean coals initiated from raw bituminous coal were burned for real-time estimation of air pollution characteristics and their thermal efficiencies in different stoves. Moreover, thermodynamic equilibrium simulations were investigated for slagging parameters using Factsage 7.1 at reaction temperature 800~1600 °C. Results revealed that the firepower of clean coals (Briquetted coal and Semi-coke) was much higher (2.2 kW and 2.1 kW) than raw coal (1.8 kW) in a traditional stove. However, the thermal efficiencies were remarkably increased (13.3% and 13.5%) in an improved stove for briquetted coal and semi-coke, respectively. The emission of major air pollutants including carbon monoxide (CO), sulfur dioxide (SO2... [more]

This perspective article aims to identify key research priorities to make the waste-to-energy sector compatible with the societal goals of circularity and carbon neutrality. These priorities range from fundamental research to process engineering innovations and socio-economic challenges. Three focus areas are highlighted: (i) the optimization of flue gas cleaning processes to minimize gaseous emissions and cross-media, (ii) the expansion of process control intelligence to meet targets for both material recovery and energy recovery, and (iii) climate neutrality, with the potential for negative emissions via the removal of atmospheric carbon dioxide across the full cycle of the waste resource. For each area, recent research trends and key aspects that are yet to be addressed are discussed.

In this study, the pyrolysis procedure was used to extract oil from pomegranate peels (PP) utilizing biomass-derived sulfonated tea waste as a catalyst. FTIR, SAA, SEM, and XRD were used to characterize the catalyst. Thermo-catalytic decomposition was carried out in a salt bath reactor and the bio-oil composition was determined through GC-MS. The oil obtained from virgin PP was observed to contain compounds in the range of C5−C13, whereas from the catalyzed reaction it was found to be rich in C5−C23. For the calculation of kinetic parameters, TG analysis was performed of virgin PP and with the catalyst at different heating rates. TG/DTG indicated weight loss in four steps. The first weight loss below 100 °C is due to the physically adsorbed water molecule evaporation. The second weight loss is attributed to hemicellulose decomposition and the third one to cellulose degradation. The fourth weight loss is due to lignin degradation. Kissinger model was used for measuring the activation en... [more]

Theft of electricity poses a significant risk to the public and is the most costly non-technical loss for an electrical supplier. In addition to affecting the quality of the energy supply and the strain on the power grid, fraudulent electricity use drives up prices for honest customers and creates a ripple effect on the economy. Using data-analysis tools, smart grids may drastically reduce this waste. Smart-grid technology produces much information, including consumers’ unique electricity-use patterns. By analyzing this information, machine-learning and deep-learning methods may successfully pinpoint those who engage in energy theft. This study presents an ensemble-learning-based system for detecting energy theft using a hybrid approach. The proposed approach uses a machine-learning-based ensemble model based on a majority voting strategy. This work aims to develop a smart-grid information-security decision support system. This study employed a theft-detection dataset to facilitate aut... [more]

Because of the unequal diameter between the pulse tube and the heat exchangers at the two sides, the fluid entering the pulse tube from the heat exchanger easily forms a complex disturbing flow in the pulse tube, which causes energy loss and affects the performance of a pulse tube refrigerator. This study proposes a numerical model for predicting the flow and heat transfer characteristics of pulse tube refrigerators. Three cases of adding conical tube transitions between the pulse tube and the heat exchanger are studied, and the results indicate that the conical tube transition can reduce the fluid flow velocity at the inlet and outlet of the pulse tube and reduce the size of the vortex at the boundary of the pulse tube. In comparison with the tapered transition of 45° on only one side of the pulse tube, both sides can maintain the temperature gradient, effectively decrease the effect of the disturbing flow, and significantly improve the cooling performance of the pulse tube.

The fast development of distributed generations enables the microgrid a popular solution for the construction of the modern power grid, where the control behaviors of power electronics converters play a crucial role. Under this scenario, the emulation of microgrid control behaviors is becoming an emerging need for the testing and teaching of the AC microgrid. However, conventional approaches, such as the dynamic simulation test and the Power-Hardware-In-Loop, are still costly or bulky to flexibly recreate the correct characteristics of microgrid including different layers of controls and the interactions among multiple converters. The dynamic simulation test is bulky and costly to emulate various types of control behaviors since all physical components in the test system may need to be adjusted. The high cost of Power-Hardware-In-Loop is mainly caused by the high-performance real-time simulator and power amplifier. In this paper, a novel emulation system is proposed for the testing of... [more]

The Paris Agreement’s objectives related to climate change put aviation under great pressure and environmental inspection. In particular, the aviation industry is committed to achieving a 50% reduction in CO2 emissions by 2050 compared to 2005 levels. A shift to alternative aviation fuels seems imperative. The International Air Transport Association (IATA) has identified the production of drop-in sustainable liquid fuels (SAFs) as the most promising strategy, at least short term, to reduce the environmental impact of the sector. Within this review, a critical summary of the current alternative aviation fuels/pathways is presented and a comparative analysis of the dominant technologies is performed considering techno-economic assessment, environmental evaluation, and future projections. The impact of the ‘ReFuelEU Aviation’ initiative on the current dominant policies and market incentives is assessed. Hydroprocessed esters and fatty acids (HEFA), Fischer−Tropsch (FT) synthesis, alcohol-... [more]

The resistance−capacitance (RC) model is one of the most applicable circuits for modeling the charging and discharging processes of supercapacitors (SCs). Although this circuit is usually used in the electric and thermal investigation of the performance of SCs, it does not include leakage currents. This paper presents exact analytical formulas of leakage-current-based supercapacitor models that can be used in industrial applications, i.e., constant-power-based applications. In the proposed model, current and voltage are represented as a solution of nonlinear equations that are solved using the standard Newton method. The proposed expressions’ accuracy is compared with the results obtained using traditional numerical integration methods with leakage current formulation and other methods, found in the literature, with no leakage current formulation. The results confirm that including leakage current represents a more accurate and realistic manner of modeling SCs. The results show that th... [more]

The space Brayton nuclear reactor system usually adopts the helium−xenon gas mixture (He−Xe) as the working fluid. The flow of He−Xe in the micro channel regenerator of the system is generally laminar. Since the properties of He−Xe are significantly different from those of common pure gases, the impact of this difference on the laminar flow and heat transfer needs to be evaluated. In present study, the numerical simulations of laminar convective heat transfer for helium, nitrogen and He−Xe are conducted by Ansys Fluent. Compared with simulation results, the applicability of existing laminar friction factor (f) and Nusselt number correlations is evaluated. By establishing the functions of property ratios with the temperature ratio and the mixing ratio, a new laminar f correlation for property-variable He−Xe is proposed. Results show that the calculation error of existing f correlations for He−Xe is obviously large, exceeding 13%. With the new f correlation, the predictions of laminar f... [more]

The stability of a hybrid AC-DC microgrid depends mainly upon the bidirectional interlinking converter (BIC), which is responsible for power transfer, power balance, voltage solidity, frequency and transients sanity. The varying generation from renewable resources, fluctuating loads, and bidirectional power flow from the utility grid, charging station, super-capacitor, and batteries produce various stability issues on hybrid microgrids, like net active-reactive power flow on the AC-bus, frequency oscillations, total harmonic distortion (THD), and voltage variations. Therefore, the control of BIC between AC and DC buses in grid-connected hybrid microgrid power systems is of great importance for the quality/smooth operation of power flow, power sharing and stability of the whole power system. In literature, various control schemes are suggested, like conventional droop control, communication-based control, model predictive control, etc., each addressing different stability issues of hybr... [more]

Agriculture activities are completely dependent upon energy production worldwide. This research presents sensorless speed control of a three-phase induction motor aided with an extended Kalman filter (EKF). Although a proportional integral (PI) controller can ensure tracking of the rotor speed, a considerable magnitude of ripples is present in the torque generated by a motor. Adding a simple derivative to have a proportional integral derivative (PID) action can cause a further increase in ripple magnitude, as it allows the addition of high-frequency noise in the system. Therefore, a fractional-order-based PID control is presented. The proposed control scheme is applied in a closed loop with the system, and simulation results are compared with the PID controller. It is evident from the results that the fractional order control not only ensures 20 times faster tracking, but ripple magnitude in torque was also reduced by a factor of 50% compared to that while using PID and ensures the eff... [more]

In this paper, we present AWEbox, a Python toolbox for modeling and optimal control of multi-aircraft systems for airborne wind energy (AWE). AWEbox provides an implementation of optimization-friendly multi-aircraft AWE dynamics for a wide range of system architectures and modeling options. It automatically formulates typical AWE optimal control problems based on these models, and finds a numerical solution in a reliable and efficient fashion. To obtain a high level of reliability and efficiency, the toolbox implements different homotopy methods for initial guess refinement. The first type of method produces a feasible initial guess from an analytic initial guess based on user-provided parameters. The second type implements a warm-start procedure for parametric sweeps. We investigate the software performance in two different case studies. In the first case study, we solve a single-aircraft reference problem for a large number of different initial guesses. The homotopy methods reduce th... [more]

The article presents an overview of experimental layout design solutions and the general operation scheme of combined heat and power systems with a high-temperature solid oxide fuel cell (SOFC). This system is an environmentally friendly and energy-saving way to produce electricity and heat. The use of high-temperature SOFCs makes it possible to obtain an electrical efficiency of 45−55%. Combining the electrochemical and mechanical system can increase the total efficiency by up to 60−65% in a hybrid power plant. This article discusses the structure and relationship between the components of a hybrid power plant and various modification options for efficient power generation. The technological schemes for existing and tested hybrid power plants with an SOFC and gas turbine are presented and described in detail. When designing a hybrid power plant, the key factors are the choice of design, heat source, and fuel-reforming method; the design of a solid oxide fuel cell and the number of mod... [more]

There is increasing interest in migrating to a carbon-neutral power system that relies on renewable energy due to concerns about greenhouse gas emissions, energy shortages, and global warming. However, the increasing share of renewable energy has added volatility and uncertainty to power system operations. Introducing new devices and using flexible resources may help solve the problem, but expanding the domain of the problem can be another solution. Sector coupling, which integrates production, consumption, conversion, and storage by connecting various energy domains, could potentially meet the needs of each energy sector. It can also reduce the generation of surplus energy and unnecessary carbon emissions. As a result, sector coupling, an integrated energy system, increases the acceptance of renewable energy in the traditional power system and makes it carbon neutral. However, difficulties in large-scale integration, low conversion efficiency and economic feasibility remain obstacles.... [more]

The use of regenerative braking systems is an important approach for improving the travel mileage of electric vehicles, and the use of an auxiliary hydraulic braking energy recovery system can improve the efficiency of the braking energy recovery process. In this paper, we present an algorithm for optimizing the energy recovery efficiency of a hydraulic regenerative braking system (HRBS) based on fuzzy Q-Learning (FQL). First, we built a test bench, which was used to verify the accuracy of the hydraulic regenerative braking simulation model. Second, we combined the HRBS with the electric vehicle in ADVISOR. Third, we modified the regenerative braking control strategy by introducing the FQL algorithm and comparing it with a fuzzy-control-based energy recovery strategy. The simulation results showed that the power savings of the vehicle optimized by the FQL algorithm were improved by about 9.62% and 8.91% after 1015 cycles and under urban dynamometer driving schedule (UDDS) cycle conditi... [more]

Grass and other herbaceous biomass are abundant, but often under- or not utilized as a renewable resource. Here, the production of biochar from extensive late-harvest grass via multiple thermochemical conversion technologies was investigated at lab and farm scale for use in soil applications. While biochar is a product with highly diverse potential applications, it has a multitude of benefits for agricultural usage as a soil amendment, if the quality adheres to certain limit values of potentially toxic constituents. The results show that the biochar can adhere to all limit values of the European Biochar Certificate (EBC) for utilization in agriculture. Generally, the contents of heavy metals were well below the proposed EBC limits and very low PAH concentrations in the biochar were achieved. The high ash content in the grass of 7.71 wt resulted in high nutrient concentrations in the biochar, of benefit in soil applications, but the ash also contains chlorine, nitrogen and sulphur, whic... [more]

State estimation (SE) is regarded as an essential tool for achieving the secure and efficient operation of distribution networks, and extensive research on SE has been conducted over the past three decades. Nonetheless, the high penetration of distribution generations (DGs) is accompanied by uncertainties and dynamics, and the extensive application of intelligent electronic devices (IEDs) is associated with data processing issues, all of which raise new challenges, and these issues must be taken care of for further development of SE in smart distribution networks. This paper attempts to present a comprehensive literature review of numerous works that address various issues in SE, examining key technical research issues and future perspectives. Hopefully, it will be able to meet the needs for the development of smart distribution networks.

Asynchronous loads (AL), because of their low negative-sequence resistance, produce the effect of reduced unbalance at their connection points. Therefore, proper modeling of unbalanced load flows in power supply systems requires properly accounting for AL. Adequate models of the induction motor can be realized in the phase frame of reference. The effective use of such models is possible only if accurate data on the parameters of induction motor equivalent circuits for positive and negative sequences are available. Our analysis shows that the techniques used to determine these parameters on the basis of reference data can yield markedly disparate results. It is possible to overcome this difficulty by applying parameter identification methods that use the phase frame of reference. The paper proposes a technique for parameter identification of models of individual induction motors and asynchronous load nodes. The results of computer-aided simulation allow us to conclude that by using para... [more]

While poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) film is an excellent piezoelectric material for mechanical energy harvesting, the piezoelectric output varies considerably with the spin coating conditions. Herein, we reported a systematic evaluation of the structural, electrical, mechanical, and microstructural properties of spin-coated P(VDF-TrFE) films obtained at various distances from the center, as well as under different rotational speeds. With increasing distance, the remnant polarization, dielectric constant, and crystallinity of the films increased, which resulted in enhanced piezoelectric power at the largest distance. With increasing rotational speed, the remnant polarization, dielectric constant, and crystallinity of the films initially increased and then decreased, while the Young’s modulus continuously increased. This resulted in an enhanced piezoelectric power at a given rotational speed. The piezoelectric power is proportional to the remnant polarization... [more]

Nuclear fusion is the gateway to a whole new paradigm of energy and is a strong candidate for the decarbonization of electricity generation on a global scale. With recent developments in high-temperature super-conducting magnets, the race is on to develop sub-systems which will support a commercially viable fusion reactor for use as a thermal power plant. The fusion of lighter elements creates an enormous amount of heat which must be transferred away from the reactor core. These intense conditions require novel approaches to efficiently transfer very high heat loads into useable thermal energy without compromising the structural integrity of the reactor core and the surrounding components. This report outlines the concept of a fundamental approach to solve the heat transfer problem as proposed by Commonwealth Fusion System’s design for a fusion reactor. A literature review was conducted for other applications that could serve as inspirations, as well as material properties and machinin... [more]

Conventional and cyclic unloading tests with different unloading rates were conducted to study the influences of unloading patterns and rates on the deformation characteristics and mechanical properties of tectonic coal. The results demonstrate that, under continuous unloading, a lower unloading rate promotes an increase in the circumferential strain but inhibits increases in axial strain. A lower unloading rate was found to be able to promote volume expansion under the cyclic unloading path, and the axial, circumferential, and volume strains increased stepwise with the unloading levels, but the increment of the strains decreased with the number of cycles in the same unloading level. It was easier for tectonic coal to reach the elastic limit by a low speed unloading rate when the unloading level was small, and volume dilatation was promoted when the unloading level was large. In both unloading patterns, the tangential modulus and the Poisson ratio were proportional to the unloading rat... [more]

The penetration of electric vehicles is becoming more and more widespread and recently electric buses and trains are fetching the attention of researchers and developers. In this review, we examine the charging systems applied to the fast charging of electric vehicles and buses as well as the charging strategies, mainly applied to electric buses. We also briefly delve into power topologies for a more electrified railway system where we discuss their different supply systems as well as their motor drive systems. Problems and charge challenges for electric buses and trains are discussed too.

The new perspectives of the water−energy nexus, water-for-energy and energy-for-water, emphasize the current and future need to find ways to produce as much energy with as low an amount of water as possible and to obtain as much water with as little energy as possible. In order to promote and implement the concept of sustainable development, the understanding of the dynamic and complex relationship between water and energy is crucial, especially in the context of energy transition. This paper presents a comprehensive analysis of the recent approaches regarding water and energy and the interlink during implementation, operation and servicing of various water and energy production systems. This endeavor is placed in the context of current energy transition from fossil fuels to renewable energy sources. A qualitative and quantitative analysis is performed with various literature solutions from water-for-energy and energy-for-water perspectives for a broader view of the impact of implement... [more]

Solar energy utilization for covering and offsetting the heating loads of buildings, is a sustainable way to reduce energy consumption (electricity, gas, etc.) for space heating. As such, a Trombe wall technology is a classic passive solar heating system used in buildings, that can be modified and applied to cold climate regions. This work presents a case study on a Trombe wall’s application in relation to its thermal energy output for space heating purposes at a factory building in central Latvia. The solar radiation and temperature measurements were carried out throughout the months of June to October. The results show that the examined wall has a monthly energy yield of 120 to 290 kWh, suggesting that Trombe wall systems are applicable as a secondary space heating source in cold climate regions such as northern Europe, however, a number of design and structural aspects have to be thoroughly considered.