Energies, Volume 12, Issue 8 (April-2 2019) – 177 articles

This study contributes to a better understanding of where to place different energy modelling tools and support better decision-making related to the sustainable development of energy systems. It is argued that through the connection of the energy field and the field of sustainable development, the current energy paradigm—encompassing economic, environmental and social aspects—has emerged. This paper provides an analysis of different categories of existing energy system models and their ability to provide answers to questions arising from the current energy paradigm formulated within this study. The current energy paradigm and the relevant questions were defined by conducting conceptual framework analysis. The overarching question of the current paradigm asks how different energy pathways impact on the (sustainable) development of the energy system and overall (sustainable) development globally and nationally. A review of energy system models was conducted to analyse what questions of the current energy paradigm are addressed by which models. The results show that most models address aspects of the current energy paradigm but often in a simplified way. To answer some of the questions of the current energy paradigm in more depth and to get novel insights on sustainable energy system development, it might be necessary use complementary methods in addition to traditional energy modelling methodological approaches. Full article

The majority of heat released during composting is contained in latent form of water vapour. To improve the rate of heat recovery, a simple heat exchanger based on condensation of compost vapours was designed. A prototype of this condenser-type heat exchanger was built and tested as a part of pilot-scale compost heat recovery system. Passively aerated static pile (modified Jean Pain mound) with enhanced aeration using vertical channels was chosen for this composting experiment. Insulation of the compost mound and adjacent hoop house further improved the efficiency of the heat recovery and utilization. Full article

This paper analyzes the use of hybrid photovoltaic/thermal (PVT) collectors in nearly zero-energy buildings (NZEBs). We present a design methodology based on the dynamic simulation of the whole energy system, which includes the building energy demand, a reversible heat pump as generator, the thermal storage, the power exchange with the grid, and both thermal and electrical energy production by solar collectors. An exhaustive search of the best equipment sizing and design is performed to minimize both the total costs and the non-renewable primary energy consumption over the system lifetime. The results show that photovoltaic/thermal technology reduces the non-renewable primary energy consumption below the nearly zero-energy threshold value, assumed as 15 kWh/(m²·yr), also reducing the total costs with respect to a non-solar solution (up to 8%). As expected, several possible optimal designs exist, with an opposite trend between energy savings and total costs. In all these optimal configurations, we figure out that photovoltaic/thermal technology favors the production of electrical energy with respect to the thermal one, which mainly occurs during the summer to meet the domestic hot water requirements and lower the temperature of the collectors. Finally, we show that, for a given solar area, photovoltaic/thermal technology leads to a higher reduction of the non-renewable primary energy and to a higher production of solar thermal energy with respect to a traditional separate production employing photovoltaic (PV) modules and solar thermal (ST) collectors. Full article

AC/AC converters that do not have a DC energy storage element, such as a matrix chopper and a matrix converter, are increasingly becoming alternatives to conventional two-stage AC/DC/AC converters and thyristor choppers. In such systems, the main DC-link capacitor does not exist, so the system provides more reliable operation and makes it possible to reduce the financial costs of its construction. It should be noted that AC/AC converters without an energy storage element in a form of DC-link capacitors have not been implemented on an industrial scale. The reasons involve technical aspects and cost components. The main aim of this paper is to present some of the challenges and selected design requirements for industrial applications of AC/AC high reliability power converters. Full article

There are many uncertain factors that contribute to process faults and this make it is hard to locate the assignable causes when a process fault occurs. The fuzzy relational equation (FRE) is effective to represent the uncertain relationship between the causes and effects, but the solving difficulties greatly limit its practical utilization. In this paper, the relation between the occurrence degree of abnormal patterns and assignable causes was modeled by FRE. Considering an objective function of least distance between the occurrence degree of abnormal patterns and its assignable cause’s contribution degree determined by FRE, the FRE solution can be obtained by solving an optimization problem with a genetic algorithm (GA). Taking the previous optimization solution as the initial solution of the following run, the GA was run repeatedly. As a result, an optimal interval FRE solution was achieved. Finally, the proposed approach was validated by an application case and some simulation cases. The results show that the model and its solving method are both feasible and effective. Full article

In order to clarify the discharge principle of the self-field magnetoplasmadynamic thruster (MPDT), a two-dimensional axisymmetric particle-in-cell/Monte Carlo collision (PIC/MCC) model is proposed. The spatial distribution and the collision characteristics of discharge plasma were calculated using this model. In addition, the influence of the operation parameters on the plasma was analyzed including the voltage and mass flow rate. The effectiveness of the model was verified by comparison to the experimentally induced magnetic field. It was found that the electrons were mainly accelerated by the electric field in the cathode sheath and the electric field shielding effect of plasma was obvious in the bulk plasma region. Due to the pinch effect, the charged particles were constrained near the cathode. The results of the present work implied that the PIC/MCC model provides an approach to investigate the plasma distribution and a kinetic description of particles for the discharge of the self-field MPDT. Full article

Photovoltaic (PV) power stations tend to have a relatively weak infeed characteristic, unlike conventional synchronous generators. The limited overcurrent capability of power electronic devices and the controllability of grid-connected inverters mean that PV power stations will cause changes in the characteristics of faults on transmission lines. To analyze the adaptability of fault component distance protection on transmission lines connected to PV power stations, a unified phasor expression for the fault current of a PV power station side under various control strategies was deduced in this paper. This expression is then used to derive the equivalent impedance on the PV power station side and the additional impedance. The equivalent impedance and additional impedance are affected greatly by the active and reactive power commands, control targets, and fault conditions. These aspects of a PV power station may cause malfunctions, which can thereby reduce the reliability of fault component distance protection on transmission lines connected to PV power stations. A simulation model of a PV power station was established in PSCAD/EMTDC and the correctness of theoretical analysis was verified by the simulation results. Full article

A considerable market share of electric vehicles (EVs) is expected in the near future, which leads to a transformation from gas stations to EV charging infrastructure for automobiles. EV charging stations will be integrated with the power grid to replace the fuel consumption at the gas stations for the same mobile needs. In order to evaluate the impact on distribution networks and the controllability of the charging load, the temporal and spatial distribution of the charging power is calculated by establishing mapping the relation between gas stations and charging facilities. Firstly, the arrival and parking period is quantified by applying queuing theory and defining membership function between EVs to parking lots. Secondly, the operational model of charging stations connected to the power distribution network is formulated, and the control variables and their boundaries are identified. Thirdly, an optimal control algorithm is proposed, which combines the configuration of charging stations and charging power regulation during the parking period of each individual EV. A two-stage hybrid optimization algorithm is developed to solve the reliability constrained optimal dispatch problem for EVs, with an EV aggregator installed at each charging station. Simulation results validate the proposed method in evaluating the controllability of EV charging infrastructure and the synergy effects between EV and renewable integration. Full article

This paper aims to propose and compare three new structures of single-phase field excited flux switching machine for pedestal fan application. Conventional six-slot/three-pole salient rotor design has better performance in terms of torque, whilst also having a higher back-EMF and unbalanced electromagnetic forces. Due to the alignment position of the rotor pole with stator teeth, the salient rotor design could not generate torque (called dead zone torque). A new structure having sub-part rotor design has the capability to eliminate dead zone torque. Both the conventional eight-slot/four-pole sub-part rotor design and six-slot/three-pole salient rotor design have an overlapped winding arrangement between armature coil and field excitation coil that depicts high copper losses as well as results in increased size of motor. Additionally, a field excited flux switching machine with a salient structure of the rotor has high flux strength in the stator-core that has considerable impact on high iron losses. Therefore, a novel topology in terms of modular rotor of single-phase field excited flux switching machine with eight-slot/six-pole configuration is proposed, which enable non-overlap arrangement between armature coil and FEC winding that facilitates reduction in the copper losses. The proposed modular rotor design acquires reduced iron losses as well as reduced active rotor mass comparatively to conventional rotor design. It is very persuasive to analyze the range of speed for these rotors to avoid cracks and deformation, the maximum tensile strength (can be measured with principal stress in research) of the rotor analysis is conducted using JMAG. A deterministic optimization technique is implemented to enhance the electromagnetic performance of eight-slot/six-pole modular rotor design. The electromagnetic performance of the conventional sub-part rotor design, doubly salient rotor design, and proposed novel-modular rotor design is analyzed by 3D-finite element analysis (3D-FEA), including flux linkage, flux distribution, flux strength, back-EMF, cogging torque, torque characteristics, iron losses, and efficiency. Full article

In the last two decades, nanotechnology has flourished due to its vast number of applications in many fields such as drug delivery, oil and gas, and thermal applications, like cooling and air-conditioning. This study focuses on the applications of nanoparticles/nanofluids in the Enhanced Oil Recovery (EOR) process to increase oil recovery efficiency. To understand the nanoparticle-assisted EOR process, the first step is to understand the flow characteristics of nanoparticles in porous media, including entrapment and release in the pores and the behavior of nanoparticles under high temperatures, pressures, and salinity levels and in the presence of external electric and magnetic fields. Also, the process looks at the roles of various pore distributions during their application as EOR agents. The experimental approaches are not only time consuming, but they are also cumbersome and expensive. Hence, the mathematical models could help to facilitate the understanding of the transport and interaction of nanofluids in a reservoir and how such processes can be optimized to get maximum oil recovery and, in turn, reduce the production cost. This paper reviews and critically analyzes the latest developments in mathematical modeling and simulation techniques that have been reported for nanofluid-assisted EOR. One section is dedicated to discussing the challenges ahead, as well as the research gaps in the modeling approach to help the readers to also contribute to further enlightening the modeling nanofluid-assisted EOR process. Full article

This paper describes a series of experiments performed to study the explosion characteristics of propanol isomer (1-propanol and 2-propanol)–air binary mixtures. The experiments were conducted in two different experimental arrangements—a 0.02 m³ oil-heated spherical vessel and a 1.00 m³ electro-heated spherical vessel—for different equivalence ratios between 0.3 and 1.7, and initial temperatures of 50, 100, and 150 °C. More than 150 pressure–time curves were recorded. The effects of temperature and test vessel volume on various explosion characteristics, such as the maximum explosion pressure, maximum rate of pressure rise, deflagration index, and the lower and upper explosion limits were investigated and the results were further compared with the results available in literature for other alcohols, namely methanol, ethanol, 1-butanol, and 1-pentanol. The most important results from evaluated experiments are the values of deflagration index 89–98 bar·m/s for 2-propanol and 105–108 bar·m/s for 1-propanol/2-propanol–air mixtures. These values are used to describe the effect of isomer blends on a deflagration process and to rate the effects of an explosion. Full article

The research examines the role of oil in the world economy and the evaluation of the oil factor in the economy of Azerbaijan. The error correction model (ECM) has been used in terms of reliability of the obtained results, and assessment has been done by the FMOLS, DOLS and CCR co-integration methods. Engel-Granger and Phillips-Ouliaris co-integration tests have been used for checking the co-integration relations among variables. Times series have been checked whether they are unit root (Augmented Dickey-Fuller (ADF), Phillips-Perron (PP) and Kwiatkowski-Phillips-Schmidt-Shin (KPSS) as a methodology of the research. The results of the research reveal that daily oil production and consumption have less effect on the formation of the world oil prices. On the other hand, the impact of the world GDP and world industry production volume is a bit more. Generally, the influence of these factors on oil market has been reduced gradually. However, the reverse process is observed during the analysis of the influence of oil production and oil price on the main indicators of Azerbaijan and Kazakhstan. Therefore, Azerbaijan and Kazakhstan are an oil-exporting countries which is why their macroeconomic indicators, especially currency, GDP and DNP, heavily depends on the oil factor. The research has been limited but highlights the obtained results to some problems and this must be considered as a new source for future research. Thus, the similar studies have been considered to be done thoroughly on several alternative econometric models, but a lack of statistical information on a yearly basis and strong currency intervention constitute some barriers to transiting to a floating currency. The practical importance of the research is to prove that the dependency of the oil prices on the world GDP and world industry production, daily oil production and world oil consumption have decreased gradually. In the second part of the research, the dependency of the Azerbaijan and Kazakhstan economies on oil was proved. This might be a signal to transfer oil resources into human capital. Full article

Non-Intrusive Load Monitoring (NILM) provides a way to acquire detailed energy consumption and appliance operation status through a single sensor, which has been proven to save energy. Further, besides load disaggregation, advanced applications (e.g., demand response) need to recognize on/off events of appliances instantly. In order to shorten the time delay for users to acquire the event information, it is necessary to analyze extremely short period electrical signals. However, the features of those signals are easily submerged in complex background loads, especially in cross-user scenarios. Through experiments and observations, it can be found that the feature of background loads is almost stationary in a short time. On the basis of this result, this paper provides a novel model called the concatenate convolutional neural network to separate the feature of the target load from the load mixed with the background. For the cross-user test on the UK Domestic Appliance-Level Electricity dataset (UK-DALE), it turns out that the proposed model remarkably improves accuracy, robustness, and generalization of load recognition. In addition, it also provides significant improvements in energy disaggregation compared with the state-of-the-art. Full article

Advanced control of heat pumps with thermal storage and photovoltaics has recently been promoted as a promising solution to help decarbonise the residential sector. Heat pumps and thermal storage offer a valuable flexibilisation mean to integrate stochastic renewable energy sources into the electricity grid. Heat pump energy conversion is nonlinear, leading to a challenging nonlinear optimisation problem. However, issues like global optimum uncertainty and the time-consuming methods of current nonlinear programming solvers draw researchers to linearise heat pump models that are then implemented in faster and globally convergent linear programming solvers. Nevertheless, these linearisations generate some inaccuracies, especially in the calculation of the heat pump’s coefficient of performance ( $\mathit{C}\mathit{O}\mathit{P}$ ). In order to solve all of these issues, this paper presents a heuristic control algorithm (HCA) to provide a fast, accurate and near-optimal solution to the original nonlinear optimisation problem for a single-family house with a photovoltaic system, using real consumption data from a typical Swiss house. Results highlight that the HCA solves this optimisation problem up to 1000 times faster, yielding an operation that is up to 49% cheaper and self-consumption rates that are 5% greater than other nonlinear solvers. Comparing the performance of the HCA and the linear solver intlinprog, it is shown that the HCA provides more accurate heat pump control with an increase of up to 9% in system Operating Expense OPEX and a decrease of 8% in self-consumption values. Full article

Primarily produced via transesterification of lipid sources, fatty acid methyl ester (FAME) of biodiesel derived from insect larvae has gained momentum in a great deal of research done over other types of feedstock. From the self-harvesting nature of black soldier fly larvae (BSFL), research had, however, only concentrated on the harvest of BSFL on sixth instar. Through rearing BSFL on coconut endosperm waste (CEW), 100 BSFL were harvested at the fifth and sixth instar, then modification on CEW with mixed-bacteria powder was carried out. It was found that the fifth instar BSFL had 34% lipid content, which was 8% more than the sixth instar. Both instars had similar corrected protein contents around 35–38%. The sixth instar BSFL contained around 19% of chitin, which was about 11% more than the fifth instar. Biodiesel products from both instars showed no differences in terms of FAME content. With modification on CEW, at 0.5 wt% of mixed-bacteria powder concentration, the maximum waste-to-biomass conversion (WBC) and protein conversion (PC) were achieved at 9% and 60%, respectively. Moreover, even with the shorter fermentation time frame of CEW, it did not affect the development of BSFL in terms of its WBC and PC when fed with 14 and 21 days fermented medium. FAME from all groups set, which predominantly constituted about C12:0 at around 60%, followed by C14:0 at around 15%, C16:0, and C18:1 both at 10% on average. Lastly, the FAME yield from BSFL was improved from 25% (sixth instar) to 33% (fifth instar) and showed its highest at 38.5% with modification on raw CEW with 0.5 wt% mixed-bacteria powder and fermented for 21 days. Thus, harvesting BSFL at earlier instar is more beneficial and practical, as it improves the FAME yield from the BSFL biomass. Full article

This article reviews the design and evaluation of different DC-DC converter topologies for Battery Electric Vehicles (BEVs) and Plug-in Hybrid Electric Vehicles (PHEVs). The design and evaluation of these converter topologies are presented, analyzed and compared in terms of output power, component count, switching frequency, electromagnetic interference (EMI), losses, effectiveness, reliability and cost. This paper also evaluates the architecture, merits and demerits of converter topologies (AC-DC and DC-DC) for Fast Charging Stations (FCHARs). On the basis of this analysis, it has found that the Multidevice Interleaved DC-DC Bidirectional Converter (MDIBC) is the most suitable topology for high-power BEVs and PHEVs (> 10kW), thanks to its low input current ripples, low output voltage ripples, low electromagnetic interference, bidirectionality, high efficiency and high reliability. In contrast, for low-power electric vehicles (<10 kW), it is tough to recommend a single candidate that is the best in all possible aspects. However, the Sinusoidal Amplitude Converter, the Z-Source DC-DC converter and the boost DC-DC converter with resonant circuit are more suitable for low-power BEVs and PHEVs because of their soft switching, noise-free operation, low switching loss and high efficiency. Finally, this paper explores the opportunity of using wide band gap semiconductors (WBGSs) in DC-DC converters for BEVs, PHEVs and converters for FCHARs. Specifically, the future roadmap of research for WBGSs, modeling of emerging topologies and design techniques of the control system for BEV and PHEV powertrains are also presented in detail, which will certainly help researchers and solution engineers of automotive industries to select the suitable converter topology to achieve the growth of projected power density. Full article

Drying and firing of ceramic products are processes that require high energy consumption. Making these processes more efficient can improve product quality, reduce processing time and energy consumption, and promote economic and environmental gains. In this sense, this work aims to quantify heat transfer in an intermittent ceramic kiln during the heating and cooling stages, with and without thermal insulation. All mathematical formulation is based on the first law of thermodynamics. From the results, we conclude that the greatest heat loss occurs by radiation in the sidewalls of the equipment, and that a considerable amount of energy is required to heat the sidewalls, base, and ceiling of the kiln. Further, with the use of thermal insulation, it was concluded that a high reduction in the heat lost through the sidewalls was achieved, thus providing a global energy gain of approximately 35% and a reduction in the maximum external surface temperature from 249.34 to 79.47 °C when compared to the kiln without thermal insulation, reducing the risks of work accidents and thermal discomfort when in operation. Full article

Advanced metering infrastructure (AMI) is an important application of smart grid communication technology used for the remote monitoring and control of smart meters. Broadband powerline communication (BB-PLC) systems could perhaps be used for AMI; however, impulsive noise (IN) greatly degrades performance. In addition to the fast Fourier transform (FFT)-based orthogonal frequency-division multiplexing (OFDM), IEEE 1901 specifications have defined the other physical layer called wavelet-based OFDM. Even though many existing studies have reported the IN mitigation algorithms for the FFT-based OFDM system, these approaches may not directly apply to the wavelet-OFDM-based PLC systems. In this paper, we propose a robust receiver for PLC systems based on wavelet-OFDM. The proposed receiver comprises a pre-IN mitigation block, an adaptive inverse discrete wavelet transform, and an iterative IN reconstruction block. The iterative cancellation of strong IN samples leads to a gradual improvement in the quality of the received signal. Instead of using the frequency domain approach, we reduce the inter-dependency of the channel estimation and per-subchannel equalization by using the time domain signal processing. Besides, we apply variable step-size adaptive algorithms to reduce the impact of IN during the training processes for the channel estimator and per-subchannel equalizer. In accordance with IEEE 1901 specifications, we built a simulation environment to evaluate the effectiveness of the proposed method. Simulation results demonstrated that conventional blanking devices fall short in terms of IN mitigation, and that the proposed scheme is able to achieve performance values approaching those obtained in cases without IN. Full article

To mitigate the increasing concentration of carbon dioxide in the atmosphere, energy production processes must change from fossil to renewable resources. Bioenergy utilization from agricultural residues can be a step towards achieving this goal. Syngas (fuel obtained from biomass gasification) has been proved to have the potential of replacing fossil fuels in stationary internal combustion engines (ICEs). The processes associated with switching from traditional fuels to alternatives have always led to intense research efforts in order to have a broad understanding of the behavior of the engine in all operating conditions. In particular, attention needs to be focused on fuels containing relatively high concentrations of hydrogen, due to its faster propagation speed with respect to traditional fossil energy sources. Therefore, a combustion study was performed in a research optical SI engine, for a comparison between a well-established fuel such as methane (the main component of natural gas) and syngas. The main goal of this work is to study the effect of inert gases in the fuel mixture and that of air dilution during lean fuelling. Thus, two pure syngas blends (mixtures of CO and H₂) and their respective diluted mixtures (CO and H₂ with 50vol% of inert gases, CO₂ and N₂) were tested in several air-fuel ratios (stoichiometric to lean burn conditions). Initially, the combustion process was studied in detail by traditional thermodynamic analysis and then optical diagnostics were applied thanks to the optical access through the piston crown. Specifically, images were taken in the UV-visible spectrum of the entire cycle to follow the propagation of the flame front. The results show that hydrogen promotes flame propagation and reduces its distortion, as well as resulting in flames evolving closer to the spark plug. All syngas blends show a stable combustion process, even in conditions of high air and fuel dilution. In the leanest case, real syngas mixtures present a decrease in terms of performance due to significant reduction in volumetric efficiency. However, this condition strongly decreases pollutant emissions, with nitrogen oxide (NO_x) concentrations almost negligible. Full article

There is a global need to increase the production of alternative sources of energy due to many issues related to conventional sources, such as environmental degradation or energy security. In this paper, decentralized liquefied natural gas production is analyzed. Liquefied natural gas, according to the analysis, can be considered a viable alternative even for decentralized applications Design and economic analysis of a small-scale biogas LNG plan together with the necessary technology and economic evaluation are presented in the paper. The results show that a project of the proposed size (EUR 3 million) offers a relatively good profitability level. Specifically, the net present value of the project is mostly positive (around EUR 0.1 million up to EUR 0.8 million). Therefore, based on the research, small LNG plants operating across the continent can be recommended for the processing of local sources of biogas. Full article

Concentrating solar power (CSP) is a promising technology for exploiting solar energy. A major advantage of CSP plants lies in their capability of integrating with thermal energy storage; hence, they can have a similar operability to that of fossil-fired power plants, i.e., their power output can be adjusted as required. For this reason, the power output of such CSP plants is generally scheduled to maximize the operating revenue by participating in electric markets, which can result in frequent changes in the power reference signal and introduces challenges to real-time power tracking. To address this issue, this paper systematically studies the execution-level power tracking control strategy of an CSP plant, primarily aiming at coordinating the control of the sluggish steam generator (including the economizer, the boiler, and the superheater) and the fast steam turbine. The governing equations of the key energy conversion processes in the CSP plant are first presented and used as the simulation platform. Then, the transient behavior of the CSP plant is analyzed to gain an insight into the system dynamic characteristics and control difficulties. Then, based on the step-response data, the transfer functions of the CSP plant are identified, which form the prediction model of the model predictive controller. Finally, two control strategies are studied through simulation experiments: (1) the heuristic PI control with two operation modes, which can be conveniently implemented but cannot coordinate the control of the power tracking speed and the main steam parameters, and (2) advanced model predictive control (MPC), which overcomes the shortcoming of PI (Proportional-Integral) control and can significantly improve the control performance. Full article

To better understand the physical and mechanical behavior of weakly cemented rock with different moisture contents for the success of water-preserved mining, this paper presents the systematic tri-axial compression tests on three typical rock samples (i.e., mudstone, sandstone, and sandy mudstone) sampled from Ili mining area, where the environmental requirements for water conservation are significantly strict. Both the influences of moisture content and confining pressure on the failure mode and the stress-strain behavior of weakly cemented rock have been discussed and compared with each other. Test results showed that: (1) compared to sandstone and sandy mudstone, both the peak stress and residual stress of the weakly cemented mudstone are much more sensitive to confining pressure and moisture content. In detail, the peak stress is very relevant to moisture content, whereas, the residual stress is more sensitive to the confining pressure, (2) with the increase of moisture content, both the yield and ductility of weakly cemented mudstone have been significantly enhanced. However, a similar experimental observation has been found for sandstone and sandy mudstone, and (3) the microstructure and the mineral component are believed to be the two main factors leading to the scatter in terms of the stress-strain behavior for different weakly cemented rocks. Experimental results and discussions presented in this paper can provide the guideline for further research on the application of water-preserved mining in other coal mines with a similar geological condition. Full article

In order to meet the twin challenges of energy shortage and water scarcity in eastern Africa, this paper looks at the feasibilities of using a geothermal water source to produce both fresh water and electricity. In this research, three geothermally sourced combined power and freshwater generation systems are investigated and compared. Two of them are based on traditional power generation systems, including a steam system (SS) and a single-flash system (SFS). The third one is a trilateral flash system (TFS) with a two-phase turbine, which processes the total geofluid flow from the wellhead directly. The power generation potential as well as the condensation process, which produces desalinized freshwater, are investigated for three systems under two typical liquid-dominated well conditions in the Aluto Langano geothermal field in Ethiopia. Results indicate that, suitable total flow turbine efficiency enables the trilateral flash system to be comparable with the steam system and the single-flash system regarding the power generation, especially when the well flow is more liquid dominated. Moreover, freshwater generation is a distinct advantage of the trilateral flash system, and its freshwater output can reach up to be 2.7 times higher than those of traditional systems, making it a promising solution for combined power and freshwater generation. Full article

The energy supply of office buildings and smart homes is a key issue in the global energy system. The growing use of microelectronics-based technology achieves new devices for a more comfortable life and wider use of electronic office equipment. On the one hand, these applications incorporate more and more sensitive electronic devices which are potentially affected by any external electrical transient. On the other hand, the existing electrical loads, which generally use electronic power systems (such as different types of battery chargers, ballasts, inverters, switching power supplies, etc.), generate different kinds of transients in their own electrical internal network. Moreover, improvements in the information of the state of the mains alternating current (AC) power line allows risk evaluation of any disturbance caused to permanently connected electronic equipment, such as computers, appliances, home security systems, phones, TVs, etc. For this reason, it is nowadays more important to introduce monitoring solutions into the electrical network to measure the level of power quality so that it can protect itself when necessary. This article describes a small and compact detector using a low-cost microcontroller and a very simple direct acquiring circuit. In addition; it analyzes different methods to implement various power quality (PQ) surveillance algorithms that can be implemented in this proposed minimum hardware platform. Hence; it is possible to achieve cheap and low-power monitoring devices that can become nodes of a wireless sensor network (WSN). The work shows that using a small computational effort; reasonable execution speed; and acceptable reliability; this solution can be used to detect a variety of large disturbance phenomena and spread the respective failure report through a 433 MHz or 2.4 GHz radio transmitter. Therefore, this work can easily be extended to the Internet of Things (IoT) paradigm. Simultaneously, a software application (PulsAC) has been developed to monitor the microcontroller’s real-time progress and detection capability. Moreover, this high-level code (C++ language), allows us to test and debug the different utilized algorithms that will be later run by the microcontroller unit. These tests have been performed with real signals introduced by a function generator and superimposed on the true AC sine wave Full article

The PV hosting capacity of low voltage feeders is restricted by voltage and current limits, and in many cases, voltage limit violations are the limiting factor for photovoltaic integration. To control the voltage, local Volt/var control strategies absorb or inject reactive power, provoking an additional current. This study analyzes the hosting capacity increase potential and the associated additional grid losses of local cosφ(P)- and Q(U)-control of photovoltaic inverters, and of local L(U)-control of inductive devices and its combination with Q-Autarkic prosumers. Therefore, four theoretical and one real low voltage test-feeders with distinct structures are considered: long overhead line, short overhead line, long cable, short cable and branched cable. While the theoretical test-feeders host homogeneously distributed PV-plants, the real one hosts heterogeneously distributed PV-plants. Each test-feeder is used to conduct load flow simulations in the presence of no-control and the different control strategies separately, while gradually increasing the PV-penetration. The minimum PV-penetration that provokes voltage or current limit violations is compared for the different control strategies and test-feeders. Simulation results of the theoretical test-feeders show that the hosting capacity increase potential of all local Volt/var control strategies is higher for the overhead line feeders than for the cable ones. Local L(U)-control, especially its combination with Q-Autarkic prosumers, increases the hosting capacity of all low voltage test-feeders significantly. The PV-inverter-based local Volt/var control strategies, i.e., Q(U)- and cosφ(P)-control, enable lower hosting capacity increases; in particular, cosφ(P)-control causes high additional currents, allowing the feeder to host only a relatively small PV-module rating per prosumer. Q(U)- and cosφ(P)-control are not sufficient to increase the hosting capacity of the long cable feeder significantly; they provoke high additional grid losses for the overhead line test-feeders. Meanwhile, L(U)-control, especially its combination with Q-Autarkic prosumers, increases the hosting capacity of the long cable feeder significantly, causing high additional grid losses during peak production of PV-plants. Regarding the real test-feeder with heterogeneously distributed PV-plants, on the one hand, the same trend concerning the HC increase prevails for the real branched cable test-feeder as for the theoretical short cable one. On the other hand, higher losses occur for the branched feeder in the case of L(U)-control and its combination with Q-Autarkic prosumers, due to the lower voltage set-points that have to be used for the inductive devices. All in all, the use of local L(U)-control, whether combined with Q-Autarkic prosumers or not, enables the effective and complete utilization of the existing radial low voltage feeders. Full article

The most relevant SESAR 2020 solutions dealing with future Capacity Management processes are Dynamic Airspace Configuration (DAC) and Flight Centric ATC (FCA). Both concepts, DAC and FCA, rely on traffic flow complexity assessment. For this reason, complexity assessments processes, methods and metrics, become one of the main constraints to deal with the growing demand and increasing airspace capacity. The aim of this work is to identify the influence of trajectories’ uncertainty in the quality of the predictions of complexity of traffic demand and the effectiveness of Demand Capacity Balance (DCB) airspace management processes, in order to overcome the limitations of existing complexity assessment approaches to support Capacity Management processes in a Trajectory-Based Operations (TBO) environment. This paper presents research conducted within COTTON project, sponsored by the SESAR Joint Undertaking and EU’s Horizon 2020 research and innovation program. The main objective is to deliver innovative solutions to maximize the performance of the Capacity Management procedures based on information in a TBO environment. Full article

In this paper we examine the influence of clean (hydropower) or dirty (fossil fuel generated) energy on bilateral exports. We focus on bilateral exports from Vietnam, a developing nation with a fast-growing economy propelled by international trade, to her top 54 trading partners over the period 1986–2010. Our key results suggest that there is a significant, positive, and stable long-term relationship between electricity and exports, with some variations across the regional panels of the trading partners and electricity sources. Trading partners of Vietnam are sensitive to how electricity is generated. For trading partners from regions excluding low income Asia, bilateral exports respond more to renewables than fossil fuel generated electricity, which indicates that exports are sensitive to certain qualities of energy sources, namely reliability and price competitiveness. Full article

The South Korean natural gas (NG) import volume in 2017 was 33.7 million tonnes per annum (13.1%), making it the second-largest NG-importing country in the world after Japan. Nevertheless, the NG wholesale market in South Korea has remained monopolistic since the Korea Gas Corporation (KOGAS) was established in 1983. Thus, the purpose of this study is to determine whether the NG wholesale market in South Korea has economies of scale by estimating the translog cost function and estimating the minimum efficient scale (MES) using robust linear regression. We used quarterly business reports of KOGAS from the first quarter of 2000 to the second quarter of 2018 to construct the data. The results showed that diseconomies of scale existed in all the years in the first and fourth quarters, and the second quarter showed the same result during 2010–2014. From 2011, the production quantity of all the quarters has exceeded the MES (5.81 million tons). The reason for these results is that the demand for NG power generation and city gas has surged since 2000, while the monopolistic structure of the past has been maintained. This study implies that it would be more efficient to allocate some of KOGAS’s additional import volume to the existing private NG companies and mitigate the regulation on resale. Full article

The existence of high proportional distributed energy resources in energy Internet (EI) scenarios has a strong impact on the power supply-demand balance of the EI system. Decision-making optimization research that focuses on the transient voltage stability is of great significance for maintaining effective and safe operation of the EI. Within a typical EI scenario, this paper conducts a study of transient voltage stability analysis based on convolutional neural networks. Based on the judgment of transient voltage stability, a reactive power compensation decision optimization algorithm via deep reinforcement learning approach is proposed. In this sense, the following targets are achieved: the efficiency of decision-making is greatly improved, risks are identified in advance, and decisions are made in time. Simulations show the effectiveness of our proposed method. Full article

This study examines the effects of ethanol and gasoline injection mode on the combustion performance and exhaust emissions of a twin cylinder port fuel injection (PFI) spark ignition (SI) engine. Generally, when using gasoline–ethanol blends, alcohol and gasoline are externally mixed with a specified blending ratio. In this activity, ethanol and gasoline were supplied into the intake manifold into two different ways: through two separated low pressure fuel injection systems (Dual-Fuel, DF) and in a blend (mix). The ratio between ethanol and gasoline was fixed at 0.85 by volume (E85). The initial reference conditions were set running the engine with full gasoline at the knock limited spark advance boundary, according to the standard engine calibration. Then E85 was injected and a spark timing sweep was carried out at rich, stoichiometric, and lean conditions. Engine performance and gaseous and particle exhaust emissions were measured. Adding ethanol could remove over-fueling with an increase in thermal efficiency without engine load penalties. Both ethanol and charge leaning resulted in a lowering of CO, HC, and PN emissions. DF injection promoted a faster evaporation of gasoline than in blend, shortening the combustion duration with a slight increase in THC and PN emissions compared to the mix mode. Full article