In this article, we aim to study systemic risk spillovers for European energy companies and to determine the spillover network of the energy sector with other economic sectors. To examine the spillovers within the energy sector, we employ three systemic risk measures. We then embed the results of these models into a Diebold−Yilmaz framework. Moreover, we consider an entropy procedure to extract a Bayesian formulation of its systemic risk spillover. This allows us to determine which company in our sample contributes the most to systemic risk, which company is the most vulnerable to systemic risk, and the place of the energy sector within risk networks. Our results reveal the fact that all companies manifest enhanced spillovers during 2008, early 2009, and 2020. These episodes are associated with the dynamics of the global financial crisis and the pandemic crisis. We notice that specific companies are risk drivers in the sector in both times of market turbulence and calm. Lastly, we obse... [more]

Over the past 20 years, net-zero energy house (NZEH) construction costs have steadily decreased because of many reasons, such as technical progress, energy-saving design obligations, and dramatic cost reductions in renewable energy systems, especially solar power systems. Currently, the costs of NZEH are estimated to be about 5% higher than similar-sized houses. These additional costs are mainly for installing PV systems, which can be offset by energy saving costs. This study assessed energy performance and load matching through remote monitoring systems, and energy costs were analyzed for two-family houses. The two houses were all-electric houses and different in both size and location. A 6 kWp grid-connected PV system and 16 kW air source heat pump for space heating and domestic hot water were equally implemented. After data analysis, 100% of the energies were supplied through the PV system for 3 years, thus achieving net-zero energy. According to the Korean residential electricity t... [more]

The three-phase H7 inverter topology installs an additional power semiconductor switch to the positive or negative node of the DC-link for reducing the common-mode voltage (CMV) by disconnecting the inverter from the DC source during the zero-voltage vectors. The conventional CMV reduction method for the three-phase H7 inverter uses modified discontinuous pulse width modulation (MDPWM) and generates a switching signal for the additional switch using logical operations. However, the conventional method is unable to eliminate the CMV for the entire dwell time of the zero-voltage vectors. It only has the effect of reducing the CMV in a limited area of the space vector where the V7 zero voltage vector is applied. Therefore, this paper proposes an optimized modulation method that can reduce the CMV during the entire dwell time of zero-voltage vectors. The proposed method moves the switching patterns by adding an offset voltage to guarantee that only one kind of zero-voltage vector, V7, is a... [more]

This paper proposes an optimal design method to suppress critical harmonics and improve the power factor by using passive power filters (PPFs). The main objectives include (1) minimizing the total harmonic distortion of voltage and current, (2) minimizing the initial investment cost, and (3) maximizing the total fundamental reactive power compensation. A methodology based on teaching−learning-based optimization (TLBO) and Pareto optimality is proposed and used to solve this multi-objective PPF design problem. The proposed method is integrated with both external archive and fuzzy decision making. The sub-group search strategy and teacher selection strategy are used to improve the diversity of non-dominated solutions (NDSs). In addition, a selection mechanism for topology combinations for PPFs is proposed. A series of case studies are also conducted to demonstrate the performance and effectiveness of the proposed method. With the proposed selection mechanisms for the topology combination... [more]

As the utilization and consumption of lignocellulosic biomass increases, so too will the need for an adequate supply of feedstock. To meet these needs, novel waste feedstock materials will need to be utilized. Exploitation of these novel feedstocks will require information both on the effects of solvent extraction on the succeeding analysis of potential novel feedstocks and how accurate current methodologies are in determining the composition of novel lignocellulosic feedstocks, particularly the carbohydrate and lignin fractions. In this study, the effects of solvent extraction on novel feedstocks, including tree foliage, tree bark and spent mushroom compost, with 95% ethanol, water and both sequentially were examined. Chemical analyses were carried out to determine the moisture content, ash, extractives, post-hydrolysis sugars, Klason lignin (KL) and acid-soluble lignin (ASL) within the selected feedstocks. The result of extraction could be seen most strongly for Klason lignin, with a... [more]

This paper provides a summary of financial instruments to address two biggest risks to renewable projects in India. These risks include the following: first, off-taker (or counterparty) risk, which relates to payment delays by public-sector distribution companies to independent power producers, which then impact project level cash flows in the domestic currency; second, currency (or foreign exchange) risk related to currency fluctuations, which impact foreign investor level cash flows in foreign currencies. This paper then describes multiple solutions for each of these risks, using public funding mechanisms. For payment delays, the category of solutions is termed Payment Security Mechanisms; whereas, for currency fluctuations, the category of solutions is termed Foreign Exchange Hedging Facilities. The coverage in this paper shows the evolution of the solutions from theory to practice over time. These solutions are likely to be applicable to other developing countries.

Based on outlier detection algorithms, a feasible quantification method for supraharmonic emission signals is presented. It is designed to tackle the requirements of high-resolution and low data volume simultaneously in the frequency domain. The proposed method was developed from the skewed distribution data model and the self-tuning parameters of density-based spatial clustering of applications with noise (DBSCAN) algorithm. Specifically, the data distribution of the supraharmonic band was analyzed first by the Jarque−Bera test. The threshold was determined based on the distribution model to filter out noise. Subsequently, the DBSCAN clustering algorithm parameters were adjusted automatically, according to the k-dist curve slope variation and the dichotomy parameter seeking algorithm, followed by the clustering. The supraharmonic emission points were analyzed as outliers. Finally, simulated and experimental data were applied to verify the effectiveness of the proposed method. On the b... [more]

As a typical wide bandgap semiconductor, ZnO has received a great deal of attention from researchers because of its strong physicochemical characteristics. During the past few years, great progress has been made in the optoelectronic applications of ZnO, particularly in the photocatalysis and photodetection fields. To enable further improvements in the material’s optoelectronic performance, construction of a variety of ZnO-based composite structures will be essential. In this paper, we review recent progress in the growth of different ZnO−graphene nanocomposite structures. The related band structures and photocatalysis and photoresponse properties of these nanocomposites are discussed. Additionally, specific examples of the materials are included to provide an insight into the common general physical properties and carrier transport characteristics involved in these unique nanocomposite structures. Finally, further directions for the development of ZnO−graphene nanocomposite materials... [more]

This paper establishes the state-space model of the cup rotor permanent-magnet doubly fed machine in the synchronous reference frame. The feedback-linearization control method is used to realize the decoupling control of flux and torque. Then, the upper and lower load torque boundaries are solved. Furthermore, to minimize the stator current magnitude of the control machine under a certain torque, the maximum torque per ampere (MTPA) control is derived. Finally, simulation results demonstrate the good decoupling performance of the feedback-linearization control method and the correctness of the load torque boundaries. In addition, the effectiveness and robustness of the proposed control methods are also demonstrated.

The present study offers a scheme to improve the performance of existing large-scale chillers. The system involves raising the temperature of the chiller’s cooling water stream using renewable energy sources by incorporating an organic Rankine cycle (ORC). The thermal analysis was conducted by raising the temperature of one-third of the approximately 200 ton chiller’s cooling water. The investigation was considered for ORC evaporator inlet temperature of 90~120 °C by the step of 10 °C. Various working fluids for the different ORC evaporator inlet temperatures were examined. Sensitivity analyses conducted on the degree of superheating, degree of subcooling, condenser saturation temperature, pinch point temperature differences of the ORC evaporator and condenser, and the mass flowrates of the heating and cooling streams were also reported. Genetic algorithm was employed to carry out the optimization. The best options for the ORC working fluid at the heating source ORC evaporator inlet te... [more]

In this paper, a triple-pass solar air heater with three inlets is analytically investigated. The effects of airflow ratios of the second and third passes (ranging from 0 to 0.4), and the Reynolds number of the third pass (ranging from 8000 to 18,000) on the thermohydraulic efficiency and entropy generation are assessed. An absorber plate equipped with rectangular fins on both sides is used to enhance heat transfer. The air temperature change in the passes is represented by ordinary differential equations and solved by numerical integration. The results demonstrate that the effect of the third pass airflow ratio on the thermohydraulic efficiency and entropy generation is more significant than that of the second pass airflow ratio. The difference in air temperature through the collector shows an insignificant reduction, but the air pressure loss is only 50% compared with that of a traditional triple-pass solar air heater. Increasing the air flow ratios dramatically reduces entropy gener... [more]

Hydrogen storage in magnesium-based composites has been an outstanding research area including a remarkable improvement of the H-sorption properties of this system in the last 5 years. Numerous additives of various morphologies have been applied with great success to accelerate the absorption/desorption reactions. Different combinations of catalysts and preparation conditions have also been explored to synthesize better hydrogen storing materials. At the same time, ball milling is still commonly and effectively applied for the fabrication of Mg-based alloys and composites in order to reduce the grain size to nanometric dimensions and to disperse the catalyst particles over the surface of the host material. In this review, we present the very recent progress, from 2016 to 2021, on catalyzing the hydrogen sorption of Mg-based materials by ball milling. The various catalyzing routes enhancing the hydrogenation performance, including in situ formation of catalysts and synergistic improveme... [more]

This paper addresses problems of reservoir fluid migrations in the process of CO2 sequestration in a partially depleted petroleum reservoir. A detailed analysis of the migrations is required to obtain fundamental characteristics of a sequestration structure, including estimation of its sequestration capacity and leakage risks. The paper presents a general discussion of the relevant mechanisms and their contributions to the analysed issues. The proposed approach to solve the problems relies on the usage of numerical structure modelling and simulations of the sequestration processes on numerical models of the structure. It is applied to a selected geological structure comprising a partially depleted gas reservoir. The modelling includes key types of reservoir fluid migrations: viscous multiphase transport and convection transport. It also takes into account other phenomena that affect fluid migrations including injected gas solubility in the formation water and gas trapping by capillary... [more]

The European Union Target Model aims to integrate European energy market by removing barriers to trade and align markets. The most important goals of the Target Model are to provide consistent prices, enhance liquidity, support cross boarder trading, facilitate interconnections, and coordinate the use of transmission system capacity. In that context, the smooth operation of both forward and spot markets is a core development that directly affects the good operation of the wholesale market. This paper examines the application of the Target Model in the wholesale electricity market of Greece and its impact on electricity prices. The study explores the time period before the implementation of the Target Model, which took place on November 2020, and the first nine months of its execution. Based on the feedback received by the rest of the European countries, which are already part of the European Single Market, this crucial period of time is considered transitional, when many distortions an... [more]

Hybrid microgrids constitute a promising solution for filling the electricity access gap that currently exists in rural areas; however, there is still relatively little information about their reliability and costs based on measured data in real working conditions. This article analyzes data obtained from the operation of a 9 kW hybrid microgrid in the fishermen’s cove of Laguna Grande, Paracas, in the Ica region of Perú, which has been running for 5 years. This microgrid has been equipped with data acquisition systems that measure and register wind speed, solar radiation, temperatures, and all the relevant electric parameters. Battery dynamics considerations are used to determine the depth of discharge in a real-time operative situation. The collected data are used to optimize the design using the specialized software HOMER, incorporating state-of-the-art technology and costs as a possible system upgrade. This work aims to contribute to better understanding the behavior of hybrid rura... [more]

Fluid-structure interaction (FSI) was used to determine the structural mechanical characteristics of full tubular and axial-flow pumps. The results showed that as the flow rate increases, the total deformation and equivalent stress are significantly reduced. The max total deformation (MTD) and the max equivalent stress (MES) of the full tubular pump impeller occur on the outer edge of the blade. There are two stress concentrations in the full tubular pump impeller, one of which is located in the outlet area of the rim, and the other is located in the outlet area of the hub. However, the MES of the axial-flow pump appears in the center of the blade hub. The performance difference between the full tubular pump and the axial-flow pump is mainly caused by the clearance backflow. The natural frequency of the full tubular pump is lower than that of the axial-flow pump on the basis of the modal results. The MES of the full tubular pump is mainly concentrated at the junction of the blade and t... [more]

Our world is facing an environmental crisis that is driving scientists to research green and smart solutions in terms of the use of renewable energy sources and low polluting technologies. In this framework, photovoltaic (PV) technology is one of the most worthy of interest. Dye-sensitized solar cells (DSSCs) are innovative PV devices known for their encouraging features of low cost and easy fabrication, good response to diffuse light and colour tunability. All these features make DSSCs technology suitable for being applied to the so-called agrovoltaic field, taking into account their dual role of filtering light and supporting energy needs. In this project, we used 40 DSSC Z-series connected modules with the aim of combining the devices’ high conversion efficiency, transparency and robustness in order to test them in a greenhouse. A maximum conversion efficiency of 3.9% on a 221 cm2 active area was achieved with a transparency in the module’s aperture (312.9 cm2) area of 35%. Moreover... [more]

Although both aggregate and per capita energy consumption in Bangladesh is increasing rapidly, its per capita consumption is still one of the lowest in the world. Bangladesh gradually shifted from petroleum-based energy to domestically sourced natural-gas-based energy sources, which are predicted to run out within next two decades. The present study first identified the determinants of aggregate commercial energy and its three major components of oil, natural gas, and coal demand for Bangladesh using a simultaneous equations framework on an annual database covering a period of 47 years (1972−2018). Next, the study forecast future demand for aggregate commercial energy and its three major components for the period of 2019−2038 under the business-as-usual and ongoing COVID-19 pandemic scenarios with some assumptions. As part of a sensitivity analysis, based on past trends, we also hypothesized four alternative GDP and population growth scenarios and forecast corresponding changes in tota... [more]

Nuclear graphite can be used in fission and fusion systems due to its excellent nuclear performance and mechanical properties where the ability of oxidation resistance is usually concerned. Although the excellent performance of new graphite ET-10 was revealed by previous experiments regarding the accident conditions of a fission reactor, further studies are needed to oxidize the graphite under the conditions recommended by the ASTM D7542 standard. A test facility was designed and developed to oxidize the cylindrical specimen with a 10 L/min airflow. According to oxidation rates and microstructures of specimens, the chemical kinetics-controlled regime was determined as 675−750 °C, where the activation energy was obtained as 172.52 kJ/mol. The experiment results revealed the excellent ability of graphite ET-10 for oxidation resistance with lower oxidation rates and longer oxidation times compared with some mainstream graphite. The main reasons are the low contents of some impurities and... [more]

Electromobility is one of the leading trends transforming public transport worldwide. Supported by international organizations, such as the European Union, and national cofounding, public transport operators and local authorities are taking strategic decisions on the direction and scope of the electrification of rolling stock. Most of the electric buses that are being put into operation replace the previously used conventional buses, and consequently, most of the electric buses are operating on existing bus lines. By applying a strategic approach to selecting bus routes for electrification, the advantages of electric vehicles can be maximized. Based on a case study of the Polish city of Gdynia, this paper explores the usefulness of the multi-criteria analysis for selecting the bus lines for electrification. Multi-criteria analysis methods help decision makers to consider and weigh diverse criteria that include, among others, economic, social, technological and environmental aspects. To... [more]

This paper proposes a modified version of the power-based control (MPBC) applied to microgrids (µGs) with multiple points of connection (i.e., utility grid itself or any other neighboring µG). Using the MPBC, single-phase distributed energy resources (DERs) arbitrarily connected between the phases share the amounts of balanced power, while the unbalanced and homopolar power are steered only to the line-to-neutral inverters. The control technique is based on a three-level hierarchical control using narrow bandwidth, low data rate communication that properly coordinates the DERs connected to three-phase four-wire µGs. The MPBC allows the DERs to steer power flow at any of the multiple points of common coupling of a multi-PCC dispatchable µG. The modified control proposed herein is evaluated through simulation results using MATLAB/SIMULINK considering a real urban distribution grid with typical operational elements and conditions. When compared to the original power-based control (PBC), r... [more]

An important trend in today’s economy is to reduce the carbon footprint of organizations, businesses and households. Modern technologies, including ICT solutions, contribute to the reduction of CO2 production. The article focuses on the potential of using the cloud computing model in managing a modern and intelligent city. Modern city offices have an extensive IT infrastructure. With the emergence of new services provided online by the offices, the server infrastructure is also developing. Server rooms together with additional devices are characterized by high demand for electricity. Along with this, significant amounts of CO2 are produced. An alternative is the use of Cloud Computing solutions, which contribute to a significant reduction of the carbon footprint. The paper analyses potential solutions that can be used in city offices. The benefits and positive impact on the environment were highlighted. The empirical research was conducted based on questionnaires received from city off... [more]

The growing interest in the negative environmental impact of overhead power lines of high and extra-high voltage stems from the increasing ecological awareness of societies. Consequently, a number of respective legal restrictions have been issued and actions have been undertaken to reduce this impact, especially in the electric field of the power frequency. The aim of this paper is to analyze the possibilities of reducing the width of electric field influence zones by changing the design parameters of power lines and defining the spatial distribution of its conductors. This analysis was carried out using the developed and experimentally verified models for determining the electric field and audible noise in the power line environment. The computational models were used to analyze the width of the electric field influence zones of 400 kV lines and the noise levels at the borders of these zones. The research focused on single and double circuit 400 kV power lines. It was revealed that a... [more]

With the increasing adoption of distributed energy resources (DERs) such as wind and solar photovoltaics (PV), many distribution networks have changed from passive to active. In turn, this has led to increased technical and operational challenges such as voltage issues and thermal loading in high DER penetration scenarios. These challenges have been further increased by the uncertainties arising from DER allocation. The implication of DER allocation uncertainty in the planning process is far-reaching as it affects critical planning processes, including conductor size selection (CSS). Most reported CSS methods in the literature do not include DER allocation uncertainty modeling as they are mostly deterministic and are set out as optimization problems. The methods, therefore, lack foresight on future loading conditions and cannot be used in a CSS process for feeders with high DER penetration. This paper proposes a novel input−process−output stochastic−probabilistic CSS framework for dist... [more]

Simultaneous removal of nitrogen and phosphorous is a recommended practice while treating wastewater. In the present study, control strategies based on proportional-integral (PI), model predictive control (MPC), and fuzzy logic are developed and implemented on a plant-wide wastewater treatment plant. Four combinations of control frameworks are developed in order to reduce the operational cost and improve the effluent quality. As a working platform, a Benchmark simulation model (BSM2-P) is used. A default control framework with PI controllers is used to control nitrate and dissolved oxygen (DO) by manipulating the internal recycle and oxygen mass transfer coefficient (KLa). Hierarchical control topology is proposed in which a lower-level control framework with PI controllers is implemented to DO in the sixth reactor by regulating the KLa of the fifth, sixth, and seventh reactors, and fuzzy and MPC are used at the supervisory level. This supervisory level considers the ammonia in the las... [more]