Biomass is one of the most promising renewable energy sources because it enables energy accumulation and controlled production. With this, however, the demand for biofuels grows and thus there is an effort to expand their portfolio. Nevertheless, to use a broader range of biofuels, it is necessary to know their fuel properties, such as coarse and elemental analysis, or lower heating value. This paper presents the results of testing the fuel properties of several new, potentially usable biofuels, such as quinoa, camelina, crambe, and safflower, which are compared with some traditional biofuels (wood, straw, sorrel, hay). Moreover, the results of the determination of water content, ash, and volatile combustible content of these fuels are included, along with the results of the elemental analysis and the determination of higher and lower heating values. Based on these properties, it is possible to implement designs of combustion plants of different outputs for these fuels.

The modern distribution networks under the smart grid paradigm have been considered both interconnected and reliable. In grid modernization concepts, the optimal asset optimization across a certain planning horizon is of core importance. Modern planning problems are more inclined towards a feasible solution amongst conflicting criteria. In this paper, an integrated decision-making planning (IDMP) approach is proposed. The proposed methodology includes voltage stability assessment indices linked with loss minimization condition-based approach, and is integrated with different multi-criteria decision-making methodologies (MCDM), followed by unanimous decision making (UDM). The proposed IDMP approach aims at optimal assets sitting and sizing in a meshed distribution network to find a trade-off solution with various asset types across normal and load growth horizons. An initial evaluation is carried out with assets such as distributed generation (DG), photovoltaic (PV)-based renewable DG,... [more]

Unmanned Aerial Vehicles (UAVs) have been regarded as a promising means to reshape future wireless communication systems. In this paper, we consider how to plan the trajectory of a solar-powered UAV under a cloudy condition to secure the communication between the UAV and a target ground node against multiple eavesdroppers. We propose a new 3D UAV trajectory optimization model by taking into account the UAV energy consumption, solar power harvesting, eavesdropping and no-fly zone avoidance. A Rapidly-exploring Random Tree (RRT) method is developed to construct the UAV trajectory. Computer simulations and comparisons with a baseline method demonstrate that the proposed method is able to produce trajectories to ensure the valid wireless communication link with the ground node and prevent eavesdropping.

Proper treatment and careful management of sewage sludge are essential because its disposal can lead to adverse environmental impacts such as public health hazards, as well as air, soil, and water pollution. Several efforts are being made currently not only to safely dispose of sewage sludge but also to utilize it as an energy source. Therefore, in this study, initiatives were taken to valorize sewage sludge cake by reducing the moisture content and increasing the calorific value by applying a hydrothermal treatment technique for efficient energy recovery. The sludge cake treated at 200 °C for 1 h was found to be the optimum condition for hydrothermal carbonization, as, in this condition, the caloric value of the treated sludge increased by 10% and the moisture content removed was 20 wt.%. To recover energy from the hydrothermally treated sludge, a gasification technology was applied at 900 °C. The results showed that the product gas from hydrothermally treated sludge cake had a higher... [more]

Characterizing the mechanical behavior of rocks plays a crucial role to optimize the fracturing process in unconventional reservoirs. However, due to the intrinsic anisotropy and heterogeneity in unconventional resources, fracture process prediction remains the most significant challenge for sustainable and economic hydrocarbon production. During the deformation tracking under compression, deploying conventional methods (strain gauge, extensometer, etc.) is insufficient to measure the deformation since the physical attachment of the device is restricted to the size of the sample, monitoring limited point-wise deformation, producing difficulties in data retrieval, and a tendency to lose track in failure points, etc. Where conventional methods are limited, the application of digital image correlation (DIC) provides detailed and additional information of strain evolution and fracture patterns under loading. DIC is an image-based optical method that records an object with a camera and moni... [more]

The purpose of this work is to formulate a method which can be used to solve nonlinear inverse heat conduction problems and to calculate the heat transfer coefficient distribution on the unknown boundary. The domain under consideration is divided into control volumes in polar coordinates, and heat balance equations are written. Based on temperature transients measured in selected points on the outer surface, temperature values in other points of the domain are determined. Finally, the heat transfer coefficient distribution on the inner surface with the unknown boundary condition is calculated from the presented heat balance equation. The proposed inverse method was verified experimentally using a collector that is part of a semi-industrial laboratory system. This collector is a horizontal, cylindrical thick-walled tank with flat side walls with outlets that enable oil supply and removal. Each side wall has an additional connector to ensure venting. The calculations made it possible to... [more]

As the world is aware, the trend of generating energy sources has been changing from conventional fossil fuels to sustainable energy. In order to reduce greenhouse gas emissions, the ratio of renewable energy sources should be increased, and solar and wind power, typically, are driving this energy change. However, renewable energy sources highly depend on weather conditions and have intermittent generation characteristics, thus embedding uncertainty and variability. As a result, it can cause variability and uncertainty in the power system, and accurate prediction of renewable energy output is essential to address this. To solve this issue, much research has studied prediction models, and machine learning is one of the typical methods. In this paper, we used a bagging model to predict solar energy output. Bagging generally uses a decision tree as a base learner. However, to improve forecasting accuracy, we proposed a bagging model using an ensemble model as a base learner and adding pas... [more]

A phase-shift full bridge converter is analyzed in detail in continuous conduction mode for one switching cycle for both the leading and lagging legs of the primary bridge. The objective of the study is to determine how the stray capacitance of the transformer, and the capacitances of the diodes in the bridge rectifier affect the converter functionality. Starting from some experimental results, Laplace equivalent circuit models and describing equations are derived for each significant time interval during the switching cycle and are validated through simulations and experimental measurements. The resulting equations are of great interest in the high-power density domain because they can be used to design a clamping circuit for the output rectifier bridge accurately.

To reduce the inaccuracy in energy efficiency evaluation, indoor and outdoor dry-bulb and wet-bulb temperature (D&WBT) tolerances in the currently enacted Chinese room air conditioner (RAC) national standard were tightened into narrower intervals in this investigation. Characteristics of cooling capacity (CC) and energy efficiency ratio (EER) changing with D&WBTs were analyzed based on performance tests. AICc (corrected Akaike Information Criterion) was applied to determine the best fitted 3D curve equations of CC and EER to find the intervals of gradient extrema of CC and EER. The corresponding intervals of indoor and outdoor D&WBTs were concluded as the tightened D&WBT tolerances. For illustration, based on the performance tests of 154 working conditions, the instantaneous indoor and outdoor D&WBT tolerances in nominal refrigerating working conditions were respectively tightened from the original ±0.5/±0.3 °C into ±0.3/±0.2 °C (indoor tolerances) and ±0.4/±0.3 °C (outdoor tolerances)... [more]

Smart grids with interoperability improve grid reliability by collecting system information and transferring it to an energy management system and associated applications through a seamless end-to-end connection. To achieve interoperability, it is required to exchange the semantic information within the different domains. The international electrotechnical commission has established the Common Information Model (CIM) tool, which is a standard application programming interface for the exchange of semantic information in power systems. CIM provides a robust framework for accurate data sharing, merging, and transformation into reusable information. However, as CIM provides a basic framework for information exchange, various practical issues arise in establishing an energy management system capable of exchanging information using CIM. This paper aims to offer a comprehensive understanding by summarizing and categorizing the research on the practical use of CIM for interoperability in smart... [more]

To design reliable high voltage cables, clean materials with superior insulating properties capable of operating at high electric field levels at elevated temperatures are required. This study aims at the electrical characterization of a byproduct-free crosslinked copolymer blend, which is seen as a promising alternative to conventional peroxide crosslinked polyethylene currently used for high voltage direct current cable insulation. The characterization entails direct current (DC) conductivity, dielectric response and surface potential decay measurements at different temperatures and electric field levels. In order to quantify the insulating performance of the new material, the electrical properties of the copolymer blend are compared with those of two reference materials; i.e., low-density polyethylene (LDPE) and peroxide crosslinked polyethylene (XLPE). It is found that, for electric fields of 10−50 kV/mm and temperatures varying from 30 °C to 70 °C, the DC conductivity of the copol... [more]

This study presents a multi-objective optimisation of building thermo-modernisation for multi-family buildings. The applied model has considered alternative solutions for insulation materials, with different thicknesses and different types of windows. The weighted sum method was applied to find a solution considering the minimisation of global cost, primary energy ratio and CO2 emissions. The solutions were compared for a building equipped with natural ventilation, and with mechanical supply—exhaust ventilation. In reference to the two considered types of ventilation, we analysed how the modification of an insulation thickness, its type and the type of installed windows, can be converted into individual evaluation criteria. The weights of the considered criteria were changed; however, this had no influence on the optimal solution. If the aim is to achieve the standards of zero-energy buildings, natural ventilation cannot be applied, despite the high value of thermal insulation of the b... [more]

One of the most important factors in determining the profitable production of microalgae biomass is the use of a cost effective growth medium that is rich in nutrients. The objective of the study was to determine the possibility of using digestates from anaerobic digestion of different feedstock mixtures as the media for Scenedesmus sp. cultivation. A different liquid digestate composition was obtained in terms of organic compounds, phosphorus, and nitrogen concentrations, depending on the substrates used in the anaerobic digestion. It was found that the highest biomass production was obtained when using digestate from anaerobic digestion of the feedstock mainly composed of microalgae biomass, which was characterized by low organic compounds concentration. In this case, the average biomass concentration reached 2382 mg total solids/L. A lower Scenedesmus sp. biomass yield was obtained using digestate from anaerobic digester processing feedstock based on maize silage and cattle menure.... [more]

By applying the Second-Order Adjoint Sensitivity Analysis Methodology (2nd-ASAM) to the polyethylene-reflected plutonium (PERP) benchmark, this work presents results for the first- and second-order sensitivities of this benchmark’s leakage response with respect to the spontaneous fission source parameters. The numerical results obtained for these sensitivities indicate that the 1st-order relative sensitivity of the leakage response to the source parameters for the two fissionable isotopes in the benchmark are all positive, signifying that an increase in the source parameters will cause an increase in the total neutron leakage from the PERP sphere. The 1st- and 2nd-order relative sensitivities with respect to the source parameters for 239Pu are very small (10−4 or less). In contradistinction, the 1st-order and several 2nd-order relative sensitivities of the leakage response with respect to the source parameters of 240Pu are large. Large values (e.g., greater than 1.0) are also displayed... [more]

The article provides an analysis of the existing methods of identifying the consumer’s contribution to voltage distortion at a point of common coupling. The considered methods do not allow correctly and fairly determining the source of harmonic distortions, or they have limited application and difficulties in implementation. The paper proposes new methods for determining the source of high harmonics. The developed methods and techniques are based on the analysis of the grid operation modes with two connected consumers using compensating devices, such as reactive power compensation devices and passive harmonic filters. It is shown that the most promising method is the application of harmonic filters, which allows determining the share of the consumer’s contribution to the voltage distortion. The present research is carried out using a computer simulation of the existing electrical grid, to which consumers with nonlinear electric load are connected. These methods can be implemented to as... [more]

A three-dimensional (3D) fibrous structure with a high active surface and conductive pathway proved to be an excellent anode current collector for rechargeable zinc−air batteries (ZABs). Herein, a cost-effective and highly stable zinc (Zn) electrode, based on Zn electrodeposited on iron fibers (Zn/IF), is duly examined. Electrochemical characteristics of the proposed electrode are seen to compete with a conventional zinc/nickel foam (Zn/NF) electrode, implying that it can be a suitable alternative for use in ZABs. Results show that the Zn/IF electrode exhibits an almost similar trend as Zn/NF in cyclic voltammetry (CV). Moreover, by using a Zn/IF electrode, electrochemical impedance spectroscopy (EIS) demonstrates lower charge transfer resistance. In the application of a rechargeable ZAB, the fibrous Zn/IF electrode exhibits a high coulombic efficiency (CE) of 78%, close to the conventional Zn/NF (80%), with almost similar capacity and lower charge transfer resistance, after 200 charge... [more]

Photovoltaic Solar Energy (PSE) sector has sparked great interest from governments over the last decade towards diminution of world’s dependency to fossil fuels, greenhouse gas emissions reduction and global warming mitigation. Photovoltaic solar energy also holds a significant role in the transition to sustainable energy systems. These systems and their optimal exploitation require an effective supply chain management system, such as design of the network, collection, storage, or transportation of this energy resource, without disregarding a country’s certain socio-economic and political conditions. In Brazil, the adoption of photovoltaic solar energy has been motivated not only by the energy matrix diversification but also from the shortages, problems, and barriers that the Brazilian energy sector has faced, lately. However, PSE development is affected by various factors with high uncertainty, such as political, social, economic, and environmental, that include critical operational s... [more]

This study investigated the adaptations of traditional dwellings to the complex regional microclimate in southern Zhejiang, China. Typical traditional dwellings in a village in the foothills and a village on the mid-slopes of Zhejiang’s alpine region were selected to study traditional construction strategies for climate responsiveness and the comfort level of indoor environments during the very humid plum rain season in early summer. Fundamental analysis of the climate and architecture, a response analysis of the dwelling form, an occupants’ comfort satisfaction survey, and field measurements of indoor and outdoor thermal environmental parameters were performed. The traditional dwellings and their design strategies for various regional environmental factors were explored from the perspective of (1) regional climate-adaptive strategies, (2) the thermal, airflow, lighting, and acoustic qualities of the indoor environment, and (3) the occupants’ indoor environment satisfaction. The result... [more]

Monitoring of the state of charge of the thermal energy storage component in solar thermal systems for space heating and/or cooling in residential buildings is a key element from the overall system control strategy point of view. According to the literature, there is not a unique method for determining the state of charge of a thermal energy storage system that could generally be applied in any system. This contribution firstly provides a classification of the state-of-the-art of available techniques for the determination of the state of charge, and secondly, it presents an experimental analysis of different methods based on established sensor technologies, namely temperature, mass flow rates, and pressure measurements, tested using a lab-scale heat exchanger filled with a commercial phase change material for cooling applications. The results indicate that, depending on the expected accuracy and available instrumentation, each of the methods studied here can be used in the present appl... [more]

This study aimed to analyze the systematic risks of wind energy investments. Within this framework, E7 countries are included in the scope of the examination. A large literature review was carried out and 12 different systematic risk factors that could exist in wind energy investments were identified. The analysis process of the study consisted of two different stages. First, the specified risk criteria were weighted with the help of the interval type 2 (IT2) fuzzy decision-making trial and evaluation laboratory (DEMATEL) method. Second, E7 countries were ranked according to the risk management effectiveness in wind energy investments. In this process, the IT2 fuzzy Vlsekriterijumska Optimizacija I Kompromisno Resenje (VIKOR) approach was taken into consideration. The findings show that volatility in exchange rates and interest rates were the most important risks in wind energy investments. In addition, it was determined that China and Indonesia were the most successful countries in ma... [more]

To investigate the oscillation problems in power systems with modular multilevel converters (MMCs), a disturbance-state model of the MMC under P/Q control mode is established based on the harmonic state-space (HSS) method. Firstly, the basic structure of the MMC with P/Q control is presented, including the circuit structure and the controller structure. Next, the dynamic characteristics of each module in the MMC are described with the time-domain state-space model or the s-domain transfer function. The complete controller structure is considered, including the P/Q outer-loop controller, the inner-loop control, the phase-locked loop (PLL), the circulating current suppression control (CCSC) and the control delay. On the basis, the disturbance-state HSS model of the MMC and its corresponding steady-state condition are established by the HSS method. Lastly, the case studies are performed to verify the accuracy of the proposed model, based on an MMC based test system in PSCAD/EMTDC. Moreove... [more]

Developing a regional power system to achieve a high level of integration of national systems requires sufficient development of the regional transmission grid. This is possible only with appropriate schemes for the complete cost−benefit analyses, and cost allocation of these transmission investments, which plays a critical role in the selection of the most efficient network investment and the proper assignment of their cost to the national systems. Network reinforcements affect the operation of power systems and, therefore, the externalities of power generation. This paper examines the impacts of integrating local air pollution damage from power production within the benefit assessment and cost allocation of transmission investments. The paper describes the methodology followed and illustrates its application in a real-life case study where a simplified version of a European network is considered. Within this case study, we have assessed the impact of considering the reduction in air... [more]

Compared with conventional silicon (Si)-based Pulse Width Modulation (PWM) rectifiers, PWM rectifiers based on silicon carbide (SiC) Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) have significant technical advantages and broad application prospects in terms of efficiency and power density, inherited from the high-speed switching feature. However, high-speed switching also induces gate-source voltage interference, which impacts the overall character of the conversion system. This paper considered the impact of gate-source voltage interference on loss, revealing an efficiency optimization for all-SiC PWM rectifiers. Firstly, this paper theoretically investigated the mechanism of improving the conversion system efficiency by using the 4-pin Kelvin packaged SiC MOSFETs. Then, based on the industrial product case study, loss distribution, using different package styles, was quantitatively analyzed. Finally, experiment test results verified the efficiency improvement of the PW... [more]

Smart cities directly rely on a variety of elements, including water, gas, electricity, buildings, services, transportation networks, and others. Lack of properly designed transportation networks may cause different economic and safety concerns. Highway−rail grade crossings are known to be a hazardous point in the transportation network, considering a remarkable number of accidents recorded annually between highway users and trains, and even solely between highway users at highway−rail grade crossings. Hence, safety improvement at highway−rail grade crossings is a challenging issue for smart city authorities, given limitations in monetary resources. In this study, two optimization models are developed for resource allocation among highway−rail grade crossings to minimize the overall hazard and the overall hazard severity, taking into account the available budget limitations. The optimization models are solved by CPLEX to the global optimality. Moreover, some heuristic algorithms are pr... [more]

In this paper, a novel combined radiation-convection floor heating system is shown. This study uses practice-based learning and investigated the thermal performance of a combined radiation-convection floor heating system with a water heat pump system by evaluating the thermal environment and energy consumption in an experimental test. A new method that analyzed the thermal performance of four different controls was developed and applied. The results of the surface temperature distributions demonstrated that Mode 1, which uses only convection, had the lowest floor temperature and was thus considered inappropriate for occupants who sleep on the floor. By contrast, Modes 2, 3, and 4 showed high floor surface temperatures as hot water was supplied to the radiant heating panel. The predicted mean vote (PMV) results suggest that radiant floor heating is not appropriate for intermittent heating. In other words, occupants of single residences who return home at night will experience a long per... [more]