The share of renewable and distributed energy resources (DERs), like wind turbines, solar photovoltaics and grid-connected batteries, interconnected to the electric grid is rapidly increasing due to reduced costs, rising efficiency, and regulatory requirements aimed at incentivizing a lower-carbon electricity system. These distributed energy resources differ from traditional generation in many ways including the use of many smaller devices connected primarily (but not exclusively) to the distribution network, rather than few larger devices connected to the transmission network. DERs being installed today often include modern communication hardware like cellular modems and WiFi connectivity and, in addition, the inverters used to connect these resources to the grid are gaining increasingly complex capabilities, like providing voltage and frequency support or supporting microgrids. To perform these new functions safely, communications to the device and more complex controls are required.... [more]

Boiling, as the most efficient type of convective heat transfer, is an area of interest in many fields of industry and science. Many works have focused on improving the heat transfer efficiency of boiling by altering the physical and chemical properties of surfaces by using different technological processes in their fabrication. This paper presents experimental investigations into pool boiling on enhanced surfaces with open microchannels. The material of the fabricated surface was copper. Parallel microchannels made by machining were about 0.2, 0.3, and 0.4 mm wide, 0.2 to 0.5 mm deep, and spaced with a pitch equal to twice the width of the microchannel. The experiments were carried out in water at atmospheric pressure. The experimental results obtained showed an increase in the heat flux and the heat transfer coefficient for surfaces with microchannels. The maximum (critical) heat flux was 2188 kW/m2, and the heat transfer coefficient was 392 kW/m2K. An improvement in the maximum heat... [more]

Energy storage systems (ESS) are becoming essential as a solution for troublesome industrial systems. This study focuses on the application of a type of ESS, a high-power technology known in the literature as supercapacitors or electric double layer capacitors (EDLC). This technology has had a huge impact during the last decade on research related to the electric traction drives, renewable sources and powergrids. Related to this aspect, this paper summarizes the most relevant scientific publications in the last five years that study the use of supercapacitor technology (SCs) in electric traction applications (drives for rail vehicles and drives for road vehicles), generation systems for renewable energy (wind, solar and wave energy), and connection systems to the electric grid (voltage and frequency regulation and microgrids). The technology based on EDLC and the practical aspects that must be taken into account in the op-eration of these systems in industrial applications are briefly... [more]

The installation of wind energy increased in the last twenty years, as its cost decreased, and it contributes to reducing GHG emissions. A race toward gigantism characterizes wind turbine development, primarily driven by offshore projects. The larger wind turbines are facing higher loads, and the imperatives of mass reduction make them more flexible. Size increase of wind turbines results in higher structural vibrations that reduce the lifetime of the components (blades, main shaft, bearings, generator, gearbox, etc.) and might lead to failure or destruction. This paper aims to present in detail the problems associated with wind turbine vibration and a thorough literature review of the different mitigation solutions. We explore the advantages, drawbacks, and challenges of the existing vibration control systems for wind turbines. These systems belong to six main categories, according to the physical principles used and how they operate to mitigate the vibrations. This paper offers a mul... [more]

The article presents a new method of automatic detection of subsidence troughs caused by underground coal mining. Land subsidence that results from mining leads to considerable damage to subsurface and surface infrastructure such as walls of buildings, road surfaces, and water relations in built-up areas. Within next 30 years, all coal mines are to be closed as part of the transformation of the mining industry in Poland. However, this is not going to solve the problem of subsidence in those areas. Thus, it is necessary to detect and constantly monitor such hazards. One of the techniques used for that purpose is DInSAR (differential interferometry synthetic aperture radar). It makes it possible to monitor land deformation over large areas with high accuracy and very good spatial and temporal resolution. Subsidence, particularly related to mining, usually manifests itself in interferograms in the form of elliptical interferometric fringes. An important issue here is partial or full autom... [more]

Carbon dioxide-based enhanced oil-recovery (CO2-EOR) processes have gained considerable interest among other EOR methods. In this paper, based on the molecular weight of paraffins (n-alkanes), pressure, and temperature, the magnitude of CO2−n-alkanes interfacial tension (IFT) was determined by utilizing soft computing and mathematical modeling approaches, namely: (i) radial basis function (RBF) neural network (optimized by genetic algorithm (GA), gravitational search algorithm (GSA), imperialist competitive algorithm (ICA), particle swarm optimization (PSO), and ant colony optimization (ACO)), (ii) multilayer perception (MLP) neural network (optimized by Levenberg-Marquardt (LM)), and (iii) group method of data handling (GMDH). To do so, a broad range of laboratory data consisting of 879 data points collected from the literature was employed to develop the models. The proposed RBF-ICA model, with an average absolute percent relative error (AAPRE) of 4.42%, led to the most reliable pred... [more]

Waterflooding remains the most commonly used method to improve oil recovery. Although the injected brine type is mainly dependent on its availability, few of its characteristics can be controlled during project design. Published laboratory work indicates that the adjustment of injected brine composition can cause an increase in oil production by wettability alteration. This research objective is to propose a novel four-step framework for modeling improved oil recovery by Engineered Water Injection from laboratory to numerical simulation for carbonate formations. We use a geochemical-based model that estimates contact angles to predict wettability alteration. The steps are (1) screening criteria, (2) geochemical evaluation, (3) wettability alteration modeling, and (4) coreflood history-match. We validate our framework by conducting history-match simulations of Brazilian Pre-Salt corefloods. Incremental oil recovery factors are between 5 to 11%, consistent with those reported during expe... [more]

Faced promising development of autonomous vehicles, the concept Mobility as a Service embraces AVs. The autonomous delivery has also been arising and tested for last-mile solution. Accordingly, passenger transportation and delivery service are to be jointly coordinated in the future MaaS. The research niche is summarized as how to embed crowdsourced parcel delivery into MaaS based on AVs. Electricity powered vehicles are to be applied considering energy consumption and air emission. Research questions are identified as what this novel service is and how it works, especially focusing on task coordination and the related information management. The system engineering process-oriented approaches, matching theory, and numerical method have been applied. The service concept has been elaborated, which contains information system architecture model and functional model. The matching condition of this service is summarized. As the embedded delivery can partially share the demand of traditional... [more]

Trolleybus transport is one of the classic means of public transport in cities. Its popularity varied in the past and was largely related to the fuel market situation. As fuel prices fell, electricity-powered transport lost popularity. The situation was similar during fuel crises. Trolleybuses gained in popularity then. Nowadays, the development of alternative power sources (APS) technology makes trolleybus transport partially independent of the overhead contact system, which is its great advantage. It is thus possible to develop trolleybus connections in areas where there is no justification for building overhead wiring infrastructure. The article analyses the development of on-board APS and their spatial diffusion in trolleybus systems in Europe. The main result of the research procedure indicates that the development of battery technologies, which could accelerate the closure of trolleybus transport due to the strong competition of electric buses not requiring an overhead contact li... [more]

The article presents issues related to the aging behavior of oil-paper insulations in transformers using different oil- and ester-based insulating fluids. Despite numerous conducted studies on the subject of oil-paper aging, the use of new insulating fluids is creating open questions. In addition, new liquids such as synthetic and natural esters, as well as oil of the newest generation, are being used. Furthermore, there is still little research on the formation of aging markers with this form of the dielectric. For this reason, in this contribution, oil-paper insulations with mineral oil-based insulating fluids, natural and synthetic esters, as well as oil from natural gas, are aged thermally accelerated at 130 °C over a duration of 15 weeks, by considering two cases of free-breathing and hermetically sealed transformers. Therefore, various aging markers are investigated to allow a condition assessment. The results show that differences exist between the fluids and design of the trans... [more]

As an independent power system, the reliability of offshore electric system is closely related to the smooth progress of offshore oil production. There are two major characteristics of this type of power system. One is that it includes a generation system, transmission system, as well as a distribution system, and the other is that the load shedding measures in the event of a fault are different from that of the onshore power grid. Therefore, traditional reliability assessment models and algorithms cannot be used directly. Based on the theory of overall reliability evaluation, a reliability evaluation method suitable for offshore electric systems and the corresponding reliability indicators are proposed in this paper. In state sampling, the overall system sampling is divided into generation system sampling, transmission system sampling, and distribution system sampling based on the hybrid sampling theory. In state assessment, the priority decoupling load shedding model and the cascade... [more]

The composition characteristics of altered coals in the Huaibei Coalfield, China, was investigated through a comparative analysis between altered and unaffected coals from the Wolonghu, Taoyuan and Renlou coal mines. Results indicated that the altered coals in Wolonghu coal mine are mostly anthracite coals, with a maximum vitrinite reflectance of 1.6−3.9% (average of 2.9%). Coals from Wolonghu coal mine were mainly consisted of vitrinite (66.2−97.0%), followed by inertinite (2.0−4.0%) and exinite (0.4−6.9%). Differences in volatile matter content were observed between the altered coals in Wolonghu coal mine and unaffected coals from neighboring coal mines, implying that the chemical composition and maturity of coals were changed after magmatic alteration. In addition, differences in hydrogen element were noted among the coals from Wolonghu, Renlou and Taoyuan coal mines, and the phenomenon of “deficient in hydrogen element” was observed in Wolonghu coals. The aliphatic hydrocarbon stru... [more]

The article discusses the selection of cables for power lines connecting wind turbine generators at the wind power plant. The screen cross-section of these cables should be selected considering the value of the screen current at double line-to-earth fault. To calculate this current, the dimensions of the cable should be known. However, these parameters are hidden and cannot be used during designing. Therefore, a highly simplified method is currently used in practice. It is shown that the errors from the highly simplified method are up to 33%. Authors propose a simplified method based on open data of cable manufacturers. The proposed method is compared with simulation results of a common model of cable power line and takes into account self and mutual inductances of the cores and screens. It is shown that the error of the proposed method is smaller than 4.0% for real cable power lines at wind power plants. However, for a long section of cable power line (2.5 km) the error of calculation... [more]

In April 2018, the International Maritime Organisation adopted an ambitious plan to contribute to the global efforts to reduce the Greenhouse Gas emissions, as set by the Paris Agreement, by targeting a 50% reduction in shipping’s Green House Gas emissions by 2050, benchmarked to 2008 levels. To meet these challenging goals, the maritime industry must introduce environmentally friendly fuels with negligible, or low SOX, NOX and CO2 emissions. Ammonia use in maritime applications is considered promising, due to its high energy density, low flammability, easy storage and low production cost. Moreover, ammonia can be used as fuel in a variety of propulsors such as fuel cells and can be produced from renewable sources. As a result, ammonia can be used as a versatile marine fuel, exploiting the existing infrastructure, and having zero SOX and CO2 emissions. However, there are several challenges to overcome for ammonia to become a compelling fuel towards the decarbonisation of shipping. Such... [more]

In mining and post-mining areas, the assessment of the risks to the surface and its infrastructure from the opening or closed mine is of the utmost importance; particular attention should be paid to mine shafts. The risks include the occurrence of undetected voids or loosening zones in the rock mass. Their detection makes it possible to prevent their impact on a mine shaft and surface infrastructure. Geophysical methods, and in particular, a microgravity method lend themselves for the detection of changes in the distribution of masses (i.e., the density) due to voids and loosening zones. The paper presents the results of surface microgravity surveys in the vicinity of three mine shafts: under construction, working, and a liquidated one. Based on the gravity anomalies, the density distribution of the rock mass for all three cases was recognized. The properties of the anomalies allowed to determine which of the identified decreased density zones may pose a threat to the surface infrastru... [more]

Energy generation and consumption in the power grid must be balanced at every single moment. Within the synchronous area of continental Europe, flexible generators and loads can provide Frequency Containment Reserve and Frequency Restoration Reserve marketed through the balancing markets. The Transmission System Operators use these flexibilities to maintain or restore the grid frequency when there are deviations. This paper shows the future flexibility potential of Germany’s household sector, in particular for single-family and twin homes in 2025 and 2030 with the assumption that households primarily optimize their self-consumption. The primary focus is directed to the flexibility potential of Electric Vehicles, Heat Pumps, Photovoltaics and Battery Storage Systems. A total of 10 different household system configurations were considered and combined in a weighted average based on the scenario framework of the German Grid Development Plan. The household generation, consumption and stora... [more]

A new single-input multiple-output (SIMO) converter is proposed in this work by incorporating flyback and buck converters in a master−slave configuration. The objective of this work is to address the cross regulation problem, achieve tight voltage regulation, improve the circuit form factor and attain a fast transient response for a SIMO flyback converter. The flyback converter maintains the output channels within 10% of their rated voltages and the SIMO buck converter is placed in series with the flyback converter such that it compensates for the output voltage deviation. Moreover, a time multiplexing switching scheme decouples output channel to eliminate the cross-regulation problem and remove the need for an additional winding transformer per each output channel. A type II compensator with a peak current mode controller was designed to achieve faster transient response which is critical for the proposed configuration. A thorough steady-state analysis was carried out on a triple outp... [more]

The constant increase in electrical energy consumption has led to a growth of photovoltaic installations (PV) along with the corresponding power converters for proper operation. Power electronics converters represent a challenge to maintain the system’s performance and safety; one such problem is series DC Arc Fault (AF). DC AFs lead to fire risk, damaging the main bus and the loads when not detected and interrupted in time. Therefore, research about DC AFs in power electronics converters must be carried out to predict the behavior and help avoid damage to the system. In this work, an innovative hybrid multilevel inverter for PV applications is used to explore the effect of series DC AFs in the converters’ internal signals, with the aims of setting the bases for the development of a detection system for power electronics. Both stages of conversion (DC/DC and DC/AC) are presented. In addition, the placement of the MPPT converter was considered for the tests. The AF experimental tests we... [more]

Currently, intensive work is underway in Poland to increase the share of renewable energy sources in the overall energy balance. Therefore, this paper presents the possibilities of using concentrated solar power in zones with a temperate climate. A simplified model based on the energy balance in the solar collectors considering the main operating parameters of the typical solar power plant was developed. It should be noted here that the model does not take into account issues related to heat accumulation and electricity generation in a Solar Thermal Power Station. The simulation of forced convection inside the solar collector absorber was additionally included in the calculations to improve its accuracy. The model was verified using actual heat measurements at the outlet of the parabolic collector installation at a Solar Thermal Power Station located in the south of Spain. The heat generated by a similar solar collector system in a selected region with a temperate climate, the city of... [more]

The interest in renewable energy to replace fossil fuel is increasing as the problem caused by climate change has become more severe. In this study, small hydropower (SHP) was evaluated as a resource with high development value because of its high energy density compared to other renewable energy sources. SHP may be an attractive and sustainable power generation environmental perspective because of its potential to be found in small rivers and streams. The power generation potential could be estimated based on the discharge in the river basin. Since the river discharge depends on the climate conditions, the hydropower generation potential changes sensitively according to climate variability. Therefore, it is necessary to analyze the SHP potential in consideration of future climate change. In this study, the future prospect of SHP potential is simulated for the period of 2021 to 2100 considering the climate change in three hydropower plants of Deoksong, Hanseok, and Socheon stations, Ko... [more]

The paper presents the results of laboratory studies on the strength−strain properties of shales representing four siltstone-claystone lithostratigraphic units occurring in the Baltic Basin. Laboratory studies in a triaxial stress state were conducted as single failure tests on cylindrical samples oriented parallel and perpendicular to lamination within the rocks. Mutually perpendicular samples were cut out from the same drill core sections in order to determine mechanical anisotropy. Samples oriented parallel to lamination were characterised by values of the static Young’s modulus twice as high as from samples oriented perpendicular to lamination. Similar variability was observed in the case of maximum differential stress values and Poisson’s ratio. Samples parallel to lamination registered notably lower axial strains, which influenced increased values of Young’s modulus and Poisson’s ratio. The rocks studied are characterised by VTI type (vertical transverse isotropy) internal anisot... [more]

The current work presents a computationally cost-effective numerical model that successfully simulates a heat pump water heater (HPWH) under typical working conditions of dwellings. The model’s main components are a stratified tank and the heat-pump unit. Both systems are coupled, since a good prediction of water temperature is needed to accurately predict the heat-pump performance. Ten thermocouples measured the tank wall temperature. Measurements and simulations were performed under challenging conditions of a heavy stratification. The 190 L tank stratification was successfully modeled employing a 1D model, experimentally adjusted by three tapping cycles, with 6 × 22, 6 × 33, and 3 × 33 L consumptions, covering flowrates of 4 and 6 L/min. Water temperature is obtained with an uncertainty of 2.6 °C while the heat-pump was ON. A black box model has been used to obtain the heat-pump performance out of the external and condenser temperatures. For the analyzed days, the COP estimation pre... [more]

This paper evaluates how changes in economic market and policy conditions, including the establishment of a per-unit tax on unabated emissions of carbon dioxide (CO2) set equal to estimates of the social cost of carbon (SCC), influence the economics of carbon capture and storage (CCS) for two hypothetical power generation facilities located in the United States. Data are provided from modified versions of models and resources created and managed by the National Energy Technology Laboratory. Changes in economic market and policy conditions are evaluated over a series of scenarios in which differences in the levelized cost of electricity (LCOE) provide estimates of the financial gap necessary to overcome for CCS to be considered the cost-minimizing choice for each power generation facility type considered. Results suggest that for the coal and natural gas power generation facilities considered, a per-unit tax set equal to an SCC exceeding $123 per metric ton of CO2 (/tCO2) emitted (2018... [more]

The use of biofuel has been researched and announced by scientists to bring benefits in terms of environmental protection. However, studies continue to be conducted to achieve stable results and confirm biofuels as an effective alternative fuel for internal combustion engines. In this study, the fuel used is biodiesel derived from fish oil and conventional diesel fuel. Specifically, the test fuel is conventional diesel mixed with fish oil biodiesel in different ratios, including B0, B10, B20, B30, B40, and B50 (respectively 0%, 10%, 20%, 30% 40%, and 50% biodiesel in the mixture). Research was carried out by both simulation (from B0 to B50) and experiment (from B0 to B30) on a single cylinder common rail diesel engine. Test modes were at 25%, 50%, and 75% load respectively at maximum torque (at 1400 revolutions per minute (rpm)) and minimum fuel consumption (at 2200 rpm). Compared with B0, the average reduction in brake power of the biodiesel decreased relative to the proportion of bio... [more]

Combined cycle power plants are characterized by high efficiency, now exceeding 60%. The record-breaking power plant listed in the Guinness Book of World Records is the Nishi-Nagoya power plant commissioned in March 2018, located in Japan, and reaching the gross efficiency of 63.08%. Research and development centers, energy companies, and scientific institutions are taking various actions to increase this efficiency. Both the gas turbine and the steam turbine of the combined cycle are modified. The main objective of this paper is to improve the gas-steam cycle efficiency and to reach the efficiency that is higher than in the record-breaking Nishi-Nagoya power plant. To do so, a number of numerical calculations were performed for the cycle design similar to the one used in the Nishi-Nagoya power plant. The paper assumes the use of the same gas turbines as in the reference power plant. The process of recovering heat from exhaust gases had to be organized so that the highest capacity and... [more]