Due to the increasing integration of renewable energy sources (RES) and a corresponding reduction of conventional generating units, there is nowadays a demand from the power-electronic converters to provide grid-forming properties through proper control of the converter systems. This paper aims to evaluate the impact of various control loops in a grid-forming control strategy equipped with a fault-ride through capability on the passivity properties of the converter system. Through the analysis of the frequency-dependent input admittance of the converter, the main factors affecting the passivity properties are identified. A simplified analytical model is derived in order to propose possible control modifications to enhance the system’s passivity at various frequencies of interest and the findings are validated through detailed time-domain simulations and experimental tests.

Environmental problems are frequently related to energy use, estimated to grow at 1.6% per year until 2035. The transport sector accounts for 30% of energy demand and aviation is growing around 2.6% per year. Thus, low-emissions policies promote the use of sustainable aviation fuels. This work simulates a gasification and Fischer-Tropsch process to obtain biojet fuel from biomass and plastic waste. Syngas obtained through cogasification is purified by amine scrubbing and subjected to a Fischer-Tropsch process to produce hydrocarbons, which are upgraded for optimal fuel properties. Pinch analysis is applied to minimize energy usage, while Rankine cycles and a cooling tower are designed to cover the demand of electricity and cooling water. Results show that mass yields of the process towards biofuels are 13.06%, with an output of 1697.45 kg/h of biojet fuel. Density, kinematic viscosity, pour and flammability points and the lower calorific value of the biojet fuel comply with the ASTM D7... [more]

This article presents a novel methodology for data integration including laboratory data, the results of standard well logging measurements and interpretation and the interpretation of XRMI imager data for determination of the porosity and permeability of the fracture system in carbonate rock. An example of the results of the micro computed tomography applied for carbonate rock is included. Data were obtained on the area of the Polish Lowland Zechstein Main Dolomite formation. The input set of data included the results of mercury injection porosimetry (MICP), thin section and polished section analysis, well logging measurements and comprehensive interpretation and micro computed tomography. The methodology of the macrofractures’ analysis based on borehole wall imagery as well as estimation of their aperture was described in detail. The petrophysical characteristics of the fracture systems were analyzed as an element of standard interpretation of well logging data along a carbonate form... [more]

To accelerate the integration of fluctuating renewable energy technologies in the power systems, it is necessary to increase the flexibility of hydropower by operating turbines at off-design conditions. Unfortunately, this strategy causes deleterious flow phenomena such as von Kármán’s vortices at the wake of the vanes and/or blades. When their shedding frequency lies in the vicinity of a structure’s natural frequency, lock-in occurs and vibration amplitudes increase significantly. Moreover, if cavitation occurs at the centers of these vortices, the structure’s dynamic response will be modified. In order to understand this interaction and to avoid its negative consequences, the vibration behavior of a NACA 0009 hydrofoil under a torsional lock-in condition was numerically simulated for cavitation-free and cavitating-flow conditions. The results showed that the presence of vortex cavitation modified the formation and growth process of shed von Kármán vortices in the near-wake region whi... [more]

The household sector contributes significantly to a country’s energy consumption. Energy carrier expenses are the highest expenditures in Polish household budgets. Households run by individuals aged 60 and older are heavily burdened with energy expenditures. The scientific aim of the research is to present and assess housing conditions, with particular emphasis on energy poverty in households run by individuals aged 60 and older. Multivariate statistical analyses were used to conduct the research objectives (cluster methods, variance methods, regression methods). This paper identifies a new index—one that has been applied to the situation in Poland. Households that consist of elderly people are strongly diversified in terms of housing conditions (including energy conditions). There are concerns that some households are not able to access energy services that are required to satisfy basic human needs, particularly individuals with low levels of education, living on social benefits, with... [more]

This paper presents a simple yet efficient control method for active power filters that can be used to improve power quality. Applying this method can open the way towards limiting the hardware and computational expenditure, which are needed for control of the active filter, while maintaining its required performance. The method is based on the indirect approach of obtaining reference signals combined with the closed-loop current control technique. Monitoring of changes of energy stored in reactance elements of the active filter is the base for obtaining reference signals for compensation. The active filter can perform classical compensation and, additionally, can perform some extra functionality for managing of active power in the system. In particular, it can stabilize the supplying source power, enable energy exchange between loads connected on DC and AC sides of the active filter, and—in a case of generating loads—enable their energy storage and redistribution amongst consuming loa... [more]

There is a need to reduce carbon-based energy and replace it with clean energy in order to counteract the negative effects of climate change. The increase in renewable energy sources may result in savings and the increasing cost of maintaining carbon-based energy. Worldwide involvement is required. The fulfillment of conditions by individual states does not solve the problem. The COVID-19 pandemic has slowed economic growth. It turns out that economic growth is not always associated with increased investments in RES (existing or emerging new clean energy points). We have a new epidemiological threat—Delta—which could become large. This will not improve the situation. Germany is an exemplary country for benchmarking in the field of renewable energy. The worrying fact is that Poland, despite economic growth, does not achieve an even growth in RES. Each of us is required to be involved, to be open to innovation and to act in accordance with the energy policy of the European Union. Basic m... [more]

As the world population and its dependency on energy is growing exponentially day by day, the existing energy generating resources are not enough to fulfill their needs. In the conventional grid system, most of the generated energy is wasted because of improper demand side management (DSM). This leads to a difficulty in keeping the equilibrium between the user need and electric power production. To overcome these difficulties, smart grid (SG) is introduced, which is composed of the integration of two-way communication between the user and utility. To utilize the existing energy resources in a better way, SG is the best option since a large portion of the generated energy is consumed by the educational institutes. Such institutes also need un-interrupted power supply at the lowest cost. Therefore, in this paper, we have taken a university campus load. We have not only applied two bio-inspired heuristic algorithms for energy scheduling—namely, the Firefly Algorithm (FA) and the Lion Algo... [more]

Using a cross-country dataset covering 9265 observations on 1785 firms representing 53 countries over the period 2004−2019, this study investigates the relation between carbon emissions reduction and corporate financial performance (CFP). We perform OLS regressions with fixed effects. We found that carbon emissions reduction increases the return on assets, the return on equity, and the return on sales, whereas it has no effect on the Tobin’s Q and the current ratio. The positive relationship with the return on assets is stronger for firms with a higher responsibility score. We study country characteristics by modeling GDP growth, overall emissions within a country, and the presence of carbon emissions legislation. Our results indicate that the overall carbon emissions of a country and the presence of carbon emissions legislation are related to both corporate carbon emissions reduction and CFP. Moderating effects of the country’s overall emissions and the presence of carbon emissions le... [more]

Hydrogen is an environmentally friendly biofuel which, if widely used, could reduce atmospheric carbon dioxide emissions. The main barrier to the widespread use of hydrogen for power generation is the lack of technologically feasible and—more importantly—cost-effective methods of production and storage. So far, hydrogen has been produced using thermochemical methods (such as gasification, pyrolysis or water electrolysis) and biological methods (most of which involve anaerobic digestion and photofermentation), with conventional fuels, waste or dedicated crop biomass used as a feedstock. Microalgae possess very high photosynthetic efficiency, can rapidly build biomass, and possess other beneficial properties, which is why they are considered to be one of the strongest contenders among biohydrogen production technologies. This review gives an account of present knowledge on microalgal hydrogen production and compares it with the other available biofuel production technologies.

The activities of the poviat are a combination of interrelated factors. The use of natural resources should be carried out in accordance with the principles of sustainable development. The aim of this research was to assess the spatial differentiation of development relationships, the natural environment, and ecology of poviats in Poland, using a synthetic measure. Empirical data were collected in the spatial terms of poviats in Poland. The choice of variables was conditioned by the availability of data of the Central Statistical Office for 2010−2019. The assessment of development of poviats indicates disproportions in terms of development variables, as well as the natural environment and ecology, and the existence of a weak impact of natural conditions for development. Poviats distinguished by a higher level of natural environment are not characterized by a higher measure of development. The reason for the low impact of non-financial conditions on the development of poviats is their d... [more]

This paper presents a literature review of the dynamics of offshore floating wind turbine platforms. When moving further offshore, there is an increase in the capacity of wind power. Generating power from renewable resources is enhanced through the extraction of wind energy from an offshore deep-water wind resource. Mounting the turbine on a platform that is not stable brings another difficulty to wind turbine modeling. There is a need to introduce platforms that are more effective to capture this energy, because of the complex dynamics and control of these platforms. This paper highlights the historical developments and progresses in the design of different types of offshore floating wind turbine platforms needed for harvesting the energy from offshore winds. The relative advantages and disadvantages of the platform types with the design challenges are discussed. The major types of floating platforms included in this study are tension leg platform (TLP) type, spar type, and semisubmer... [more]

This article presents the results of the design of acoustic−magnetic device thermal protection technology based on simulation. The acoustic−magnetic device (AMD) was installed in the heat supply system of a greenhouse complex with a geothermal heat source, developed and patented by the authors of this paper. Simulation was performed to investigate the possibility of maintaining the acoustic transmitter temperature of the acoustic−magnetic device in its operating range. The QuickField Student Edition v 6.4 simulation environment was used for this purpose. Based on the results of the simulation, the optimum thermal mode of the acoustic−magnetic device was developed and implemented. The optimum temporal operating mode of the acoustic−magnetic device is necessary for the optimization of the non-reagent treatment of geothermal water in a heat supply system of a greenhouse complex. It allows for a considerable reduction in the intensity of scale formation in the heat exchanger and equipment... [more]

Geomechanical characterization plays a key role in optimizing the stimulation treatment of tight reservoir formations. Petrophysical models help classify the reservoir rock as the conventional or unconventional type and determine hydrocarbon-saturated zones. Geomechanical and petrophysical models are fundamentally based on well-log data that provide reliable and high-resolution information, and are used to determine various relationships between measured borehole parameters and modeled physical rock properties in 3D space, with the support of seismic data. This paper presents the geomechanical characterization of the Middle Cambrian (Cm2) sediments from Eastern Pomerania, north Poland. To achieve the aim of this study, 1D well-log-based and 3D models based on seismic data of the rocks’ petrophysical, elastic, and strength properties, as well as numerical methods, were used. The analysis of the Middle Cambrian deposits revealed vertical and horizontal heterogeneity in brittleness, the d... [more]

This study focused on the efficiency improvement and acoustic noise reduction of brushless DC (BLDC) motors by reducing current harmonics using a novel BLDC commutation method. To achieve these goals, we designed an improved 150° commutation method for a three-phase permanent magnet BLDC motor that can improve the current waveform. Although the 120° commutation method is generally employed for BLDC motors, an improved 150° commutation method is introduced to operate the BLDC with increased efficiency and acoustic noise similar to a brushless AC motor. This study investigated the attributes of various commutation methods, both theoretically and experimentally, to determine the optimal commutation method. The results of this study indicate that the improved 150° commutation method is optimal in terms of harmonic attributes and reduced torque ripple, allowing it to improve motor efficiency and reduce acoustic noise.

Research on forecasting the seasonality and growth trend of natural gas (NG) production and consumption will help organize an analysis base for NG inspection and development, social issues, and allow industrials elements to operate effectively and reduce economic issues. In this situation, we handle a comparison structure on the application of different models in monthly NG production and consumption forecasting using the cross-correlation function and then analyze the association between exogenous variables. Moreover, the SARIMA-X model is tested for US monthly NG production and consumption prediction via the proposed method for the first time in the literature review in this study. The performance of that model has been compared with SARIMA (p, d, q) * (P, D, Q)s. The results from RMSE and MAPE indicate that the superiority of the best model. By applying this method, the US monthly NG production and consumption is forecast until 2025. The success of the proposed method allows the use... [more]

A Flying Ad-hoc network constitutes many sensor nodes with limited processing speed and storage capacity as they institute a minor battery-driven device with a limited quantity of energy. One of the primary roles of the sensor node is to store and transmit the collected information to the base station (BS). Thus, the life span of the network is the main criterion for the efficient design of the FANETS Network, as sensor nodes always have limited resources. In this paper, we present a methodology of an energy-efficient clustering algorithm for collecting and transmitting data based on the Optimized Low-Energy Adaptive Clustering Hierarchy (LEACH) protocol. The selection of CH is grounded on the new optimized threshold function. In contrast, LEACH is a hierarchical routing protocol that randomly selects cluster head nodes in a loop and results in an increased cluster headcount, but also causes more rapid power consumption. Thus, we have to circumvent these limitations by improving the LE... [more]

The Caspian Sea is a region of active hydrocarbon production, where apart from conventional accumulations, gas hydrates (GH) are known to exist. GH are a potential future source of energy, however, currently they pose danger for development of conventional fields. The goal of this research was to determine the area of GH distribution and thickness of their stability zone in the Caspian Sea using numerical modeling and to define how certain parameters affect the calculated thickness. As a result of the research, cartographic schemes were created for the South and Middle Caspian, where GH were predicted. For the South Caspian, conditions for methane hydrates formation exist at depths of more than 419−454 m, and for the Middle Caspian, more than 416−453 m. The maximal thicknesses of methane hydrates stability zones for the South Caspian can reach 900−956 m, and for the Middle Caspian, 226−676 m. Variations of parameters of seafloor depth, geothermal gradient and gas composition can signif... [more]

The discrimination of inrush currents and internal fault currents in transformers is an important feature of a transformer protection scheme. The harmonic current restrained feature is used in conventional differential relay protection of transformers. A literature survey shows that the discrimination between the inrush currents and internal fault currents is still an area that is open to research. In this paper, the classification of internal fault currents and magnetic inrush currents in the transformer is performed by using an extended Kalman filter (EKF) algorithm. When a transformer is energized under normal conditions, the EKF estimates the primary side winding current and, hence, the absolute residual signal (ARS) value is zero. The ARS value will not be equal to zero for internal fault and inrush phenomena conditions; hence, the EKF algorithm will be used for discriminating the internal faults and inrush faults by keeping the threshold level to the ARS value. The simulation res... [more]

Unmanned aerial systems (UAS) provide two main functions with regards to bridge inspections: (1) high-quality digital imaging to detect element defects; (2) spatial point cloud data for the reconstruction of 3D asset models. With UAS being a relatively new inspection method, there is little in the way of existing framework for storing, processing and managing the resulting inspection data. This study has proposed a novel methodology for a digital information model covering data acquisition through to a 3D GIS visualisation environment, also capable of integrating within a bridge management system (BMS). Previous efforts focusing on visualisation functionality have focused on BIM and GIS as separate entities, which has a number of problems associated with it. This methodology has a core focus on the integration of BIM and GIS, providing an effective and efficient information model, which provides vital visual context to inspectors and users of the BMS. Three-dimensional GIS visualisatio... [more]

Breaks in the so-called “continuous” (unspliced) belt sections, and not in the spliced areas, are infrequent but do happen in practice. This article presents some aspects, which may account for such breaks in conveyor belts. It indicates the so-called “sensitive points” in design, especially in the transition section of the conveyor belt and in identifying the actual strength of the belt. The presented results include the influence of the width of a belt specimen on the identified belt tensile strength. An increase in the specimen width entails a decrease in the belt strength. The research involved develops a universal theoretical model of the belt on a transition section of a troughed conveyor in which, in the case of steel-cord belts, the belt is composed of cords and layers of rubber, and in the case of a textile belt, of narrow strips. The article also describes geometrical forces in the transition section of the belt and an illustrative analysis of loads acting on the belt. Attent... [more]

Regarding different challenges, such as integration of green energy and autonomy of microgrid (MG) in the multi-microgrid (MMG) system, this paper presents an optimized and coordinated strategy for energy management of MMG systems that consider multiple scenarios of MGs. The proposed strategy operates at two optimization levels: local and global. At an MG level, each energy management system satisfies its local demand by utilizing all available resources via local optimization, and only sends surplus/deficit energy data signals to MMG level, which enhances customer privacy. Thereafter, at an MMG level, a central energy management system performs global optimization and selects optimized options from the available resources, which include charging/discharging energy to/from the community battery energy storage system, selling/buying power to/from other MGs, and trading with the grid. Two types of loads are considered in this model: sensitive and non-sensitive. The algorithm tries to mak... [more]

Energy management in protected cropping is critical due to the high cost of energy use in high-tech greenhouse facilities. The main purpose of this research was to investigate the optimal strategy to reduce cooling energy consumption, by regulating the settings (opening/closing) of either vents or curtains during the day, at the protected cropping facility at Western Sydney University. We measured daily changes in air temperature and energy consumption under four treatments (open/closed combinations of vents and shade screens) and developed an optimal cooling strategy for energy management using multi-temperature acquisition points at different heights within a greenhouse compartment. The optimal treatment (vents open/curtains closed) reduced energy load at the rooftop, thereby maintaining a desirable plant canopy temperature profile, and reducing cooling energy. Daily energy consumption was lowest for vents open/curtains closed (70.5 kWh) and highest for vents closed/curtains open (12... [more]

Thermochemical energy storage systems from carbonates, mainly those based on calcium carbonate, have been gaining momentum in the last few years. However, despite the considerable interest in the process, the Technology Readiness Level (TRL) is still low. Therefore, facing the progressive development of the technology at different scales is essential to carry out a comprehensive risk assessment and a Failure Mode Effect and Analysis (FMEA) process to guarantee the safety and operation of the technology systems. In this study, the methodology was applied to a first-of-its-kind prototype, and it is a valuable tool for assessing safe design and operation and potential scaling up. The present work describes the methodology for carrying out these analyses to construct a kW-scale prototype of an energy storage system based on calcium carbonate. The main potential risks occur during the testing and operation stages (>50% of identified risks), being derived mainly from potential overheating in... [more]

The main purpose of this paper is to investigate the contributions of building-integrated photovoltaic (BIPV) systems to the notion of nearly zero-energy cities in the capitals of the European Union member states (EU), Norway, and Switzerland. Moreover, an in-depth investigation of the barriers and challenges ahead of the widespread rollout of BIPV technology is undertaken. This study investigates the scalability of the nearly zero-energy concept using BIPV technology in moving from individual buildings to entire cities. This study provide a metric for architects and urban planners that can be used to assess how much of the energy consumed by buildings in Europe could be supplied by BIPV systems when installed as building envelope materials on the outer skins of buildings. The results illustrate that by 2030, when buildings in the EU become more energy-efficient and the efficiency of BIPV systems will have improved considerably, BIPV envelope materials will be a reasonable option for b... [more]