This paper proposes a new hybrid islanding detection method for grid-connected photovoltaic system (GCPVS)-based microgrid. In the presented technique, the suspicious islanding event is initially recognized whilst the absolute deviation of the point of common coupling (PCC) voltage surpasses a threshold. After an intentional delay, a transient disturbance is injected into the voltage source inverter’s d-axis reference current to decline the active power output. As a result, the PCC voltage reduces in islanding operating mode whilst its variation is negligible in the grid presence. Therefore, the simultaneous drop of PCC voltage and active power output is used as an islanding detection criterion. The effectiveness of the proposed algorithm is investigated for various islanding and non-islanding scenarios for a practical distribution network with three GCPVSs. The simulation results in MATLAB/Simulink show successful islanding detection with a small non-detection zone within 300 ms witho... [more]

Optimal management of thermal energy storage in a building is essential to provide predictable energy flexibility to a smart grid. Active technologies such as Electric Thermal Storage (ETS) can assist in building heating load management and can complement the building’s passive thermal storage capacity. The presented paper outlines a methodology that utilizes the concept of Building Energy Flexibility Index (BEFI) and shows that implementing Model Predictive Control (MPC) with dedicated thermal storage can provide predictable energy flexibility to the grid during critical times. When the utility notifies the customer 12 h before a Demand Response (DR) event, a BEFI up to 65 kW (100% reduction) can be achieved. A dynamic rate structure as the objective function is shown to be successful in reducing the peak demand, while a greater reduction in energy consumption in a 24-hour period is seen with a rate structure with a demand charge. Contingency reserve participation was also studied and... [more]

This paper presents the possibilities of adapting active mines to generate green energy after their closure using their resources and/or infrastructure. For this purpose, firstly, the temporal horizon of selected mines in Poland was determined, its basic assumption being the analysis of the current state. In the research, 18 mining plants operating within 12 mines in the Upper Silesian Coal Basin (USCB) were analyzed. The analyzed mines belong to three of the five largest hard coal producers in Poland, and the main object of exploitation is hard coal of energy types. Severe restrictions or even abandonment of further investments in the development of the coal mining industry were taken into consideration (regarding the construction of new shafts or the development of new exploitation levels). When determining the temporal horizon, the challenges that hamper the exploitation based at the levels of natural hazards and depth of exploitation in each mine were considered. Secondly, the crit... [more]

Gas turbine inlet air-cooling (TIAC) is an established technology for augmenting gas turbine output and efficiency, especially in hot regions. TIAC using evaporative cooling is suitable for hot, dry regions; however, the cooling is limited by the ambient wet-bulb temperature. This study investigates two-stage evaporative TIAC under the harsh weather of Riyadh city. The two-stage evaporative TIAC system consists of indirect and direct evaporative stages. In the indirect stage, air is precooled using water cooled in a cooling tower. In the direct stage, adiabatic saturation cools the air. This investigation was conducted for the GE 7001EA gas turbine model. Thermoflex software was used to simulate the GE 7001EA gas turbine using different TIAC systems including evaporative, two-stage evaporative, hybrid absorption refrigeration evaporative and hybrid vapor-compression refrigeration evaporative cooling systems. Comparisons of different performance parameters of gas turbines were conducted... [more]

In power systems, high renewable energy penetration generally results in conventional synchronous generators being displaced. Hence, the power system inertia reduces, thus causing a larger frequency deviation when an imbalance between load and generation occurs, and thus potential system instability. The problem associated with this increase in the system’s dynamic response can be addressed by various means, for example, flywheels, supercapacitors, and battery energy storage systems (BESSs). This paper investigates the application of BESSs for primary frequency control in power systems with very high penetration of renewable energy, and consequently, low levels of synchronous generation. By re-creating a major Australian power system separation event and then subsequently simulating the event under low inertia conditions but with BESSs providing frequency support, it has been demonstrated that a droop-controlled BESS can greatly improve frequency response, producing both faster reactio... [more]

A small rotating detonation engine (RDE) model and the corresponding experimental setup were constructed for the experimental investigation of the detonation propagation characteristics and thrust performance of a circular RDE. Experiments were conducted at a range of 0.3−2.5 equivalence ratio with a total mass flow rate of less than 180.0 g/s using a C2H4/O2 mixture. Irregularly unstable detonative combustion occurs immediately after the detonation initiation, which includes initiation, propagation, decaying, and the merging of detonation waves. Following this, periodically unsteady detonative combustion occurs in the circular channel, resulting in the stable operation of the RDE. During stable operation, two detonation waves are predominant, rotating along the wall at a speed lower than the Chapman−Jouguet (CJ) detonation speed. The characteristic velocity efficiency is approximately 73% on average. The low characteristic velocity efficiency is presumed to be caused by the unoptimize... [more]

Recently, micro-grids (MGs) have had a great impact on power system issues due to their clear environmental and economic advantages. This paper proposes an equilibrium optimizer (EO) technique for solving the energy management problem of MGs incorporating energy storage devices concerning the emissions from renewable energy sources (RES) of MGs. Because of the imprecision and uncertainties related to the RESs, market prices, and forecast load demand, the optimization problem is described in a probabilistic manner using a 2m + 1 point estimation approach. Then, the EO approach is utilized for solving the probabilistic energy management (EM) problem. The EM problem is described according to the market policy on the basis of minimizing the total operating cost and emission from RESs through optimal settings of the power generated from distributed generators (DGs) and grids connected under the condition of satisfying the operational constraints of the system. The proposed EO is evaluated b... [more]

Earth to air heat exchangers are widely utilized to cool or heat passive buildings for energy savings. They often need to deal with high humidity air conditions, especially in the greenhouse due to plant transpiration, and the condensation phenomenon is frequently observed during the cooling process. To evaluate the effect of humidity and condensation on thermal performance, a three dimensional computational fluid dynamic (3D-CFD) model was developed. The distribution of relative humidity in each pipe was investigated, and the impact of inlet air relative humidity on the integrated performance of the earth to air heat exchanger was discussed. The effects of inlet air temperature and volume flow rate were also analyzed. Moreover, the influence of the heat exchanger configurations on the performance of the air condensation was researched. The results indicated that condensation had few effects on the airflow distribution uniformity of the earth to air heat exchanger, while it acted obser... [more]

The article presents the experimental investigation of low-lifting capacity hydraulic scissor lift energy consumption. The analysis is based on experimental tests of two individual drives of the scissor lift: the conventional one and the variable-speed electro-hydraulic one. The investigation focuses on the study of the total energy consumption for lifting and lowering the scissor lift with different masses of transported cargo and also power consumptions of each element supplying these systems. Particular attention was paid to the significant impact of power supply on each control component as the main factor of reduction in the energetic efficiency of the low-lifting capacity scissor lift. A comparison of both drives indicated that the mass of transported cargo has a significant influence on the choice of the drive used. Results of the research show that significant energetic savings are obtained, as the modernized propulsion system consumes 67% energy of the standard one. A decrease... [more]

This paper presents Nyström minimum kernel risk-sensitive loss (NysMKRSL) based control of a three-phase four-wire grid-tied dual-stage PV-hybrid energy storage system, under varying conditions such as irradiation variation, unbalanced load, and abnormal grid voltage. The Voltage Source Converter (VSC) control enables the system to perform multifunctional operations such as reactive power compensation, load balancing, power balancing, and harmonics elimination while maintaining Unity Power Factor (UPF). The proposed VSC control delivers more accurate weights with fewer oscillations, hence reducing overall losses and providing better stability to the system. The seamless control with the Hybrid Energy Storage System (HESS) facilitates the system’s grid-tied and isolated operation. The HESS includes the battery, fuel cell, and ultra-capacitor to accomplish the peak shaving, managing the disturbances of sudden and prolonged nature occurring due to load unbalancing and abnormal grid voltag... [more]

This article presents a comparative analysis for the design considerations for a solar power generation transformer. One of the main existing problems in transformer manufacturing is in the renewable energy field, specifically the solar power generation, where the transformer connected to the inverter is operated under a certain harmonic content and operating conditions. The operating conditions of the transformer connected to the inverter are particularly unknown for each solar power plant; thus, the transformer will be subject to a particular harmonic content, which is defined by the inverter of the solar power plant. First, the fundamental calculations for solar power plant transformer and the proposed methodology for the design calculation of the distribution pad-mounted three phase transformer are presented. Then, a design study case is described where a distribution transformer and an inverter of a particular solar power plant are used for the analysis. Next, the transformer unde... [more]

Lithium-ion (Li-I) batteries have recently become pervasive and are used in many physical assets. For the effective management of the batteries, reliable predictions of the end-of-discharge (EOD) and end-of-life (EOL) are essential. Many detailed electrochemical models have been developed for the batteries. Their parameters are calibrated before they are taken into operation and are typically not re-calibrated during operation. However, the degradation of batteries increases the reality gap between the computational models and the physical systems and leads to inaccurate predictions of EOD/EOL. The current calibration approaches are either computationally expensive (model-based calibration) or require large amounts of ground truth data for degradation parameters (supervised data-driven calibration). This is often infeasible for many practical applications. In this paper, we introduce a reinforcement learning-based framework for reliably inferring calibration parameters of battery model... [more]

Maximum-power point tracking of wind turbines is a challenging issue considering fast changing wind conditions of urban areas. For this purpose, an adaptive control approach that is fast and robust is required. Conventional approaches based on simple step perturbations and subsequent observation, however, are difficult to design and too slow for the demanding wind conditions of urban areas including gusts and turbulence. In this paper, an extremum seeking control scheme to the recently developed wind turbine MOWEA (Modulare Windenergieanlagen GmbH) is proposed and successfully applied. To this end, a comprehensive aero-electromechanical model of the wind turbine under study including basic control is formulated. Next, the extremum seeking control scheme is adapted to the system. Several aspects to increase adaptation speed are highlighted, including a novel phase compensation. Finally, a validation of the proposed approach is performed considering real wind data, thus demonstrating its... [more]

With the increasing demand for renewable energy power generation systems, high-power DC transmission technology is drawing considerable attention. As a result, stability issues associated with high power DC transmission have been highlighted. One of these problems is the fault current that appears when a fault occurs in the transmission line. If the fault current flows in the transmission line, it has a serious adverse effect on the rectifier stage, inverter stage and transmission line load. This makes the transmission technology less reliable and can lead to secondary problems such as fire. Therefore, fault current must be managed safely. DC circuit breaker technology has been proposed to solve this problem. However, conventional technologies generally do not take into account the effects of fault current on the transmission line, and their efficiency is relatively low. The purpose of this study is to introduce an improved DC circuit breaker that uses a blocking inductor to minimize t... [more]

Carbon nanofibers decorated with various metal oxide nanoparticles were fabricated by combining an electrospinning technique of bicomponent polymer mixture and a sol-gel reaction and subsequent carbonization process. Electrospun polymer nanofibers consisting of polyacrylonitrile (PAN) and poly(vinyl pyrrolidone) (PVP) with controllable diameters were fabricated with PAN/PVP core/shell types via phase-separation due to the immiscibility between two polymers. The electrospun nanofibers served as supporting materials with binding sites of PVP to incorporate titanium oxide precursor. Subsequently, the carbonization of the fibers led to the formation of carbon nanofibers@TiO2 for energy application, in which rutile TiO2 nanoparticles were decorated on the surface of carbon nanofiber. Especially, this TiO2 decorated carbon nanofiber electrode exhibited excellent electrochemical property in lithium-ion batteries (≈600 mA h g−1 at C/5 rate for 100 cycles). Furthermore, the carbon nanofibers we... [more]

Local implementation projects for sector coupling play an important role in the transformation to a more sustainable energy system. Despite various technical possibilities, there are various barriers to the realisation of local projects. Against this backdrop, we introduce an inter- and transdisciplinary approach to identifying and evaluating different power-to-X paths as well as setting up robust local implementation projects, which account for existing drivers and potential hurdles early on. After developing the approach conceptually, we exemplify our elaborations by applying them to a use case in the German city of Wuppertal. It can be shown that a mix of several interlinked interdisciplinary methods as well as several participatory elements is suitable for triggering a collective, local innovation process. However, the timing and extent of end-user integration remain a balancing act. The paper does not focus on a detailed description of power-to-X (PtX) as a central pillar of the s... [more]

This paper aims to design thermal dummy cells (TDCs) that can be used in the development of lithium-ion battery thermal management systems. Based on physical property and geometry of real 18,650 cylindrical cells, a three-dimensional model of TDCs was designed, and it is used to numerically simulate the thermal performance of TDCs. Simulations show that the TDC can mimic the temperature change on the surface of a real cell both at static and dynamic current load. Experimental results show that the rate of heating resistance of TDC is less than 0.43% for temperatures between 27.5 °C and 90.5 °C. Powered by a two-step voltage source of 12 V, the temperature difference of TDCs is 1 °C and 1.6 °C along the circumference and the axial directions, respectively. Powered by a constant voltage source of 6 V, the temperature rising rates on the surface and in the core are higher than 1.9 °C/min. Afterwards, the proposed TDC was used to simulate a real cell for investigating its thermal performan... [more]

The present work considers the dramatic changes the COVID-19 pandemic has brought to the global economy, with particular emphasis on energy. Focusing on the European Union, the article discusses the opportunities policy makers can implement to reduce the climate impacts and achieve the Paris Agreement 2050 targets. The analysis specifically looks at the fossil fuels industry and the future of the fossil sector post COVID-19 pandemic. The analysis first revises the fossil fuel sector, and then considers the need for a shift of the global climate change policy from promoting the deployment of renewable energy sources to curtailing the use of fossil fuels. This will be a change to the current global approach, from a relative passive one to a strategically dynamic and proactive one. Such a curtailment should be based on actual volumes of fossil fuels used and not on percentages. Finally, conclusions are preliminary applied to the European Union policies for net zero by 2050 based on a two-... [more]

Ukraine is an energy-dependent country, with less that 50% of its energy consumption fulfilled by its own resources. Natural gas is of paramount importance, especially for industry and society. Therefore, there is an urgent need to search for alternative and potential energy sources, such as gas hydrate deposits in the Black Sea, which can reduce the consumption of imported gas. It is necessary to refine the process parameters of the dissociation of gas hydrate deposits with a heterogeneous structure. The analyzed known geological−geophysical data devoted to the study of the offshore area and the seabed give grounds to assert the existence of a significant amount of hydrate deposits in the Black Sea. An integrated methodological approach is applied, which consists of the development of algorithms for analytical and laboratory studies of gas volumes obtained during the dissociation of deposits with a heterogeneous structure. These data are used for the computer modelling of the dissocia... [more]

The increasing penetration of electrical vehicles (EVs), on the way to decarbonizing the transportation sector, presents several challenges and opportunities for the end users, the distribution grid, and the electricity markets. Uncontrollable EV charging may increase peak demand and impact the grid stability and reliability, especially in the case of non-interconnected microgrids such as the distribution grids of small islands. On the other hand, if EVs are considered as flexible loads and distributed storage, they may offer Vehicle to Grid (V2G) services and contribute to demand-side management through smart charging and discharging. In this work, we present a study on the penetration of EVs and the flexibility they may offer for services to the grid, using a genetic algorithm for optimum valley filling and peak shaving for the case of a non-interconnected island where the electricity demand is several times higher during the summer due to the influx of tourists. Test cases have been... [more]

Many islands around the world present considerable energy supply problems, while their energy mixture is controlled by oil products. Meanwhile, several of these isolated islands enjoy excellent RES potential that support actions to maximize RES integration. In order to ameliorate energy supply security and energy autonomy of the Aegean Archipelagos Greek islands, an integrated solution is deployed based on the exploitation of the existing RES potential in conjunction with the application of an appropriate energy storage scheme, as well as complementary smart-grid elements. The proposed solution has been applied for the Greek Tilos island in the framework of the Tilos-Horizon 2020 program. In this context, the implementation of the integrated Tilos energy solution under the current local legislative frame is a great success story introducing several important innovative characteristics in the European market, like the combined operation of a wind turbine and a PV installation, the appli... [more]

The Zn(II) and Mn(II) removal by an ion flotation process from model and real dilute aqueous solutions derived from waste batteries was studied in this work. The research aimed to determine optimal conditions for the removal of Zn(II) and Mn(II) from aqueous solutions after acidic leaching of Zn-C and Zn-Mn waste batteries. The ion flotation process was carried out at ambient temperature and atmospheric pressure. Two organic compounds used as collectors were applied, i.e., m-dodecylphosphoric acid 32 and m-tetradecylphosphoric 33 acid in the presence of a non-ionic foaming agent (Triton X-100, 29). It was found that both compounds can be used as collectors in the ion flotation for Zn(II) and Mn(II) removal process. Process parameters for Zn(II) and Mn(II) flotation have been established for collective or selective removal metals, e.g., good selectivity coefficients equal to 29.2 for Zn(II) over Mn(II) was achieved for a 10 min process using collector 32 in the presence of foaming agent... [more]

Global warming requires a changeover from fossil fuel based to renewable energy sources on the electrical supply side and electrification of the demand side. Due to the transient nature of renewables and fluctuating demand, buffer capacities are necessary to compensate for supply/demand imbalances. Battery energy storage systems are promising. However, the initial costs are high. Repurposing electric vehicle batteries can reduce initial costs. Further, storage design optimization could significantly improve costs. Therefore, a battery control algorithm was developed, and a simulation study was performed to identify the optimal storage design and its economic potential. The algorithm used is based on autonomous (on-site) optimization, which relies on an incentive determining the operation mode (charge, discharge, or idle). The incentive used was the historic day-ahead stock market price for electricity, and the resulting potential economic gains for different European countries were com... [more]

Formic acid is a liquid organic hydrogen carrier giving hydrogen on demand using catalysts. Metal complexes are known to be used as efficient catalysts for the hydrogen production from formic acid decomposition. Their performance could be better than those of supported catalysts with metal nanoparticles. However, difficulties to separate metal complexes from the reaction mixture limit their industrial applications. This problem can be resolved by supporting metal complexes on the surface of different supports, which may additionally provide some surface sites for the formic acid activation. The review analyzes the literature on the application of supported metal complexes in the hydrogen production from formic acid. It shows that the catalytic activity of some stable Ru and Ir supported metal complexes may exceed the activity of homogeneous metal complexes used for deposition. Non-noble metal-based complexes containing Fe demonstrated sufficiently high performance in the reaction; howe... [more]

This article presents the results of noise tests, measurements and proposals of solutions that have an impact for reducing noise at one of the Jastrzębska Spółka Węglowa S.A. mines. All units and workstations at the mechanical coal processing plant were tested. Coal enrichment, aimed at adjusting its quality parameters to the requirements of various customers, is considered as a stage of mineral resources management. The adaptation of the quality of commercial coal products to the needs of specific customers consists in removing useless components from the excavated material. The processes of coal processing are carried out on various machines, the power of which reaches several dozen kilowatts. The energy of these machines, in addition to the useful power, is converted into heat, friction and noise. From the energy point of view, noise is not important, but it is very harmful to employees. The issue of noise pollution, although very dangerous to employees’ health, is often underestima... [more]