Ground-coupled heat pumps (GCHPs) are an efficient thermal energy production system that can satisfy the gap between heating and air-conditioning. Be that as it may, exploratory research on GCHPs is still lacking. The first objective of this article is to describe a utilitarian energy-efficiency improvement device for a vertical GCHP system that includes a buffer tank (BT) between the heat pump unit and the fan coil units and user supply, utilizing the quantitative regulation of water flow rate with a variable-speed circulation pump. At that point, the investigative estimations are utilized to test the performances of the GCHP system in various operating modes. Fundamental efficiency parameters (coefficient of performance (COP) and CO2 emission) are achieved for one month of running utilizing two control strategies of the GCHP—standard and optimized regulation of the water pump speed—and a benchmarking of these parameters is achieved. Exploratory research has indicated higher efficienc... [more]

The economic value of photovoltaic (PV) systems depends on country-specific conditions. This study investigates the impact of grid fees, solar irradiance and local consumption on the profitability and penetration of PV systems and batteries in renewable energy communities. The linear optimization model calculates the optimal investments into PV and storages applied on a test community, which represents the European housing situation. The comparison of eight countries considers individual heat and cooling demands as well as sector coupling. Results show that renewable energy communities have the potential to reduce electricity costs due to community investments and load aggregation but do not necessarily lead to more distributed PV. Besides full-load hours, the energy component of electricity tariffs has the highest impact on PV distribution. Under current market conditions, battery energy storage systems are rarely profitable for increasing PV self-consumption but there is potential wi... [more]

Large-scale integration of renewable generation into power systems invariably affects the system ramping capability. However, the vehicle-to-grid (V2G) concept that allows for using electric vehicles (EVs) as energy storages with the capability of bidirectional energy transfer between the EVs and the grid, can be employed to mitigate the above adverse effect. This paper proposes a game-theory-based V2G coordination strategy that uses EV clusters to improve ramping flexibility in power systems. In the proposed strategy, the V2G concept, representing the interactions between the distribution system operator (DSO) and EV clusters, is formulated as a Stackelberg game. The DSO acts as a leader who decides the charging prices for the buses to which the EV clusters are connected, while the EV clusters simply serve as followers, scheduling their own charging and discharging. This bi-level model is further reduced to a single-level, mixed-integer second-order cone programming (MISOCP) problem b... [more]

Small modular reactors (SMRs) represent a key area of interest to nuclear industry developers, which have been making significant progress during the past few years. Generally, these reactors are promising owing to their improved safety due to passive systems, enhanced containment efficiency, and fewer capital costs in comparison to traditional nuclear reactors. An important advantage of SMRs is their adaptability in being coupled to other energy-consuming systems, such as desalination plants (DPs) to create a cogeneration plant. Considering the serious challenges regarding the freshwater shortage in many regions of the world and the necessity of using low-carbon energy sources, it is advantageous to use SMR for supplying the required heat and electricity of DPs. As a high-performance desalination technology, the hybrid desalination (HD) systems can be exploited, which retain the advantages of both thermal and membrane desalination methods. In this study, several SMR coupling schemes t... [more]

The present study aims at investigating the effects of porous structure development and ash content on the observed reactivity during steam gasification of biochar residues from a commercial gasifier. The experiments were conducted at a temperature range of 700 to 800 °C using biochar, derived from entrained flow gasification of biomass, under isothermal conditions using a thermogravimetric analyzer. The pore size distribution, surface area and morphology of char samples were determined by N2 physiosorption and scanning electron microscopy (SEM). The results showed that the gasification temperature does not affect the porous structure development considerably. The total surface area of char exhibits a threefold increase, while the total pore volume increase ranges between 2.0 and 5.3 times, at all temperatures. Both properties are directly proportional to the observed reactivity, especially at conversions up to 70%. Catalytic effects of the mineral matter of the char (mainly potassium)... [more]

In the context of electric vehicle (EV) development and positive energy districts with the growing penetration of non-programmable sources, this paper provides a method to predict and manage the aggregate power flows of charging stations to optimize the self-consumption and load profiles. The prediction method analyzes each charging event belonging to the EV population, and it considers the main factors that influence a charging process, namely the EV’s characteristics, charging ratings, and driver behavior. EV’s characteristics and charging ratings are obtained from the EV model’s and charging stations’ specifications, respectively. The statistical analysis of driver behavior is performed to calculate the daily consumptions and the charging energy request. Then, a model to estimate the parking time of each vehicle is extrapolated from the real collected data of the arrival and departure times in parking lots. A case study was carried out to evaluate the proposed method. This consisted... [more]

The presence of injectors with strongly swirled flows, used to promote flame stability in the combustion chambers of gas turbines, influences the behaviour of the effusion cooling jets and consequently of the liner’s cooling capabilities. For this reason, unsteady behaviour of the jets in the presence of swirling flow requires a characterization by means of experimental flow field analyses. The experimental setup of this work consists of a non-reactive single-sector linear combustor test rig, scaled up with respect to the real engine geometry to increase spatial resolution and to reduce the frequencies of the unsteadiness. It is equipped with a radial swirler and multi-perforated effusion plates to simulate the liner cooling system. Two effusion plates were tested and compared: with cylindrical and with laid-back fan-shaped 7-7-7 holes in staggered arrangement. Time resolved Particle Image Velocimetry has been carried out: the unsteady characteristics of the jets, promoted by the inter... [more]

Countries around the world are expanding their investment in the new and renewable energy industry for strengthening energy security, improving air pollution, responding to climate change, and tackling energy poverty. In Korea, with the nuclear phase-out declaration in 2017, the government has announced a policy to expand the ratio of new and renewable energy from 4.7% to 20% by 2030. This study examines a floating photovoltaic power generation system, which is a new and renewable energy source. A structure composed of high-durability steel with excellent corrosion resistance and durability was designed for constructing and installing a 500-kW-class floating photovoltaic power generation structure. In addition, the safety of the structure was verified through finite element analysis. By reviewing the safety of the structure with respect to the wave height, the behavior of the structure was confirmed through the design wave height formula proposed in the domestic standard. The verificat... [more]

To obtain the real-time drilling trajectory of radial horizontal jet drilling (RHJD), a magnetized nozzle localization method based on magnetic gradient tensor (MGT) is proposed. The MGT system consisting of five tri-axial magnetometers, a tri-axial accelerometer, and a tri-axial gyroscope are installed in the casing. The magnetized nozzle is made of a strong magnetic permanent magnet whose position can be obtained by measuring the MGT generated by itself at the measurement point. The simulation and experiment of the localization method are carried out, which show that the method has high accuracy. When the detection distance is 40 m, the error is only 0.07 m, which meets the requirements of engineering practice. The accuracy of the magnetometer, the baseline distance and the magnetization strength of the nozzle are the main factors affecting the localization error. This localization method can meet the requirements of positioning accuracy in practical engineering, which greatly avoids... [more]

Heat and fluid flow at the edge of steam chambers found in thermal recovery processes such as steam-assisted gravity drainage and cyclic steam stimulation remain unresolved. Given the multiple phases present and contrast of thermophysical properties, it remains unclear where instabilities occur within this thin, yet critical, zone of the process. In the research reported here, heat and fluid flow are examined in vertical and horizontal sections of a steam chamber to understand the differences between the two orientations by using detailed and fine-gridded thermal reservoir simulation models. The results show that heat transfer in vertical and horizontal directions are different with greater heat transfer found in the vertical orientation. In the vertical direction, heat transfer occurs with mobilized bitumen draining with subsequent steam moving into the emptied pore space. Conduction beyond the edge of the chamber dominates and heated, low viscosity bitumen fingers into cold, higher v... [more]

Forest biomass is and will remain a primary source of renewable energy in many EU countries in the coming years. The aim of this study was to determine the energy potential of forest biomass on a regional scale with regard to the needs of its inhabitants in terms of electricity and heat consumption. The study was carried out in south-eastern Poland. Energy potential was calculated based on the determined wood mass and calorific value of wood. The current level of forest biomass acquisition satisfies 4.2% of the needs of the local market in terms of electricity and heat consumption. Taking into account high forest cover of the region (40%), the 60% annual increment of total harvesting, and obtaining biomass at the level of 30% of the total harvesting, waste wood from the forest can meet 58.1% of the needs of the local market in terms of electricity consumption and 14.4% of the need for thermal energy consumption. There is a certain niche in the fuel wood market that is currently unused,... [more]

The purpose of the work is a comparison of indirect carbon dioxide emissions between the different heat pump types that operate in Polish climate conditions. The analysis embraces air-to-water heat pump, ground-to-water heat pump, water-to-water heat pump and water-to-water heat pump with separating heat exchanger in the selected towns one in each climatic zone in the country. The study starts from determining seasonal coefficient of performance in each location using heating degree days to estimate seasonal heat demand. Seasonal coefficient of performance values enable an assessment which kind of heat pump meets the European Union requirements in every location. Eventually, indirect CO2 emissions that is caused by electrical energy production, are estimated for every heat pump in each location. Ground-to-water heat pump and water-to-water heat pump satisfy these requirements in each climatic zone in Poland. Air-to-water heat pump would be an energetic and ecological viable on a condit... [more]

The oxygen reduction reaction is an important reaction at the cathode in solid oxide fuel cells. Materials that exhibit high chemical and mechanical stability, high ionic and electronic conductivity, and are non-toxic are of great interest as cathodes for the reduction of oxygen. Here, we use density functional theory simulations to examine the efficacy of 12CaO·7Al2O3 and 12SrO·7Al2O3 electrides and their doped forms for the conversion of O2 gas to form O2− in their nanocages via encapsulation. Calculations show that encapsulation is exoergic in the un-doped electrides, and the formation of O2− is confirmed by the charge analysis. A stronger encapsulation is noted for C12A7 electride than the S12A7 electride. The C12A7 electride doped with B or Ga also exhibits exoergic encapsulation, but its encapsulation energy is slightly lower than that calculated for the un-doped C12A7 electride. There is an enhancement in the encapsulation for the S12A7 electride doped with B compared to its un-... [more]

A significant growth in PV (photovoltaic) system installations have been observed during the last decade. The PV array has a nonlinear output characteristic because of weather intermittency. Partial shading is an environmental phenomenon that causes multiple peaks in the power curve and has a negative effect on the efficiency of the conventional maximum power point tracking (MPPT) methods. This tends to have a substantial effect on the overall performance of the PV system. Therefore, to enhance the performance of the PV system under shading conditions, the global MPPT technique is mandatory to force the PV system to operate close to the global maximum. In this paper, for the first time, a stochastic fractal search (SFS) optimization algorithm is applied to solve the dilemma of tracking the global power of PV system based triple-junction solar cells under shading conditions. SFS has been nominated because it can converge to the best solution at a fast rate. Moreover, balance between exp... [more]

In this paper, a peer-to-peer (P2P) renewable energy trading mechanism for microgrids when energy suppliers are equipped with storage devices is studied. A dynamic energy storage management strategy based on the local trading price is proposed and each supplier decides the amount of energy to be sold and stored in real time. An iterative auction algorithm is presented to obtain the market equilibrium and optimal energy allocation schedule. The economic analysis of introducing energy storage devices in this trading market is further studied. Numerical examples of two 7 × 24-h energy trading scenarios with 20 consumers and 20 solar energy producers are used to illustrate the feasibility of this proposed trading mechanism, with sensitivity analysis of different parameters on social welfare. A comparison of the hourly optimal local trading price of these two markets is demonstrated to explain the dynamic process. It is found that in those days with high solar radiation, compared with the m... [more]

The 2018 IEEE International Conference on High Voltage Engineering and Application (ICHVE 2018) was organized by the National Technical University of Athens, Greece and endorsed by the IEEE Dielectrics and Electrical Insulation Society [...]

Building energy codes are key policy tools for improving building energy efficiency by defining the minimum requirement for the energy performance of new buildings. In Korea, the building energy code was focused on prescriptive criteria for a long time but is now gradually introducing performance criteria. However, switching to performance criteria is not straightforward because of the resistance of the market to abandoning the well-consolidated prescriptive criteria. The objective of this study is to derive appropriate measures to strengthen the prescriptive criteria and the performance criteria, considering both the energy-saving effect and the economic efficiency for new office buildings and educational buildings to increase the market acceptance of the building energy codes. To this end, the energy-saving effects of reference buildings resulting from the reinforcement of the prescriptive criteria in the past have been first analyzed. Then, based on the collected energy performance... [more]

The interaction between natural gas and electricity networks is becoming more significant due to the projected large penetration of renewables into the energy system to meet the emission targets. This is due to the role of gas-fired plants in providing backup to renewables as the linkage between these networks. Therefore, this paper proposes a deterministic coordinated model for the secure and optimal operation of integrated natural gas and electricity transmission networks by taking into account the N-1 contingency analysis on both networks. In order to reduce the computational burden and time, an iterative algorithm is proposed to select the critical cases and neglect other contingencies, which do not have a significant impact on the energy system. The proposed integrated mixed-integer nonlinear programming operational model is evaluated and compared to another enhanced separated model on the IEEE 24-bus and 15-node gas test systems. The results emphasize the importance and effective... [more]

A series of experimental coal pyrolysis studies were conducted to define the parameters of a kinetic model to enable complete mass and energy balances by identifying basic process products. The developed model determines the chemical enthalpy of pyrolytic reactions, making it possible to determine the share of exothermic conversions in the coking process. To validate the model, a series of experimental pyrolysis tests of coking coals used in the coke plant and their blends were conducted, including TGA, retort, and industrial coke oven scale. Despite significant differences in the chemical composition of various coal types, element balancing allowed detection of the difference in product composition and the heat effects of the chemical conversion of such a complex substance as coal. Analysis of the heat effects of pyrolytic coal decomposition indicates substantial variability. In the first coking period, there are endothermic reactions; in the second, exothermic reactions occur. Averag... [more]

This paper deals with the problem of the leakage inductance calculations in power transformers. Commonly, the leakage flux in the air zone is represented by short-circuit inductance, which determines the short-circuit voltage, which is a very important factor for power transformers. That inductance is a good representation of the typical power transformer windings, but it is insufficient for multi-winding ones. This paper presents simple formulae for self- and mutual leakage inductance calculations for an arbitrary pair of windings. It follows from a simple 1D approach to analyzing the stray field using a discrete differential operator, and it was verified by the finite element method (FEM) calculation results.

Configurations, coordinated controller design and applications of various off-grid systems with distributed energy resources (DERs) for an uninterrupted supply, are presented in this paper. The performances for the optimal operation of a diesel generator (DG) in the presence of nonlinear loads, fuel-savings, voltage and frequency regulation, a soft and secure transition among different operating modes, an optimization, and power management control, are validated through simulated results and test results on the prototype to demonstrate the suitability of these configurations with natural energy resources (NERs) for continuous development in remote as well as in isolated locations.

To increase the adoption of electric vehicles (EVs), significant efforts in terms of reducing the charging time are required. Consequently, ultrafast charging (UFC) stations require extensive investigation, particularly considering their higher power level requirements. Accordingly, this paper introduces a hybrid multimodule DC-DC converter-based dual-active bridge (DAB) topology for EV-UFC to achieve high-efficiency and high-power density. The hybrid concept is achieved through employing two different groups of multimodule converters. The first is designed to be in charge of a high fraction of the total required power, operating at a relatively low switching frequency, while the second is designed for a small fraction of the total power, operating at a relatively high switching frequency. To support the power converter controller design, a generalized small-signal model for the hybrid converter is studied. Also, cross feedback output current sharing (CFOCS) control for the hybrid inpu... [more]

In the present study, a novel probabilistic approach is proposed to optimize a stand-alone hybrid wind-photovoltaic renewable energy system installed in the South China Sea. In detail, the probability distribution of power generated from a hybrid wind-photovoltaic system is estimated based on the probabilistic descriptions of wind and solar energy resources in the South China Sea. In addition, the present study proposed a battery level coefficient model to calculate the battery capacity of the hybrid system. As the battery level coefficient implies the expected power deficit in a specific continuous duration, it reflects the reliability of the battery system and, hence, the performance of the system under the power deficit condition. Given the probabilistic models estimated the stability of power generations, a genetic algorithm is applied to optimize the sizes of the system components (the installed capacities of wind turbines and photovoltaic modules and the load) when the levelized... [more]

Primary energy consumption is one of the key drivers of global CO2 emissions that, in turn, heavily depends on the efficiency of involved technologies. Either improvement in technology efficiency or the expansion of non-fossil fuel consumption requires large investments. The planning and financing of such investments by global policy makers or global energy firms require, in turn, reliable measures of associated global spread and their evolution in time, at least from the point of view of the principles for responsible investment (PRI). In this paper, our main contribution is the introduction of index measures for accessing global spread (that is, measures of inequality or inhomogeneity in the statistical distribution of a related quantity of interest) of technology efficiency and CO2 emission in primary energy consumption. These indexes are based on the Gini index, as used in economical sciences, and generalized entropy measures. Regarding primary energy sources, we consider petroleum... [more]

In this paper, coal gasification characteristics in the reductor were investigated in a full-scale two-stage pressurized entrained-flow gasifier, which has been seldom conducted previously. The present study aimed at elucidating the effects of gasifying agent concentration, coal input rate, and operation period under full reductor load on the performance of a utility two-stage pressurized entrained-flow gasifier for the first time. When the steam input in the combustor was raised from 3318 kg/h to 5722 kg/h, the total outputs of H2, CO, and CO2 were increased by 1765 Nm3/h and 2063 Nm3/h, respectively, while the CH4 output was decreased by 49 Nm3/h. The coal conversion rate was minimal at low steam input. In addition, more coal gasified in the reductor could increase the output of CH4, while CH4 could reach 1.24% with the coal input in the range of 8000−10,000 kg/h. The present work can offer a further understanding of the gasification performance in the reductor of the full-scale two-... [more]