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Energies, Volume 9, Issue 8 (August 2016)

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Cover Story (view full-size image) To protect the battery, a battery management system (BMS) is used to monitor its state and maintain [...] Read more.
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Open AccessArticle
Thermoeconomic Modeling and Parametric Study of a Photovoltaic-Assisted 1 MWe Combined Cooling, Heating, and Power System
Energies 2016, 9(8), 663; https://doi.org/10.3390/en9080663 - 20 Aug 2016
Cited by 8 | Viewed by 1781 | Correction
Abstract
In this study a small-scale, completely autonomous combined cooling, heating, and power (CCHP) system is coupled to a photovoltaic (PV) subsystem, to investigate the possibility of reducing fuel consumption. The CCHP system generates electrical energy with the use of a simple gas turbine [...] Read more.
In this study a small-scale, completely autonomous combined cooling, heating, and power (CCHP) system is coupled to a photovoltaic (PV) subsystem, to investigate the possibility of reducing fuel consumption. The CCHP system generates electrical energy with the use of a simple gas turbine cycle, with a rated nominal power output of 1 MWe. The nominal power output of the PV subsystem is examined in a parametric study, ranging from 0 to 600 kWe, to investigate which configuration results in a minimum lifecycle cost (LCC) for a system lifetime of 20 years of service. The load profile considered is applied for a complex of households in Nicosia, Cyprus. The solar data for the PV subsystem are taken on an hourly basis for a whole year. The results suggest that apart from economic benefits, the proposed system also results in high efficiency and reduced CO2 emissions. The parametric study shows that the optimum PV capacity is 300 kWe. The minimum lifecycle cost for the PV-assisted CCHP system is found to be 3.509 million €, as compared to 3.577 million € for a system without a PV subsystem. The total cost for the PV subsystem is 547,445 €, while the total cost for operating the system (fuel) is 731,814 € (compared to 952,201 € for a CCHP system without PVs). Overall, the proposed system generates a total electrical energy output of 52,433 MWh (during its whole lifetime), which translates to a unit cost of electricity of 0.067 €/kWh. Full article
(This article belongs to the Special Issue Simulation of Polygeneration Systems)
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Open AccessArticle
Potential of Reversible Solid Oxide Cells as Electricity Storage System
Energies 2016, 9(8), 662; https://doi.org/10.3390/en9080662 - 19 Aug 2016
Cited by 14 | Viewed by 1849
Abstract
Electrical energy storage (EES) systems allow shifting the time of electric power generation from that of consumption, and they are expected to play a major role in future electric grids where the share of intermittent renewable energy systems (RES), and especially solar and [...] Read more.
Electrical energy storage (EES) systems allow shifting the time of electric power generation from that of consumption, and they are expected to play a major role in future electric grids where the share of intermittent renewable energy systems (RES), and especially solar and wind power plants, is planned to increase. No commercially available technology complies with all the required specifications for an efficient and reliable EES system. Reversible solid oxide cells (ReSOC) working in both fuel cell and electrolysis modes could be a cost effective and highly efficient EES, but are not yet ready for the market. In fact, using the system in fuel cell mode produces high temperature heat that can be recovered during electrolysis, when a heat source is necessary. Before ReSOCs can be used as EES systems, many problems have to be solved. This paper presents a new ReSOC concept, where the thermal energy produced during fuel cell mode is stored as sensible or latent heat, respectively, in a high density and high specific heat material and in a phase change material (PCM) and used during electrolysis operation. The study of two different storage concepts is performed using a lumped parameters ReSOC stack model coupled with a suitable balance of plant. The optimal roundtrip efficiency calculated for both of the configurations studied is not far from 70% and results from a trade-off between the stack roundtrip efficiency and the energy consumed by the auxiliary power systems. Full article
(This article belongs to the Special Issue Solid Oxide Fuel Cells)
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Open AccessArticle
Energy Management of an Off-Grid Hybrid Power Plant with Multiple Energy Storage Systems
Energies 2016, 9(8), 661; https://doi.org/10.3390/en9080661 - 19 Aug 2016
Cited by 14 | Viewed by 2533
Abstract
In this paper, an off-grid hybrid power plant with multiple storage systems for an artificial island is designed and two possible strategies for the management of the stored energy are proposed. Renewable power sources (wind/solar technologies) are used as primary power suppliers. A [...] Read more.
In this paper, an off-grid hybrid power plant with multiple storage systems for an artificial island is designed and two possible strategies for the management of the stored energy are proposed. Renewable power sources (wind/solar technologies) are used as primary power suppliers. A lead-acid battery pack (BAT) and a reversible polymer electrolyte fuel cell are employed to fulfill the power demand and to absorb extra power. The reversible fuel cell allows reducing costs and occupied space and the fuel cell can be fed by the pure hydrogen produced by means of its reversible operation as an electrolyzer. A diesel engine is employed as backup system. While HOMER Pro® has been employed for a full-factorial-based optimization of the sizes of the renewable sources and the BAT, Matlab/Simulink® has been later used for simulating the plant operation and compare two possible power management control strategies. For the reversible fuel cell sizing, a sensitivity analysis has been carried out varying stack and hydrogen tank sizes. The final choice for plant configuration and power management control strategy has been made on the basis of a comparative analysis of the results, aimed at minimizing fossil fuel consumption and CO2 emissions, battery aging rate and at maximizing the power plant overall efficiency. The obtained results demonstrate the possibility of realizing a renewable power plant, able to match the needs of electrical power in a remote area, by achieving a good integration of different energy sources and facing the intermittent nature of renewable power sources, with very low use of fossil fuels. Full article
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Open AccessArticle
The Hidden Burden of Food Waste: The Double Energy Waste in Italy
Energies 2016, 9(8), 660; https://doi.org/10.3390/en9080660 - 19 Aug 2016
Cited by 11 | Viewed by 2582
Abstract
The energy intensity of modern food systems represents a major issue in a scenario of decreasing oil resources and increasing population. Beside the use of renewable energy, an increased efficiency in food systems could contribute to reduce fossil fuels dependence. In this sense, [...] Read more.
The energy intensity of modern food systems represents a major issue in a scenario of decreasing oil resources and increasing population. Beside the use of renewable energy, an increased efficiency in food systems could contribute to reduce fossil fuels dependence. In this sense, food losses and waste (FLW) have crucial consequences on the energy balance. Based on the concept of “embodied energy”, food wastage can be framed as a double waste of energy, both in terms of non-consumed food energy and the inputs used for production. Secondary data regarding direct and indirect energy inputs and FLW have been collected for the Italian food chain to estimate the embodied energy of food waste. Since in 2011 the production and distribution of food implied the use of 822 PJ and 18 Mt of food was discarded, 67 PJ of food energy and 100 PJ of embodied energy were wasted. These figures are equivalent to 12.2% of the total nutritional energy output and to 1.3% of the final energy use in Italy, respectively. The concept of double energy waste sheds new light on the intertwined relationship between energy and food security, suggesting that appropriate food waste reduction policies could result in a higher food production level and relevant energy savings. Full article
(This article belongs to the Special Issue Waste Energy Harvesting)
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Open AccessArticle
Effect on Particulate and Gas Emissions by Combusting Biodiesel Blend Fuels Made from Different Plant Oil Feedstocks in a Liquid Fuel Burner
Energies 2016, 9(8), 659; https://doi.org/10.3390/en9080659 - 19 Aug 2016
Cited by 5 | Viewed by 1691
Abstract
This paper focuses on the combustion performance of various blends of biodiesel fuels and diesel fuel from lean to rich mixtures. The biodiesel blend fuel combustion experiments were carried out using a liquid fuel burner and biodiesel fuel made from various plant oil [...] Read more.
This paper focuses on the combustion performance of various blends of biodiesel fuels and diesel fuel from lean to rich mixtures. The biodiesel blend fuel combustion experiments were carried out using a liquid fuel burner and biodiesel fuel made from various plant oil feedstocks, including jatropha, palm and coconut oils. The results show that jatropha oil methyl ester blend 25 (JOME B25) and coconut oil methyl ester blend 25 (COME B25) blended at 25% by volume in diesel fuel produced lower carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions due to more complete combustion. Overall, JOME B25 had the highest CO emission reduction, at about 42.25%, followed by COME B25 at 26.44% emission reduction relative to pure diesel fuel. By contrast, the palm oil methyl ester blend 25 (POME B25) showed a 48.44% increase in these emissions. The results showed that the nitrogen oxides (NOx) emissions were slightly higher for all biodiesel blend fuels compared with pure diesel fuel combustion. In case of sulphur dioxide (SO2) and UHC emissions, all biodiesel blends fuels have significantly reduced emissions. In the case of SO2 emission, the POME B25, JOME B25 and COME B25 emissions were reduced 14.62%, 14.45% and 21.39%, respectively, relative to SO2 emission from combusting pure diesel fuel. UHC emissions of POME B25, JOME B25 and COME B25 showed 51%, 71% and 70% reductions, respectively, compared to diesel fuel. The conclusion from the results is that all the biodiesel blend fuels are suitable and can be recommended for use in liquid fuel burners in order to get better and ‘greener’ environmental outcomes. Full article
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Open AccessArticle
DMFC Performance of Polymer Electrolyte Membranes Prepared from a Graft-Copolymer Consisting of a Polysulfone Main Chain and Styrene Sulfonic Acid Side Chains
Energies 2016, 9(8), 658; https://doi.org/10.3390/en9080658 - 19 Aug 2016
Cited by 1 | Viewed by 2311
Abstract
Polymer electrolyte membranes (PEMs) for direct methanol fuel cell (DMFC) applications were prepared from a graft-copolymer (PSF-g-PSSA) consisting of a polysulfone (PSF) main chain and poly(styrene sulfonic acid) (PSSA) side chains with various average distances between side chains (Lav) [...] Read more.
Polymer electrolyte membranes (PEMs) for direct methanol fuel cell (DMFC) applications were prepared from a graft-copolymer (PSF-g-PSSA) consisting of a polysulfone (PSF) main chain and poly(styrene sulfonic acid) (PSSA) side chains with various average distances between side chains (Lav) and side chain lengths (Lsc). The polymers were synthesized by grafting ethyl p-styrenesulfonate (EtSS) on macro-initiators of chloromethylated polysulfone with different contents of chloromethyl (CM) groups, and by changing EtSS content in the copolymers by using atom transfer radical polymerization (ATRP). The DMFC performance tests using membrane electrode assemblis (MEAs) with the three types of the PEMs revealed that: a PSF-g-PSSA PEM (SF-6) prepared from a graft copolymer with short average distances between side chains (Lav) and medium Lsc had higher DMFC performance than PEMs with long Lav and long Lsc or with short Lav and short Lsc. SF-6 had about two times higher PDmax (68.4 mW/cm2) than Nafion® 112 at 30 wt % of methanol concentration. Furthermore, it had 58.2 mW/cm2 of PDmax at 50 wt % of methanol concentration because of it has the highest proton selectivity during DMFC operation of all the PSF-g-PSSA PEMs and Nafion® 112. Full article
(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells 2016)
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Open AccessArticle
Land Suitability Analysis for Solar Farms Exploitation Using GIS and Fuzzy Analytic Hierarchy Process (FAHP)—A Case Study of Iran
Energies 2016, 9(8), 643; https://doi.org/10.3390/en9080643 - 19 Aug 2016
Cited by 27 | Viewed by 3643
Abstract
Considering the geographical location and climatic conditions of Iran, solar energy can provide a considerable portion of the energy demand for the country. This study develops a two-step framework. In the first step, the map of unsuitable regions is extracted based on the [...] Read more.
Considering the geographical location and climatic conditions of Iran, solar energy can provide a considerable portion of the energy demand for the country. This study develops a two-step framework. In the first step, the map of unsuitable regions is extracted based on the defined constraints. In the next step, in order to identify the suitability of different regions, 11 defined criteria, including solar radiation, average annual temperatures, distance from power transmission lines, distance from major roads, distance from residential area, elevation, slope, land use, average annual cloudy days, average annual humidity and average annual dusty days, are identified. The relative weights of defined criteria and sub-criteria are also determined applying fuzzy analytical hierarchy process (FAHP) technique. Next, by overlaying these criteria layers, the final map of prioritization of different regions of Iran for exploiting solar photovoltaic (PV) plants is developed. Based on Iran’s political divisions, investigation and analysis of the results have been presented for a total of 1057 districts of the country, where each district stands in one of the five defined classes of excellent, good, fair, low, and poor level. The obtained data indicate that 14.7% (237,920 km2), 17.2% (278,270 km2), 19.2% (311,767 km2), 11.3% (183,057 km2), 1.8% (30,549 km2) and 35.8% (580,264 km2) of Iran’s area are positioned as excellent, good, fair, low, poor and unsuitable areas, respectively. Moreover, Kerman, Yazd, Fars, Sisitan and Baluchestan, Southern Khorasan and Isfahan are included in the regions as the most excellent suitable provinces for exploiting solar PV plants. Full article
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Open AccessArticle
Electromagnetohydrodynamic Effects on Steam Bubble Formation in Vertical Heated Upward Flow
Energies 2016, 9(8), 657; https://doi.org/10.3390/en9080657 - 18 Aug 2016
Cited by 4 | Viewed by 1256
Abstract
In this paper, the modeling of a steady state two phase flow heated through a vertical upward flow under electro-magneto-hydro-dynamic forces is presented. The thermal non-equilibrium, non-homogeneous, two-phase flow model consisting of mass, momentum and energy conservation in each phase has been adjusted [...] Read more.
In this paper, the modeling of a steady state two phase flow heated through a vertical upward flow under electro-magneto-hydro-dynamic forces is presented. The thermal non-equilibrium, non-homogeneous, two-phase flow model consisting of mass, momentum and energy conservation in each phase has been adjusted for subcooled inlet conditions close to saturation. The P-1 approximation, viscous dissipation and Joule heating are included in the energy equations. It was seen that the Lorentz force can decrease and postpone the bubble generation, as well as affect the slip velocity, flow forces, viscous dissipation and Joule heating. Furthermore, two correlations for the slip velocity under magnetohydrodynamic (MHD) forces are presented. As shown, skin friction and Joule heating increase with the magnetic field strength. Full article
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Open AccessArticle
Study on Reaction Characteristics of Chemical-Looping Combustion between Maize Stalk and High Index Facet Iron Oxide
Energies 2016, 9(8), 656; https://doi.org/10.3390/en9080656 - 18 Aug 2016
Cited by 2 | Viewed by 1850
Abstract
In this work, experiments were performed to investigate the activity and regeneration ability of iron-based oxygen carrier with high index facet (104) during chemical looping combustion (CLC), suggesting that morphological control of the oxygen carrier is very rewarding. Fe2O3(104) [...] Read more.
In this work, experiments were performed to investigate the activity and regeneration ability of iron-based oxygen carrier with high index facet (104) during chemical looping combustion (CLC), suggesting that morphological control of the oxygen carrier is very rewarding. Fe2O3(104) supported on Al2O3 was synthesized by a morphology controlled method to undertake maize stalk CLC experiments. Compared with the referenced Fe2O3/Al2O3 prepared by the impregnation method, Fe2O3(104)/Al2O3 presents better reactivity, showing higher fuel conversion rate and CO2 concentration in gaseous products. Further, structural characterizations, including X-ray diffraction (XRD), scanning electron microscopy (SEM) (LEO-1450) and Brunauer-Emmett-Teller (BET) analysis, and multi-cycles CLC reactions were performed to verify the good regeneration and stability of the Fe2O3(104)/Al2O3. The findings indicate that the Fe2O3(104)/Al2O3 is efficient when used for CLC of maize stalk. Full article
(This article belongs to the Special Issue Combustion and Propulsion)
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Open AccessArticle
Research on the Combustion Characteristics of a Free-Piston Gasoline Engine Linear Generator during the Stable Generating Process
Energies 2016, 9(8), 655; https://doi.org/10.3390/en9080655 - 18 Aug 2016
Cited by 23 | Viewed by 2747
Abstract
The free-piston gasoline engine linear generator (FPGLG) is a new kind of power plant consisting of free-piston gasoline engines and a linear generator. Due to the elimination of the crankshaft mechanism, the piston motion process and the combustion heat release process affect each [...] Read more.
The free-piston gasoline engine linear generator (FPGLG) is a new kind of power plant consisting of free-piston gasoline engines and a linear generator. Due to the elimination of the crankshaft mechanism, the piston motion process and the combustion heat release process affect each other significantly. In this paper, the combustion characteristics during the stable generating process of a FPGLG were presented using a numerical iteration method, which coupled a zero-dimensional piston dynamic model and a three-dimensional scavenging model with the combustion process simulation. The results indicated that, compared to the conventional engine (CE), the heat release process of the FPGLG lasted longer with a lower peak heat release rate. The indicated thermal efficiency of the engine was lower because less heat was released around the piston top dead centre (TDC). Very minimal difference was observed on the ignition delay duration between the FPGLG and the CE, while the post-combustion period of the FPGLG was significantly longer than that of the CE. Meanwhile, the FPGLG was found to operate more moderately due to lower peak in-cylinder gas pressure and a lower pressure rising rate. The potential advantage of the FPGLG in lower NOx emission was also proven with the simulation results presented in this paper. Full article
(This article belongs to the Special Issue Combustion and Propulsion)
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Open AccessArticle
An Algorithmic Game Approach for Demand Side Management in Smart Grid with Distributed Renewable Power Generation and Storage
Energies 2016, 9(8), 654; https://doi.org/10.3390/en9080654 - 18 Aug 2016
Cited by 7 | Viewed by 2297
Abstract
In this paper, the problem of minimizing electricity cost and the peak system load in smart grids with distributed renewable energy resources is studied. Unlike prior research works that either assume all of the jobs are interruptible or power-shiftable, this paper focuses on [...] Read more.
In this paper, the problem of minimizing electricity cost and the peak system load in smart grids with distributed renewable energy resources is studied. Unlike prior research works that either assume all of the jobs are interruptible or power-shiftable, this paper focuses on more challenging scenarios in which jobs are non-interruptible and non-power-shiftable. In addition, as more and more newly-built homes have rooftop solar arrays, it is assumed that all users are equipped with a solar-plus-battery system in this paper. Thus, power can be drawn from the battery as needed to reduce the cost of electricity or to lower the overall system load. With a quadratic load-dependent cost function, this paper first shows that the electricity cost minimization problem in such a setting is NP-hard and presents a distributed demand-side management algorithm, called DDSM, to solve this. Experimental results show that the proposed DDSM algorithm is effective, scalable and converges to a Nash equilibrium in finite rounds. Full article
(This article belongs to the collection Smart Grid)
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Open AccessArticle
Proposing Wavelet-Based Low-Pass Filter and Input Filter to Improve Transient Response of Grid-Connected Photovoltaic Systems
Energies 2016, 9(8), 653; https://doi.org/10.3390/en9080653 - 18 Aug 2016
Viewed by 1899
Abstract
Available photovoltaic (PV) systems show a prolonged transient response, when integrated into the power grid via active filters. On one hand, the conventional low-pass filter, employed within the integrated PV system, works with a large delay, particularly in the presence of system’s low-order [...] Read more.
Available photovoltaic (PV) systems show a prolonged transient response, when integrated into the power grid via active filters. On one hand, the conventional low-pass filter, employed within the integrated PV system, works with a large delay, particularly in the presence of system’s low-order harmonics. On the other hand, the switching of the DC (direct current)–DC converters within PV units also prolongs the transient response of an integrated system, injecting harmonics and distortion through the PV-end current. This paper initially develops a wavelet-based low-pass filter to improve the transient response of the interconnected PV systems to grid lines. Further, a damped input filter is proposed within the PV system to address the raised converter’s switching issue. Finally, Matlab/Simulink simulations validate the effectiveness of the proposed wavelet-based low-pass filter and damped input filter within an integrated PV system. Full article
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Open AccessArticle
Heat Transfer and Energy Performance of a PVA Wall Tile Containing Macro-Encapsulated PCM
Energies 2016, 9(8), 652; https://doi.org/10.3390/en9080652 - 18 Aug 2016
Cited by 5 | Viewed by 1667
Abstract
This study integrated building material engineering, building construction practices, and heat transfer mechanisms to develop a polyvinyl acetate (PVA) based wall tile, containing macro-encapsulated phase change material (macro-encapsulated PCM, macroPCM) and PVA. The heat transfer characteristics and energy performances of the proposed prototype [...] Read more.
This study integrated building material engineering, building construction practices, and heat transfer mechanisms to develop a polyvinyl acetate (PVA) based wall tile, containing macro-encapsulated phase change material (macro-encapsulated PCM, macroPCM) and PVA. The heat transfer characteristics and energy performances of the proposed prototype were investigated experimentally. The results indicated that the PVA-based macroPCM wall tile is suitable for use in exterior walls to enhance the thermal performance. The tile shows a lower heat indoor heat flux than other tested similar building materials and increases the time lag of peak load, effectively shifting the summer peak demand. Full article
(This article belongs to the Special Issue PCM Applications in Building Energy)
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Open AccessArticle
A Coordinated Control for Photovoltaic Generators and Energy Storages in Low-Voltage AC/DC Hybrid Microgrids under Islanded Mode
Energies 2016, 9(8), 651; https://doi.org/10.3390/en9080651 - 17 Aug 2016
Cited by 11 | Viewed by 2451
Abstract
The increasing penetration of renewable generators can be a significant challenge due to the fluctuation of their power generation. Energy storage (ES) units are one solution to improve power supply quality and guarantee system stability. In this paper, a hybrid microgrid is built [...] Read more.
The increasing penetration of renewable generators can be a significant challenge due to the fluctuation of their power generation. Energy storage (ES) units are one solution to improve power supply quality and guarantee system stability. In this paper, a hybrid microgrid is built based on photovoltaic (PV) generator and ES; and coordinated control is proposed and developed to achieve power management in a decentralized manner. This control scheme contains three different droop strategies according to characteristics of PV and ES. First, the modified droop control is proposed for PV, which can take full utilization of renewable energy and avoid regulating output active power frequently. Second, to maintain the direct current (DC) bus voltage stability, a novel droop control incorporating a constant power band is presented for DC-side ES. Third, a cascade droop control is designed for alternating current (AC)-side ES. Thus, the ES lifetime is prolonged. Moreover, interlinking converters (ICs) provide a bridge between AC/DC buses in a hybrid microgrid. The power control of IC is enabled when the AC- or DC-side suffer from active power demand shortage. In particular, if the AC microgrid does not satisfy the reactive power demand, IC then acts as a static synchronous compensator (STATCOM). The effectiveness of the proposed strategies is verified by simulations. Full article
(This article belongs to the Special Issue Decentralized Management of Energy Streams in Smart Grids)
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Open AccessArticle
A Price-Based Demand Response Scheme for Discrete Manufacturing in Smart Grids
Energies 2016, 9(8), 650; https://doi.org/10.3390/en9080650 - 17 Aug 2016
Cited by 7 | Viewed by 2404
Abstract
Demand response (DR) is a key technique in smart grid (SG) technologies for reducing energy costs and maintaining the stability of electrical grids. Since manufacturing is one of the major consumers of electrical energy, implementing DR in factory energy management systems (FEMSs) provides [...] Read more.
Demand response (DR) is a key technique in smart grid (SG) technologies for reducing energy costs and maintaining the stability of electrical grids. Since manufacturing is one of the major consumers of electrical energy, implementing DR in factory energy management systems (FEMSs) provides an effective way to manage energy in manufacturing processes. Although previous studies have investigated DR applications in process manufacturing, they were not conducted for discrete manufacturing. In this study, the state-task network (STN) model is implemented to represent a discrete manufacturing system. On this basis, a DR scheme with a specific DR algorithm is applied to a typical discrete manufacturing—automobile manufacturing—and operational scenarios are established for the stamping process of the automobile production line. The DR scheme determines the optimal operating points for the stamping process using mixed integer linear programming (MILP). The results show that parts of the electricity demand can be shifted from peak to off-peak periods, reducing a significant overall energy costs without degrading production processes. Full article
(This article belongs to the Special Issue Smart Microgrids: Developing the Intelligent Power Grid of Tomorrow)
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Open AccessArticle
Structure Optimization of Stand-Alone Renewable Power Systems Based on Multi Object Function
Energies 2016, 9(8), 649; https://doi.org/10.3390/en9080649 - 17 Aug 2016
Cited by 6 | Viewed by 2215
Abstract
This paper presents a methodology for the size optimization of a stand-alone hybrid PV/wind/diesel/battery system while considering the following factors: total annual cost (TAC), loss of power supply probability (LPSP), and the fuel cost of the diesel generator required by the user. A [...] Read more.
This paper presents a methodology for the size optimization of a stand-alone hybrid PV/wind/diesel/battery system while considering the following factors: total annual cost (TAC), loss of power supply probability (LPSP), and the fuel cost of the diesel generator required by the user. A new optimization algorithm and an object function (including a penalty method) are also proposed; these assist with designing the best structure for a hybrid system satisfying the constraints. In hybrid energy system sources such as photovoltaic (PV), wind, diesel, and energy storage devices are connected as an electrical load supply. Because the power produced by PV and wind turbine sources is dependent on the variation of the resources (sun and wind) and the load demand fluctuates, such a hybrid system must be able to satisfy the load requirements at any time and store the excess energy for use in deficit conditions. Therefore, reliability and cost are the two main criteria when designing a stand-alone hybrid system. Moreover, the operation of a diesel generator is important to achieve greater reliability. In this paper, TAC, LPSP, and the fuel cost of the diesel generator are considered as the objective variables and a hybrid teaching–learning-based optimization algorithm is proposed and used to choose the best structure of a stand-alone hybrid PV/wind/diesel/battery system. Simulation results from MATLAB support the effectiveness of the proposed method and confirm that it is more efficient than conventional methods. Full article
(This article belongs to the Special Issue Next-Generation Low-Carbon Power and Energy Systems)
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Open AccessArticle
Solar Farm Suitability Using Geographic Information System Fuzzy Sets and Analytic Hierarchy Processes: Case Study of Ulleung Island, Korea
Energies 2016, 9(8), 648; https://doi.org/10.3390/en9080648 - 17 Aug 2016
Cited by 17 | Viewed by 2654
Abstract
Solar farm suitability in remote areas will involve a multi-criteria evaluation (MCE) process, particularly well suited for the geographic information system (GIS) environment. Photovoltaic (PV) solar farm criteria were evaluated for an island-based case region having complex topographic and regulatory criteria, along with [...] Read more.
Solar farm suitability in remote areas will involve a multi-criteria evaluation (MCE) process, particularly well suited for the geographic information system (GIS) environment. Photovoltaic (PV) solar farm criteria were evaluated for an island-based case region having complex topographic and regulatory criteria, along with high demand for low-carbon local electricity production: Ulleung Island, Korea. Constraint variables that identified areas forbidden to PV farm development were consolidated into a single binary constraint layer (e.g., environmental regulation, ecological protection, future land use). Six factor variables were selected as influential on-site suitability within the geospatial database to seek out increased annual average power performance and reduced potential investment costs, forming new criteria layers for site suitability: solar irradiation, sunshine hours, average temperature in summer, proximity to transmission line, proximity to roads, and slope. Each factor variable was normalized via a fuzzy membership function (FMF) and parameter setting based on the local characteristics and criteria for a fixed axis PV system. Representative weighting of the relative importance for each factor variable was assigned via pairwise comparison completed by experts. A suitability index (SI) with six factor variables was derived using a weighted fuzzy summation method. Sensitivity analysis was conducted to assess four different SI based on the development scenarios (i.e., the combination of factors being considered). From the resulting map, three highly suitable regions were suggested and validated by comparison with satellite images to confirm the candidate sites for solar farm development. The GIS-MCE method proposed can also be applicable widely to other PV solar farm site selection projects with appropriate adaption for local variables. Full article
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Open AccessArticle
Distributed Energy Storage Control for Dynamic Load Impact Mitigation
Energies 2016, 9(8), 647; https://doi.org/10.3390/en9080647 - 17 Aug 2016
Cited by 9 | Viewed by 1892
Abstract
The future uptake of electric vehicles (EV) in low-voltage distribution networks can cause increased voltage violations and thermal overloading of network assets, especially in networks with limited headroom at times of high or peak demand. To address this problem, this paper proposes a [...] Read more.
The future uptake of electric vehicles (EV) in low-voltage distribution networks can cause increased voltage violations and thermal overloading of network assets, especially in networks with limited headroom at times of high or peak demand. To address this problem, this paper proposes a distributed battery energy storage solution, controlled using an additive increase multiplicative decrease (AIMD) algorithm. The improved algorithm (AIMD+) uses local bus voltage measurements and a reference voltage threshold to determine the additive increase parameter and to control the charging, as well as discharging rate of the battery. The used voltage threshold is dependent on the network topology and is calculated using power flow analysis tools, with peak demand equally allocated amongst all loads. Simulations were performed on the IEEE LV European Test feeder and a number of real U.K. suburban power distribution network models, together with European demand data and a realistic electric vehicle charging model. The performance of the standard AIMD algorithm with a fixed voltage threshold and the proposed AIMD+ algorithm with the reference voltage profile are compared. Results show that, compared to the standard AIMD case, the proposed AIMD+ algorithm further improves the network’s voltage profiles, reduces thermal overload occurrences and ensures a more equal battery utilisation. Full article
(This article belongs to the Special Issue Control of Energy Storage) Printed Edition available
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Open AccessArticle
Static Formation Temperature Prediction Based on Bottom Hole Temperature
Energies 2016, 9(8), 646; https://doi.org/10.3390/en9080646 - 17 Aug 2016
Cited by 4 | Viewed by 2333
Abstract
Static formation temperature (SFT) is required to determine the thermophysical properties and production parameters in geothermal and oil reservoirs. However, it is not easy to determine SFT by both experimental and physical methods. In this paper, a mathematical approach to predicting SFT, based [...] Read more.
Static formation temperature (SFT) is required to determine the thermophysical properties and production parameters in geothermal and oil reservoirs. However, it is not easy to determine SFT by both experimental and physical methods. In this paper, a mathematical approach to predicting SFT, based on a new model describing the relationship between bottom hole temperature (BHT) and shut-in time, has been proposed. The unknown coefficients of the model were derived from the least squares fit by the particle swarm optimization (PSO) algorithm. Additionally, the ability to predict SFT using a few BHT data points (such as the first three, four, or five points of a data set) was evaluated. The accuracy of the proposed method to predict SFT was confirmed by a deviation percentage less than ±4% and a high regression coefficient R2 (>0.98). The proposed method could be used as a practical tool to predict SFT in both geothermal and oil wells. Full article
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Capacitor Current Feedback-Based Active Resonance Damping Strategies for Digitally-Controlled Inductive-Capacitive-Inductive-Filtered Grid-Connected Inverters
Energies 2016, 9(8), 642; https://doi.org/10.3390/en9080642 - 17 Aug 2016
Cited by 13 | Viewed by 3451
Abstract
Inductive-capacitive-inductive (LCL)-type line filters are widely used in grid-connected voltage source inverters (VSIs), since they can provide substantially improved attenuation of switching harmonics in currents injected into the grid with lower cost, weight and power losses than their L-type counterparts. However, the inclusion [...] Read more.
Inductive-capacitive-inductive (LCL)-type line filters are widely used in grid-connected voltage source inverters (VSIs), since they can provide substantially improved attenuation of switching harmonics in currents injected into the grid with lower cost, weight and power losses than their L-type counterparts. However, the inclusion of third order LCL network complicates the current control design regarding the system stability issues because of an inherent resonance peak which appears in the open-loop transfer function of the inverter control system near the control stability boundary. To avoid passive (resistive) resonance damping solutions, due to their additional power losses, active damping (AD) techniques are often applied with proper control algorithms in order to damp the LCL filter resonance and stabilize the system. Among these techniques, the capacitor current feedback (CCF) AD has attracted considerable attention due to its effective damping performance and simple implementation. This paper thus presents a state-of-the-art review of resonance and stability characteristics of CCF-based AD approaches for a digitally-controlled LCL filter-based grid-connected inverter taking into account the effect of computation and pulse width modulation (PWM) delays along with a detailed analysis on proper design and implementation. Full article
(This article belongs to the Special Issue Microgrids 2016)
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Open AccessArticle
A Concentrator Photovoltaic System Based on a Combination of Prism-Compound Parabolic Concentrators
Energies 2016, 9(8), 645; https://doi.org/10.3390/en9080645 - 16 Aug 2016
Cited by 8 | Viewed by 2761
Abstract
We present a cost-effective concentrating photovoltaic system composed of a prism and a compound parabolic concentrator (P-CPC). In this approach, the primary collector consists of a prism, a solid compound parabolic concentrator (CPC), and a slab waveguide. The prism, which is placed on [...] Read more.
We present a cost-effective concentrating photovoltaic system composed of a prism and a compound parabolic concentrator (P-CPC). In this approach, the primary collector consists of a prism, a solid compound parabolic concentrator (CPC), and a slab waveguide. The prism, which is placed on the input aperture of CPC, directs the incoming sunlight beam to be parallel with the main axes of parabolic rims of CPC. Then, the sunlight is reflected at the parabolic rims and concentrated at the focal point of these parabolas. A slab waveguide is coupled at the output aperture of the CPC to collect focused sunlight beams and to guide them to the solar cell. The optical system was modeled and simulated with commercial ray tracing software (LightTools™). Simulation results show that the optical efficiency of a P-CPC can achieve up to 89%. when the concentration ratio of the P-CPC is fixed at 50. We also determine an optimal geometric structure of P-CPC based on simulation. Because of the simplicity of the P-CPC structure, a lower-cost mass production process is possible. A simulation based on optimal structure of P-CPC was performed and the results also shown that P-CPC has high angular tolerance for input sunlight. The high tolerance of the input angle of sunlight allows P-CPC solar concentrator utilize a single sun tracking system instead of a highly precise dual suntracking system as cost effective solution. Full article
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Open AccessArticle
A New Switching Impulse Generator Based on Transformer Boosting and Insulated Gate Bipolar Transistor Trigger Control
Energies 2016, 9(8), 644; https://doi.org/10.3390/en9080644 - 16 Aug 2016
Cited by 1 | Viewed by 2637
Abstract
To make the switching impulse (SI) generator more compact, portable and feasible in field tests, a new approach based on transformer boosting was developed. To address problems such as triggering synchronization and electromagnetic interference involved with the traditional spark gap, an insulated gate [...] Read more.
To make the switching impulse (SI) generator more compact, portable and feasible in field tests, a new approach based on transformer boosting was developed. To address problems such as triggering synchronization and electromagnetic interference involved with the traditional spark gap, an insulated gate bipolar transistor (IGBT) module with drive circuit was employed as the impulse trigger. An optimization design for the component parameters of the primary winding side of the transformer was realized by numerical calculation and error correction. Experiment showed that the waveform parameters of SI and oscillating switching impulse (OSI) voltages generated by the new generator were consistent with the numerical calculation and the error correction. The generator was finally built on a removable high voltage transformer with small size. Thus the volume of the generator is significantly reduced. Experiments showed that the waveform parameters of SI and OSI voltages generated by the new generator were basically consistent with the numerical calculation and the error correction. Full article
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Open AccessArticle
Comparative Study of Hybrid Models Based on a Series of Optimization Algorithms and Their Application in Energy System Forecasting
Energies 2016, 9(8), 640; https://doi.org/10.3390/en9080640 - 16 Aug 2016
Cited by 7 | Viewed by 1939
Abstract
Big data mining, analysis, and forecasting play vital roles in modern economic and industrial fields, especially in the energy system. Inaccurate forecasting may cause wastes of scarce energy or electricity shortages. However, forecasting in the energy system has proven to be a challenging [...] Read more.
Big data mining, analysis, and forecasting play vital roles in modern economic and industrial fields, especially in the energy system. Inaccurate forecasting may cause wastes of scarce energy or electricity shortages. However, forecasting in the energy system has proven to be a challenging task due to various unstable factors, such as high fluctuations, autocorrelation and stochastic volatility. To forecast time series data by using hybrid models is a feasible alternative of conventional single forecasting modelling approaches. This paper develops a group of hybrid models to solve the problems above by eliminating the noise in the original data sequence and optimizing the parameters in a back propagation neural network. One of contributions of this paper is to integrate the existing algorithms and models, which jointly show advances over the present state of the art. The results of comparative studies demonstrate that the hybrid models proposed not only satisfactorily approximate the actual value but also can be an effective tool in the planning and dispatching of smart grids. Full article
(This article belongs to the Special Issue Energy Time Series Forecasting)
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Open AccessArticle
Analysis and Modeling for Short- to Medium-Term Load Forecasting Using a Hybrid Manifold Learning Principal Component Model and Comparison with Classical Statistical Models (SARIMAX, Exponential Smoothing) and Artificial Intelligence Models (ANN, SVM): The Case of Greek Electricity Market
Energies 2016, 9(8), 635; https://doi.org/10.3390/en9080635 - 16 Aug 2016
Cited by 7 | Viewed by 2669
Abstract
In this work we propose a new hybrid model, a combination of the manifold learning Principal Components (PC) technique and the traditional multiple regression (PC-regression), for short and medium-term forecasting of daily, aggregated, day-ahead, electricity system-wide load in the Greek Electricity Market for [...] Read more.
In this work we propose a new hybrid model, a combination of the manifold learning Principal Components (PC) technique and the traditional multiple regression (PC-regression), for short and medium-term forecasting of daily, aggregated, day-ahead, electricity system-wide load in the Greek Electricity Market for the period 2004–2014. PC-regression is shown to effectively capture the intraday, intraweek and annual patterns of load. We compare our model with a number of classical statistical approaches (Holt-Winters exponential smoothing of its generalizations Error-Trend-Seasonal, ETS models, the Seasonal Autoregressive Moving Average with exogenous variables, Seasonal Autoregressive Integrated Moving Average with eXogenous (SARIMAX) model as well as with the more sophisticated artificial intelligence models, Artificial Neural Networks (ANN) and Support Vector Machines (SVM). Using a number of criteria for measuring the quality of the generated in-and out-of-sample forecasts, we have concluded that the forecasts of our hybrid model outperforms the ones generated by the other model, with the SARMAX model being the next best performing approach, giving comparable results. Our approach contributes to studies aimed at providing more accurate and reliable load forecasting, prerequisites for an efficient management of modern power systems. Full article
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Open AccessArticle
Non-Vacuum Processed Polymer Composite Antireflection Coating Films for Silicon Solar Cells
Energies 2016, 9(8), 633; https://doi.org/10.3390/en9080633 - 15 Aug 2016
Cited by 5 | Viewed by 2260
Abstract
A non-vacuum processing method for preparing polymer-based ZrO2/TiO2 multilayer structure antireflection coating (ARC) films for crystalline silicon solar cells by spin coating is introduced. Initially, ZrO2, TiO2 and surface deactivated-TiO2 (SD-TiO2) based films were [...] Read more.
A non-vacuum processing method for preparing polymer-based ZrO2/TiO2 multilayer structure antireflection coating (ARC) films for crystalline silicon solar cells by spin coating is introduced. Initially, ZrO2, TiO2 and surface deactivated-TiO2 (SD-TiO2) based films were examined separately and the effect of photocatalytic properties of TiO2 film on the reflectivity on silicon surface was investigated. Degradation of the reflectance performance with increasing reflectivity of up to 2% in the ultraviolet region was confirmed. No significant change of the reflectance was observed when utilizing SD-TiO2 and ZrO2 films. Average reflectance (between 300 nm–1100 nm) of the silicon surface coated with optimized polymer-based ZrO2 single or ZrO2/SD-TiO2 multilayer composite films was decreased down to 6.5% and 5.5%, respectively. Improvement of photocurrent density (Jsc) and conversion efficiency (η) of fabricated silicon solar cells owing to the ZrO2/SD-TiO2 multilayer ARC could be confirmed. The photovoltaic properties of Jsc, the open-circuit photo voltage (VOC), the fill factor (FF), and the η were 31.42 mA cm−2, 575 mV, 71.5% and 12.91%. Efficiency of the solar cells was improved by the ZrO2-polymer/SD-TiO2 polymer ARC composite layer by a factor of 0.8% with an increase of Jsc (2.07 mA cm−2) compared to those of fabricated without the ARC. Full article
(This article belongs to the Special Issue Nano-Structured Solar Cells)
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Open AccessArticle
Effect of Photoanode Design on the Photoelectrochemical Performance of Dye-Sensitized Solar Cells Based on SnO2 Nanocomposite
Energies 2016, 9(8), 641; https://doi.org/10.3390/en9080641 - 13 Aug 2016
Cited by 6 | Viewed by 2751
Abstract
Li-doped ZnO (LZO) aggregated nanoparticles are used as an insulating layer in SnO2 nanocomposite (SNC) photoanodes to suppress the recombination process in dye-sensitized solar cells (DSSCs). Various weight percentages of SnO2 nanoparticles (SNPs) and SnO2 nanoflowers (SNFs) were used to [...] Read more.
Li-doped ZnO (LZO) aggregated nanoparticles are used as an insulating layer in SnO2 nanocomposite (SNC) photoanodes to suppress the recombination process in dye-sensitized solar cells (DSSCs). Various weight percentages of SnO2 nanoparticles (SNPs) and SnO2 nanoflowers (SNFs) were used to prepare SNC photoanodes. The photocurrent-voltage characteristics showed that the incorporation of an LZO insulating layer in an SNC photoanode increased the conversion efficiency of DSSCs. This was due to an increase in the surface area, charge injection, and charge collection, and the minimization of the recombination rate of photoanodes. Electrochemical impedance spectroscopy (EIS) results showed lower series resistance, charge injection resistance, and shorter lifetimes for DSSCs based on an SNC photoanode with an LZO insulating layer. The open circuit voltage and fill factor of the DSSCs based on SNC photoanodes with an LZO insulating layer significantly increased. The DSSC based on a SNC photoanode with a SNC:SNF weight ratio of 1:1 had a high current density of 4.73 mA/cm2, open circuit voltage of 630 mV, fill factor of 69%, and efficiency of 2.06%. Full article
(This article belongs to the Special Issue Dye Sensitized Solar Cells)
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Open AccessArticle
Estimation of Total Transport CO2 Emissions Generated by Medium- and Heavy-Duty Vehicles (MHDVs) in a Sector of Korea
Energies 2016, 9(8), 638; https://doi.org/10.3390/en9080638 - 13 Aug 2016
Cited by 5 | Viewed by 1533
Abstract
In order to mitigate carbon dioxide (CO2) emissions, policy action that addresses vehicle emissions is essential. While many previous studies have focused on light-duty vehicles (LDV), little is known about medium- and heavy-duty vehicles (MHDV). This study lays the groundwork for [...] Read more.
In order to mitigate carbon dioxide (CO2) emissions, policy action that addresses vehicle emissions is essential. While many previous studies have focused on light-duty vehicles (LDV), little is known about medium- and heavy-duty vehicles (MHDV). This study lays the groundwork for future MHDV investigations in the Republic of Korea by developing an MHDV CO2 emissions inventory. The bottom-up approach was used to calculate national CO2 emissions. Simulation methods that calculated the CO2 emissions of each vehicle and statistical data, such as vehicle miles traveled (VMT) and the number of registered vehicles were used to predict CO2 emissions. The validity of this simulation model was examined by comparing it with the chassis dynamometer test results. The results of this study showed that the CO2 emissions of MHDV in 2015 were 24.47 million tons, which was 25.5% of the total road transportation CO2 emissions, despite only comprising 4.2% of the total vehicles. Trucks emitted 69.6% and buses emitted 30.4% of the total MHDV CO2 emissions. Using the results between 2012 and 2015, the level of business-as-usual (BAU) CO2 emissions will be 25.37 million tons in 2020. Full article
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Open AccessArticle
A Novel Dynamic Co-Simulation Analysis for Overall Closed Loop Operation Control of a Large Wind Turbine
Energies 2016, 9(8), 637; https://doi.org/10.3390/en9080637 - 13 Aug 2016
Cited by 6 | Viewed by 1763
Abstract
A novel dynamic co-simulation methodology of overall wind turbine systems is presented. This methodology combines aerodynamics, mechanism dynamics, control system dynamics, and subsystems dynamics. Aerodynamics and turbine properties were modeled in FAST (Fatigue, Aerodynamic, Structures, and Turbulence), and ADAMS (Automatic Dynamic Analysis of [...] Read more.
A novel dynamic co-simulation methodology of overall wind turbine systems is presented. This methodology combines aerodynamics, mechanism dynamics, control system dynamics, and subsystems dynamics. Aerodynamics and turbine properties were modeled in FAST (Fatigue, Aerodynamic, Structures, and Turbulence), and ADAMS (Automatic Dynamic Analysis of Mechanical Systems) performed the mechanism dynamics; control system dynamics and subsystem dynamics such as generator, pitch control system, and yaw control system were modeled and built in MATLAB/SIMULINK. Thus, this comprehensive integration of methodology expands both the flexibility and controllability of wind turbines. The dynamic variations of blades, rotor dynamic response, and tower vibration can be performed under different inputs of wind profile, and the control strategies can be verified in the different closed loop simulation. Besides, the dynamic simulation results are compared with the measuring results of SCADA (Supervisory Control and Data Acquisition) of a 2 MW wind turbine for ensuring the novel dynamic co-simulation methodology. Full article
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Open AccessArticle
Theoretical Framework of Organizational Intelligence: A Managerial Approach to Promote Renewable Energy in Rural Economies
Energies 2016, 9(8), 639; https://doi.org/10.3390/en9080639 - 12 Aug 2016
Cited by 3 | Viewed by 2518
Abstract
The companies involved in the energy sector must reinvent themselves to be innovative and adaptable to contemporary environmental changes. The promotion of renewable energy in rural communities is a great challenge for these companies. They should focus on improving the environment scanning actions [...] Read more.
The companies involved in the energy sector must reinvent themselves to be innovative and adaptable to contemporary environmental changes. The promotion of renewable energy in rural communities is a great challenge for these companies. They should focus on improving the environment scanning actions and the knowledge management (KM) system and enhancing the collective intelligence to avoid the loss of information, to foster innovation, and to maintain a competitive advantage. To achieve these goals, energy companies require appropriate management tools and practices. The purpose of this study is to propose a theoretical framework of organizational intelligence (OI) supported by a cross-perspective analysis of various aspects: economic intelligence (EI) and KM practices, entropy processes, and organizational enablers. A pilot investigation for testing the framework in the case of Transelectrica S.A. has been elaborated. The findings reveal that the elements of the OI framework are embedded in Transelectrica’s system and they need to be further developed. As an intelligent company acting in the Romanian energy market, Transelectrica has a higher potential to promote projects in the renewable energy sector. The main conclusion highlights that OI is a multidimensional construct that provides the organization the ability to deal with environmental challenges in a “new economy”. Full article
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Open AccessArticle
Design and Implementation of a Test-Bench for Efficiency Measurement of Domestic Induction Heating Appliances
Energies 2016, 9(8), 636; https://doi.org/10.3390/en9080636 - 12 Aug 2016
Cited by 2 | Viewed by 1245
Abstract
The operation of a domestic induction cooktop is based on the wireless energy transfer from the inductor to the pot. In such systems, the induction efficiency is defined as the ratio between the power delivered to the pot and the consumed power from [...] Read more.
The operation of a domestic induction cooktop is based on the wireless energy transfer from the inductor to the pot. In such systems, the induction efficiency is defined as the ratio between the power delivered to the pot and the consumed power from the supplying converter. The non-transferred power is dissipated in the inductor, raising its temperature. Most efficiency-measuring methods are based on measuring the effective power (pot) and the total power (converter output). While the converter output power is directly measurable, the measurement of the power dissipation in the pot is usually a cause of inaccuracy. In this work, an alternative method to measure the system’s efficiency is proposed and implemented. The method is based on a pot with a reversible base to which the inductor is attached. In the standard configuration, the inductor is placed below the pot in such a way that the delivered power is used to boil water, and the power losses are dissipated to the air. When the pot base is flipped, the inductor is immersed into the water. In this case the losses in the inductor also contribute to heating up and boiling the water. The induction efficiency is calculated from the boiling rates in both configurations. A commercial inductor was tested under real working conditions with consistent results. Full article
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