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Energies, Volume 10, Issue 3 (March 2017)

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Cover Story Still the ultimate achievable power conversion efficiency (PCE) of organic bulk-heterojunction [...] Read more.
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Editorial

Jump to: Research, Review, Other

Open AccessEditorial Smart Home Energy Management
Energies 2017, 10(3), 382; doi:10.3390/en10030382
Received: 15 March 2017 / Revised: 16 March 2017 / Accepted: 16 March 2017 / Published: 17 March 2017
Cited by 3 | PDF Full-text (167 KB) | HTML Full-text | XML Full-text
Abstract
The new challenges on Information and Communication Technologies (ICT) in Automatic Home Systems (AHS) focus on the methods useful to monitor, control, and optimize the data management flow and the use of energy.[...] Full article
(This article belongs to the Special Issue Smart Home Energy Management)

Research

Jump to: Editorial, Review, Other

Open AccessArticle Circulating Current Reduction Strategy for Parallel-Connected Inverters Based IPT Systems
Energies 2017, 10(3), 261; doi:10.3390/en10030261
Received: 29 November 2016 / Revised: 12 February 2017 / Accepted: 20 February 2017 / Published: 23 February 2017
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Abstract
Multiple inverters connected in parallel is a promising method to upgrade the power capacity of inductive power transfer (IPT) systems. Due to a slight unbalance of the control signals, the inner resistances of the inverters and other uncertainties, circulating currents exist among the
[...] Read more.
Multiple inverters connected in parallel is a promising method to upgrade the power capacity of inductive power transfer (IPT) systems. Due to a slight unbalance of the control signals, the inner resistances of the inverters and other uncertainties, circulating currents exist among the parallel units which reduce the reliability of IPT systems. Firstly, the series-parallel resonant tank is employed in the multiple inverters based IPT system to eliminate the DC and harmonic circulating currents. The fundamental circulating currents in the paralleled inverter units are analyzed in detail. Then, for eliminating the fundamental circulating currents, a current decomposition method and a control diagram are proposed to avoid acquiring the phase of the current by detecting zero cross current point which increases the accuracy of the control algorithm. Finally, a 1-kW parallel-connected inverter IPT system is provided to verify the proposed approach. The experimental results show that the proposed method is effective for eliminating the fundamental circulating currents. The maximum efficiency of the system is up to 92.18% which is 0.53% higher compared to that without the current phasor control (91.65%). Full article
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Open AccessArticle The Business Model Evaluation Tool for Smart Cities: Application to SmartSantander Use Cases
Energies 2017, 10(3), 262; doi:10.3390/en10030262
Received: 1 October 2016 / Revised: 22 January 2017 / Accepted: 4 February 2017 / Published: 23 February 2017
Cited by 1 | PDF Full-text (3738 KB) | HTML Full-text | XML Full-text
Abstract
New technologies open up the door to multiple business models applied to public services in smart cities. However, there is not a commonly adopted methodology for evaluating business models in smart cities that can help both practitioners and researchers to choose the best
[...] Read more.
New technologies open up the door to multiple business models applied to public services in smart cities. However, there is not a commonly adopted methodology for evaluating business models in smart cities that can help both practitioners and researchers to choose the best option. This paper addresses this gap introducing the Business Model Evaluation Tool for Smart Cities. This methodology is a simple, organized, flexible and the transparent system that facilitates the work of the evaluators of potential business models. It is useful to compare two or more business models and take strategic decisions promptly. The method is part of a previous process of content analysis and it is based on the widely utilized Business Model Canvas. The evaluation method has been assessed by 11 experts and, subsequently it has been validated applying it to the case studies of Santander’s waste management and street lighting systems, which take advantage of innovative technologies commonly used in smart cities. Full article
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Open AccessArticle High-Titer Methane from Organosolv-Pretreated Spruce and Birch
Energies 2017, 10(3), 263; doi:10.3390/en10030263
Received: 25 January 2017 / Revised: 15 February 2017 / Accepted: 17 February 2017 / Published: 23 February 2017
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Abstract
The negative impact of fossil fuels and the increased demand for renewable energy sources has led to the use of novel raw material sources. Lignocellulosic biomass could serve as a possible raw material for anaerobic digestion and production of biogas. This work is
[...] Read more.
The negative impact of fossil fuels and the increased demand for renewable energy sources has led to the use of novel raw material sources. Lignocellulosic biomass could serve as a possible raw material for anaerobic digestion and production of biogas. This work is aimed at using forest biomass, both softwood (spruce) and hardwood (birch), as a raw material for anaerobic digestion. We examined the effect of different operational conditions for the organosolv pretreatment (ethanol content, duration of treatment, and addition of acid catalyst) on the methane yield. In addition, we investigated the effect of addition of cellulolytic enzymes during the digestion. We found that inclusion of an acid catalyst during organosolv pretreatment improved the yields from spruce, but it did not affect the yields from birch. Shorter duration of treatment was advantageous with both materials. Methane yields from spruce were higher with lower ethanol content whereas higher ethanol content was more beneficial for birch. The highest yields obtained were 185 mL CH4/g VS from spruce and 259.9 mL CH4/g VS from birch. Addition of cellulolytic enzymes improved these yields to 266.6 mL CH4/g VS and 284.2 mL CH4/g VS, respectively. Full article
(This article belongs to the Special Issue Thermo-Chemical Conversion of Waste Biomass)
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Open AccessArticle Design and Implementation of Novel Smart Battery Management System for FPGA Based Portable Electronic Devices
Energies 2017, 10(3), 264; doi:10.3390/en10030264
Received: 1 December 2016 / Revised: 13 February 2017 / Accepted: 20 February 2017 / Published: 23 February 2017
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Abstract
This paper presents the analysis and design of a smart battery management system for Field Programmable Gate Array (FPGA) based portable electronic devices. It is a novel concept of incorporating the functionality of a smart battery management system into the FPGA used by
[...] Read more.
This paper presents the analysis and design of a smart battery management system for Field Programmable Gate Array (FPGA) based portable electronic devices. It is a novel concept of incorporating the functionality of a smart battery management system into the FPGA used by portable electronic devices, which provides the following advantages. (1) It lowers cost since the conventional commercial independent battery management circuit can be eliminated; (2) It offers more flexibility because FPGA based battery management algorithms can be specifically designed for different battery chemistries of different devices and can provide the flexibility of algorithms and functionalities updating as well. Smart battery management system concepts include four aspects: (1) smart charging; (2) battery balancing; (3) smart discharging; and (4) safety operating. One novel charging algorithm, which combines the merits of multistage charging and pulse charging, is proposed to charge a Li-ion battery pack smartly. A Proportional Integral (PI) control method is introduced to achieve the current control of charging circuit with considerable close loop stability. Simulation results from the PSIM 9.0.4 software package and experimental results from the prototype built in the lab are demonstrated to verify the effectiveness of smart charging. The realizations of battery balancing, smart discharging, and safety operating are also briefly described by taking advantage of the proposed FPGA based smart battery management system topology, which verify the feasibility of the proposed FPGA based smart battery management system for portable electronic devices. Full article
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Open AccessArticle Qualitative Analysis of Transesterification of Waste Pig Fat in Supercritical Alcohols
Energies 2017, 10(3), 265; doi:10.3390/en10030265
Received: 23 January 2017 / Revised: 16 February 2017 / Accepted: 17 February 2017 / Published: 23 February 2017
Cited by 2 | PDF Full-text (1564 KB) | HTML Full-text | XML Full-text
Abstract
In this work, the characteristics of waste pig fat degradation using supercritical alcohols have been studied. Comparative analysis of the influence of supercritical methanol and supercritical ethanol as solvents on the transesterification was the primary focus of this research. The experiments were carried
[...] Read more.
In this work, the characteristics of waste pig fat degradation using supercritical alcohols have been studied. Comparative analysis of the influence of supercritical methanol and supercritical ethanol as solvents on the transesterification was the primary focus of this research. The experiments were carried out with waste pig fat to alcohol weight ratios of 1:1.5 (molar ratio: 1:40.5 for methanol and 1:28 for ethanol), 1:2.0 (molar ratio: 1:54 for methanol and 1:37.5 for ethanol) and 1:2.5 (molar ratio: 1:67.5 for methanol and 1:47 for ethanol) at transesterification temperatures 250, 270 and 290 °C for holding time 0, 15, 30, 45 and 60 min. Increase in the transesterification and holding time increased the conversion while increase in alcohol amount from 1:1.5 to 1:2.0 and 1:2.5 had minimal effect on the conversion. Further, majority of the ester composition in using SCM as solvent falls in the carbon range of C17:0, C19:1 and C19:2 while that for SCE falls in the carbon range of C18:0, C20:1 and C20:2. Glycerol was only present while using SCM as solvent. Full article
(This article belongs to the Special Issue Thermo-Chemical Conversion of Waste Biomass)
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Open AccessArticle A Numerical Study on Natural Convection Heat Transfer of Handheld Projectors with a Fin Array
Energies 2017, 10(3), 266; doi:10.3390/en10030266
Received: 8 December 2016 / Revised: 1 February 2017 / Accepted: 20 February 2017 / Published: 23 February 2017
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Abstract
This study numerically investigates the effects of the number of bottom openings and the fin spacing on both the natural convection heat transfer and airflow field of the handheld projector with various orientations. The horizontally-oriented 120 mm × 53 mm × 19 mm
[...] Read more.
This study numerically investigates the effects of the number of bottom openings and the fin spacing on both the natural convection heat transfer and airflow field of the handheld projector with various orientations. The horizontally-oriented 120 mm × 53 mm × 19 mm handheld projector, which had 11 bottom openings and was installed with either 7 plate fins or 13 rows of square pin, was considered as the primary case. The fin number varied from 6 plates to 13 plates or from 7 pin rows to 16 pin rows, while the bottom openings varied from 11 to 15 in this study with handheld projector held at a specified inclination ranging from −90° to 90°. The results showed that the heat transfer coefficient of a specific surface of the plate-fin array installed in the primary handheld projector increased from 6 to 7 W/m2·K as the heating power increased from 2 W to 7 W. The optimal fin spacing in the handheld projector possessing 11 bottom openings was 2.875 mm and 3.375 mm for the plate-fin and pin-fin, respectively, at a heating power of 7 W. Although the velocity magnitude of the airflow between fins increased as the bottom opening increased, it was not able to offset the reduction of the airflow velocity resulting from the fin spacing reduction. Full article
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Open AccessArticle A Cyber Physical Model Based on a Hybrid System for Flexible Load Control in an Active Distribution Network
Energies 2017, 10(3), 267; doi:10.3390/en10030267
Received: 23 November 2016 / Revised: 23 January 2017 / Accepted: 16 February 2017 / Published: 24 February 2017
Cited by 2 | PDF Full-text (7011 KB) | HTML Full-text | XML Full-text
Abstract
To strengthen the integration of the primary and secondary systems, a concept of Cyber Physical Systems (CPS) is introduced to construct a CPS in Power Systems (Power CPS). The most basic work of the Power CPS is to build an integration model which
[...] Read more.
To strengthen the integration of the primary and secondary systems, a concept of Cyber Physical Systems (CPS) is introduced to construct a CPS in Power Systems (Power CPS). The most basic work of the Power CPS is to build an integration model which combines both a continuous process and a discrete process. The advanced form of smart grid, the Active Distribution Network (ADN) is a typical example of Power CPS. After designing the Power CPS model architecture and its application in ADN, a Hybrid System based model and control method of Power CPS is proposed in this paper. As an application example, ADN flexible load is modeled and controlled with ADN feeder power control by a control strategy which includes the normal condition and the underpowered condition. In this model and strategy, some factors like load power consumption and load functional demand are considered and optimized. In order to make up some of the deficiencies of centralized control, a distributed control method is presented to reduce model complexity and improve calculation speed. The effectiveness of all the models and methods are demonstrated in the case study. Full article
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Open AccessArticle Equivalent Circulation Density Analysis of Geothermal Well by Coupling Temperature
Energies 2017, 10(3), 268; doi:10.3390/en10030268
Received: 20 October 2016 / Accepted: 24 January 2017 / Published: 23 February 2017
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Abstract
The accurate control of the wellbore pressure not only prevents lost circulation/blowout and fracturing formation by managing the density of the drilling fluid, but also improves productivity by mitigating reservoir damage. Calculating the geothermal pressure of a geothermal well by constant parameters would
[...] Read more.
The accurate control of the wellbore pressure not only prevents lost circulation/blowout and fracturing formation by managing the density of the drilling fluid, but also improves productivity by mitigating reservoir damage. Calculating the geothermal pressure of a geothermal well by constant parameters would easily bring big errors, as the changes of physical, rheological and thermal properties of drilling fluids with temperature are neglected. This paper researched the wellbore pressure coupling by calculating the temperature distribution with the existing model, fitting the rule of density of the drilling fluid with the temperature and establishing mathematical models to simulate the wellbore pressures, which are expressed as the variation of Equivalent Circulating Density (ECD) under different conditions. With this method, the temperature and ECDs in the wellbore of the first medium-deep geothermal well, ZK212 Yangyi Geothermal Field in Tibet, were determined, and the sensitivity analysis was simulated by assumed parameters, i.e., the circulating time, flow rate, geothermal gradient, diameters of the wellbore, rheological models and regimes. The results indicated that the geothermal gradient and flow rate were the most influential parameters on the temperature and ECD distribution, and additives added in the drilling fluid should be added carefully as they change the properties of the drilling fluid and induce the redistribution of temperature. To ensure the safe drilling and velocity of pipes tripping into the hole, the depth and diameter of the wellbore are considered to control the surge pressure. Full article
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Open AccessArticle Thermoeconomic Evaluation of Modular Organic Rankine Cycles for Waste Heat Recovery over a Broad Range of Heat Source Temperatures and Capacities
Energies 2017, 10(3), 269; doi:10.3390/en10030269
Received: 2 January 2017 / Revised: 17 February 2017 / Accepted: 21 February 2017 / Published: 24 February 2017
Cited by 2 | PDF Full-text (5552 KB) | HTML Full-text | XML Full-text
Abstract
Industrial waste heat recovery by means of an Organic Rankine Cycle (ORC) can contribute to the reduction of CO2 emissions from industries. Before market penetration, high efficiency modular concepts have to be developed to achieve appropriate economic value for industrial decision makers.
[...] Read more.
Industrial waste heat recovery by means of an Organic Rankine Cycle (ORC) can contribute to the reduction of CO2 emissions from industries. Before market penetration, high efficiency modular concepts have to be developed to achieve appropriate economic value for industrial decision makers. This paper aims to investigate modularly designed ORC systems from a thermoeconomic point of view. The main goal is a recommendation for a suitable chemical class of working fluids, preferable ORC design and a range of heat source temperatures and thermal capacities in which modular ORCs can be economically feasible. For this purpose, a thermoeconomic model has been developed which is based on size and complexity parameters of the ORC components. Special emphasis has been laid on the turbine model. The paper reveals that alkylbenzenes lead to higher exergetic efficiencies compared to alkanes and siloxanes. However, based on the thermoeconomic model, the payback periods of the chemical classes are almost identical. With the ORC design, the developed model and the boundary conditions of this study, hexamethyldisiloxane is a suitable working fluid and leads to a payback period of less than 5 years for a heat source temperature of 400 to 600 °C and a mass flow rate of the gaseous waste heat stream of more than 4 kg/s. Full article
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Open AccessArticle Optimization of External Envelope Insulation Thickness: A Parametric Study
Energies 2017, 10(3), 270; doi:10.3390/en10030270
Received: 11 January 2017 / Revised: 16 February 2017 / Accepted: 20 February 2017 / Published: 24 February 2017
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Abstract
Almost four years after the implementation deadline of the energy performance of buildings Directive recast (2010/31/EU) and after being referred to the Court of Justice of the EU by the European Commission, Greece has not yet proceeded with the necessary calculations and legislative
[...] Read more.
Almost four years after the implementation deadline of the energy performance of buildings Directive recast (2010/31/EU) and after being referred to the Court of Justice of the EU by the European Commission, Greece has not yet proceeded with the necessary calculations and legislative measures on the minimum, cost-optimal energy performance requirements for buildings. This paper aims to identify the optimal thickness of insulation that is cost-effective to apply in urban multi-family domestic buildings in the four climate zones of Greece. A reference building is selected in order to perform calculations over ten scenarios of external insulation thickness for each climate zone on a basic and three sensitivity analysis calculations according to the EU comparative methodology framework. The resulting energy savings for each insulation scenario are calculated, and then the cost-effectiveness of the measure is examined in financial and macroeconomic perspective for an economic lifecycle of 30 years. The results demonstrate the inadequacy of the national regulation’s current insulation limits and the externalities (funding gaps) that need to be addressed in order to achieve the effective improvement of energy efficiency in Greek homes. Full article
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Open AccessArticle Fuzzy Logic-Based Operation of Battery Energy Storage Systems (BESSs) for Enhancing the Resiliency of Hybrid Microgrids
Energies 2017, 10(3), 271; doi:10.3390/en10030271
Received: 14 December 2016 / Revised: 9 February 2017 / Accepted: 21 February 2017 / Published: 24 February 2017
Cited by 3 | PDF Full-text (4834 KB) | HTML Full-text | XML Full-text
Abstract
The resiliency of power systems can be enhanced during emergency situations by using microgrids, due to their capability to supply local loads. However, precise prediction of disturbance events is very difficult rather the occurrence probability can be expressed as, high, medium, or low,
[...] Read more.
The resiliency of power systems can be enhanced during emergency situations by using microgrids, due to their capability to supply local loads. However, precise prediction of disturbance events is very difficult rather the occurrence probability can be expressed as, high, medium, or low, etc. Therefore, a fuzzy logic-based battery energy storage system (BESS) operation controller is proposed in this study. In addition to BESS state-of-charge and market price signals, event occurrence probability is taken as crisp input for the BESS operation controller. After assessing the membership levels of all the three inputs, BESS operation controller decides the operation mode (subservient or resilient) of BESS units. In subservient mode, BESS is fully controlled by an energy management system (EMS) while in the case of resilient mode, the EMS follows the commands of the BESS operation controller for scheduling BESS units. Therefore, the proposed hybrid microgrid model can operate in normal, resilient, and emergency modes with the respective objective functions and scheduling horizons. Due to the consideration of resilient mode, load curtailment can be reduced during emergency operation periods. Numerical simulations have demonstrated the effectiveness of the proposed strategy for enhancing the resiliency of hybrid microgrids. Full article
(This article belongs to the Special Issue Resilience of Energy Systems 2017)
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Open AccessFeature PaperArticle An Enhanced VOF Method Coupled with Heat Transfer and Phase Change to Characterise Bubble Detachment in Saturated Pool Boiling
Energies 2017, 10(3), 272; doi:10.3390/en10030272
Received: 4 November 2016 / Revised: 5 February 2017 / Accepted: 20 February 2017 / Published: 24 February 2017
Cited by 1 | PDF Full-text (24357 KB) | HTML Full-text | XML Full-text
Abstract
The present numerical investigation identifies quantitative effects of fundamental controlling parameters on the detachment characteristics of isolated bubbles in cases of pool boiling in the nucleate boiling regime. For this purpose, an improved Volume of Fluid (VOF) approach, developed previously in the general
[...] Read more.
The present numerical investigation identifies quantitative effects of fundamental controlling parameters on the detachment characteristics of isolated bubbles in cases of pool boiling in the nucleate boiling regime. For this purpose, an improved Volume of Fluid (VOF) approach, developed previously in the general framework of OpenFOAM Computational Fluid Dynamics (CFD) Toolbox, is further coupled with heat transfer and phase change. The predictions of the model are quantitatively verified against an existing analytical solution and experimental data in the literature. Following the model validation, four different series of parametric numerical experiments are performed, exploring the effect of the initial thermal boundary layer (ITBL) thickness for the case of saturated pool boiling of R113 as well as the effects of the surface wettability, wall superheat and gravity level for the cases of R113, R22 and R134a refrigerants. It is confirmed that the ITBL is a very important parameter in the bubble growth and detachment process. Furthermore, for all of the examined working fluids the bubble detachment characteristics seem to be significantly affected by the triple-line contact angle (i.e., the wettability of the heated plate) for equilibrium contact angles higher than 45°. As expected, the simulations revealed that the heated wall superheat is very influential on the bubble growth and detachment process. Finally, besides the novelty of the numerical approach, a last finding is the fact that the effect of the gravity level variation in the bubble detachment time and the volume diminishes with the increase of the ambient pressure. Full article
(This article belongs to the Special Issue Advanced Thermal Simulation of Energy Systems)
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Open AccessArticle The Influence of BMSs on the Characterization and Modeling of Series and Parallel Li-Ion Packs
Energies 2017, 10(3), 273; doi:10.3390/en10030273
Received: 3 January 2017 / Revised: 21 February 2017 / Accepted: 22 February 2017 / Published: 25 February 2017
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Abstract
This work analyzes the effects of a BMS (battery management system) on the characterization and modeling of series and parallel connections of Li-ion cell packs. The Li-ion pack studied consists of four series modules connected in parallel. This pack has been characterized by
[...] Read more.
This work analyzes the effects of a BMS (battery management system) on the characterization and modeling of series and parallel connections of Li-ion cell packs. The Li-ion pack studied consists of four series modules connected in parallel. This pack has been characterized by means of charge, discharge and frequency tests. As a result of these tests, series and parallel influence on battery parameters have been determined. A model considering the effects of a BMS is established and compared with a model based on a single-cell approach. Experimental validations show that the single cell based approach gives poor results in comparison with a model that considers BMS effects. Full article
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Open AccessArticle Numerical Analysis of Shell-and-Tube Type Latent Thermal Energy Storage Performance with Different Arrangements of Circular Fins
Energies 2017, 10(3), 274; doi:10.3390/en10030274
Received: 1 December 2016 / Revised: 15 February 2017 / Accepted: 20 February 2017 / Published: 25 February 2017
Cited by 2 | PDF Full-text (2656 KB) | HTML Full-text | XML Full-text
Abstract
Latent thermal energy storage (LTS) systems are versatile due to their high-energy storage density within a small temperature range. In shell-and-tube type storage systems fins can be used in order to achieve enhanced charging and discharging power. Typically, circular fins are evenly distributed
[...] Read more.
Latent thermal energy storage (LTS) systems are versatile due to their high-energy storage density within a small temperature range. In shell-and-tube type storage systems fins can be used in order to achieve enhanced charging and discharging power. Typically, circular fins are evenly distributed over the length of the heat exchanger pipe. However, it is yet to be proven that this allocation is the most suitable for every kind of system and application. Consequently, within this paper, a simulation model was developed in order to examine the effect of different fin distributions on the performance of shell-and-tube type latent thermal storage units at discharge. The model was set up in MATLAB Simulink R2015b (The MathWorks, Inc., Natick, MA, USA) based on the enthalpy method and validated by a reference model designed in ANSYS Fluent 15.0 (ANSYS, Inc., Canonsburg, PA, USA). The fin density of the heat exchanger pipe was increased towards the pipe outlet. This concentration of fins was implemented linearly, exponentially or suddenly with the total number of fins remaining constant during the variation of fin allocations. Results show that there is an influence of fin allocation on storage performance. However, the average storage performance at total discharge only increased by three percent with the best allocation compared to an equidistant arrangement. Full article
(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))
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Open AccessArticle Thermodynamic Performance Analysis of a Biogas-Fuelled Micro-Gas Turbine with a Bottoming Organic Rankine Cycle for Sewage Sludge and Food Waste Treatment Plants
Energies 2017, 10(3), 275; doi:10.3390/en10030275
Received: 9 January 2017 / Revised: 17 February 2017 / Accepted: 21 February 2017 / Published: 26 February 2017
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Abstract
In the Republic of Korea, efficient biogas-fuelled power systems are needed to use the excess biogas that is currently burned due to a lack of suitable power technology. We examined the performance of a biogas-fuelled micro-gas turbine (MGT) system and a bottoming organic
[...] Read more.
In the Republic of Korea, efficient biogas-fuelled power systems are needed to use the excess biogas that is currently burned due to a lack of suitable power technology. We examined the performance of a biogas-fuelled micro-gas turbine (MGT) system and a bottoming organic Rankine cycle (ORC). The MGT provides robust operation with low-grade biogas, and the exhaust can be used for heating the biodigester. Similarly, the bottoming ORC generates additional power output with the exhaust gas. We selected a 1000-kW MGT for four co-digestion plants with 28,000-m3 capacity. A 150-kW ORC system was selected for the MGT exhaust gas. We analysed the effects of the system size, methane concentration, and ORC operating conditions. Based on the system performance, we analysed the annual performance of the MGT with a combined heat and power (CHP) system, bottoming ORC, or both a bottoming ORC and CHP system. The annual net power outputs for each system were 7.4, 8.5, and 9.0 MWh per year, respectively. Full article
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Open AccessArticle Using a Hybrid Cost-FMEA Analysis for Wind Turbine Reliability Analysis
Energies 2017, 10(3), 276; doi:10.3390/en10030276
Received: 20 December 2016 / Revised: 14 February 2017 / Accepted: 17 February 2017 / Published: 27 February 2017
Cited by 2 | PDF Full-text (3721 KB) | HTML Full-text | XML Full-text
Abstract
Failure mode and effects analysis (FMEA) has been proven to be an effective methodology to improve system design reliability. However, the standard approach reveals some weaknesses when applied to wind turbine systems. The conventional criticality assessment method has been criticized as having many
[...] Read more.
Failure mode and effects analysis (FMEA) has been proven to be an effective methodology to improve system design reliability. However, the standard approach reveals some weaknesses when applied to wind turbine systems. The conventional criticality assessment method has been criticized as having many limitations such as the weighting of severity and detection factors. In this paper, we aim to overcome these drawbacks and develop a hybrid cost-FMEA by integrating cost factors to assess the criticality, these costs vary from replacement costs to expected failure costs. Then, a quantitative comparative study is carried out to point out average failure rate, main cause of failure, expected failure costs and failure detection techniques. A special reliability analysis of gearbox and rotor-blades are presented. Full article
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Open AccessArticle A Refined Self-Tuning Filter-Based Instantaneous Power Theory Algorithm for Indirect Current Controlled Three-Level Inverter-Based Shunt Active Power Filters under Non-sinusoidal Source Voltage Conditions
Energies 2017, 10(3), 277; doi:10.3390/en10030277
Received: 10 January 2017 / Revised: 16 February 2017 / Accepted: 21 February 2017 / Published: 27 February 2017
Cited by 3 | PDF Full-text (4299 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a refined reference current generation algorithm based on instantaneous power (pq) theory is proposed, for operation of an indirect current controlled (ICC) three-level neutral-point diode clamped (NPC) inverter-based shunt active power filter (SAPF) under non-sinusoidal source voltage conditions. SAPF is
[...] Read more.
In this paper, a refined reference current generation algorithm based on instantaneous power (pq) theory is proposed, for operation of an indirect current controlled (ICC) three-level neutral-point diode clamped (NPC) inverter-based shunt active power filter (SAPF) under non-sinusoidal source voltage conditions. SAPF is recognized as one of the most effective solutions to current harmonics due to its flexibility in dealing with various power system conditions. As for its controller, pq theory has widely been applied to generate the desired reference current due to its simple implementation features. However, the conventional dependency on self-tuning filter (STF) in generating reference current has significantly limited mitigation performance of SAPF. Besides, the conventional STF-based pq theory algorithm is still considered to possess needless features which increase computational complexity. Furthermore, the conventional algorithm is mostly designed to suit operation of direct current controlled (DCC) SAPF which is incapable of handling switching ripples problems, thereby leading to inefficient mitigation performance. Therefore, three main improvements are performed which include replacement of STF with mathematical-based fundamental real power identifier, removal of redundant features, and generation of sinusoidal reference current. To validate effectiveness and feasibility of the proposed algorithm, simulation work in MATLAB-Simulink and laboratory test utilizing a TMS320F28335 digital signal processor (DSP) are performed. Both simulation and experimental findings demonstrate superiority of the proposed algorithm over the conventional algorithm. Full article
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Open AccessArticle Tuning the Complexity of Photovoltaic Array Models to Meet Real-time Constraints of Embedded Energy Emulators
Energies 2017, 10(3), 278; doi:10.3390/en10030278
Received: 22 December 2016 / Revised: 9 February 2017 / Accepted: 21 February 2017 / Published: 27 February 2017
Cited by 1 | PDF Full-text (351 KB) | HTML Full-text | XML Full-text
Abstract
Reproducibility of experimental conditions is a fundamental requirement for designing energy efficient, self-sustainable wireless sensor networks (WSNs). At the same time, it represents a significant challenge because of the variability and the unpredictability of many energy harvesting sources, and because of the dynamic
[...] Read more.
Reproducibility of experimental conditions is a fundamental requirement for designing energy efficient, self-sustainable wireless sensor networks (WSNs). At the same time, it represents a significant challenge because of the variability and the unpredictability of many energy harvesting sources, and because of the dynamic operating conditions of the devices to which energy is supplied. Energy source emulation is considered a suitable solution to enable the exploration of the design space of networked embedded systems. However, in order to guarantee the compatibility with real-time performance of resource-constrained embedded platforms, particular attention has to be paid to the complexity of the models. In this paper, we propose an approach aimed at tuning the complexity of models of photovoltaic (PV) arrays implemented on a target embedded emulator, featuring low cost and small form factor. Experimental results performed on different models of PV array, show that the proposed solution is flexible and accurate enough to meet the real-time constraints of typical sensor networks applications without impairing the precision in the emulation of the energy sources. Full article
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Open AccessArticle Comparison Study of Two Semi-Active Hybrid Energy Storage Systems for Hybrid Electric Vehicle Applications and Their Experimental Validation
Energies 2017, 10(3), 279; doi:10.3390/en10030279
Received: 5 December 2016 / Revised: 18 February 2017 / Accepted: 21 February 2017 / Published: 28 February 2017
Cited by 1 | PDF Full-text (5729 KB) | HTML Full-text | XML Full-text
Abstract
Both the battery/supercapacitor (SC) and SC/battery are two common semi-active configurations of hybrid energy storage systems (HESSs) in hybrid electric vehicles, which can take advantage of the battery’s and supercapacitor’s respective characteristics, including the energy ability, power ability and the long lifetime. To
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Both the battery/supercapacitor (SC) and SC/battery are two common semi-active configurations of hybrid energy storage systems (HESSs) in hybrid electric vehicles, which can take advantage of the battery’s and supercapacitor’s respective characteristics, including the energy ability, power ability and the long lifetime. To explore in depth the characteristics and applicability of the two kinds of HESS, an analysis and comparison study is proposed in this paper. Based on the data collected from public transit hybrid electric bus (PTHEB) with battery-only on-board energy storage, the range and distribution probability of electric power/energy demand is comprehensively statistically analyzed with the decomposing and normalizing methods. Accordingly, the performance of each topology under different parameter matching conditions but same mass, volume and cost values with battery-only energy storage, are presented and compared quantitatively. The results show that both HESS configurations can meet the electric power demand of the hybrid electric vehicle (HEV) through reasonable design. In particular, the SC/battery can make better use of the SC features resulting in high efficiency and long life cycles compared with the battery/SC. Equally, it proves that the SC/battery topology is a better choice for the HEV. Finally, an experimental validation of a real HEV is carried out, which indicated that a 7% fuel economy improvement can be achieved by a SC/battery system compared with battery-only topology. Full article
(This article belongs to the collection Electric and Hybrid Vehicles Collection)
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Open AccessArticle An Efficient Phase-Locked Loop for Distorted Three-Phase Systems
Energies 2017, 10(3), 280; doi:10.3390/en10030280
Received: 6 December 2016 / Accepted: 20 February 2017 / Published: 27 February 2017
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Abstract
This paper proposed an efficient phase-locked loop (PLL) that features zero steady-state error of phase and frequency under voltage sag, phase jump, harmonics, DC offsets and step-and ramp-changed frequency. The PLL includes the sliding Goertzel discrete Fourier transform (SGDFT) filter-based fundamental positive sequence
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This paper proposed an efficient phase-locked loop (PLL) that features zero steady-state error of phase and frequency under voltage sag, phase jump, harmonics, DC offsets and step-and ramp-changed frequency. The PLL includes the sliding Goertzel discrete Fourier transform (SGDFT) filter-based fundamental positive sequence component separator (FPSCS), the synchronousreference-frame PLL (SRF-PLL) and the secondary control path (SCP). In order to obtain an accurate fundamental positive sequence component, SGDFT filter is introduced as it features better filtering ability at the frequencies that are integer times of fundamental frequency. Meanwhile, the second order Lagrange-interpolation method is employed to approximate the actual sampling number including both integer and fractional parts as grid frequency may deviate from the rated value. Moreover, an improved SCP with single-step comparison filtering algorithm is employed as it updates reference angular frequency according to the FPSC, which promises a zero steady-state error of phase and improves the frequency tracking speed. In this paper, the mathematical model of the proposed PLL is constructed, its stability is analyzed. Also, design procedure of the control parameters is presented. The effectiveness of the proposed PLL is confirmed by experimental results and comparison with advanced pre-filtering PLLs. Full article
(This article belongs to the Special Issue Power Electronics and Power Quality)
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Open AccessArticle Relative Voltage Control of the Wind Farms Based on the Local Reactive Power Regulation
Energies 2017, 10(3), 281; doi:10.3390/en10030281
Received: 7 October 2016 / Accepted: 22 February 2017 / Published: 27 February 2017
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Abstract
The fast and coordinated voltage control of distributed nodes inside a large scale wind farm is a stringent issue. To achieve the reactive power compensation without a dedicated upper communication system, this paper proposes a relative control strategy based on the local reactive
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The fast and coordinated voltage control of distributed nodes inside a large scale wind farm is a stringent issue. To achieve the reactive power compensation without a dedicated upper communication system, this paper proposes a relative control strategy based on the local reactive power regulation. This method can realize the voltage coordination of the key equipment and feeder line nodes, on the basis of the relative voltage observations. Firstly, the stability analysis of a certain wind farm with pre-known parameters and structure is studied under the wind power fluctuations. Secondly, the optimal capacity configurations of the reactive power compensators are discussed, with multiple nodes inside the wind farms. Simulation results of a specific wind farm in North Hebei, China, validate the effectiveness of the proposed control, which is equipped with fast and stable voltage dynamic responses, as well as local reactive power compensations without remote communication. Full article
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Open AccessArticle Performance Analyses of Counter-Flow Closed Wet Cooling Towers Based on a Simplified Calculation Method
Energies 2017, 10(3), 282; doi:10.3390/en10030282
Received: 14 January 2017 / Accepted: 23 February 2017 / Published: 27 February 2017
Cited by 2 | PDF Full-text (4351 KB) | HTML Full-text | XML Full-text
Abstract
As one of the most widely used units in water cooling systems, the closed wet cooling towers (CWCTs) have two typical counter-flow constructions, in which the spray water flows from the top to the bottom, and the moist air and cooling water flow
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As one of the most widely used units in water cooling systems, the closed wet cooling towers (CWCTs) have two typical counter-flow constructions, in which the spray water flows from the top to the bottom, and the moist air and cooling water flow in the opposite direction vertically (parallel) or horizontally (cross), respectively. This study aims to present a simplified calculation method for conveniently and accurately analyzing the thermal performance of the two types of counter-flow CWCTs, viz. the parallel counter-flow CWCT (PCFCWCT) and the cross counter-flow CWCT (CCFCWCT). A simplified cooling capacity model that just includes two characteristic parameters is developed. The Levenberg–Marquardt method is employed to determine the model parameters by curve fitting of experimental data. Based on the proposed model, the predicted outlet temperatures of the process water are compared with the measurements of a PCFCWCT and a CCFCWCT, respectively, reported in the literature. The results indicate that the predicted values agree well with the experimental data in previous studies. The maximum absolute errors in predicting the process water outlet temperatures are 0.20 and 0.24 °C for the PCFCWCT and CCFCWCT, respectively. These results indicate that the simplified method is reliable for performance prediction of counter-flow CWCTs. Although the flow patterns of the two towers are different, the variation trends of thermal performance are similar to each other under various operating conditions. The inlet air wet-bulb temperature, inlet cooling water temperature, air flow rate, and cooling water flow rate are crucial for determining the cooling capacity of a counter-flow CWCT, while the cooling tower effectiveness is mainly determined by the flow rates of air and cooling water. Compared with the CCFCWCT, the PCFCWCT is much more applicable in a large-scale cooling water system, and the superiority would be amplified when the scale of water distribution system increases. Without multiple iterative calculations and extensive experimental data, the simplified method could be used to effectively analyze the thermal performance of counter-flow CWCTs in operation. It is useful for optimization operation of counter-flow CWCTs such that to improve the energy efficiency of the overall cooling water system. Full article
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Open AccessCommunication Sustainability of the Renewable Energy Extraction Close to the Mediterranean Islands
Energies 2017, 10(3), 283; doi:10.3390/en10030283
Received: 10 December 2016 / Accepted: 21 February 2017 / Published: 27 February 2017
Cited by 15 | PDF Full-text (5972 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this work is to explore the possibility of transitioning a fuel powered island to a renewable powered one. This transition is analyzed for the real MV/LV distribution system of the island of Pantelleria, in the Mediterranean Sea. Particularly, this work
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The aim of this work is to explore the possibility of transitioning a fuel powered island to a renewable powered one. This transition is analyzed for the real MV/LV distribution system of the island of Pantelleria, in the Mediterranean Sea. Particularly, this work is focused on a renewable source nowadays totally unused: wave energy. Thanks to the innovative generator prototype designed by Department of Energy of University of Palermo (Italy), wave energy is able to represent a primary source for the production of electric energy in the Mediterranean islands. The procedures applied in the present article, as well as the main equations used, are the result of previous applications made in different technical fields that show a good replicability. Full article
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Open AccessArticle Development of a Real-Time Virtual Nitric Oxide Sensor for Light-Duty Diesel Engines
Energies 2017, 10(3), 284; doi:10.3390/en10030284
Received: 9 January 2017 / Revised: 10 February 2017 / Accepted: 21 February 2017 / Published: 1 March 2017
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Abstract
This study describes the development of a semi-physical, real-time nitric oxide (NO) prediction model that is capable of cycle-by-cycle prediction in a light-duty diesel engine. The model utilizes the measured in-cylinder pressure and information obtained from the engine control unit (ECU). From the
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This study describes the development of a semi-physical, real-time nitric oxide (NO) prediction model that is capable of cycle-by-cycle prediction in a light-duty diesel engine. The model utilizes the measured in-cylinder pressure and information obtained from the engine control unit (ECU). From the inputs, the model takes into account the pilot injection burning and mixing, which affects the in-cylinder mixture formation. The representative in-cylinder temperature for NO formation was determined from the mixture composition calculation. The selected temperature and mixture composition was substituted using a simplified form of the NO formation rate equation for the cycle-by-cycle estimation. The reactive area and the duration of NO formation were assumed to be limited by the fuel quantity. The model predictability was verified not only using various steady-state conditions, including the variation of the EGR rate, the boost pressure, the rail pressure, and the injection timing, but also using transient conditions, which represent the worldwide harmonized light vehicles test procedure (WLTC). The WLTC NO prediction results produced less than 3% error with the measured value. In addition, the proposed model maintained its reliability in terms of hardware aging, the changing and artificial perturbations during steady-state and transient engine operations. The model has been shown to require low computational effort because of the cycle-by-cycle, engine-out NO emission prediction and control were performed simultaneously in an embedded system for the automotive application. We expect that the developed NO prediction model can be helpful in emission calibration during the engine design stage or in the real-time controlling of the exhaust NO emission for improving fuel consumption while satisfying NO emission legislation. Full article
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Open AccessArticle Sensitivity of the Drift-Diffusion Approach in Estimating the Power Conversion Efficiency of Bulk Heterojunction Polymer Solar Cells
Energies 2017, 10(3), 285; doi:10.3390/en10030285
Received: 12 January 2017 / Revised: 12 February 2017 / Accepted: 21 February 2017 / Published: 28 February 2017
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Abstract
There are numerous theoretical approaches to estimating the power conversion efficiency (PCE) of organic solar cells (OSCs), ranging from the empirical approach to calculations based on general considerations of thermodynamics. Depending on the level of abstraction and model assumptions, the accuracy of PCE
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There are numerous theoretical approaches to estimating the power conversion efficiency (PCE) of organic solar cells (OSCs), ranging from the empirical approach to calculations based on general considerations of thermodynamics. Depending on the level of abstraction and model assumptions, the accuracy of PCE estimation and complexity of the calculation can change dramatically. In particular, PCE estimation with a drift-diffusion approach (widely investigated in the literature), strongly depends on the assumptions made for the physical models and optoelectrical properties of semiconducting materials. This has led to a huge deviation as well as complications in the analysis of simulated results aiming to understand the factors limiting the performance of OSCs. In this work, we intend to highlight the complex relation between mobility, exciton dynamics, nanoscale dimension, and loss mechanisms in one framework. Our systematic analysis represents key information on the sensitivity of the drift-diffusion approach, to estimate how physical parameters and physical processes bind the PCE of the device under the influence of structure, contact, and material layer properties. The obtained results ultimately led to recommendations for putting effort into certain properties to get the most out of avoidable losses, presented the impact and importance of modification of material properties, and in particular, recommended to what degree the design of new material could improve OSC performance. Full article
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Open AccessArticle Reduction of Furfural to Furfuryl Alcohol in Liquid Phase over a Biochar-Supported Platinum Catalyst
Energies 2017, 10(3), 286; doi:10.3390/en10030286
Received: 7 December 2016 / Revised: 15 February 2017 / Accepted: 23 February 2017 / Published: 28 February 2017
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Abstract
In this work, the liquid phase hydrogenation of furfural has been studied using a biochar-supported platinum catalyst in a batch reactor. Reactions were performed between 170 °C and 320 °C, using 3 wt % and 5 wt % of Pt supported on a
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In this work, the liquid phase hydrogenation of furfural has been studied using a biochar-supported platinum catalyst in a batch reactor. Reactions were performed between 170 °C and 320 °C, using 3 wt % and 5 wt % of Pt supported on a maple-based biochar under hydrogen pressure varying from 500 psi to 1500 psi for reaction times between 1 h and 6 h in various solvents. Under all reactive conditions, furfural conversion was significant, whilst under specific conditions furfuryl alcohol (FA) was obtained in most cases as the main product showing a selectivity around 80%. Other products as methylfuran (MF), furan, and trace of tetrahydrofuran (THF) were detected. Results showed that the most efficient reaction conditions involved a 3% Pt load on biochar and operations for 2 h at 210 °C and 1500 psi using toluene as solvent. When used repetitively, the catalyst showed deactivation although only a slight variation in selectivity toward FA at the optimal experimental conditions was observed. Full article
(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications)
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Open AccessArticle Improving the Reliability of Optimised Link State Routing in a Smart Grid Neighbour Area Network based Wireless Mesh Network Using Multiple Metrics
Energies 2017, 10(3), 287; doi:10.3390/en10030287
Received: 1 January 2017 / Accepted: 21 February 2017 / Published: 28 February 2017
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Abstract
Reliable communication is the backbone of advanced metering infrastructure (AMI). Within the AMI, the neighbourhood area network (NAN) transports a multitude of traffic, each with unique requirements. In order to deliver an acceptable level of reliability and latency, the underlying network, such as
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Reliable communication is the backbone of advanced metering infrastructure (AMI). Within the AMI, the neighbourhood area network (NAN) transports a multitude of traffic, each with unique requirements. In order to deliver an acceptable level of reliability and latency, the underlying network, such as the wireless mesh network(WMN), must provide or guarantee the quality-of-service (QoS) level required by the respective application traffic. Existing WMN routing protocols, such as optimised link state routing (OLSR), typically utilise a single metric and do not consider the requirements of individual traffic; hence, packets are delivered on a best-effort basis. This paper presents a QoS-aware WMN routing technique that employs multiple metrics in OLSR optimal path selection for AMI applications. The problems arising from this approach are non deterministic polynomial time (NP)-complete in nature, which were solved through the combined use of the analytical hierarchy process (AHP) algorithm and pruning techniques. For smart meters transmitting Internet Protocol (IP) packets of varying sizes at different intervals, the proposed technique considers the constraints of NAN and the applications’ traffic characteristics. The technique was developed by combining multiple OLSR path selection metrics with the AHP algorithminns-2. Compared with the conventional link metric in OLSR, the results show improvements of about 23% and 45% in latency and Packet Delivery Ratio (PDR), respectively, in a 25-node grid NAN. Full article
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Open AccessArticle The Production of Engineered Biochars in a Vertical Auger Pyrolysis Reactor for Carbon Sequestration
Energies 2017, 10(3), 288; doi:10.3390/en10030288
Received: 12 January 2017 / Accepted: 21 February 2017 / Published: 28 February 2017
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Abstract
Biomass pyrolysis and the valorization of co-products (biochar, bio-oil, syngas) could be a sustainable management solution for agricultural and forest residues. Depending on its properties, biochar amended to soil could improve fertility. Moreover, biochar is expected to mitigate climate change by reducing soil
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Biomass pyrolysis and the valorization of co-products (biochar, bio-oil, syngas) could be a sustainable management solution for agricultural and forest residues. Depending on its properties, biochar amended to soil could improve fertility. Moreover, biochar is expected to mitigate climate change by reducing soil greenhouse gas emissions, if its C/N ratio is lower than 30, and sequestrating carbon if its O/Corg and H/Corg ratios are lower than 0.2 and 0.7, respectively. However, the yield and properties of biochar are influenced by biomass feedstock and pyrolysis operating parameters. The objective of this research study was to validate an approach based on the response surface methodology, to identify the optimal pyrolysis operating parameters (temperature, solid residence time, and carrier gas flowrate), in order to produce engineered biochars for carbon sequestration. The pyrolysis of forest residues, switchgrass, and the solid fraction of pig manure, was carried out in a vertical auger reactor following a Box-Behnken design, in order to develop response surface models. The optimal pyrolysis operating parameters were estimated to obtain biochar with the lowest H/Corg and O/Corg ratios. Validation pyrolysis experiments confirmed that the selected approach can be used to accurately predict the optimal operating parameters for producing biochar with the desired properties to sequester carbon. Full article
(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications)
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Open AccessArticle Optimizing the Performance of Solo Duck Wave Energy Converter in Tide
Energies 2017, 10(3), 289; doi:10.3390/en10030289
Received: 24 January 2017 / Accepted: 22 February 2017 / Published: 28 February 2017
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Abstract
The high efficiency performance of the Edinburgh Duck wave energy converter (WEC) in 2D regular wave tests makes it a promising wave energy conversion scheme. A solo Duck WEC will be able to apply the point absorber effect to further enhance its performance.
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The high efficiency performance of the Edinburgh Duck wave energy converter (WEC) in 2D regular wave tests makes it a promising wave energy conversion scheme. A solo Duck WEC will be able to apply the point absorber effect to further enhance its performance. Since released degree of freedom will decrease the efficiency, a Duck WEC with fixed pitching axis will be a better option. However, for fixed supported WECs, tide is a non-ignorable consideration. In this paper, a movable mass method is utilized in the whole tidal range to not only balance the Duck to appropriate beak angles, but also follow the variation of hydrodynamic coefficients to keep cancelling the reactance of the system impedance so that complex conjugate control can be realized to optimize the power capture performance of the Duck WEC in tide. Results show that the beak angle should be adjusted to as large a value as possible so that the response amplitude of the Duck at maximum relative capture width will be reasonable small, and the lowest weight of the movable mass is found when its designed position locates at the center of the Duck profile. Full article
(This article belongs to the Special Issue Numerical Modelling of Wave and Tidal Energy)
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Open AccessFeature PaperArticle In Situ Surface-Enhanced Raman Spectroscopy Study of the Electrocatalytic Effect of PtFe/C Nanocatalyst on Ethanol Electro-Oxidation in Alkaline Medium
Energies 2017, 10(3), 290; doi:10.3390/en10030290
Received: 19 December 2016 / Revised: 20 February 2017 / Accepted: 21 February 2017 / Published: 1 March 2017
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Abstract
Currently, the ethanol electro-oxidation reaction has attracted considerable attention in fuel cells because of new green ethanol synthetic methods based on biomass processes that have emerged. In this study, PtFe/C and Pt/C nanoparticles were synthesized by a chemical reduction method and tested in
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Currently, the ethanol electro-oxidation reaction has attracted considerable attention in fuel cells because of new green ethanol synthetic methods based on biomass processes that have emerged. In this study, PtFe/C and Pt/C nanoparticles were synthesized by a chemical reduction method and tested in the ethanol electro-oxidation reaction. Furthermore, the electrocatalytic effect of the PtFe bimetallic catalyst was analyzed by in situ surface-enhanced Raman spectroscopy (SERS) coupled to an electrochemical cell. X-ray diffractograms showed typical face-centered cubic structures with crystallite sizes of 3.31 and 3.94 for Pt/C and PtFe/C, respectively. TEM micrographs revealed nanoparticle sizes of 2 ± 0.4 nm and 3 ± 0.6 nm for Pt/C and PtFe/C respectively. PtFe/C exhibited a Pt90Fe10 composition by both X-ray fluorescence and energy-dispersive X-ray spectroscopy. A better electrocatalytic activity as function of concentration was obtained through the incorporation of a small amount of Fe into the Pt lattice and the presence of Fe2+/Fe3+ (observed by X-ray photoelectron spectroscopy). According to SERS experiments, the presence of these iron species promotes the chemisorption of ethanol, the formation of formic acid as main product and renewal of the catalytic sites, resulting in current densities that were at least three fold higher than the values obtained for the Pt/C nanocatalyst. Full article
(This article belongs to the Special Issue Direct Alcohol Fuel Cells)
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Open AccessArticle Decentralized Framework for Optimal Price-Based Power System Operation Using Feedback Control Mechanism
Energies 2017, 10(3), 291; doi:10.3390/en10030291
Received: 28 December 2016 / Revised: 11 January 2017 / Accepted: 20 February 2017 / Published: 1 March 2017
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Abstract
Future power systems are expected to have distributed energy resources (DERs). A price-based operation (PBO), where dynamic prices are used as the control signal, can be an alternative scheme to address challenging operational issues in the future power systems. In this paper, a
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Future power systems are expected to have distributed energy resources (DERs). A price-based operation (PBO), where dynamic prices are used as the control signal, can be an alternative scheme to address challenging operational issues in the future power systems. In this paper, a decentralized framework for optimal PBO using a feedback control mechanism is proposed to determine the nodal prices for power balance and congestion management. The substructures and feedback controllers of the proposed framework are derived based on the optimal power flow (OPF) method. Thus, the framework guarantees optimality for all situations in real-time and enables the use of various types of controllers. The effectiveness of the proposed framework is verified with the IEEE 39 bus network under some scenarios, such as the failure of a generator and a transmission line. The results clearly demonstrate that the proposed framework successfully resolves the balance and congestion problems by generating appropriate nodal prices in the PBO and provides a solution similar to the optimal solution determined by the conventional OPF method. Full article
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Open AccessArticle Mechanical Behavior and Permeability Evolution of Reconstituted Coal Samples under Various Unloading Confining Pressures—Implications for Wellbore Stability Analysis
Energies 2017, 10(3), 292; doi:10.3390/en10030292
Received: 14 December 2016 / Accepted: 28 February 2017 / Published: 2 March 2017
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Abstract
Low pressure, low permeability, and low saturation of Chinese coal-bed methane (CBM) reservoirs make underbalanced drilling (UBD) widely used for mining CBM in China. In this study, mechanical behavior and permeability of coal rock were investigated under different degrees of unloading confining pressure
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Low pressure, low permeability, and low saturation of Chinese coal-bed methane (CBM) reservoirs make underbalanced drilling (UBD) widely used for mining CBM in China. In this study, mechanical behavior and permeability of coal rock were investigated under different degrees of unloading confining pressure (UCP)-reloading axial stress (RAS) by a triaxial experimental apparatus. These tests revealed that: (1) peak deviatoric stress of coal rock in UCP-RAS is lower than that in a conventional triaxial compression (CTC) test, and the peak deviatoric stress linearly relates the degree of unloading confining pressure. The deformation modulus of coal in UCP-RAS is lower than that in CTC, while the lateral expansion ratio is larger than that in CTC; (2) higher UCP leads to a faster increase of permeability during RAS until the failure of coal; (3) the cohesion and internal friction angle tested by UCP-RAS are lower by 4.57% and 15.18% than those tested by CTC. In addition, a field case (Zhaozhuang well, Qinshui Basin, China) of a well collapse problem validates the higher probability of wellbore collapse due to the increase of equivalent collapse fluid density, which is calculated by using coal rock parameters tested by UCP-RAS rather than by CTC. Full article
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Open AccessArticle Optimal Cooperative Management of Energy Storage Systems to Deal with Over- and Under-Voltages
Energies 2017, 10(3), 293; doi:10.3390/en10030293
Received: 4 January 2017 / Revised: 24 February 2017 / Accepted: 28 February 2017 / Published: 2 March 2017
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Abstract
This paper presents an optimal cooperative voltage control approach, which coordinates storage units in a distribution network. This technique is developed for storage systems’ active power management with a local strategy to provide robust voltage control and a distributed strategy to deliver optimal
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This paper presents an optimal cooperative voltage control approach, which coordinates storage units in a distribution network. This technique is developed for storage systems’ active power management with a local strategy to provide robust voltage control and a distributed strategy to deliver optimal storage utilization. Accordingly, three control criteria based on predefined node voltage limits are used for network operation including normal, over-voltage, and under-voltage control modes. The contribution of storage units for voltage support is determined using the control modes and the coordination strategies proposed in this paper. This technique is evaluated in two case studies to assess its capability. Full article
(This article belongs to the collection Smart Grid)
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Open AccessArticle Analysis of Pressure Rise in a Closed Container Due to Internal Arcing
Energies 2017, 10(3), 294; doi:10.3390/en10030294
Received: 30 October 2016 / Revised: 23 February 2017 / Accepted: 25 February 2017 / Published: 2 March 2017
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Abstract
When an arc fault occurs in a medium-voltage (MV) metal enclosed switchgear, the arc heats the filling gas, resulting in a pressure rise, which may seriously damage the switchgear, the building it is contained in, or even endanger maintenance personnel. A pressure rise
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When an arc fault occurs in a medium-voltage (MV) metal enclosed switchgear, the arc heats the filling gas, resulting in a pressure rise, which may seriously damage the switchgear, the building it is contained in, or even endanger maintenance personnel. A pressure rise calculation method based on computational fluid dynamics (CFD) has been put forward in this paper. The pressure rise was calculated and the arc tests between the copper electrodes were performed in the container under different gap lengths by the current source. The results show that the calculated pressure rise agrees well with the measurement, and the relative error of the average pressure rise is about 2%. Arc volume has less effect on the pressure distribution in the container. Arc voltage Root-Mean-Square (RMS) has significant randomness with the change of arc current, and increases with the increase of gap length. The average arc voltage gradients measure at about 26, 20 and 16 V/cm when the gap lengths are 5, 10 and 15 cm, respectively. The proportion (thermal transfer coefficient kp) of the arc energy leading to the pressure rise in the container is about 44.9%. The pressure is symmetrically distributed in the container before the pressure wave reaches the walls and the process of the energy release is similar to an explosion. The maximum overpressure in the corner is increased under the reflection and superimposition effects of the pressure wave, but the pressure waves will be of no importance any longer than a few milliseconds in the closed container. Full article
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Open AccessArticle On Long-Term Transmission Rights in the Nordic Electricity Markets
Energies 2017, 10(3), 295; doi:10.3390/en10030295
Received: 3 May 2016 / Accepted: 23 February 2017 / Published: 2 March 2017
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Abstract
In vein with the new energy market rules drafted in the EU this paper presents and discusses two contract types for hedging the risks connected to long-term transmission rights, the financial transmission right (FTR) and the electricity price area differentials (EPAD) that are
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In vein with the new energy market rules drafted in the EU this paper presents and discusses two contract types for hedging the risks connected to long-term transmission rights, the financial transmission right (FTR) and the electricity price area differentials (EPAD) that are used in the Nordic electricity markets. The possibility to replicate the FTR contracts with a combination of EPAD contracts is presented and discussed. Based on historical evidence and empirical analysis of ten Nordic interconnectors and twenty bidding areas, we investigate the pricing accuracy of the replicated FTR contracts by quantifying ex-post forward risk premia. The results show that the majority of the studied FTR contain a negative risk premium, especially the monthly and the quarterly contracts. Reverse flow (unnatural) pricing was identified for two interconnectors. From a theoretical policy point of view the results imply that it may be possible to continue with the EPAD-based system by using EPAD Combos in the Nordic countries, even if FTR contracts would prevail elsewhere in the EU. In practice the pricing of bi-directional EPAD contracts is more complex and may not always be very efficient. The efficiency of the EPAD market structure should be discussed from various points of view before accepting their status quo as a replacement for FTRs in the Nordic electricity markets. Full article
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Open AccessArticle Isolated DC-DC Converter for Bidirectional Power Flow Controlling with Soft-Switching Feature and High Step-Up/Down Voltage Conversion
Energies 2017, 10(3), 296; doi:10.3390/en10030296
Received: 29 December 2016 / Accepted: 27 February 2017 / Published: 2 March 2017
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Abstract
In this paper, a novel isolated bidirectional DC-DC converter is proposed, which is able to accomplish high step-up/down voltage conversion. Therefore, it is suitable for hybrid electric vehicle, fuel cell vehicle, energy backup system, and grid-system applications. The proposed converter incorporates a coupled
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In this paper, a novel isolated bidirectional DC-DC converter is proposed, which is able to accomplish high step-up/down voltage conversion. Therefore, it is suitable for hybrid electric vehicle, fuel cell vehicle, energy backup system, and grid-system applications. The proposed converter incorporates a coupled inductor to behave forward-and-flyback energy conversion for high voltage ratio and provide galvanic isolation. The energy stored in the leakage inductor of the coupled inductor can be recycled without the use of additional snubber mechanism or clamped circuit. No matter in step-up or step-down mode, all power switches can operate with soft switching. Moreover, there is a inherit feature that metal–oxide–semiconductor field-effect transistors (MOSFETs) with smaller on-state resistance can be adopted because of lower voltage endurance at primary side. Operation principle, voltage ratio derivation, and inductor design are thoroughly described in this paper. In addition, a 1-kW prototype is implemented to validate the feasibility and correctness of the converter. Experimental results indicate that the peak efficiencies in step-up and step-down modes can be up to 95.4% and 93.6%, respectively. Full article
(This article belongs to the Special Issue Grid-Connected Photovoltaic Systems)
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Open AccessFeature PaperArticle An Active Power Filter Based on a Three-Level Inverter and 3D-SVPWM for Selective Harmonic and Reactive Compensation
Energies 2017, 10(3), 297; doi:10.3390/en10030297
Received: 15 December 2016 / Revised: 22 February 2017 / Accepted: 24 February 2017 / Published: 3 March 2017
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Abstract
Active Power Filters (APFs) have been used for reducing waveform distortion and improving power quality. However, this function can be improved by means of a selective harmonic compensation. Since an APF has rating restrictions, it is convenient to have the option of selecting
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Active Power Filters (APFs) have been used for reducing waveform distortion and improving power quality. However, this function can be improved by means of a selective harmonic compensation. Since an APF has rating restrictions, it is convenient to have the option of selecting an individual or a set of particular harmonics in order to compensate and apply the total APF capabilities to eliminate these harmonics, in particular those with a greater impact on the Total Harmonic Distortion (THD). This paper presents the development of a new APF prototype based on a three-phase three-level Neutral Point Clamped (NPC) inverter with selective harmonic compensation capabilities and reactive power compensation. The selective harmonic compensation approach uses several Synchronous Rotating Frames (SRF), to detect and control individual or a set of harmonics using d and q variables. The APF includes a Three-Dimensional Space Vector Modulator (3D-SVPWM) in order to generate the compensation currents. Because of its multilevel topology, the proposed active power filter can be used in diverse power quality applications at sub-transmission and distribution voltage levels. Simulation and experimental results are shown to validate the proposed solution and assess the prototype performance in different scenarios. Full article
(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)
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Open AccessArticle Heavy Metals and Polycyclic Aromatic Hydrocarbons in Urban Leaf Litter Designated for Combustion
Energies 2017, 10(3), 298; doi:10.3390/en10030298
Received: 10 January 2017 / Revised: 21 February 2017 / Accepted: 24 February 2017 / Published: 3 March 2017
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Abstract
Vast amounts of leaf litter have to be disposed of by city administrations. This biomass has the potential for energy conversion, but contamination with pollutants can adversely affect this usage. We investigated leaf litter samples from the city of Kassel by analyzing their
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Vast amounts of leaf litter have to be disposed of by city administrations. This biomass has the potential for energy conversion, but contamination with pollutants can adversely affect this usage. We investigated leaf litter samples from the city of Kassel by analyzing their heavy metal and polycyclic aromatic hydrocarbon (PAH) concentrations. Leaf samples were indeed contaminated with heavy metals and PAHs and contamination was influenced by provenience and collection technique. A simple cleaning system of washing and subsequent mechanical dewatering significantly reduced heavy metal concentration. Regression models were developed for contamination with heavy metals which showed that contamination could be successfully estimated using the total ash content of the sample as a predictor, with an R2 of up to 0.77. It can be concluded that leaf litter from cities is a possible feedstock for energetic conversion, provided a cleaning step is applied. Full article
(This article belongs to the Special Issue Biomass Combustion for Heat and Power Generation)
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Open AccessArticle Optimum Design and Operation of an HVAC Cooling Tower for Energy and Water Conservation
Energies 2017, 10(3), 299; doi:10.3390/en10030299
Received: 11 January 2017 / Revised: 15 February 2017 / Accepted: 17 February 2017 / Published: 3 March 2017
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Abstract
The energy consumption increase in the last few years has contributed to developing energy efficiency policies in many countries, the main goal of which is decreasing CO2 emissions. One of the reasons for this increment has been caused by the use of
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The energy consumption increase in the last few years has contributed to developing energy efficiency policies in many countries, the main goal of which is decreasing CO 2 emissions. One of the reasons for this increment has been caused by the use of air conditioning systems due to new comfort standards. In that regard, cooling towers and evaporative condensers are presented as efficient devices that operate with low-level water temperature. Moreover, the energy consumption and the cost of the equipment are lower than other systems like air condensers at the same operation conditions. This work models an air conditioning system in TRNSYS software, the main elements if which are a cooling tower, a water-water chiller and a reference building. The cooling tower model is validated using experimental data in a pilot plant. The main objective is to implement an optimizing control strategy in order to reduce both energy and water consumption. Furthermore a comparison between three typical methods of capacity control is carried out. Additionally, different cooling tower configurations are assessed, involving six drift eliminators and two water distribution systems. Results show the influence of optimizing the control strategy and cooling tower configuration, with a maximum energy savings of 10.8% per story and a reduction of 4.8% in water consumption. Full article
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Open AccessArticle A Dynamic Economic Dispatch Model for Uncertain Power Demands in an Interconnected Microgrid
Energies 2017, 10(3), 300; doi:10.3390/en10030300
Received: 9 November 2016 / Revised: 21 February 2017 / Accepted: 22 February 2017 / Published: 3 March 2017
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Abstract
In this paper, we propose a dynamic economic dispatch (DED) model with sharing of responsibility for supply–demand balance under uncertain demands in a microgrid (MG). For developing the proposed model, an energy band operation scheme, including a tie-line flow (TLF) contraction between the
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In this paper, we propose a dynamic economic dispatch (DED) model with sharing of responsibility for supply–demand balance under uncertain demands in a microgrid (MG). For developing the proposed model, an energy band operation scheme, including a tie-line flow (TLF) contraction between the main grid and the microgrid (MG), is constructed for preventing considerable changes in the TLFs caused by DED optimization. The proposed scheme generalizes the relationship between TLF contractions and MG operational costs. Moreover, a chance-constrained approach is applied to prevent short- and over-supply risks caused by unpredictable demands in the MG. Based on this approach, it is possible to determine the reasonable ramping capability versus operational cost under uncertain power demands in the MG. Full article
(This article belongs to the collection Smart Grid)
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Open AccessArticle A Novel Parametric Modeling Method and Optimal Design for Savonius Wind Turbines
Energies 2017, 10(3), 301; doi:10.3390/en10030301
Received: 27 November 2016 / Accepted: 28 February 2017 / Published: 3 March 2017
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Abstract
Under the inspiration of polar coordinates, a novel parametric modeling and optimization method for Savonius wind turbines was proposed to obtain the highest power output, in which a quadratic polynomial curve was bent to describe a blade. Only two design parameters are needed
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Under the inspiration of polar coordinates, a novel parametric modeling and optimization method for Savonius wind turbines was proposed to obtain the highest power output, in which a quadratic polynomial curve was bent to describe a blade. Only two design parameters are needed for the shape-complicated blade. Therefore, this novel method reduces sampling scale. A series of transient simulations was run to get the optimal performance coefficient (power coefficient C p) for different modified turbines based on computational fluid dynamics (CFD) method. Then, a global response surface model and a more precise local response surface model were created according to Kriging Method. These models defined the relationship between optimization objective Cp and design parameters. Particle swarm optimization (PSO) algorithm was applied to find the optimal design based on these response surface models. Finally, the optimal Savonius blade shaped like a “hook” was obtained. Cm (torque coefficient), Cp and flow structure were compared for the optimal design and the classical design. The results demonstrate that the optimal Savonius turbine has excellent comprehensive performance. The power coefficient Cp is significantly increased from 0.247 to 0.262 (6% higher). The weight of the optimal blade is reduced by 17.9%. Full article
(This article belongs to the Special Issue Wind Turbine 2017)
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Open AccessArticle Experimental Investigation of the Transpired Solar Air Collectors and Metal Corrugated Packing Solar Air Collectors
Energies 2017, 10(3), 302; doi:10.3390/en10030302
Received: 19 January 2017 / Revised: 26 February 2017 / Accepted: 28 February 2017 / Published: 3 March 2017
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Abstract
The thermal performance of three novel solar air collectors with perforating corrugated plate, slit-perforated plate, and corrugated packing were experimentally studied in this paper. Experiments were conducted in Tianjin to study the thermal and dynamic performance of the collectors in cold and severe
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The thermal performance of three novel solar air collectors with perforating corrugated plate, slit-perforated plate, and corrugated packing were experimentally studied in this paper. Experiments were conducted in Tianjin to study the thermal and dynamic performance of the collectors in cold and severe cold regions. A chamber with a PID (Proportion Integration Differentiation) temperature controller was designed to control the inlet air temperature of the three collectors. Effects of radiation intensity, inlet air temperature, and flow rate on the thermal efficiency and outlet air temperature were experimentally studied. The results indicated that the thermal efficiency of the three collectors in severe cold regions could be much higher than 50% and the collector with perforating corrugated plate had the highest thermal efficiency. The inlet air flow rate had significant effects on the thermal comfort of buildings in cold and severe cold regions and it should be lower than 45 m3/h. The results indicated that the pressure drops of collectors with perforating corrugated plate were a little larger than the collectors with slit-perforated plate, but the thermal efficiency and outlet air temperature was higher. Therefore, the collector with perforating corrugated plate was more suitable to use in cold and severe cold regions. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle Study on the Progressive Failure Characteristics of Longmaxi Shale under Uniaxial Compression Conditions by X-ray Micro-Computed Tomography
Energies 2017, 10(3), 303; doi:10.3390/en10030303
Received: 12 January 2017 / Accepted: 28 February 2017 / Published: 3 March 2017
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Abstract
To investigate the deformation-failure process of Longmaxi shale under uniaxial compression conditions from the mesoscopic and macroscopic points of view, novel X-ray microComputed Tomography (micro-CT) equipment combined with unique loading apparatus was used. Cylindrical shale samples (4 mm in diameter and 8 mm
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To investigate the deformation-failure process of Longmaxi shale under uniaxial compression conditions from the mesoscopic and macroscopic points of view, novel X-ray microComputed Tomography (micro-CT) equipment combined with unique loading apparatus was used. Cylindrical shale samples (4 mm in diameter and 8 mm in height) were produced to perform a series of uniaxial compression tests. CT scanning images at different time points during the loading process were obtained to study the characteristics of the progressive failure. In addition, stereograms were reconstructed and vertical slices were selected to explain the failure mechanism. From the results of the testing the low-density area, local per-peak cracks, numerous post-peak cracks and secondary cracks consecutively appeared in the CT images. Vertical and inclined fissures in the samples could be observed from the stereograms’ surfaces and from internal slices. The cracking indicates that the failure process of shale is progressive and the failure mechanism of shale under uniaxial compression is mainly tension destruction or comprehensive tension-shear destruction. Full article
(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries)
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Open AccessArticle A Study on the Optimization of Surfactants in the Main and Vice Slug in Weak Base ASP Flooding
Energies 2017, 10(3), 304; doi:10.3390/en10030304
Received: 25 November 2016 / Accepted: 28 February 2017 / Published: 3 March 2017
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Abstract
In ASP (Alkali-Surfactant-Polymer) flooding processes, surfactants help to enhance oil recovery by lowering the interfacial tension between the oil and water. However, due to the high cost of surfactants and the stability of the emulsion that varies with surfactant concentration, it is necessary
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In ASP (Alkali-Surfactant-Polymer) flooding processes, surfactants help to enhance oil recovery by lowering the interfacial tension between the oil and water. However, due to the high cost of surfactants and the stability of the emulsion that varies with surfactant concentration, it is necessary to optimize the surfactant concentration in ASP flooding. In this study, we combined numerical simulation and physical experimental research to solve this problem. In order to screen for the optimal surfactant concentration in the main and vice slugs, CMG (Computer Measurement Group) numerical simulation software was used to change the surfactant concentration in the injected compound system and the oil recovery factor and the recovery percent of reserves were compared. The physical experiments were also carried out with different surfactant concentrations and the results verified the simulation results. It shows that the recovery factor increases with the surfactant concentration. The optimal surfactant concentration in the main and vice slug are 0.3% and 0.15%, respectively. As for improving the recovery factor, it is more efficient to increase the mass fraction of the surfactant in the vice slug than in the main slug. It demonstrates that the amount of surfactant in the main slug plays a more important role in displacing oil from the formation. Full article
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Open AccessArticle Control Strategy Optimization for Parallel Hybrid Electric Vehicles Using a Memetic Algorithm
Energies 2017, 10(3), 305; doi:10.3390/en10030305
Received: 15 January 2017 / Accepted: 1 March 2017 / Published: 3 March 2017
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Abstract
Hybrid electric vehicle (HEV) control strategy is a management approach for generating, using, and saving energy. Therefore, the optimal control strategy is the sticking point to effectively manage hybrid electric vehicles. In order to realize the optimal control strategy, we use a robust
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Hybrid electric vehicle (HEV) control strategy is a management approach for generating, using, and saving energy. Therefore, the optimal control strategy is the sticking point to effectively manage hybrid electric vehicles. In order to realize the optimal control strategy, we use a robust evolutionary computation method called a “memetic algorithm (MA)” to optimize the control parameters in parallel HEVs. The “local search” mechanism implemented in the MA greatly enhances its search capabilities. In the implementation of the method, the fitness function combines with the ADvanced VehIcle SimulatOR (ADVISOR) and is set up according to an electric assist control strategy (EACS) to minimize the fuel consumption (FC) and emissions (HC, CO, and NOx) of the vehicle engine. At the same time, driving performance requirements are also considered in the method. Four different driving cycles, the new European driving cycle (NEDC), Federal Test Procedure (FTP), Economic Commission for Europe + Extra-Urban driving cycle (ECE + EUDC), and urban dynamometer driving schedule (UDDS) are carried out using the proposed method to find their respectively optimal control parameters. The results show that the proposed method effectively helps to reduce fuel consumption and emissions, as well as guarantee vehicle performance. Full article
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Open AccessArticle Optimization of a Bubbling Fluidized Bed Plant for Low-Temperature Gasification of Biomass
Energies 2017, 10(3), 306; doi:10.3390/en10030306
Received: 8 February 2017 / Revised: 24 February 2017 / Accepted: 28 February 2017 / Published: 4 March 2017
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Abstract
Investigation into clean energies has been focused on finding an alternative to fossil fuels in order to reduce global warming while at the same time satisfying the world’s energy needs. Biomass gasification is seen as a promising thermochemical conversion technology as it allows
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Investigation into clean energies has been focused on finding an alternative to fossil fuels in order to reduce global warming while at the same time satisfying the world’s energy needs. Biomass gasification is seen as a promising thermochemical conversion technology as it allows useful gaseous products to be obtained from low-energy-density solid fuels. Air–steam mixtures are the most commonly used gasification agents. The gasification performances of several biomass samples and their mixtures were compared. One softwood (pine) and one hardwood (chestnut), their torrefied counterparts, and other Spanish-based biomass wastes such as almond shell, olive stone, grape and olive pomaces or cocoa shell were tested, and their behaviors at several different stoichiometric ratios (SR) and steam/air ratios (S/A) were compared. The optimum SR was found to be in the 0.2–0.3 range for S/A = 75/25. At these conditions a syngas stream with 35% of H2 + CO and a gas yield of 2 L gas/g fuel were obtained, which represents a cold-gas efficiency of almost 50%. The torrefaction process does not significantly affect the quality of the product syngas. Some of the obtained chars were analyzed to assess their use as precursors for catalysts, combustion fuel or for agricultural purposes such as soil amendment. Full article
(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications)
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Open AccessArticle Wind Energy Potential and Power Law Indexes Assessment for Selected Near-Coastal Sites in Malaysia
Energies 2017, 10(3), 307; doi:10.3390/en10030307
Received: 14 November 2016 / Revised: 10 February 2017 / Accepted: 17 February 2017 / Published: 5 March 2017
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Abstract
This paper investigated the wind energy potential by analysing a certain amount of gathered 10-min measured data at four stations located at coastal sites in Malaysia, i.e., Kudat, Mersing, Kijal, and Langkawi. The wind data are collected from a total of four new
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This paper investigated the wind energy potential by analysing a certain amount of gathered 10-min measured data at four stations located at coastal sites in Malaysia, i.e., Kudat, Mersing, Kijal, and Langkawi. The wind data are collected from a total of four new wind measurement masts with sensors mounted at various heights on the tower. The measured data have enabled the establishment of wind resource maps and the power law indexes (PLIs) analysis. In addition, the dependence of PLI upon surface temperature and terrain types is studied, as they are associated to the form of exponential fits. Moreover, the accuracy of exponential fits is assessed by comparing the results with the 1/7 law via the capacity factor (CF) discrepancies. In order to do so, the wind turbine with a hub-height similar to the maximum height of the measured data at each site is selected to simulate energy production. Accordingly, the discrepancy of CF based on the extrapolated data by employing 1/7 laws and exponential fits, in spite of being computed using measured data, is determined as well. Furthermore, the large discrepancy of the wind data and the CF, which has been determined with the application of 1/7, is compared to the exponential fits. This is because; discrepancy in estimation of vertical wind speed could lead to inaccurate CF computation. Meanwhile, from the energy potential analysis based on the computed CF, only Kudat and Mersing display a promising potential to develop a medium capacity of wind turbine power, while the other sites may be suitable for wind turbines at a small scale. Full article
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Open AccessArticle Angle Control-Based Multi-Terminal Out-of-Step Protection System
Energies 2017, 10(3), 308; doi:10.3390/en10030308
Received: 18 January 2017 / Revised: 20 February 2017 / Accepted: 24 February 2017 / Published: 4 March 2017
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Abstract
From time to time a sequence of unexpected and overlapping contingencies may lead to power system angular instability and even blackouts if not addressed adequately by means of an out-of-step (OOS) protection system. The motivation of the paper is an attempt to develop
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From time to time a sequence of unexpected and overlapping contingencies may lead to power system angular instability and even blackouts if not addressed adequately by means of an out-of-step (OOS) protection system. The motivation of the paper is an attempt to develop a workable prototype of the OOS protection system. The deficiencies of the protection currently used in the Latvian Power System network are highlighted and a new protection structure is proposed. The protection system comprises of several strategically located terminals, exchanging information in real time by means of a communication network. The OOS condition detection method is based on system-wide generation sources, electromotive forces, vectors, and angle control. The network splitting decision is based on generator coherence evaluation. Protection terminals determine online the groups of coherent generators and choose the splitting boundary from a predefined transmission lines (TLs) cut sets list. The protection system structure, algorithm of operation, and possible IEC 61850 communication standard-based implementation are described. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle A Novel High-Frequency Voltage Standing-Wave Ratio-Based Grounding Electrode Line Fault Supervision in Ultra-High Voltage DC Transmission Systems
Energies 2017, 10(3), 309; doi:10.3390/en10030309
Received: 28 December 2016 / Revised: 21 February 2017 / Accepted: 28 February 2017 / Published: 5 March 2017
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Abstract
In order to improve the fault monitoring performance of grounding electrode lines in ultra-high voltage DC (UHVDC) transmission systems, a novel fault monitoring approach based on the high-frequency voltage standing-wave ratio (VSWR) is proposed in this paper. The VSWR is defined considering a
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In order to improve the fault monitoring performance of grounding electrode lines in ultra-high voltage DC (UHVDC) transmission systems, a novel fault monitoring approach based on the high-frequency voltage standing-wave ratio (VSWR) is proposed in this paper. The VSWR is defined considering a lossless transmission line, and the characteristics of the VSWR under different conditions are analyzed. It is shown that the VSWR equals 1 when the terminal resistance completely matches the characteristic impedance of the line, and when a short circuit fault occurs on the grounding electrode line, the VSWR will be greater than 1. The VSWR will approach positive infinity under metallic earth fault conditions, whereas the VSWR in non-metallic earth faults will be smaller. Based on these analytical results, a fault supervision criterion is formulated. The effectiveness of the proposed VSWR-based fault supervision technique is verified with a typical UHVDC project established in Power Systems Computer Aided Design/Electromagnetic Transients including DC(PSCAD/EMTDC). Simulation results indicate that the proposed strategy can reliably identify the grounding electrode line fault and has strong anti-fault resistance capability. Full article
(This article belongs to the collection Smart Grid)
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Open AccessArticle Pressure Losses in Hydraulic Manifolds
Energies 2017, 10(3), 310; doi:10.3390/en10030310
Received: 7 December 2016 / Revised: 7 February 2017 / Accepted: 1 March 2017 / Published: 6 March 2017
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Abstract
Hydraulic manifolds are used to realize compact circuit layout, but may introduce a high pressure drop in the system. Their design is in fact oriented more toward achieving minimum size and weight than to reducing pressure losses. This work studies the pressure losses
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Hydraulic manifolds are used to realize compact circuit layout, but may introduce a high pressure drop in the system. Their design is in fact oriented more toward achieving minimum size and weight than to reducing pressure losses. This work studies the pressure losses in hydraulic manifolds using different methods: Computational Fluid Dynamic (CFD) analysis; semi-empirical formulation derived from the scientific literature, when available; and experimental characterization. The purpose is to obtain the pressure losses when the channels’ connections within the manifold are not ascribable to the few classic cases studied in the literature, in particular for 90° bends (elbows) with expansion/contraction and offset intersection of channels. Moreover, since CFD analysis is used to predict pressure losses, general considerations of the manifold design may be outlined and this will help the design process in the optimization of flow passages. The main results obtained show how CFD analysis overestimates the experimental results; nevertheless, the numerical analysis represents the correct trends of the pressure losses. Full article
(This article belongs to the Special Issue Energy Efficiency and Controllability of Fluid Power Systems)
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Open AccessArticle Analysis of Power Loss and Improved Simulation Method of a High Frequency Dual-Buck Full-Bridge Inverter
Energies 2017, 10(3), 311; doi:10.3390/en10030311
Received: 24 January 2017 / Accepted: 2 March 2017 / Published: 6 March 2017
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Abstract
A high frequency dual-buck full-bridge inverter for small power renewable energy application is proposed in this paper. A switching frequency of 400 kHz is achieved with the adoption of the SiC power device. A two-pole two-zero (2P2Z) compensator is employed in the outer
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A high frequency dual-buck full-bridge inverter for small power renewable energy application is proposed in this paper. A switching frequency of 400 kHz is achieved with the adoption of the SiC power device. A two-pole two-zero (2P2Z) compensator is employed in the outer voltage loop to generate the current reference for inner current loop. A 3P3Z compensator is adopted in the inner current loop to track the current reference. A systematic way for calculating the losses of high frequency inverter is presented, and the losses of the components are thoroughly analyzed. The turn-on and turn-off procedures of the inverter are discussed in detail. The losses caused by high frequency are calculated accurately, and the loss distribution is established as well. The procedure of the loss analysis gives a practical example for calculating the loss of similar type inverters. Moreover, deviation between pulse width modulation (PWM) control signal and switching response in high frequency switching is thoroughly analyzed. The influence of deviation is verified by designed experiment. Hence, a compensation method is proposed in order to minimize the influence. The compensation effect is validated by experiment and simulation. Finally, a 1-kW prototype is built to verify the feasibility of the theoretical analyses. The grid-connected maximum output power experiment is completed at 1 kW with the efficiency of 96.1% and the total harmonic distortion (THD) of 1.8%. The comparison experiments of power loss between Si and SiC power devices are carried out. The experiment results confirm the loss calculation method to be valid. Full article
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Open AccessArticle A Redundancy Mechanism Design for Hall-Based Electronic Current Transformers
Energies 2017, 10(3), 312; doi:10.3390/en10030312
Received: 21 January 2017 / Accepted: 28 February 2017 / Published: 6 March 2017
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Abstract
Traditional current transformers (CTs) suffer from DC and AC saturation and remanent magnetization in many industrial applications. Moreover, the drawbacks of traditional CTs, such as closed iron cores, bulky volume, and heavy weight, further limit the development of an intelligent power protection system.
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Traditional current transformers (CTs) suffer from DC and AC saturation and remanent magnetization in many industrial applications. Moreover, the drawbacks of traditional CTs, such as closed iron cores, bulky volume, and heavy weight, further limit the development of an intelligent power protection system. In order to compensate for these drawbacks, we proposed a novel current measurement method by using Hall sensors, which is called the Hall-effect current transformer (HCT). The existing commercial Hall sensors are electronic components, so the reliability of the HCT is normally worse than that of the traditional CT. Therefore, our study proposes a redundancy mechanism for the HCT to strengthen its reliability. With multiple sensor modules, the method has the ability to improve the accuracy of the HCT as well. Additionally, the proposed redundancy mechanism monitoring system provides a condition-based maintenance for the HCT. We verify our method with both simulations and an experimental test. The results demonstrate that the proposed HCT with a redundancy mechanism can almost achieve Class 0.2 for measuring CTs according to IEC Standard 60044-8. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Strategic Maintenance Scheduling of an Offshore Wind Farm in a Deregulated Power System
Energies 2017, 10(3), 313; doi:10.3390/en10030313
Received: 21 December 2016 / Accepted: 1 March 2017 / Published: 6 March 2017
Cited by 5 | PDF Full-text (1322 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a model for strategic maintenance scheduling of offshore wind farms (SMSOWF) in a deregulated power system. The objective of the model is to plan the maintenance schedules in a way to maximize the profit of the offshore wind farm. In
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This paper proposes a model for strategic maintenance scheduling of offshore wind farms (SMSOWF) in a deregulated power system. The objective of the model is to plan the maintenance schedules in a way to maximize the profit of the offshore wind farm. In addition, some network constraints, such as transmission lines capacity, and wind farm constraints, such as labor working shift, wave height limit and wake effect, as well as unexpected outages, are included in deterministic and stochastic studies. Moreover, the proposedmodel provides theability to incorporate information from condition monitoring systems. SMSOWF is formulated through a bi-level formulation and then transformed into a single-level through Karush–Kuhn–Tucker conditions. The model is validated through a test system, and the results demonstrate applicability, advantages and challenges of harnessing the full potential of the model. Full article
(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)
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Open AccessArticle Simulation of Steam Gasification in a Fluidized Bed Reactor with Energy Self-Sufficient Condition
Energies 2017, 10(3), 314; doi:10.3390/en10030314
Received: 29 November 2016 / Accepted: 2 March 2017 / Published: 6 March 2017
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Abstract
The biomass gasification process is widely accepted as a popular technology to produce fuel for the application in gas turbines and Organic Rankine Cycle (ORC). Chemical reactions of this process can be separated into three reaction zones: pyrolysis, combustion, and reduction. In this
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The biomass gasification process is widely accepted as a popular technology to produce fuel for the application in gas turbines and Organic Rankine Cycle (ORC). Chemical reactions of this process can be separated into three reaction zones: pyrolysis, combustion, and reduction. In this study, sensitivity analysis with respect to three input parameters (gasification temperature, equivalence ratio, and steam-to-biomass ratio) has been carried out to achieve energy self-sufficient conditions in a steam gasification process under the criteria that the carbon conversion efficiency must be more than 70%, and carbon dioxide gas is lower than 20%. Simulation models of the steam gasification process have been carried out by ASPEN Plus and validated with both experimental data and simulation results from Nikoo & Mahinpey (2008). Gasification temperature of 911 °C, equivalence ratio of 0.18, and a steam-to-biomass ratio of 1.78, are considered as an optimal operation point to achieve energy self-sufficient condition. This operating point gives the maximum of carbon conversion efficiency at 91.03%, and carbon dioxide gas at 15.18 volumetric percentages. In this study, life cycle assessment (LCA) is included to compare the environmental performance of conventional and energy self-sufficient gasification for steam biomass gasification. Full article
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Open AccessArticle An Autonomous Coil Alignment System for the Dynamic Wireless Charging of Electric Vehicles to Minimize Lateral Misalignment
Energies 2017, 10(3), 315; doi:10.3390/en10030315
Received: 2 January 2017 / Revised: 27 February 2017 / Accepted: 2 March 2017 / Published: 7 March 2017
Cited by 4 | PDF Full-text (13699 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This paper proposes an autonomous coil alignment system (ACAS) for electric vehicles (EVs) with dynamic wireless charging (DWC) to mitigate the reduction in received power caused by lateral misalignment between the source and load coils. The key component of the ACAS is a
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This paper proposes an autonomous coil alignment system (ACAS) for electric vehicles (EVs) with dynamic wireless charging (DWC) to mitigate the reduction in received power caused by lateral misalignment between the source and load coils. The key component of the ACAS is a novel sensor coil design, which can detect the load coil’s left or right position relative to the source coil by observing the change in voltage phase. This allows the lateral misalignment to be estimated through the wireless power transfer (WPT) system alone, which is a novel tracking method for vehicular applications. Once misalignment is detected, the vehicle’s lateral position is self-adjusted by an autonomous steering function. The feasibility of the overall operation of the ACAS was verified through simulation and experiments. In addition, an analysis based on experimental results was conducted, demonstrating that 26% more energy can be transferred during DWC with the ACAS, just by keeping the vehicle’s load coil aligned with the source coil. Full article
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Open AccessArticle Reluctance Machine for a Hollow Cylinder Flywheel
Energies 2017, 10(3), 316; doi:10.3390/en10030316
Received: 28 October 2016 / Revised: 20 February 2017 / Accepted: 28 February 2017 / Published: 7 March 2017
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Abstract
A hollow cylinder flywheel rotor with a novel outer rotor switched reluctance machine (SRM) mounted on the interior rim is presented, with measurements, numerical analysis and analytical models. Practical experiences from the construction process are also discussed. The flywheel rotor does not have
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A hollow cylinder flywheel rotor with a novel outer rotor switched reluctance machine (SRM) mounted on the interior rim is presented, with measurements, numerical analysis and analytical models. Practical experiences from the construction process are also discussed. The flywheel rotor does not have a shaft and spokes and is predicted to store 181 Wh / kg at ultimate tensile strength (UTS) according to simulations. The novel SRM is an axial flux machine, chosen due to its robustness and tolerance for high strain. The computed maximum tip speed of the motor at UTS is 1050 m / s . A small-scale proof-of-concept electric machine prototype has been constructed, and the machine inductance has been estimated from measurements of voltage and current and compared against results from analytical models and finite element analysis (FEA). The prototype measurements were used to simulate operation during maximal speed for a comparison towards other high-speed electric machines, in terms of tip speed and power. The mechanical design of the flywheel was performed with an analytical formulation assuming planar stress in concentric shells of orthotropic (unidirectionally circumferentially wound) carbon composites. The analytical approach was verified with 3D FEA in terms of stress and strain. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle Wind Farm Wake: The 2016 Horns Rev Photo Case
Energies 2017, 10(3), 317; doi:10.3390/en10030317
Received: 22 December 2016 / Revised: 24 February 2017 / Accepted: 27 February 2017 / Published: 7 March 2017
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Abstract
Offshore wind farm wakes were observed and photographed in foggy conditions at Horns Rev 2 on 25 January 2016 at 12:45 UTC. These new images show highly contrasting conditions regarding the wind speed, turbulence intensity, atmospheric stability, weather conditions and wind farm wake
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Offshore wind farm wakes were observed and photographed in foggy conditions at Horns Rev 2 on 25 January 2016 at 12:45 UTC. These new images show highly contrasting conditions regarding the wind speed, turbulence intensity, atmospheric stability, weather conditions and wind farm wake development as compared to the Horns Rev 1 photographs from 12 February 2008. The paper examines the atmospheric conditions from satellite images, radiosondes, lidar and wind turbine data and compares the observations to results from atmospheric meso-scale modelling and large eddy simulation. Key findings are that a humid and warm air mass was advected from the southwest over cold sea and the dew-point temperature was such that cold-water advection fog formed in a shallow layer. The flow was stably stratified and the freestream wind speed was 13 m/s at hub height, which means that most turbines produced at or near rated power. The wind direction was southwesterly and long, narrow wakes persisted several rotor diameters downwind of the wind turbines. Eventually mixing of warm air from aloft dispersed the fog in the far wake region of the wind farm. Full article
(This article belongs to the collection Wind Turbines)
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Open AccessArticle Detent Force Reduction of a C-Core Linear Flux-Switching Permanent Magnet Machine with Multiple Additional Teeth
Energies 2017, 10(3), 318; doi:10.3390/en10030318
Received: 10 January 2017 / Revised: 2 March 2017 / Accepted: 2 March 2017 / Published: 7 March 2017
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Abstract
C-core linear flux-switching permanent magnet (PM) machines (LFSPMs) are attracting more and more attention due to their advantages of simplicity and robustness of the secondary side, high power density and high torque density, in which both PMs and armature windings are housed in
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C-core linear flux-switching permanent magnet (PM) machines (LFSPMs) are attracting more and more attention due to their advantages of simplicity and robustness of the secondary side, high power density and high torque density, in which both PMs and armature windings are housed in the primary side. The primary salient tooth wound with a concentrated winding consists of C-shaped iron core segments between which PMs are sandwiched and the magnetization directions of these PMs are adjacent and alternant in the horizontal direction. On the other hand, the secondary side is composed of a simple iron core with salient teeth so that it is very suitable for long stroke applications. However, the detent force of the C-core LFSPM machine is relatively high and the magnetic circuit is unbalanced due to the end effect. Thus, a new multiple additional tooth which consists of an active and a traditional passive additional tooth, is employed at each end side of the primary in this paper, so that the asymmetry due to end effect can be depressed and the detent force can be reduced by adjusting the passive additional tooth position. By using the finite element method, the characteristics and performances of the proposed machine are analyzed and verified. Full article
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Open AccessArticle A Hybrid Genetic Wind Driven Heuristic Optimization Algorithm for Demand Side Management in Smart Grid
Energies 2017, 10(3), 319; doi:10.3390/en10030319
Received: 8 November 2016 / Revised: 5 February 2017 / Accepted: 24 February 2017 / Published: 7 March 2017
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Abstract
In recent years, demand side management (DSM) techniques have been designed for residential, industrial and commercial sectors. These techniques are very effective in flattening the load profile of customers in grid area networks. In this paper, a heuristic algorithms-based energy management controller is
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In recent years, demand side management (DSM) techniques have been designed for residential, industrial and commercial sectors. These techniques are very effective in flattening the load profile of customers in grid area networks. In this paper, a heuristic algorithms-based energy management controller is designed for a residential area in a smart grid. In essence, five heuristic algorithms (the genetic algorithm (GA), the binary particle swarm optimization (BPSO) algorithm, the bacterial foraging optimization algorithm (BFOA), the wind-driven optimization (WDO) algorithm and our proposed hybrid genetic wind-driven (GWD) algorithm) are evaluated. These algorithms are used for scheduling residential loads between peak hours (PHs) and off-peak hours (OPHs) in a real-time pricing (RTP) environment while maximizing user comfort (UC) and minimizing both electricity cost and the peak to average ratio (PAR). Moreover, these algorithms are tested in two scenarios: (i) scheduling the load of a single home and (ii) scheduling the load of multiple homes. Simulation results show that our proposed hybrid GWD algorithm performs better than the other heuristic algorithms in terms of the selected performance metrics. Full article
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Open AccessArticle Analytical Calculation of Magnetic Field Distribution and Stator Iron Losses for Surface-Mounted Permanent Magnet Synchronous Machines
Energies 2017, 10(3), 320; doi:10.3390/en10030320
Received: 22 December 2016 / Revised: 23 February 2017 / Accepted: 28 February 2017 / Published: 7 March 2017
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Abstract
Permanent-magnet synchronous machines (PMSMs) are widely used in electric vehicles owing to many advantages, such as high power density, high efficiency, etc. Iron losses can account for a significant component of the total loss in permanent-magnet (PM) machines. Consequently, these losses should be
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Permanent-magnet synchronous machines (PMSMs) are widely used in electric vehicles owing to many advantages, such as high power density, high efficiency, etc. Iron losses can account for a significant component of the total loss in permanent-magnet (PM) machines. Consequently, these losses should be carefully considered during the PMSM design. In this paper, an analytical calculation method has been proposed to predict the magnetic field distribution and stator iron losses in the surface-mounted permanent magnet (SPM) synchronous machines. The method introduces the notion of complex relative air-gap permeance to take into account the effect of slotting. The imaginary part of the relative air-gap permeance is neglected to simplify the calculation of the magnetic field distribution in the slotted air gap for the surface-mounted permanent-magnet (SPM) machine. Based on the armature reaction magnetic field analysis, the stator iron losses can be estimated by the modified Steinmetz equation. The stator iron losses under load conditions are calculated according to the varying d-q-axis currents of different control methods. In order to verify the analysis method, finite element simulation results are compared with analytical calculations. The comparisons show good performance of the proposed analytical method. Full article
(This article belongs to the collection Electric and Hybrid Vehicles Collection)
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Open AccessFeature PaperArticle An Economic Model-Based Predictive Control to Manage the Users’ Thermal Comfort in a Building
Energies 2017, 10(3), 321; doi:10.3390/en10030321
Received: 2 December 2016 / Revised: 16 February 2017 / Accepted: 2 March 2017 / Published: 7 March 2017
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Abstract
The goal of maintaining users’ thermal comfort conditions in indoor environments may require complex regulation procedures and a proper energy management. This problem is being widely analyzed, since it has a direct effect on users’ productivity. This paper presents an economic model-based predictive
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The goal of maintaining users’ thermal comfort conditions in indoor environments may require complex regulation procedures and a proper energy management. This problem is being widely analyzed, since it has a direct effect on users’ productivity. This paper presents an economic model-based predictive control (MPC) whose main strength is the use of the day-ahead price (DAP) in order to predict the energy consumption associated with the heating, ventilation and air conditioning (HVAC). In this way, the control system is able to maintain a high thermal comfort level by optimizing the use of the HVAC system and to reduce, at the same time, the energy consumption associated with it, as much as possible. Later, the performance of the proposed control system is tested through simulations with a non-linear model of a bioclimatic building room. Several simulation scenarios are considered as a test-bed. From the obtained results, it is possible to conclude that the control system has a good behavior in several situations, i.e., it can reach the users’ thermal comfort for the analyzed situations, whereas the HVAC use is adjusted through the DAP; therefore, the energy savings associated with the HVAC is increased. Full article
(This article belongs to the Special Issue Smart Home Energy Management)
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Open AccessArticle Study of the Effect of Clay Particles on Low Salinity Water Injection in Sandstone Reservoirs
Energies 2017, 10(3), 322; doi:10.3390/en10030322
Received: 22 December 2016 / Revised: 1 March 2017 / Accepted: 2 March 2017 / Published: 7 March 2017
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Abstract
The need for optimal recovery of crude oil from sandstone and carbonate reservoirs around the world has never been greater for the petroleum industry. Water-flooding has been applied to the supplement primary depletion process or as a separate secondary recovery method. Low salinity
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The need for optimal recovery of crude oil from sandstone and carbonate reservoirs around the world has never been greater for the petroleum industry. Water-flooding has been applied to the supplement primary depletion process or as a separate secondary recovery method. Low salinity water injection is a relatively new method that involves injecting low salinity brines at high pressure similar to conventional water-flooding techniques, in order to recover crude oil. The effectiveness of low salinity water injection in sandstone reservoirs depends on a number of parameters such as reservoir temperature, pressure, type of clay particle and salinity of injected brine. Clay particles present on reservoir rock surfaces adsorb polar components of oil and modify wettability of sandstone rocks to the oil-wet state, which is accountable for the reduced recovery rates by conventional water-flooding. The extent of wettability alteration caused by three low salinity brines on oil-wet sandstone samples containing varying clay content (15% or 30%) and type of clay (kaolinite/montmorillonite) were analyzed in the laboratory experiment. Contact angles of mica powder and clay mixture (kaolinite/montmorillonite) modified with crude oil were measured before and after injection with three low salinity sodium chloride brines. The effect of temperature was also analyzed for each sample. The results of the experiment indicate that samples with kaolinite clay tend to produce higher contact angles than samples with montmorillonite clay when modified with crude oil. The highest degree or extent of wettability alteration from oil-wet to intermediate-wet state upon injection with low salinity brines was observed for samples injected with brine having salinity concentration of 2000 ppm. The increase in temperature tends to produce contact angles values lying in the higher end of the intermediate-wet range (75°–115°) for samples treated at 50 °C, while their corresponding samples treated at 25 °C produced contact angle values lying in the lower end of intermediate-wet range. Full article
(This article belongs to the Special Issue Oil and Gas Engineering)
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Open AccessArticle A Witricity-Based High-Power Device for Wireless Charging of Electric Vehicles
Energies 2017, 10(3), 323; doi:10.3390/en10030323
Received: 14 January 2017 / Accepted: 1 March 2017 / Published: 7 March 2017
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Abstract
In this paper, a Witricity-based high-power device is proposed for wireless charging of electric vehicles. According to the specific requirements of three-stage charging for electric vehicles, four compensation modes of the Witricity system are analyzed by the Loosely Coupled Theory among transformer coils
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In this paper, a Witricity-based high-power device is proposed for wireless charging of electric vehicles. According to the specific requirements of three-stage charging for electric vehicles, four compensation modes of the Witricity system are analyzed by the Loosely Coupled Theory among transformer coils and the Substitution Theorem in circuit theory. In addition, when combining voltage withstand levels, the current withstand capability, the switching frequency of electronic switching tubes, and the features of the resonant circuit, the series-parallel (SP) compensation mode is selected as the best compensation mode for matching the capacitor of the system. The performances of coils with different ferrite core arrangements are compared by simulations and models. The feasibility of the system is verified theoretically and the system functions are evaluated by the joint simulation of Simplorer and Maxwell. Finally, a Witricity-based high-power device is proposed as designed, and the correctness of theoretical analyses and simulation results are verified. Full article
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Open AccessArticle Development of Decision Support Process for Building Energy Conservation Measures and Economic Analysis
Energies 2017, 10(3), 324; doi:10.3390/en10030324
Received: 17 August 2016 / Accepted: 21 February 2017 / Published: 7 March 2017
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Abstract
As policies for energy efficiency of buildings are being actively implemented, building energy performance improvement is urgently required. However, in Korea, information on measures and technologies for building energy efficiency is dispersed and concrete methods are not established, making it difficult to apply
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As policies for energy efficiency of buildings are being actively implemented, building energy performance improvement is urgently required. However, in Korea, information on measures and technologies for building energy efficiency is dispersed and concrete methods are not established, making it difficult to apply effective measures. Therefore, it is required to apply and evaluate energy efficiency measures through database construction integrating diverse information. In this study, the energy efficiency measures in the architectural sector that satisfy domestic legal standards are built. Because of the economic evaluation is necessary for the constructed alternatives, an economic efficiency database was established. The target building was set up, and energy efficiency measures were derived. In addition, a methodology that can induce energy efficient decision making of buildings was proposed, and the energy use evaluation and the economic analysis for each of the alternatives derived from applying the methodology to the target building were carried out. Furthermore, the optimal energy efficiency measures for the target building were suggested through the application of the decision-making process. Full article
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Open AccessArticle Effects of Biogas Substrate Recirculation on Methane Yield and Efficiency of a Liquid-Manure-Based Biogas Plant
Energies 2017, 10(3), 325; doi:10.3390/en10030325
Received: 7 December 2016 / Revised: 25 February 2017 / Accepted: 3 March 2017 / Published: 8 March 2017
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Abstract
Biogas plants are the most complex systems and are heavily studied in the field of renewable energy. A biogas system is mainly influenced by biological and technical parameters that strongly interact with each other. One recommended practice when operating a biogas plant is
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Biogas plants are the most complex systems and are heavily studied in the field of renewable energy. A biogas system is mainly influenced by biological and technical parameters that strongly interact with each other. One recommended practice when operating a biogas plant is the recirculation of the substrate from the second fermenter into the first fermenter, which extends the recirculation amount (RA) and, in turn, the recirculation rate (RR). This technique should be applied to support and secure the biogas process. In this investigation, the RA was varied, starting with the recommended “best practice” of 10.0 m3/d (RR 40%). Every ten days, the RA was reduced in steps of 1.5 m3/d, with 5.5 m3/d (RR 27%) being the final value. The basic question to be addressed concerns to what extent the RR influences the methane yield and thereby influence the efficiency of a manure-based biogas plant in practice. Diverting the “best practice” to a RR of 27% stabilised the fermentation process and lead to significantly higher methane yields with smaller standard deviations. In addition, with a reduced RR, the standard optimal acid concentration within the biogas substrate was approximately reached. Full article
(This article belongs to the Special Issue Energy and Waste Management)
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Open AccessArticle A Chance-Constrained Economic Dispatch Model in Wind-Thermal-Energy Storage System
Energies 2017, 10(3), 326; doi:10.3390/en10030326
Received: 22 January 2017 / Revised: 20 February 2017 / Accepted: 2 March 2017 / Published: 8 March 2017
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Abstract
As a type of renewable energy, wind energy is integrated into the power system with more and more penetration levels. It is challenging for the power system operators (PSOs) to cope with the uncertainty and variation of the wind power and its forecasts.
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As a type of renewable energy, wind energy is integrated into the power system with more and more penetration levels. It is challenging for the power system operators (PSOs) to cope with the uncertainty and variation of the wind power and its forecasts. A chance-constrained economic dispatch (ED) model for the wind-thermal-energy storage system (WTESS) is developed in this paper. An optimization model with the wind power and the energy storage system (ESS) is first established with the consideration of both the economic benefits of the system and less wind curtailments. The original wind power generation is processed by the ESS to obtain the final wind power output generation (FWPG). A Gaussian mixture model (GMM) distribution is adopted to characterize the probabilistic and cumulative distribution functions with an analytical expression. Then, a chance-constrained ED model integrated by the wind-energy storage system (W-ESS) is developed by considering both the overestimation costs and the underestimation costs of the system and solved by the sequential linear programming method. Numerical simulation results using the wind power data in four wind farms are performed on the developed ED model with the IEEE 30-bus system. It is verified that the developed ED model is effective to integrate the uncertain and variable wind power. The GMM distribution could accurately fit the actual distribution of the final wind power output, and the ESS could help effectively decrease the operation costs. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Biogas Engine Waste Heat Recovery Using Organic Rankine Cycle
Energies 2017, 10(3), 327; doi:10.3390/en10030327
Received: 5 February 2017 / Revised: 1 March 2017 / Accepted: 4 March 2017 / Published: 8 March 2017
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Abstract
Italy is a leading country in the biogas sector. Energy crops and manure are converted into biogas using anaerobic digestion and, then, into electricity using internal combustion engines (ICEs). Therefore, there is an urgent need for improving the efficiency of these engines taking
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Italy is a leading country in the biogas sector. Energy crops and manure are converted into biogas using anaerobic digestion and, then, into electricity using internal combustion engines (ICEs). Therefore, there is an urgent need for improving the efficiency of these engines taking the real operation into account. To this purpose, in the present work, the organic Rankine cycle (ORC) technology is used to recover the waste heat contained in the exhaust gases of a 1 MWel biogas engine. The ICE behavior being affected by the biogas characteristics, the ORC unit is designed, firstly, using the ICE nameplate data and, then, with data measured during a one-year monitoring activity. The optimum fluid and the plant configuration are selected in both cases using an “in-house” optimization tool. The optimization goal is the maximization of the net electric power while the working fluid is selected among 115 pure fluids and their mixtures. Results show that a recuperative ORC designed using real data guarantees a 30% higher net electric power than the one designed with ICE nameplate conditions. Full article
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Open AccessArticle Optimized Design and Feasibility of a Heating System with Energy Storage by Pebble Bed in a Solar Attic
Energies 2017, 10(3), 328; doi:10.3390/en10030328
Received: 14 January 2017 / Revised: 25 February 2017 / Accepted: 27 February 2017 / Published: 8 March 2017
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Abstract
For efficient application of solar energy, a pebble bed energy storage heating system in a solar attic is optimally designed and operated. To study the characteristics of the heating system, a numerical model for the system is presented and is validated with the
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For efficient application of solar energy, a pebble bed energy storage heating system in a solar attic is optimally designed and operated. To study the characteristics of the heating system, a numerical model for the system is presented and is validated with the experiment data in the literature. Based on the model, the influence of the envelopes of the solar house and the meteorological condition on the system performance is investigated. The results show that the envelopes, except those on the north face, with more glazed exterior surfaces can be beneficial to raise the temperature of the solar house. It is also found that outdoor temperature may have less impact on the energy storage in the system compared with solar radiation. Furthermore, through optimizing the system design and operation, solar energy can account for 56% of the energy requirement in the heating season in Xi’an (about 34° N, 108° E), which has an average altitude of 397.5 m and moderate solar irradiation. Also, the suitability of the system in northwest China is investigated, and the outcome demonstrates that the external comprehensive temperature should be more than 269 K if a 50% energy saving rate is expected. Full article
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