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Energies, Volume 8, Issue 2 (February 2015) , Pages 684-1546

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Open AccessArticle
The Economics of Wind Power in China and Policy Implications
Energies 2015, 8(2), 1529-1546; https://doi.org/10.3390/en8021529
Received: 6 December 2014 / Revised: 15 January 2015 / Accepted: 4 February 2015 / Published: 17 February 2015
Cited by 19 | Viewed by 2818 | PDF Full-text (642 KB) | HTML Full-text | XML Full-text
Abstract
In 2009, the implementation of feed-in tariff (FIT) and attractive public subsidies for onshore wind farms aroused great investment enthusiasm and spurred remarkable development of wind power in China. Meanwhile, rapid learning-by-doing has significantly cut down the cost of wind turbines and the [...] Read more.
In 2009, the implementation of feed-in tariff (FIT) and attractive public subsidies for onshore wind farms aroused great investment enthusiasm and spurred remarkable development of wind power in China. Meanwhile, rapid learning-by-doing has significantly cut down the cost of wind turbines and the capital cost of wind farms as well. Therefore, it is the right time to examine the appropriateness of the existing FIT policy for wind power in China. In this paper, we employ the analytical framework for levelized cost of electricity (LCOE) to model the generation cost of wind power. Results show that the existing FIT policy is attractive to investors, but serious curtailment and turbine quality issues could make wind power unprofitable. Meanwhile, rapid substantial decreases in the cost of wind power have made it competitive to coal power in 2013, implying that it is possible and necessary to reform the FIT policy for new wind farms. In the future, energy policies for onshore wind power in China could be concentrated on reducing the integration cost, so as to reduce the overall system cost. Full article
Open AccessArticle
Energy Coordinative Optimization of Wind-Storage-Load Microgrids Based on Short-Term Prediction
Energies 2015, 8(2), 1505-1528; https://doi.org/10.3390/en8021505
Received: 18 November 2014 / Revised: 5 February 2015 / Accepted: 9 February 2015 / Published: 16 February 2015
Cited by 9 | Viewed by 3110 | PDF Full-text (709 KB) | HTML Full-text | XML Full-text
Abstract
According to the topological structure of wind-storage-load complementation microgrids, this paper proposes a method for energy coordinative optimization which focuses on improvement of the economic benefits of microgrids in the prediction framework. First of all, the external characteristic mathematical model of distributed generation [...] Read more.
According to the topological structure of wind-storage-load complementation microgrids, this paper proposes a method for energy coordinative optimization which focuses on improvement of the economic benefits of microgrids in the prediction framework. First of all, the external characteristic mathematical model of distributed generation (DG) units including wind turbines and storage batteries are established according to the requirements of the actual constraints. Meanwhile, using the minimum consumption costs from the external grid as the objective function, a grey prediction model with residual modification is introduced to output the predictive wind turbine power and load at specific periods. Second, based on the basic framework of receding horizon optimization, an intelligent genetic algorithm (GA) is applied to figure out the optimum solution in the predictive horizon for the complex non-linear coordination control model of microgrids. The optimum results of the GA are compared with the receding solution of mixed integer linear programming (MILP). The obtained results show that the method is a viable approach for energy coordinative optimization of microgrid systems for energy flow and reasonable schedule. The effectiveness and feasibility of the proposed method is verified by examples. Full article
(This article belongs to the Special Issue Microgrids)
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Open AccessArticle
A Study on the Variation of Heating and Cooling Load According to the Use of Horizontal Shading and Venetian Blinds in Office Buildings in Korea
Energies 2015, 8(2), 1487-1504; https://doi.org/10.3390/en8021487
Received: 23 November 2014 / Accepted: 4 February 2015 / Published: 16 February 2015
Cited by 12 | Viewed by 2594 | PDF Full-text (1638 KB) | HTML Full-text | XML Full-text
Abstract
The construction industry has made considerable energy-saving efforts in buildings, and studies of energy-savings are ongoing. Shading is used to control the solar radiation transferred through windows. Many studies have examined the position and type of shading in different countries, but few have [...] Read more.
The construction industry has made considerable energy-saving efforts in buildings, and studies of energy-savings are ongoing. Shading is used to control the solar radiation transferred through windows. Many studies have examined the position and type of shading in different countries, but few have investigated the effects of shading installation in Korea. In this study, the case of the shading installation according to the standard of Korea, and variations of the heating and cooling load in the unit area on the performance of the windows were examined. This study compared the variations of the heating and cooling load in the case of horizontal shading and the changing position of venetian blinds. This study confirmed that horizontal shading longer than the standard length in Korea saved a maximum of 13% energy consumption. This study confirmed the point of change of energy consumption by the Solar Heat Gain Coefficient (SHGC) variations. The exterior venetian blinds and those between glazing were unaffected by the SHGC. On the other hand, in the case of a south façade, the interior venetian blinds resulted in 24% higher energy consumption than the installation of horizontal shading in case of Window to Wall Ratio (WWR): 80%, U-value: 2.1 and SHGC: 0.4. Full article
(This article belongs to the Special Issue Energy Policy and Climate Change) Printed Edition available
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Open AccessArticle
Effects of Disruption Risks on Biorefinery Location Design
Energies 2015, 8(2), 1468-1486; https://doi.org/10.3390/en8021468
Received: 27 September 2014 / Accepted: 27 January 2015 / Published: 13 February 2015
Cited by 19 | Viewed by 2557 | PDF Full-text (617 KB) | HTML Full-text | XML Full-text
Abstract
While ever-growing bio-ethanol production poses considerable challenges to the bioenergy supply chain, the risk of refinery operation disruptions further compromises the efficiency and reliability of the energy supply system. This paper applies discrete and continuous reliable facility location models to the design of [...] Read more.
While ever-growing bio-ethanol production poses considerable challenges to the bioenergy supply chain, the risk of refinery operation disruptions further compromises the efficiency and reliability of the energy supply system. This paper applies discrete and continuous reliable facility location models to the design of reliable bio-ethanol supply chains so that the system can hedge against potential operational disruptions. The discrete model is shown to be suitable for obtaining the exact optimality for small or moderate instances, while the continuous model has superior computational tractability for large-scale applications. The impacts of both site-independent and dependent disruptions (i.e., due to flooding) are analyzed in empirical case study for the State of Illinois (one of the main biomass supply states in the U.S.). The reliable solution is compared with a deterministic solution under the same setting. It is found that refinery disruptions, especially those site-dependent ones, affect both optimal refinery deployment and the supply chain cost. Sensitivity analysis is also conducted to show how refinery failure probability and fixed cost (for building biorefineries) affect optimal supply chain configuration and the total expected system cost. Full article
(This article belongs to the Special Issue Biomass Resource Efficiency for the Biobased Industries)
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Open AccessArticle
Monetization of External Costs Using Lifecycle Analysis—A Comparative Case Study of Coal-Fired and Biomass Power Plants in Northeast China
Energies 2015, 8(2), 1440-1467; https://doi.org/10.3390/en8021440
Received: 23 December 2014 / Revised: 29 January 2015 / Accepted: 4 February 2015 / Published: 13 February 2015
Cited by 12 | Viewed by 3484 | PDF Full-text (1751 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the structures of external costs are built in line with coal-fired and biomass power plant life cycle activities in Northeast China. The external cost of coal-fired and biomass power plants was compared, using the lifecycle approach. In addition, the external [...] Read more.
In this study, the structures of external costs are built in line with coal-fired and biomass power plant life cycle activities in Northeast China. The external cost of coal-fired and biomass power plants was compared, using the lifecycle approach. In addition, the external costs of a biomass power plant are calculated for each stage for comparison with those of a coal-fired power plant. The results highlight that the external costs of a coal-fired plant are 0.072 US $/kWh, which are much higher than that of a biomass power plant, 0.00012 US$/kWh. The external cost of coal-fired power generation is as much as 90% of the current price of electricity generated by coal, while the external cost of a biomass power plant is 1/1000 of the current price of electricity generated by biomass. In addition, for a biomass power plant, the external cost associated with SO2, NOX, and PM2.5 are particularly lower than those of a coal-fired power plant. The prospect of establishing precise estimations for external cost mechanisms and sustainable energy policies is discussed to show a possible direction for future energy schemes in China. The paper has significant value for supporting the biomass power industry and taxing or regulating coal-fired power industry to optimize the energy structure in China. Full article
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Open AccessArticle
Impact of the Taxes on Used Nuclear Fuel on the Fuel Cycle Economics in Spain
Energies 2015, 8(2), 1426-1439; https://doi.org/10.3390/en8021426
Received: 7 November 2014 / Revised: 28 January 2015 / Accepted: 6 February 2015 / Published: 13 February 2015
Cited by 3 | Viewed by 2387 | PDF Full-text (327 KB) | HTML Full-text | XML Full-text
Abstract
In 2013, the Spanish government created two new taxes on used nuclear fuel. This article aims to present the results of an economic study carried out to compare the costs of long-term storage of used nuclear fuel –open cycle strategy–, with [...] Read more.
In 2013, the Spanish government created two new taxes on used nuclear fuel. This article aims to present the results of an economic study carried out to compare the costs of long-term storage of used nuclear fuel –open cycle strategy–, with the cost of the strategy of reprocessing and recycling used fuel– closed cycle strategy– taking into account the impact of the new taxes on the global cost of the fuel cycle. The results show that the costs of open-cycle and closed-cycle spent fuel management, evaluated in Spain after the introduction of the taxes, are sufficiently similar (within the bounds of uncertainty), that the choice between both is predicated on other than purely economic criteria. Full article
(This article belongs to the Special Issue Advances in Nuclear Reactor and Fuel Cycle Technologies)
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Open AccessArticle
Tuning of the PI Controller Parameters of a PMSG Wind Turbine to Improve Control Performance under Various Wind Speeds
Energies 2015, 8(2), 1406-1425; https://doi.org/10.3390/en8021406
Received: 2 January 2015 / Accepted: 2 February 2015 / Published: 13 February 2015
Cited by 17 | Viewed by 3917 | PDF Full-text (663 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a method to seek the PI controller parameters of a PMSG wind turbine to improve control performance. Since operating conditions vary with the wind speed, therefore the PI controller parameters should be determined as a function of the wind speed. [...] Read more.
This paper presents a method to seek the PI controller parameters of a PMSG wind turbine to improve control performance. Since operating conditions vary with the wind speed, therefore the PI controller parameters should be determined as a function of the wind speed. Small-signal modeling of a PMSG WT is implemented to analyze the stability under various operating conditions and with eigenvalues obtained from the small-signal model of the PMSG WT, which are coordinated by adjusting the PI controller parameters. The parameters to be tuned are chosen by investigating participation factors of state variables, which simplifies the problem by reducing the number of parameters to be tuned. The process of adjusting these PI controller parameters is carried out using particle swarm optimization (PSO). To characterize the improvements in the control method due to the PSO method of tuning the PI controller parameters, the PMSG WT is modeled using the MATLAB/SimPowerSystems libraries with the obtained PI controller parameters. Full article
(This article belongs to the collection Wind Turbines) Printed Edition available
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Open AccessArticle
Harmonic Injection-Based Power Fluctuation Control of Three-Phase PV Systems under Unbalanced Grid Voltage Conditions
Energies 2015, 8(2), 1390-1405; https://doi.org/10.3390/en8021390
Received: 7 November 2014 / Accepted: 5 January 2015 / Published: 11 February 2015
Cited by 2 | Viewed by 2601 | PDF Full-text (661 KB) | HTML Full-text | XML Full-text
Abstract
Unbalanced voltage will inevitably cause power and DC voltage fluctuations in a three-phase PV system. The deterioration of power quality will do great harm to the PV panels and the loads, so it is necessary to suppress the power fluctuations. This paper further [...] Read more.
Unbalanced voltage will inevitably cause power and DC voltage fluctuations in a three-phase PV system. The deterioration of power quality will do great harm to the PV panels and the loads, so it is necessary to suppress the power fluctuations. This paper further explores the coefficients control strategy of PV converters under unbalanced voltage conditions, aiming to suppress power fluctuations by controlling the injection of some specific orders of current harmonics into the grid. In order to achieve this, the current reference of the PV inverter has been changed by bringing in two control coefficients, and the expression of each order of the current harmonics has been deduced. Based on the standards of PV systems, the regions from which the coefficients can be selected are determined. Then, by tuning these coefficients in the feasible regions, the output parameters (power fluctuation, current THD and odd harmonics) can be controlled precisely. The model of this method is built and simulated in PSCAD/EMTDC, and as a result, it is shown that the power fluctuations can be restricted according to different power quality requirements. Full article
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Open AccessArticle
A Reflex Charger with ZVS and Non-Dissipative Cells for Photovoltaic Energy Conversion
Energies 2015, 8(2), 1373-1389; https://doi.org/10.3390/en8021373
Received: 30 October 2014 / Revised: 9 December 2014 / Accepted: 22 January 2015 / Published: 11 February 2015
Cited by 4 | Viewed by 2539 | PDF Full-text (1013 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a reflex charger with zero-voltage-switching (ZVS) and non-dissipative cells for photovoltaic (PV) energy conversion is presented. The proposed reflex charger has the following advantages: (1) A ZVS cell is incorporated to reduce the switching losses of the main and auxiliary [...] Read more.
In this paper, a reflex charger with zero-voltage-switching (ZVS) and non-dissipative cells for photovoltaic (PV) energy conversion is presented. The proposed reflex charger has the following advantages: (1) A ZVS cell is incorporated to reduce the switching losses of the main and auxiliary switches. Therefore, the conversion efficiency of the proposed reflex charger can be improved significantly; (2) A non-dissipative charging/discharging reflex cell is used to increase charging efficiency and extend lifecycle of battery. Finally, a prototype reflex charger with ZVS and non-dissipative cells is built and implemented. Experimental results are presented to verify the performance and the feasibility of the proposed reflex charger for PV energy conversion. Full article
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Open AccessArticle
Simulating Dynamic Stall Effects for Vertical Axis Wind Turbines Applying a Double Multiple Streamtube Model
Energies 2015, 8(2), 1353-1372; https://doi.org/10.3390/en8021353
Received: 21 December 2014 / Accepted: 21 January 2015 / Published: 11 February 2015
Cited by 17 | Viewed by 2744 | PDF Full-text (315 KB) | HTML Full-text | XML Full-text
Abstract
The complex unsteady aerodynamics of vertical axis wind turbines (VAWT) poses significant challenges to the simulation tools. Dynamic stall is one of the phenomena associated with the unsteady conditions for VAWTs, and it is in the focus of the study. Two dynamic stall [...] Read more.
The complex unsteady aerodynamics of vertical axis wind turbines (VAWT) poses significant challenges to the simulation tools. Dynamic stall is one of the phenomena associated with the unsteady conditions for VAWTs, and it is in the focus of the study. Two dynamic stall models are compared: the widely-used Gormont model and a Leishman–Beddoes-type model. The models are included in a double multiple streamtube model. The effects of flow curvature and flow expansion are also considered. The model results are assessed against the measured data on a Darrieus turbine with curved blades. To study the dynamic stall effects, the comparison of force coefficients between the simulations and experiments is done at low tip speed ratios. Simulations show that the Leishman–Beddoes model outperforms the Gormont model for all tested conditions. Full article
(This article belongs to the collection Wind Turbines) Printed Edition available
Open AccessArticle
Lifecycle CO2 Reduction by Implementing Double Window Casement Systems in Residential Units in Korea
Energies 2015, 8(2), 1336-1352; https://doi.org/10.3390/en8021336
Received: 10 October 2014 / Accepted: 3 February 2015 / Published: 10 February 2015
Viewed by 2033 | PDF Full-text (1527 KB) | HTML Full-text | XML Full-text
Abstract
This study investigated lifecycle CO2 (LCCO2) emission reductions through application of double-window casement systems (DWCS) in residential units in Korea, compared with conventional single windows (SWs). The DWCS is a double window system that is energy-efficient, reducing energy consumption during [...] Read more.
This study investigated lifecycle CO2 (LCCO2) emission reductions through application of double-window casement systems (DWCS) in residential units in Korea, compared with conventional single windows (SWs). The DWCS is a double window system that is energy-efficient, reducing energy consumption during operation. However, this system incorporates increased embodied CO2 emissions. We evaluated LCCO2 reductions associated with use of the DWCS by calculating CO2 emissions during space conditioning as well as the embodied CO2 emissions of the DWCS. The results showed that use of DWCS in a residential unit during the cooling season had 26.2 and 27.4 t CO2 fewer emissions than SWs in the natural ventilation and minimum ventilation modes, respectively. Although implementation of DWCS is expected to substantially reduce LCCO2 emissions, the large embodied CO2 emissions of the aluminum frame reduce the benefits of the DWCS. Full article
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Open AccessArticle
On the Scale-up of Gas-Hydrate-Forming Reactors: The Case of Gas-Dispersion-Type Reactors
Energies 2015, 8(2), 1317-1335; https://doi.org/10.3390/en8021317
Received: 25 December 2014 / Accepted: 24 January 2015 / Published: 10 February 2015
Cited by 7 | Viewed by 2617 | PDF Full-text (655 KB) | HTML Full-text | XML Full-text
Abstract
For establishing hydrate-based technologies for natural-gas storage/transport, CO2 capture from industrial flue gases, etc., we need appropriate guidelines for the scale-up of hydrate production/processing equipment from laboratory scales to industrial scales. This paper aims to provide technical remarks on the scale-up [...] Read more.
For establishing hydrate-based technologies for natural-gas storage/transport, CO2 capture from industrial flue gases, etc., we need appropriate guidelines for the scale-up of hydrate production/processing equipment from laboratory scales to industrial scales. This paper aims to provide technical remarks on the scale-up of hydrate-forming reactors, the central components of hydrate production/processing equipment, particularly focusing on such a reactor design that hydrate-forming gas is dispersed in an aqueous phase which is either stirred in a tank or forced to flow through a tube. Based on the principles of classical fluid mechanics and heat-transfer analysis, the paper derives semi-empirical formulas that show how the capacity for heat discharge from each reactor and the power for operating the reactor are required to change with an increase in its size. Consequently, it is concluded that the stirred-tank design is unfavorable for significant scale-up and that the scale-up of tubular reactors should be made without significantly increasing the in-tube flow velocity. Full article
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Open AccessArticle
A Novel Ground Fault Non-Directional Selective Protection Method for Ungrounded Distribution Networks
Energies 2015, 8(2), 1291-1316; https://doi.org/10.3390/en8021291
Received: 5 November 2014 / Revised: 23 December 2014 / Accepted: 20 January 2015 / Published: 9 February 2015
Cited by 4 | Viewed by 2719 | PDF Full-text (2158 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a new selective and non-directional protection method to detect ground faults in neutral isolated power systems. The new proposed method is based on the comparison of the rms value of the residual current of all the lines connected to a [...] Read more.
This paper presents a new selective and non-directional protection method to detect ground faults in neutral isolated power systems. The new proposed method is based on the comparison of the rms value of the residual current of all the lines connected to a bus, and it is able to determine the line with ground defect. Additionally, this method can be used for the protection of secondary substation. This protection method avoids the unwanted trips produced by wrong settings or wiring errors, which sometimes occur in the existing directional ground fault protections. This new method has been validated through computer simulations and experimental laboratory tests. Full article
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Open AccessArticle
Single DC-Sourced 9-level DC/AC Topology as Transformerless Power Interface for Renewable Sources
Energies 2015, 8(2), 1273-1290; https://doi.org/10.3390/en8021273
Received: 14 December 2014 / Accepted: 23 January 2015 / Published: 5 February 2015
Cited by 3 | Viewed by 2841 | PDF Full-text (3832 KB) | HTML Full-text | XML Full-text
Abstract
This paper introduces an advanced transformerless multilevel hybrid-conversion topology intended for the interconnection of renewable DC sources at small-scale. The most important contribution presented in this paper is the generation of two isolated DC sources from a single DC source without the use [...] Read more.
This paper introduces an advanced transformerless multilevel hybrid-conversion topology intended for the interconnection of renewable DC sources at small-scale. The most important contribution presented in this paper is the generation of two isolated DC sources from a single DC source without the use of any type of transformer. The DC sources feed a nine-level DC/AC hybrid cascade multilevel converter. This advanced topology is achieved by redesigning the conventional DC/DC Buck topology, attached to the multilevel converter, and embedding a suitable switching strategy along with a Field Programmable Gate Array (FPGA)-based control. The advantages of the proposed structure, when compared to other proposals in the literature, are higher efficiency, reduced number of power switches, and high power density derived of transformerless characteristic. As a way to highlight differences and advantages of this converter over other options recently available in the literature, this paper carries out a quantitative evaluation comparing the number of voltage levels and the number of elements involved in the structure of DC/AC multilevel converters. The mathematical model and control strategy of the converter are explained and analyzed by means of simulations. Finally experimental results, obtained from a laboratory-scale prototype, show the performance of the system and demonstrate its relative advantages. Full article
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Open AccessArticle
Coordinated Charging Strategy for Electric Taxis in Temporal and Spatial Scale
Energies 2015, 8(2), 1256-1272; https://doi.org/10.3390/en8021256
Received: 5 December 2014 / Revised: 20 January 2015 / Accepted: 29 January 2015 / Published: 5 February 2015
Cited by 11 | Viewed by 2466 | PDF Full-text (723 KB) | HTML Full-text | XML Full-text
Abstract
Currently, electric taxis have been deployed in many cities of China. However, the charging unbalance in both temporal and spatial scale has become a rising problem, which leads to low charging efficiency or charging congestion in different stations or time periods. This paper [...] Read more.
Currently, electric taxis have been deployed in many cities of China. However, the charging unbalance in both temporal and spatial scale has become a rising problem, which leads to low charging efficiency or charging congestion in different stations or time periods. This paper presents a multi-objective coordinated charging strategy for electric taxis in the temporal and spatial scale. That is, the objectives are maximizing the utilization efficiency of charging facilities, minimizing the load unbalance of the regional power system and minimizing the customers’ cost. Besides, the basic configuration of a charging station and operation rules of electric taxis would be the constraints. To tackle this multi-objective optimizing problems, a fuzzy mathematical method has been utilized to transfer the multi-objective optimization to a single optimization issue, and furthermore, the Improved Particle Swarm Optimization (IPSO) Algorithm has been used to solve the optimization problem. Moreover, simulation cases are carried out, Case 1 is the original charging procedure, and Cases 2 and 3 are the temporal and spatial scale optimized separately, followed with Case 4, the combined coordinated charging. The simulation shows the significant improvement in charging facilities efficiency and users’ benefits, as well as the better dispatching of electric taxis’ charging loads. Full article
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Open AccessArticle
Experimental Investigation into the Combustion Characteristics of Propane Hydrates in Porous Media
Energies 2015, 8(2), 1242-1255; https://doi.org/10.3390/en8021242
Received: 11 November 2014 / Revised: 26 December 2014 / Accepted: 26 January 2015 / Published: 5 February 2015
Cited by 8 | Viewed by 2370 | PDF Full-text (1233 KB) | HTML Full-text | XML Full-text
Abstract
The combustion characteristics of both pure propane hydrates and the mixtures of hydrates and quartz sands were investigated by combustion experiments. The flame propagation, flame appearance, burning time and temperature in different hydrate layers were studied. For pure propane hydrate combustion, the initial [...] Read more.
The combustion characteristics of both pure propane hydrates and the mixtures of hydrates and quartz sands were investigated by combustion experiments. The flame propagation, flame appearance, burning time and temperature in different hydrate layers were studied. For pure propane hydrate combustion, the initial flame falls in the “premixed” category. The flame propagates very rapidly, mainly as a result of burnt gas expansion. The flame finally self-extinguishes with some proportion of hydrates remaining unburned. For the hydrate-sand mixture combustion, the flame takes the form of many tiny discontinuous flames appearing and disappearing at different locations. The burn lasts for a much shorter amount of time than pure hydrate combustion. High porosity and high hydrate saturation is beneficial to the combustion. The hydrate combustion is the combustion of propane gas resulting from the dissociation of the hydrates. In both combustion test scenarios, the hydrate-dissociated water plays a key role in the fire extinction, because it is the main resistance that restrains the heat transfer from the flame to the hydrates and that prevents the hydrate-dissociated gas from releasing into the combustion zone. Full article
(This article belongs to the Special Issue Coastal Ocean Natural Gas Hydrate 2014)
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Open AccessArticle
Reliability Evaluation of a Distribution Network with Microgrid Based on a Combined Power Generation System
Energies 2015, 8(2), 1216-1241; https://doi.org/10.3390/en8021216
Received: 1 November 2014 / Revised: 12 January 2015 / Accepted: 20 January 2015 / Published: 4 February 2015
Cited by 8 | Viewed by 3229 | PDF Full-text (1393 KB) | HTML Full-text | XML Full-text
Abstract
Distributed generation (DG), battery storage (BS) and electric vehicles (EVs) in a microgrid constitute the combined power generation system (CPGS). A CPGS can be applied to achieve a reliable evaluation of a distribution network with microgrids. To model charging load and discharging capacity, [...] Read more.
Distributed generation (DG), battery storage (BS) and electric vehicles (EVs) in a microgrid constitute the combined power generation system (CPGS). A CPGS can be applied to achieve a reliable evaluation of a distribution network with microgrids. To model charging load and discharging capacity, respectively, the EVs in a CPGS can be divided into regular EVs and ruleless EVs, according to their driving behavior. Based on statistical data of gasoline-fueled vehicles and the probability distribution of charging start instant and charging time, a statistical model can be built to describe the charging load and discharging capacity of ruleless EVs. The charge and discharge curves of regular EVs can also be drawn on the basis of a daily dispatch table. The CPGS takes the charge and discharge curves of EVs, daily load and DG power generation into consideration to calculate its power supply time during islanding. Combined with fault duration, the power supply time during islanding will be used to analyze and determine the interruption times and interruption duration of loads in islands. Then the Sequential Monte Carlo method is applied to complete the reliability evaluation of the distribution system. The RBTS Bus 4 test system is utilized to illustrate the proposed technique. The effects on the system reliability of BS capacity and V2G technology, driving behavior, recharging mode and penetration of EVs are all investigated. Full article
(This article belongs to the Special Issue Microgrids)
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Open AccessArticle
Numerical Evaluation of the Use of Aluminum Particles for Enhancing Solid Rocket Motor Combustion Stability
Energies 2015, 8(2), 1195-1215; https://doi.org/10.3390/en8021195
Received: 24 November 2014 / Revised: 4 January 2015 / Accepted: 27 January 2015 / Published: 3 February 2015
Cited by 5 | Viewed by 2031 | PDF Full-text (885 KB) | HTML Full-text | XML Full-text
Abstract
The ability to predict the expected internal behaviour of a given solid-propellant rocket motor under transient conditions is important. Research towards predicting and quantifying undesirable transient axial combustion instability symptoms typically necessitates a comprehensive numerical model for internal ballistic simulation under dynamic flow [...] Read more.
The ability to predict the expected internal behaviour of a given solid-propellant rocket motor under transient conditions is important. Research towards predicting and quantifying undesirable transient axial combustion instability symptoms typically necessitates a comprehensive numerical model for internal ballistic simulation under dynamic flow and combustion conditions. On the mitigation side, one in practice sees the use of inert or reactive particles for the suppression of pressure wave development in the motor chamber flow. With the focus of the present study placed on reactive particles, a numerical internal ballistic model incorporating relevant elements, such as a transient, frequency-dependent combustion response to axial pressure wave activity above the burning propellant surface, is applied to the investigation of using aluminum particles within the central internal flow (particles whose surfaces nominally regress with time, as a function of current particle size, as they move downstream) as a means of suppressing instability-related symptoms in a cylindrical-grain motor. The results of this investigation reveal that the loading percentage and starting size of the aluminum particles have a significant influence on reducing the resulting transient pressure wave magnitude. Full article
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Open AccessArticle
Energy Management of a Hybrid AC–DC Micro-Grid Based on a Battery Testing System
Energies 2015, 8(2), 1181-1194; https://doi.org/10.3390/en8021181
Received: 3 December 2014 / Revised: 14 January 2015 / Accepted: 28 January 2015 / Published: 3 February 2015
Cited by 10 | Viewed by 3280 | PDF Full-text (3479 KB) | HTML Full-text | XML Full-text
Abstract
Energy Recovery Battery Testing Systems (ERBTS) plays an important role in battery manufacture. The conventional ERBTS configuration contains a fundamental transformer, and a bidirectional Direct Current (DC)–DC and Alternating Current (AC)–DC converter. All ERBTS are connected in parallel, thus constituting a special and [...] Read more.
Energy Recovery Battery Testing Systems (ERBTS) plays an important role in battery manufacture. The conventional ERBTS configuration contains a fundamental transformer, and a bidirectional Direct Current (DC)–DC and Alternating Current (AC)–DC converter. All ERBTS are connected in parallel, thus constituting a special and complicated AC micro-grid system. Aiming at addressing their low energy recovery efficiency, complex grid-connected control algorithm issues for islanded detection, and complicated power circuit topology issues, a hierarchical DC-link voltage hybrid AC–DC micro-grid that contains composite energy storing devices is proposed. Moreover, an energy management optimal scheme for the proposed scheme is put forward. The system configuration of the proposed scheme is described in detail. Compared to the conventional scheme, the proposed scheme has the merits of simplified power circuit topology, no need for phase synchronous control, and much higher energy recovery efficiency and reliability. The validity and effectiveness of the proposed technique is verified through numerous experimental results. Full article
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Open AccessArticle
Hot Water Pretreatment of Boreal Aspen Woodchips in a Pilot Scale Digester
Energies 2015, 8(2), 1166-1180; https://doi.org/10.3390/en8021166
Received: 26 November 2014 / Revised: 23 January 2015 / Accepted: 27 January 2015 / Published: 3 February 2015
Cited by 6 | Viewed by 2069 | PDF Full-text (891 KB) | HTML Full-text | XML Full-text
Abstract
Hot water extraction of aspen woodchips was treated at about 160 °C for 2 h with a liquor-to-solid ratio of 4.76:1 in a 1.84 m3 batch reactor with external liquor circulation. Both five-carbon and six-carbon sugars are obtained in the extraction liquor. [...] Read more.
Hot water extraction of aspen woodchips was treated at about 160 °C for 2 h with a liquor-to-solid ratio of 4.76:1 in a 1.84 m3 batch reactor with external liquor circulation. Both five-carbon and six-carbon sugars are obtained in the extraction liquor. Xylose and xylooligomers are the main five-carbon sugar in the hot water extract, which reached a maximum concentration of 0.016 mol/L, and 0.018 mol/L, respectively. Minor monosaccharides including galactose, mannose, rhamnose, glucose, and arabinose are also obtained during the hot water extraction. Rhamnose is the main six-carbon sugar in the extraction liquor, which has a maximum concentration of 0.0042 mol/L. The variations of acetyl groups and formic acid are investigated due to their catalytic effect on the extraction reactions. Zeroth-order kinetics models are found to be adequate in describing the dissolved solids, acids, xylose, and xylooligomers. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle
Fatty Acid Characteristics of Isochrysis galbana Lipids Extracted Using a Microwave-Assisted Method
Energies 2015, 8(2), 1154-1165; https://doi.org/10.3390/en8021154
Received: 14 November 2014 / Revised: 24 December 2014 / Accepted: 22 January 2015 / Published: 3 February 2015
Cited by 3 | Viewed by 2503 | PDF Full-text (442 KB) | HTML Full-text | XML Full-text
Abstract
Lipids were extracted from Isochrysis galbana using a microwave-assisted method accompanied by various types of organic solvents. The effects of organic solvent type and microwave input energy on the fatty acid characteristics of the extracted lipids and their biodiesel product were investigated. Variations [...] Read more.
Lipids were extracted from Isochrysis galbana using a microwave-assisted method accompanied by various types of organic solvents. The effects of organic solvent type and microwave input energy on the fatty acid characteristics of the extracted lipids and their biodiesel product were investigated. Variations in the characteristics of the lipids extracted using a combination of n-hexane and iso-propanol solvents in both emulsion and direct mixtures were also compared. The experimental results showed that greater quantities of Isochrysis galbana lipids, and fatty acid methyl esters transesterified from those lipids, were extracted when using microwave irradiation with an organic solvent mixture of n-hexane and isopropanol in a 2:1 volumetric ratio than when using either n-hexane or isopropanol as the sole solvent. A greater quantity of Isochrysis galbana lipids was extracted when an emulsion of isopropanol solvent evenly dispersed in the continuous phase of n-hexane solvent was used than when a direct mixture of the two solvents was used. In addition, the quantity of lipids extracted from the dried Isochrysis galbana powder with the assistance of microwave irradiation was 9.08 wt% greater than when using traditional Soxhlet extraction without microwave irradiation. Full article
(This article belongs to the Special Issue Algae Based Technologies)
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Open AccessArticle
A Physical Hybrid Artificial Neural Network for Short Term Forecasting of PV Plant Power Output
Energies 2015, 8(2), 1138-1153; https://doi.org/10.3390/en8021138
Received: 19 November 2014 / Revised: 22 December 2014 / Accepted: 23 January 2015 / Published: 3 February 2015
Cited by 43 | Viewed by 3415 | PDF Full-text (870 KB) | HTML Full-text | XML Full-text
Abstract
The main purpose of this work is to lead an assessment of the day ahead forecasting activity of the power production by photovoltaic plants. Forecasting methods can play a fundamental role in solving problems related to renewable energy source (RES) integration in smart [...] Read more.
The main purpose of this work is to lead an assessment of the day ahead forecasting activity of the power production by photovoltaic plants. Forecasting methods can play a fundamental role in solving problems related to renewable energy source (RES) integration in smart grids. Here a new hybrid method called Physical Hybrid Artificial Neural Network (PHANN) based on an Artificial Neural Network (ANN) and PV plant clear sky curves is proposed and compared with a standard ANN method. Furthermore, the accuracy of the two methods has been analyzed in order to better understand the intrinsic errors caused by the PHANN and to evaluate its potential in energy forecasting applications. Full article
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Open AccessArticle
Total Site Heat Integration Considering Pressure Drops
Energies 2015, 8(2), 1114-1137; https://doi.org/10.3390/en8021114
Received: 10 December 2014 / Accepted: 22 January 2015 / Published: 2 February 2015
Cited by 15 | Viewed by 3033 | PDF Full-text (915 KB) | HTML Full-text | XML Full-text
Abstract
Pressure drop is an important consideration in Total Site Heat Integration (TSHI). This is due to the typically large distances between the different plants and the flow across plant elevations and equipment, including heat exchangers. Failure to consider pressure drop during utility targeting [...] Read more.
Pressure drop is an important consideration in Total Site Heat Integration (TSHI). This is due to the typically large distances between the different plants and the flow across plant elevations and equipment, including heat exchangers. Failure to consider pressure drop during utility targeting and heat exchanger network (HEN) synthesis may, at best, lead to optimistic energy targets, and at worst, an inoperable system if the pumps or compressors cannot overcome the actual pressure drop. Most studies have addressed the pressure drop factor in terms of pumping cost, forbidden matches or allowable pressure drop constraints in the optimisation of HEN. This study looks at the implication of pressure drop in the context of a Total Site. The graphical Pinch-based TSHI methodology is extended to consider the pressure drop factor during the minimum energy requirement (MER) targeting stage. The improved methodology provides a more realistic estimation of the MER targets and valuable insights for the implementation of the TSHI design. In the case study, when pressure drop in the steam distribution networks is considered, the heating and cooling duties increase by 14.5% and 4.5%. Full article
(This article belongs to the Special Issue Energy Policy and Climate Change) Printed Edition available
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Open AccessArticle
Slagging and Fouling Characteristics of HRSG for Ferrosilicon Electric Furnaces
Energies 2015, 8(2), 1101-1113; https://doi.org/10.3390/en8021101
Received: 15 October 2014 / Accepted: 19 January 2015 / Published: 2 February 2015
Cited by 3 | Viewed by 2733 | PDF Full-text (994 KB) | HTML Full-text | XML Full-text
Abstract
The slagging and fouling characteristics of the heat recovery steam generator (HRSG) for ferrosilicon electric furnaces are discussed in this paper. Three ash samples were taken from the HRSG of a ferrosilicon furnace in Ningxia Province, China, which suffered from serious slagging and [...] Read more.
The slagging and fouling characteristics of the heat recovery steam generator (HRSG) for ferrosilicon electric furnaces are discussed in this paper. Three ash samples were taken from the HRSG of a ferrosilicon furnace in Ningxia Province, China, which suffered from serious slagging and fouling. X-ray fluorescence (XRF), X-ray powder diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the ash samples. The results show that low melting point salt Na2SO4 and composite salts Na (AlSi3O8) and 3K2SO4·CaSO4 deposit on the superheater tube walls in aerosol form and solidify to form the initial slag layer. With the continuous deposition of the low melting point compounds, more and more ash particles in the flue gas adhere to the slag surface to form a thicker slag. Low melting point composite salt NaO·Al2O3·SiO2 is absorbed on the evaporator tube walls in aerosol form. With the deposition of NaO·Al2O3·SiO2, more and more ash particles are absorbed to form the fouling. Since there is less space between pin-finned tubes, the large iron-rich slag particles are easily deposited on tube walls and fin surfaces, which is advantageous to the fouling process. There are large quantities of superfine ash particles in the flue gas that easily adhere to other particles or tube walls, which facilitates the slagging and fouling process. Full article
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Open AccessArticle
Optimal Real-Time Scheduling of Wind Integrated Power System Presented with Storage and Wind Forecast Uncertainties
Energies 2015, 8(2), 1080-1100; https://doi.org/10.3390/en8021080
Received: 17 September 2014 / Revised: 23 January 2015 / Accepted: 28 January 2015 / Published: 2 February 2015
Cited by 10 | Viewed by 2288 | PDF Full-text (611 KB) | HTML Full-text | XML Full-text
Abstract
The volatility of wind power poses great challenges to the operation of power systems. This paper deals with the economic dispatch problems presented by energy storage in wind integrated systems. A policy iteration algorithm for deriving the cost optimal policy of real-time scheduling [...] Read more.
The volatility of wind power poses great challenges to the operation of power systems. This paper deals with the economic dispatch problems presented by energy storage in wind integrated systems. A policy iteration algorithm for deriving the cost optimal policy of real-time scheduling is proposed, taking the effect of wind forecast uncertainties into account. First, energy loss and use of fast-ramping generation are selected as the performance metrics. Then, a policy iteration algorithm is developed using the Perturbed Markov decision process. This algorithm has a two-level optimization structure in which both the long-term and short-term behaviors of real-time scheduling policy are optimized. In addition, a unified optimal storage control strategy is presented. The feasibility of the proposed methodology is demonstrated via the wind power archive of Electric Reliability Council of Texas (ERCOT). Through comparative numerical experiments, both the performance of the policy iteration algorithm in the short-term and long-term are verified and the consistency, robustness, good convergence and high computational efficiency of the proposed algorithm are also corroborated. Full article
(This article belongs to the collection Smart Grid)
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Open AccessArticle
Impacts of the CAP 2014–2020 on the Agroenergy Sector in Tuscany, Italy
Energies 2015, 8(2), 1058-1079; https://doi.org/10.3390/en8021058
Received: 26 August 2014 / Revised: 18 November 2014 / Accepted: 20 January 2015 / Published: 2 February 2015
Cited by 9 | Viewed by 2057 | PDF Full-text (242 KB) | HTML Full-text | XML Full-text
Abstract
The agricultural sectors’ contribution to the provision of energy is a central issue in Horizon 2020 strategies and has shaped the public and research debates on the future of the bioeconomy. The common agricultural policy (CAP) has been one of the main drivers [...] Read more.
The agricultural sectors’ contribution to the provision of energy is a central issue in Horizon 2020 strategies and has shaped the public and research debates on the future of the bioeconomy. The common agricultural policy (CAP) has been one of the main drivers of farmers’ behavioural changes and represents the main agricultural policy instrument to address viability of rural areas and maintaining the profitability of the agricultural sector. To contribute to the ongoing policy debate towards CAP reform, this paper will provide an empirical model to simulate the impact of an alternative CAP mechanism on the provision of renewable energy. By applying a dynamic mathematical programming model, the paper tests the impact new policy measures will have on the provision of a second-generation of bio fuel crops that represent a relevant option for Tuscan farmers. Results show that CAP reform positively impacts the supply of energy crops mainly due to the introduction of greening payments, which allows an enlarging of crop diversification. Model results stress also the income stabilisation effects of energy production introduction at farm level, due to reduction of farm exposure to market prices fluctuations. Full article
(This article belongs to the Special Issue Renewable Energy for Agriculture)
Open AccessArticle
Thermal Model of a Dish Stirling Cavity-Receiver
Energies 2015, 8(2), 1042-1057; https://doi.org/10.3390/en8021042
Received: 8 September 2014 / Revised: 4 January 2015 / Accepted: 26 January 2015 / Published: 30 January 2015
Cited by 11 | Viewed by 2596 | PDF Full-text (1592 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a thermal model for a dish Stirling cavity based on the finite differences method. This model is a theoretical tool to optimize the cavity in terms of thermal efficiency. One of the main outcomes of this work is the evaluation [...] Read more.
This paper presents a thermal model for a dish Stirling cavity based on the finite differences method. This model is a theoretical tool to optimize the cavity in terms of thermal efficiency. One of the main outcomes of this work is the evaluation of radiative exchange using the radiosity method; for that purpose, the view factors of all surfaces involved have been accurately calculated. Moreover, this model enables the variation of the cavity and receiver dimensions and the materials to determine the optimal cavity design. The tool has been used to study the cavity optimization regarding geometry parameters and material properties. Receiver absorptivity has been identified as the most influential property of the materials. The optimal aperture height depends on the minimum focal space. Full article
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Open AccessArticle
Modeling the Distribution of Solar Radiation on a Two-Axis Tracking Plane for Photovoltaic Conversion
Energies 2015, 8(2), 1025-1041; https://doi.org/10.3390/en8021025
Received: 3 November 2014 / Accepted: 16 January 2015 / Published: 30 January 2015
Cited by 15 | Viewed by 1993 | PDF Full-text (919 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The paper presents selected isotropic and anisotropic mathematical models to calculate the distribution of solar radiation on the photovoltaic module plane with any spatial orientation. A comparison of solar radiation models for Poland is based on measured data and received from the Institute [...] Read more.
The paper presents selected isotropic and anisotropic mathematical models to calculate the distribution of solar radiation on the photovoltaic module plane with any spatial orientation. A comparison of solar radiation models for Poland is based on measured data and received from the Institute of Meteorology and Water Management. Power density of solar radiation for different angular positions, especially for representative days of each month, was calculated. Based on the statistical analysis of the percentage root-mean-square error (RMSE%), mean-bias error (MBE%) and the Pearson correlation coefficient of an individual mathematical model, our own correction factor for diffuse radiation was proposed. A modified Liu-Jordan model was compared with six common mathematical models showing better agreement of measured and calculated values of solar radiation density. The presented analysis explains which mathematical model is the most suitable for central Poland (Poznań, 52°25’ N, 16°56’ E) and shows the validity of applying the modified model to improve the accuracy of determination of the radiation power density for a given elevation and azimuth angle using values for a horizontal plane. Full article
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Open AccessArticle
Thermoeconomic Optimization of a Renewable Polygeneration System Serving a Small Isolated Community
Energies 2015, 8(2), 995-1024; https://doi.org/10.3390/en8020995
Received: 28 November 2014 / Accepted: 20 January 2015 / Published: 30 January 2015
Cited by 16 | Viewed by 2365 | PDF Full-text (1169 KB) | HTML Full-text | XML Full-text
Abstract
During the last years, special attention has been paid to renewable polygeneration technologies, able of simultaneously producing thermal, cooling, electrical energy and desalinated water from seawater. This paper focuses on an innovative polygeneration system driven by renewable energy sources, including the following technologies: [...] Read more.
During the last years, special attention has been paid to renewable polygeneration technologies, able of simultaneously producing thermal, cooling, electrical energy and desalinated water from seawater. This paper focuses on an innovative polygeneration system driven by renewable energy sources, including the following technologies: hybrid photovoltaic/thermal collectors, concentrating parabolic trough (CPVT), a biomass heater, a single-stage absorption chiller and a multiple-effect distillation desalination system. The system is designed to cover the base load of an isolated small community. In previous papers, the dynamic simulation model about plant operation is discussed. In this paper, a detailed exergy, economic and environmental analysis of the plant is presented. In addition, the plant was optimized using different objective functions, applying the Design of Experiment (DoE) methodology which evaluates the sensitivity of the different objective functions with respect to the selected design parameters. The results show that an increase of the storage volume is generally negative, whereas increasing the solar field area involves an increase of the exergy destruction rate, but also an improvement of the CPVT exergy output provided; the final result is an increase of both the exergy efficiency and the economic profitability of the polygeneration system. Full article
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Open AccessArticle
A Study to Improve the Quality of Street Lighting in Spain
Energies 2015, 8(2), 976-994; https://doi.org/10.3390/en8020976
Received: 24 October 2014 / Revised: 11 December 2014 / Accepted: 21 January 2015 / Published: 29 January 2015
Cited by 7 | Viewed by 2941 | PDF Full-text (601 KB) | HTML Full-text | XML Full-text
Abstract
Street lighting has a big impact on the energy consumption of Spanish municipalities. To decrease this consumption, the Spanish government has developed two different regulations to improve energy savings and efficiency, and consequently, reduce greenhouse-effect gas emissions. However, after these efforts, they have [...] Read more.
Street lighting has a big impact on the energy consumption of Spanish municipalities. To decrease this consumption, the Spanish government has developed two different regulations to improve energy savings and efficiency, and consequently, reduce greenhouse-effect gas emissions. However, after these efforts, they have not obtained the expected results. To improve the effectiveness of these regulations and therefore to optimize energy consumption, a study has been done to analyze the different devices which influence energy consumption with the intention of better understanding their behavior and performance. The devices analyzed were lamps, ballasts, street lamp globes, control systems and dimmable lighting systems. To improve their performance, they have been analyzed from three points of view: changes in technology, use patterns and standards. Thanks to this study, some aspects have been found that could be taken into account if we really wanted to use energy efficiently. Full article
(This article belongs to the Special Issue Energy Policy and Climate Change) Printed Edition available
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