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Energies, Volume 8, Issue 3 (March 2015), Pages 1547-2294

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Open AccessEditorial Energies Best Paper Awards for 2015
Energies 2015, 8(3), 2292-2294; https://doi.org/10.3390/en8032292
Received: 12 March 2015 / Accepted: 13 March 2015 / Published: 23 March 2015
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Abstract
We are pleased to announce the Energies Best Papers awards for 2015. Energies is an open access journal of energy-related scientific research, technology development, and policy and management studies. It publishes reviews, regular research articles, and communications in a number of fields related
[...] Read more.
We are pleased to announce the Energies Best Papers awards for 2015. Energies is an open access journal of energy-related scientific research, technology development, and policy and management studies. It publishes reviews, regular research articles, and communications in a number of fields related to the procurement, conversion and final uses of energy.[...] Full article
Open AccessCorrection Menéndez, R.P.; Martínez, J.A.; Prieto, M.J.; Barcia, L.A.; Sánchez, J.M.M. A Novel Modeling of Molten-Salt Heat Storage Systems in Thermal Solar Power Plants. Energies 2014, 7, 6721–6740
Energies 2015, 8(3), 2290-2291; https://doi.org/10.3390/en8032290
Received: 19 January 2015 / Revised: 6 February 2015 / Accepted: 11 February 2015 / Published: 23 March 2015
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Abstract
The authors wish to make the following corrections to this paper [1]: Figure 8 on page 6730 is replaced as follows:[...] Full article
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Open AccessArticle Optimal Dispatch Strategy of a Virtual Power Plant Containing Battery Switch Stations in a Unified Electricity Market
Energies 2015, 8(3), 2268-2289; https://doi.org/10.3390/en8032268
Received: 12 October 2014 / Revised: 28 January 2015 / Accepted: 16 March 2015 / Published: 23 March 2015
Cited by 12 | PDF Full-text (928 KB) | HTML Full-text | XML Full-text
Abstract
A virtual power plant takes advantage of interactive communication and energy management systems to optimize and coordinate the dispatch of distributed generation, interruptible loads, energy storage systems and battery switch stations, so as to integrate them as an entity to exchange energy with
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A virtual power plant takes advantage of interactive communication and energy management systems to optimize and coordinate the dispatch of distributed generation, interruptible loads, energy storage systems and battery switch stations, so as to integrate them as an entity to exchange energy with the power market. This paper studies the optimal dispatch strategy of a virtual power plant, based on a unified electricity market combining day-ahead trading with real-time trading. The operation models of interruptible loads, energy storage systems and battery switch stations are specifically described in the paper. The virtual power plant applies an optimal dispatch strategy to earn the maximal expected profit under some fluctuating parameters, including market price, retail price and load demand. The presented model is a nonlinear mixed-integer programming with inter-temporal constraints and is solved by the fruit fly algorithm. Full article
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Open AccessArticle Modeling Innovative Power Take-Off Based on Double-Acting Hydraulic Cylinders Array for Wave Energy Conversion
Energies 2015, 8(3), 2230-2267; https://doi.org/10.3390/en8032230
Received: 28 January 2015 / Revised: 27 February 2015 / Accepted: 2 March 2015 / Published: 20 March 2015
Cited by 3 | PDF Full-text (5232 KB) | HTML Full-text | XML Full-text
Abstract
One of the key systems of a Wave Energy Converter for extraction of wave energy is the Power Take-Off (PTO) device. This device transforms the mechanical energy of a moving body into electrical energy. This paper describes the model of an innovative PTO
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One of the key systems of a Wave Energy Converter for extraction of wave energy is the Power Take-Off (PTO) device. This device transforms the mechanical energy of a moving body into electrical energy. This paper describes the model of an innovative PTO based on independently activated double-acting hydraulic cylinders array. The model has been developed using a simulation tool, based on a port-based approach to model hydraulics systems. The components and subsystems used in the model have been parameterized as real components and their values experimentally obtained from an existing prototype. In fact, the model takes into account most of the hydraulic losses of each component. The simulations show the flexibility to apply different restraining torques to the input movement depending on the geometrical configuration and the hydraulic cylinders on duty, easily modified by a control law. The combination of these two actions allows suitable flexibility to adapt the device to different sea states whilst optimizing the energy extraction. The model has been validated using a real test bench showing good correlations between simulation and experimental tests. Full article
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Open AccessArticle Modelling of a Solid Oxide Fuel Cell CHP System Coupled with a Hot Water Storage Tank for a Single Household
Energies 2015, 8(3), 2211-2229; https://doi.org/10.3390/en8032211
Received: 3 November 2014 / Revised: 4 March 2015 / Accepted: 12 March 2015 / Published: 20 March 2015
Cited by 3 | PDF Full-text (1101 KB) | HTML Full-text | XML Full-text
Abstract
In this paper a solid oxide fuel cell (SOFC) system for cogeneration of heat and power integrated with a stratified heat storage tank is studied. The use of a storage tank with thermal stratification allows one to increase the annual operating hours of
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In this paper a solid oxide fuel cell (SOFC) system for cogeneration of heat and power integrated with a stratified heat storage tank is studied. The use of a storage tank with thermal stratification allows one to increase the annual operating hours of CHP: heat can be produced when the request is low (for instance during the night), taking advantage of thermal stratification to increases the heat recovery performance. A model of the SOFC system is presented to estimate the energy required to meet the average electric energy demand of the residence. Two fuels are considered, namely syngas produced by gasification and natural gas. The tank model considers the temperature gradients over the tank height. The results of the numerical simulation are used to size the SOFC system and storage heat tank to provide energy for a small household using two different fuels. In particular it was shown that in the case of syngas, due to larger system heat output, a larger tank volume was required in order to accumulate unused heat over the night. The detailed description of the tank model will be useful to energy system modelers when sizing hot water tanks. Problem formulation is reported also using a Matlab script. Full article
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Open AccessArticle Experimental Analysis of Cool Traditional Solar Shading Systems for Residential Buildings
Energies 2015, 8(3), 2197-2210; https://doi.org/10.3390/en8032197
Received: 9 February 2015 / Revised: 10 March 2015 / Accepted: 12 March 2015 / Published: 20 March 2015
Cited by 11 | PDF Full-text (2441 KB) | HTML Full-text | XML Full-text
Abstract
In recent years there has been a growing interest in the development and thermal-energy analysis of passive solutions for reducing building cooling needs and thus improving indoor thermal comfort conditions. In this view, several studies were carried out about cool roofs and cool
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In recent years there has been a growing interest in the development and thermal-energy analysis of passive solutions for reducing building cooling needs and thus improving indoor thermal comfort conditions. In this view, several studies were carried out about cool roofs and cool coatings, producing acknowledged mitigation effects on urban heat island phenomenon. The purpose of this work is to investigate the thermal-energy performance of cool louvers of shutters, usually installed in residential buildings, compared to dark color traditional shading systems. To this aim, two full-scale prototype buildings were continuously monitored under summer conditions and the role of the cool shutter in reducing the overheating of the shading system and the energy requirements for cooling was analyzed. After an in-lab optical analysis of the cool coating, showing a huge solar reflectance increase with respect to the traditional configuration, i.e., by about 75%, field monitoring results showed that the cool shutter is able to decrease the indoor air temperature up to 2 °C under free floating conditions. The corresponding energy saving was about 25%, with even much higher peaks during very hot summer conditions. Full article
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Open AccessArticle Estimation of CO2 Transport Costs in South Korea Using a Techno-Economic Model
Energies 2015, 8(3), 2176-2196; https://doi.org/10.3390/en8032176
Received: 16 December 2014 / Revised: 5 March 2015 / Accepted: 16 March 2015 / Published: 19 March 2015
Cited by 2 | PDF Full-text (1406 KB) | HTML Full-text | XML Full-text
Abstract
In this study, a techno–economic model was used to calculate the costs of CO2 transport and specify the major equipment required for transport in order to demonstrate and implement CO2 sequestration in the offshore sediments of South Korea. First, three different
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In this study, a techno–economic model was used to calculate the costs of CO2 transport and specify the major equipment required for transport in order to demonstrate and implement CO2 sequestration in the offshore sediments of South Korea. First, three different carbon capture and storage demonstration scenarios were set up involving the use of three CO2 capture plants and one offshore storage site. Each transport scenario considered both the pipeline transport and ship transport options. The temperature and pressure conditions of CO2 in each transport stage were determined from engineering and economic viewpoints, and the corresponding specifications and equipment costs were calculated. The transport costs for a 1 MtCO2/year transport rate were estimated to be US$33/tCO2 and US$28/tCO2 for a pipeline transport of ~530 km and ship transport of ~724 km, respectively. Through the economies of scale effect, the pipeline and ship transport costs for a transport rate of 3 MtCO2/year were reduced to approximately US$21/tCO2 and US$23/tCO2, respectively. A CO2 hub terminal did not significantly reduce the cost because of the short distance from the hub to the storage site and the small number of captured sources. Full article
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Open AccessArticle The Impact of a Mild Sub-Critical Hydrothermal Carbonization Pretreatment on Umbila Wood. A Mass and Energy Balance Perspective
Energies 2015, 8(3), 2165-2175; https://doi.org/10.3390/en8032165
Received: 8 October 2014 / Revised: 24 December 2014 / Accepted: 3 March 2015 / Published: 19 March 2015
Cited by 1 | PDF Full-text (419 KB) | HTML Full-text | XML Full-text
Abstract
Over the last years, the pretreatment of biomass as a source of energy has become one of the most important steps of biomass conversion. In this work the effect of a mild subcritical hydrothermal carbonization of a tropical woody biomass was studied. Results
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Over the last years, the pretreatment of biomass as a source of energy has become one of the most important steps of biomass conversion. In this work the effect of a mild subcritical hydrothermal carbonization of a tropical woody biomass was studied. Results indicate considerable change in carbon content from 52.78% to 65.1%, reduction of oxygen content from 41.14% to 28.72% and ash slagging and fouling potential. Even though decarboxylation, decarbonylation and dehydration reactions take place, dehydration is the one that prevails. The mass and energy balance was affected by the treatment conditions than the severity of the treatment. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Load Frequency Control in Isolated Micro-Grids with Electrical Vehicles Based on Multivariable Generalized Predictive Theory
Energies 2015, 8(3), 2145-2164; https://doi.org/10.3390/en8032145
Received: 16 October 2014 / Accepted: 4 March 2015 / Published: 18 March 2015
Cited by 24 | PDF Full-text (533 KB) | HTML Full-text | XML Full-text
Abstract
In power systems, although the inertia energy in power sources can partly cover power unbalances caused by load disturbance or renewable energy fluctuation, it is still hard to maintain the frequency deviation within acceptable ranges. However, with the vehicle-to-grid (V2G) technique, electric vehicles
[...] Read more.
In power systems, although the inertia energy in power sources can partly cover power unbalances caused by load disturbance or renewable energy fluctuation, it is still hard to maintain the frequency deviation within acceptable ranges. However, with the vehicle-to-grid (V2G) technique, electric vehicles (EVs) can act as mobile energy storage units, which could be a solution for load frequency control (LFC) in an isolated grid. In this paper, a LFC model of an isolated micro-grid with EVs, distributed generations and their constraints is developed. In addition, a controller based on multivariable generalized predictive control (MGPC) theory is proposed for LFC in the isolated micro-grid, where EVs and diesel generator (DG) are coordinated to achieve a satisfied performance on load frequency. A benchmark isolated micro-grid with EVs, DG, and wind farm is modeled in the Matlab/Simulink environment to demonstrate the effectiveness of the proposed method. Simulation results demonstrate that with MGPC, the energy stored in EVs can be managed intelligently according to LFC requirement. This improves the system frequency stability with complex operation situations including the random renewable energy resource and the continuous load disturbances. Full article
(This article belongs to the Special Issue Microgrids)
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Open AccessArticle Design of an LLC Resonant Converter for Driving Multiple LED Lights Using Current Balancing of Capacitor and Transformer
Energies 2015, 8(3), 2125-2144; https://doi.org/10.3390/en8032125
Received: 3 November 2014 / Accepted: 12 March 2015 / Published: 18 March 2015
Cited by 8 | PDF Full-text (2265 KB) | HTML Full-text | XML Full-text
Abstract
In this study, to achieve the constant current drive and brightness control without a separate pulse width modulation (PWM) converter, a single converter is designed and verified by experiment under the condition of a multiple LED light load with different output voltage (Vf)
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In this study, to achieve the constant current drive and brightness control without a separate pulse width modulation (PWM) converter, a single converter is designed and verified by experiment under the condition of a multiple LED light load with different output voltage (Vf) characteristics. In the case of the input of 140 Watt class level, the proposed converter can drive two voltage type 95 Vdc (300 mA) light emitting diode (LED) lights loads and 120 Vdc (300 mA) LED lights loads simultaneously. In addition, to improve commercial compatibility, the proposed converter is operated in a wide range of the input voltage 90~264 Vac; also, the Power Factor Correction (PFC) circuit with the input power factor of more than 0.9 is added. In order to maximize the power conversion efficiency, a LLC resonant converter is applied to the PFC block with the output voltage of 380 Vdc and to a DC-DC conversion block. Finally, reliability of the proposed converter is verified through total harmonic distortion (THD) and electromagnetic interference (EMI) tests. Full article
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Open AccessArticle Thermo-Economic Evaluation of Organic Rankine Cycles for Geothermal Power Generation Using Zeotropic Mixtures
Energies 2015, 8(3), 2097-2124; https://doi.org/10.3390/en8032097
Received: 30 January 2015 / Revised: 4 March 2015 / Accepted: 11 March 2015 / Published: 17 March 2015
Cited by 24 | PDF Full-text (470 KB) | HTML Full-text | XML Full-text
Abstract
We present a thermo-economic evaluation of binary power plants based on the Organic Rankine Cycle (ORC) for geothermal power generation. The focus of this study is to analyse if an efficiency increase by using zeotropic mixtures as working fluid overcompensates additional requirements regarding
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We present a thermo-economic evaluation of binary power plants based on the Organic Rankine Cycle (ORC) for geothermal power generation. The focus of this study is to analyse if an efficiency increase by using zeotropic mixtures as working fluid overcompensates additional requirements regarding the major power plant components. The optimization approach is compared to systems with pure media. Based on process simulations, heat exchange equipment is designed and cost estimations are performed. For heat source temperatures between 100 and 180 °C selected zeotropic mixtures lead to an increase in second law efficiency of up to 20.6% compared to pure fluids. Especially for temperatures about 160 °C, mixtures like propane/isobutane, isobutane/isopentane, or R227ea/R245fa show lower electricity generation costs compared to the most efficient pure fluid. In case of a geothermal fluid temperature of 120 °C, R227ea and propane/isobutane are cost-efficient working fluids. The uncertainties regarding fluid properties of zeotropic mixtures, mainly affect the heat exchange surface. However, the influence on the determined economic parameter is marginal. In general, zeotropic mixtures are a promising approach to improve the economics of geothermal ORC systems. Additionally, the use of mixtures increases the spectrum of potential working fluids, which is important in context of present and future legal requirements considering fluorinated refrigerants. Full article
(This article belongs to the Special Issue Organic Rankine Cycle (ORC))
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Open AccessArticle Fabrication and Test of an Air-Breathing Microfluidic Fuel Cell
Energies 2015, 8(3), 2082-2096; https://doi.org/10.3390/en8032082
Received: 18 January 2015 / Revised: 23 February 2015 / Accepted: 5 March 2015 / Published: 16 March 2015
Cited by 4 | PDF Full-text (3094 KB) | HTML Full-text | XML Full-text
Abstract
An air-breathing direct formic acid microfluidic fuel cell, which had a self-made anode electrode of 10 mg/cm2 Pd loading and 6 mg/cm2 Nafion content, was fabricated and tested. The microfluidic fuel cell was achieved by bonding a PDMS microchannel that was
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An air-breathing direct formic acid microfluidic fuel cell, which had a self-made anode electrode of 10 mg/cm2 Pd loading and 6 mg/cm2 Nafion content, was fabricated and tested. The microfluidic fuel cell was achieved by bonding a PDMS microchannel that was fabricated by a soft-lithography process and a PMMA sheet that was machined by a CO2 laser for obtaining 50 through holes of 0.5 mm in diameter. Formic acid of 0.3 M, 0.5 M, and 1.0 M, mixed with 0.5-M H2SO4, was supplied at a flow rate ranging from 0.1 to 0.7 mL/min as fuel. The maximum power density of the fuel cell fed with 0.5-M HCOOH was approximately 31, 32.16, and 31 mW/cm2 at 0.5, 0.6, and 0.7 mL/min, respectively. The simultaneous recording of the flow in the microchannel and the current density of the fuel cell at 0.2 V, within a 100-s duration, showed that the period and amplitude of each unsteady current oscillation were associated with the bubble resident time and bubble dimension, respectively. The effect of bubble dimension included the longitudinal and transverse bubble dimension, and the distance between two in-line bubbles as well. Full article
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Open AccessArticle Radiological Impacts and Regulation of Rare Earth Elements in Non-Nuclear Energy Production
Energies 2015, 8(3), 2066-2081; https://doi.org/10.3390/en8032066
Received: 4 December 2014 / Revised: 4 March 2015 / Accepted: 5 March 2015 / Published: 13 March 2015
Cited by 3 | PDF Full-text (471 KB) | HTML Full-text | XML Full-text
Abstract
Energy industries account for a significant portion of total rare earth usage, both in the US and worldwide. Rare earth minerals are frequently collocated with naturally occurring radioactive material, imparting an occupational radiological dose during recovery. This paper explores the extent to which
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Energy industries account for a significant portion of total rare earth usage, both in the US and worldwide. Rare earth minerals are frequently collocated with naturally occurring radioactive material, imparting an occupational radiological dose during recovery. This paper explores the extent to which rare earths are used by various non-nuclear energy industries and estimates the radiological dose which can be attributed to these industries on absolute and normalized scales. It was determined that typical rare earth mining results in an occupational collective dose of approximately 0.0061 person-mSv/t rare earth elements, amounting to a total of 330 person-mSv/year across all non-nuclear energy industries (about 60% of the annual collective dose from one pressurized water reactor operated in the US, although for rare earth mining the impact is spread out over many more workers). About half of the collective dose from non-nuclear energy production results from use of fuel cracking catalysts for oil refining, although given the extent of the oil industry, it is a small dose when normalized to the energy equivalent of the oil that is used annually. Another factor in energy industries’ reliance on rare earths is the complicated state of the regulation of naturally occurring radiological materials; correspondingly, this paper also explores regulatory and management implications. Full article
(This article belongs to the Special Issue Advances in Nuclear Reactor and Fuel Cycle Technologies)
Open AccessArticle Integration of a Water Scrubbing Technique and Two-Stage Pressurized Anaerobic Digestion in One Process
Energies 2015, 8(3), 2048-2065; https://doi.org/10.3390/en8032048
Received: 23 December 2014 / Revised: 13 February 2015 / Accepted: 15 February 2015 / Published: 13 March 2015
Cited by 7 | PDF Full-text (998 KB) | HTML Full-text | XML Full-text
Abstract
Two-stage pressurized anaerobic digestion is a promising technology. This technology integrates in one process biogas production with upgrading and pressure boosting for grid injection. To investigate whether the efficiency of this novel system could be further increased, a water scrubbing system was integrated
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Two-stage pressurized anaerobic digestion is a promising technology. This technology integrates in one process biogas production with upgrading and pressure boosting for grid injection. To investigate whether the efficiency of this novel system could be further increased, a water scrubbing system was integrated into the methanogensis step. Therefore, six leach-bed reactors were used for hydrolysis/acidification and a 30-L pressurized anaerobic filter operated at 9 bar was adopted for acetogenesis/methanogenesis. The fermentation liquid of the pressurized anaerobic filter was circulated periodically via a flash tank, operating at atmospheric pressure. Due to the pressure drop, part of dissolved carbon dioxide was released from the liquid phase into the flash tank. The depressurized fermentation liquid was then recycled to the pressurized reactor. Three different flow rates (0 L·day−1, 20 L·day−1 and 40 L·day−1) were tested with three repetitions. As the daily recycled flashed liquid flow was increased from 0 to 40 L, six times as much as the daily feeding, the methane content in the biogas increased from 75 molar percent (mol%) to 87 mol%. The pH value of the substrate in the methane reactor rose simultaneously from 6.5 to 6.7. The experimental data were verified by calculation. Full article
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Open AccessArticle A Varied VSVM Strategy for Balancing the Neutral-Point Voltage of DC-Link Capacitors in Three-Level NPC Converters
Energies 2015, 8(3), 2032-2047; https://doi.org/10.3390/en8032032
Received: 6 January 2015 / Revised: 18 February 2015 / Accepted: 28 February 2015 / Published: 13 March 2015
Cited by 6 | PDF Full-text (823 KB) | HTML Full-text | XML Full-text
Abstract
In the research field of multilevel converters, three-level NPC (neutral-point-clamped) converters, which unfortunately may cause the deviation of the neutral-point voltage of DC-link capacitors, are widely discussed. Theoretically, virtual space vector modulation (VSVM) could guarantee the balance control of the neutral-point voltage. However,
[...] Read more.
In the research field of multilevel converters, three-level NPC (neutral-point-clamped) converters, which unfortunately may cause the deviation of the neutral-point voltage of DC-link capacitors, are widely discussed. Theoretically, virtual space vector modulation (VSVM) could guarantee the balance control of the neutral-point voltage. However, there still exist some uncontrollable space vector regions. Based on VSVM, this paper proposes a varied virtual space vector modulation (VVSVM) method for three-level NPC converters. Under complete modulation conditions, this method can control the balance of the neutral-point voltage of DC-link capacitors by adjusting the duty cycle of small vectors and regulating the current generated by virtual medium vectors. Compared with commonly used VSVM methods and mixed modulation strategies, this method is simpler and more practical. The effectiveness and validity of this method are verified by simulations and experiments. Full article
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