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

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Editorial

Jump to: Research, Review, Other

Open AccessEditorial Energies Best Paper Awards for 2015
Energies 2015, 8(3), 2292-2294; doi:10.3390/en8032292
Received: 12 March 2015 / Accepted: 13 March 2015 / Published: 23 March 2015
PDF Full-text (253 KB) | HTML Full-text | XML Full-text
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

Research

Jump to: Editorial, Review, Other

Open AccessArticle Effect of Extended Extinction from Gold Nanopillar Arrays on the Absorbance Spectrum of a Bulk Heterojunction Organic Solar Cell
Energies 2015, 8(3), 1547-1560; doi:10.3390/en8031547
Received: 7 November 2014 / Accepted: 14 January 2015 / Published: 18 February 2015
Cited by 2 | PDF Full-text (1811 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We report on the effects of enhanced absorption/scattering from arrays of Au nanopillars of varied size and spacing on the spectral response of a P3HT:PCBM bulk heterojunction solar cell. Nanopillar array-patterned devices do show increased optical extinction within a narrow range of wavelengths
[...] Read more.
We report on the effects of enhanced absorption/scattering from arrays of Au nanopillars of varied size and spacing on the spectral response of a P3HT:PCBM bulk heterojunction solar cell. Nanopillar array-patterned devices do show increased optical extinction within a narrow range of wavelengths compared to control samples without such arrays. The measured external quantum efficiency and calculated absorbance, however, both show a decrease near the corresponding wavelengths. Numerical simulations indicate that for relatively narrow nanopillars, the increased optical extinction is dominated by absorption within the nanopillars, rather than scattering, and is likely dissipated by Joule heating. Full article
(This article belongs to the Special Issue Next Generation of Photovoltaic (PV) Technology)
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Open AccessArticle Deep Sediment-Sourced Methane Contribution to Shallow Sediment Organic Carbon: Atwater Valley, Texas-Louisiana Shelf, Gulf of Mexico
Energies 2015, 8(3), 1561-1583; doi:10.3390/en8031561
Received: 23 August 2014 / Accepted: 11 February 2015 / Published: 18 February 2015
Cited by 4 | PDF Full-text (2484 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Coastal methane hydrate deposits are globally abundant. There is a need to understand the deep sediment sourced methane energy contribution to shallow sediment carbon relative to terrestrial sources and phytoplankton. Shallow sediment and porewater samples were collected from Atwater Valley, Texas-Louisiana Shelf, Gulf
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Coastal methane hydrate deposits are globally abundant. There is a need to understand the deep sediment sourced methane energy contribution to shallow sediment carbon relative to terrestrial sources and phytoplankton. Shallow sediment and porewater samples were collected from Atwater Valley, Texas-Louisiana Shelf, Gulf of Mexico near a seafloor mound feature identified in geophysical surveys as an elevated bottom seismic reflection. Geochemical data revealed off-mound methane diffusion and active fluid advection on-mound. Gas composition (average methane/ethane ratio ~11,000) and isotope ratios of methane on the mound (average δ13CCH4(g) = −71.2‰; D14CCH4(g) = −961‰) indicate a deep sediment, microbial source. Depleted sediment organic carbon values on mound (δ13CSOC = −25.8‰; D14CSOC = −930‰) relative to off-mound (δ13CSOC = −22.5‰; D14CSOC = −629‰) suggest deep sourced ancient carbon is incorporated into shallow sediment organic matter. Porewater and sediment data indicate inorganic carbon fixed during anaerobic oxidation of methane is a dominant contributor to on-mound shallow sediment organic carbon cycling. A simple stable carbon isotope mass balance suggests carbon fixation of dissolved inorganic carbon (DIC) associated with anaerobic oxidation of hydrate-sourced CH4 contributes up to 85% of shallow sediment organic carbon. Full article
(This article belongs to the Special Issue Coastal Ocean Natural Gas Hydrate 2014)
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Open AccessArticle Active Power Filtering Using the ZDPC Method under Unbalanced and Distorted Grid Voltage Conditions
Energies 2015, 8(3), 1584-1605; doi:10.3390/en8031584
Received: 16 October 2014 / Revised: 7 February 2015 / Accepted: 10 February 2015 / Published: 27 February 2015
Cited by 4 | PDF Full-text (2315 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, we propose a new Zero Direct Power Control (ZDPC) technique for active compensation of harmonics and reactive power, using shunt active power filter (SAPF), based on cancellation of instantaneous active and reactive power disturbances by comparison with their zero references.
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In this paper, we propose a new Zero Direct Power Control (ZDPC) technique for active compensation of harmonics and reactive power, using shunt active power filter (SAPF), based on cancellation of instantaneous active and reactive power disturbances by comparison with their zero references. To separate harmonic and fundamental components of the line voltage and current a highly selective filter (HSF) has been used. Depending on the power errors and line voltage vector position, a switching table produces the appropriate control vectors leading to the active and reactive power variation required to reach the zero power references, even under grid voltage unbalanced and distorted conditions. The experimental validation of the proposed ZDPC has been performed. The results are compared to other recent techniques to demonstrate the superiority and feasibility of the proposed strategy. Full article
Open AccessArticle Design of a Four-Branch LCL-Type Grid-Connecting Interface for a Three-Phase, Four-Leg Active Power Filter
Energies 2015, 8(3), 1606-1627; doi:10.3390/en8031606
Received: 6 January 2015 / Revised: 15 February 2015 / Accepted: 16 February 2015 / Published: 27 February 2015
Cited by 8 | PDF Full-text (1223 KB) | HTML Full-text | XML Full-text
Abstract
Compared with the three-phase, two-split-capacitor active power filter (3P2C-APF), the three-phase, four-leg active power filter (3P4L-APF) has been widely used in three-phase, four-wire grid utility for power quality control due to its numerous advantages, such as higher current output capability, particularly in phase
[...] Read more.
Compared with the three-phase, two-split-capacitor active power filter (3P2C-APF), the three-phase, four-leg active power filter (3P4L-APF) has been widely used in three-phase, four-wire grid utility for power quality control due to its numerous advantages, such as higher current output capability, particularly in phase N, lower current and easier voltage control on the DC-side. However, designing the grid-connecting interface, which is between the voltage source converter (VSC) and grid utility, is rather difficult due to the higher requirement for current ripple filtering in phase N, cross-coupling in four phases and lack of relevant design methodology and specification. In this paper, a four-branch LCL-type (4B-LCL) grid-connecting interface is proposed for 3P4L-APF, which features better current ripple filtering performance without decreasing the current output capability in all phases. First, this paper describes the mathematical models of 4B-LCL in the fully-complex-vector form from the zero and non-zero sequence perspective, resulting in two independent and uniform equivalent circuits without cross coupling terms. Then, the 4B-LCL parameter design method based on the most comprehensive performance index is proposed, including three main stages as the specification: performance index requirement determination, fulfillment of that requirement, and verification. Finally, the validity and effectiveness of the proposed design are proven by the simulated and experimental results of a 3P4L-APF with 4B-LCL. Full article
Open AccessArticle Life Cycle Assessment of New Oxy-Fuels from Biodiesel-Derived Glycerol
Energies 2015, 8(3), 1628-1643; doi:10.3390/en8031628
Received: 19 November 2014 / Revised: 27 January 2015 / Accepted: 11 February 2015 / Published: 27 February 2015
Cited by 10 | PDF Full-text (1072 KB) | HTML Full-text | XML Full-text
Abstract
Biodiesel is obtained by the process of transesterification of vegetable oils and animal fats and crude glycerol is the main by-product of the biodiesel manufacturing chain. As a result glycerol production has rapidly increased in the last decades. This work focuses on the
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Biodiesel is obtained by the process of transesterification of vegetable oils and animal fats and crude glycerol is the main by-product of the biodiesel manufacturing chain. As a result glycerol production has rapidly increased in the last decades. This work focuses on the development and the validation of a process to convert biodiesel-derived glycerol into a fuel for internal combustion engines. In order to obtain a higher conversion efficiency it was necessary to convert crude glycerol to tert-butyl ethers by means of an etherification process that was carried out in the laboratory. Then the obtained glycol-ethers mixture (GEM) was blended with a commercial diesel fuel to improve its thermal efficiency. In this paper a life cycle analysis for these GEM/diesel blends was carried out using a Life Cycle Assessment (LCA) methodology, in order to evaluate the environmental impacts of these new oxy-fuels; from GEM production to GEM use as an additive for diesel fuel. The LCA results highlight that the use of these new oxy-fuels in diesel engines can lead to an effective reduction in terms of greenhouse gases emissions throughout the entire life cycle. Full article
Open AccessArticle Research on Shaft Subsynchronous Oscillation Characteristics of Parallel Generators and SSDC Application in Mitigating SSO of Multi-Generators
Energies 2015, 8(3), 1644-1662; doi:10.3390/en8031644
Received: 10 November 2014 / Revised: 4 January 2015 / Accepted: 9 February 2015 / Published: 27 February 2015
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Abstract
Subsynchronous oscillation (SSO) of generators caused by high voltage direct current (HVDC) systems can be solved by applying supplemental subsynchronous damping controller (SSDC). SSDC application in mitigating SSO of single-generator systems has been studied intensively. This paper focuses on SSDC application in mitigating
[...] Read more.
Subsynchronous oscillation (SSO) of generators caused by high voltage direct current (HVDC) systems can be solved by applying supplemental subsynchronous damping controller (SSDC). SSDC application in mitigating SSO of single-generator systems has been studied intensively. This paper focuses on SSDC application in mitigating SSO of multi-generator systems. The phase relationship of the speed signals of the generators under their common mechanical natural frequencies is a key consideration in SSDC design. The paper studies in detail the phase relationship of the speed signals of two generators in parallel under their shared mechanical natural frequency, revealing regardless of whether the two generators are identical or not, there always exists a common-mode and an anti-mode under their common natural frequency, and the phase relationship of the speed signals of the generators depends on the extent to which the anti-mode is stimulated. The paper further demonstrates that to guarantee the effectiveness of SSDC, the anti-phase mode component of its input signal should be eliminated. Based on the above analysis, the paper introduces the design process of SSDC for multi-generator systems and verifies its effectiveness through simulation in Power Systems Computer Aided Design/Electromagnetic Transients including Direct Current (PSCAD/EMTDC). Full article
(This article belongs to the collection Smart Grid)
Open AccessArticle Research on an Axial Flux PMSM with Radially Sliding Permanent Magnets
Energies 2015, 8(3), 1663-1684; doi:10.3390/en8031663
Received: 26 December 2014 / Revised: 6 February 2015 / Accepted: 15 February 2015 / Published: 27 February 2015
Cited by 6 | PDF Full-text (2639 KB) | HTML Full-text | XML Full-text
Abstract
Axial flux permanent-magnet synchronous machines (PMSMs) are very suitable candidates for the power train of electric vehicles (EVs) due to high power density and high efficiency. This paper researches an axial flux PMSM with radially sliding permanent magnets (PMs) to fulfill field-weakening control.
[...] Read more.
Axial flux permanent-magnet synchronous machines (PMSMs) are very suitable candidates for the power train of electric vehicles (EVs) due to high power density and high efficiency. This paper researches an axial flux PMSM with radially sliding permanent magnets (PMs) to fulfill field-weakening control. The field weakening principle and the structure of this kind of axial flux PMSM by mechanical method of sliding PMs are proposed and analyzed. The influences of radially sliding PMs on magnetic flux density distribution, inductance, flux linkage and torque are analyzed and discussed based on 3D finite element method (FEM). The field weakening capabilities by mechanical method and electrical method are compared. The field weakening capability of the machine can be much improved by the optimized combination of the two methods, which is very satisfying for EV drive application. The forces on the PMs are analyzed and calculated. The hysteretic characteristics caused by the friction of the PMs are investigated, which provide useful reference for designing this kind of machine. Full article
(This article belongs to the Special Issue Advances in Plug-in Hybrid Vehicles and Hybrid Vehicles)
Open AccessArticle Potential of Offshore Wind Energy and Extreme Wind Speed Forecasting on the West Coast of Taiwan
Energies 2015, 8(3), 1685-1700; doi:10.3390/en8031685
Received: 21 November 2014 / Revised: 6 February 2015 / Accepted: 11 February 2015 / Published: 27 February 2015
Cited by 5 | PDF Full-text (1721 KB) | HTML Full-text | XML Full-text
Abstract
It is of great importance and urgency for Taiwan to develop offshore wind power. However, relevant data on offshore wind energy resources are limited. This study imported wind speeds measured by a tidal station and a buoy into the software WAsP to estimate
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It is of great importance and urgency for Taiwan to develop offshore wind power. However, relevant data on offshore wind energy resources are limited. This study imported wind speeds measured by a tidal station and a buoy into the software WAsP to estimate the high-altitude wind speeds in the two areas. A light detection and ranging (Lidar) system was set up near the tidal station and buoy. High-altitude wind speeds measured by the Lidar system were compared with the WAsP-estimated values, and it was discovered that the two data sets were consistent. Then, long-term wind speed data observed by buoys and tidal stations at various locations were imported into WAsP to forecast wind speeds at heights of 55–200 m on the west coast of Taiwan. The software WAsP Engineering was used to analyze the extreme wind speeds in the same areas. The results show that wind speeds at 100 m are approximately 9.32–11.24 m/s, which means that the coastal areas of west Taiwan are rich in wind energy resources. When a long-term 10-min average wind speed is used, the extreme wind speed on the west coast is estimated to be between 36.4 and 55.3 m/s. Full article
Open AccessArticle A Path Forward for Low Carbon Power from Biomass
Energies 2015, 8(3), 1701-1715; doi:10.3390/en8031701
Received: 15 December 2014 / Revised: 14 January 2015 / Accepted: 9 February 2015 / Published: 27 February 2015
Cited by 5 | PDF Full-text (652 KB) | HTML Full-text | XML Full-text
Abstract
The two major pathways for energy utilization from biomass are conversion to a liquid fuel (i.e., biofuels) or conversion to electricity (i.e., biopower). In the United States (US), biomass policy has focused on biofuels. However, this paper will investigate
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The two major pathways for energy utilization from biomass are conversion to a liquid fuel (i.e., biofuels) or conversion to electricity (i.e., biopower). In the United States (US), biomass policy has focused on biofuels. However, this paper will investigate three options for biopower: low co-firing (co-firing scenarios refer to combusting a given percentage of biomass with coal) (5%–10% biomass), medium co-firing (15%–20% biomass), and dedicated biomass firing (100% biomass). We analyze the economic and greenhouse gas (GHG) emissions impact of each of these options, with and without CO2 capture and storage (CCS). Our analysis shows that in the absence of land use change emissions, all biomass co-combustion scenarios result in a decrease in GHG emissions over coal generation alone. The two biggest barriers to biopower are concerns about carbon neutrality of biomass fuels and the high cost compared to today’s electricity prices. This paper recommends two policy actions. First, the need to define sustainability criteria and initiate a certification process so that biomass providers have a fixed set of guidelines to determine whether their feedstocks qualify as renewable energy sources. Second, the need for a consistent, predictable policy that provides the economic incentives to make biopower economically attractive. Full article
(This article belongs to the Special Issue Carbon Capture and Storage (CCS): Bio-Energy vs Fossil Fuels)
Open AccessArticle Biohydrogen Fermentation from Sucrose and Piggery Waste with High Levels of Bicarbonate Alkalinity
Energies 2015, 8(3), 1716-1729; doi:10.3390/en8031716
Received: 24 November 2014 / Revised: 15 January 2015 / Accepted: 23 January 2015 / Published: 2 March 2015
Cited by 1 | PDF Full-text (750 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This study examined the influence of biohydrogen fermentation under the high bicarbonate alkalinity (BA) and pH to optimize these critical parameters. When sucrose was used as a substrate, hydrogen was produced over a wide range of pH values (5–9) under no BA supplementation;
[...] Read more.
This study examined the influence of biohydrogen fermentation under the high bicarbonate alkalinity (BA) and pH to optimize these critical parameters. When sucrose was used as a substrate, hydrogen was produced over a wide range of pH values (5–9) under no BA supplementation; however, BA affected hydrogen yield significantly under different initial pHs (5–10). The actual effect of high BA using raw piggery waste (pH 8.7 and BA 8.9 g CaCO3/L) showed no biogas production or propionate/acetate accumulation. The maximum hydrogen production rate (0.32 L H2/g volatile suspended solids (VSS)-d) was observed at pH 8.95 and 3.18 g CaCO3/L. BA greater than 4 g CaCO3/L also triggered lactate-type fermentation, leading to propionate accumulation, butyrate reduction and homoacetogenesis, potentially halting the hydrogen production rate. These results highlight that the substrate with high BA need to amend adequately to maximize hydrogen production. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Double Distribution Activation Energy Model as Suitable Tool in Explaining Biomass and Coal Pyrolysis Behavior
Energies 2015, 8(3), 1730-1744; doi:10.3390/en8031730
Received: 20 January 2015 / Revised: 12 February 2015 / Accepted: 13 February 2015 / Published: 2 March 2015
Cited by 5 | PDF Full-text (1041 KB) | HTML Full-text | XML Full-text
Abstract
Understanding and modeling of coal and biomass pyrolysis assume particular importance being the first step occurring in both gasification and combustion processes. The complex chemical reaction network occurring in this step leads to a necessary effort in developing a suitable model framework capable
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Understanding and modeling of coal and biomass pyrolysis assume particular importance being the first step occurring in both gasification and combustion processes. The complex chemical reaction network occurring in this step leads to a necessary effort in developing a suitable model framework capable of grasping the physics of the phenomenon and allowing a deeper comprehension of the sequence of events. The aim of this work is to show how the intrinsic flexibility of a model based on a double distribution of the activation energy is able to properly describe the two separate steps of primary and secondary pyrolysis, which characterize the thermochemical processing of most of the energetic materials. The model performance was tested by fitting the kinetic parameters from experimental data obtained by thermogravimetric analysis of two materials, which represent very different classes of energy source: a microalgae biomass and a sub-bituminous coal. The model reproduces with high accuracy the pyrolysis behavior of both the materials and adds important information about the relative occurring of the two pyrolysis steps. Full article
(This article belongs to the collection Bioenergy and Biofuel)
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Open AccessArticle Analysis on Storage Off-Gas Emissions from Woody, Herbaceous, and Torrefied Biomass
Energies 2015, 8(3), 1745-1759; doi:10.3390/en8031745
Received: 26 November 2014 / Revised: 9 February 2015 / Accepted: 12 February 2015 / Published: 2 March 2015
Cited by 4 | PDF Full-text (680 KB) | HTML Full-text | XML Full-text
Abstract
Wood chips, torrefied wood chips, ground switchgrass, and wood pellets were tested for off‑gas emissions during storage. Storage canisters with gas‑collection ports were used to conduct experiments at room temperature of 20 °C and in a laboratory oven set at 40 °C. Commercially-produced
[...] Read more.
Wood chips, torrefied wood chips, ground switchgrass, and wood pellets were tested for off‑gas emissions during storage. Storage canisters with gas‑collection ports were used to conduct experiments at room temperature of 20 °C and in a laboratory oven set at 40 °C. Commercially-produced wood pellets yielded the highest carbon monoxide (CO) emissions at both 20 and 40 °C (1600 and 13,000 ppmv), whereas torrefied wood chips emitted the lowest of about <200 and <2000 ppmv. Carbon dioxide (CO2) emissions from wood pellets were 3000 ppmv and 42,000 ppmv, whereas torrefied wood chips registered at about 2000 and 25,000 ppmv, at 20 and 40 °C at the end of 11 days of storage. CO emission factors (milligrams per kilogram of biomass) calculated were lowest for ground switchgrass and torrefied wood chips (2.68 and 4.86 mg/kg) whereas wood pellets had the highest CO of about 10.60 mg/kg, respectively, at 40 °C after 11 days of storage. In the case of CO2, wood pellets recorded the lowest value of 55.46 mg/kg, whereas switchgrass recorded the highest value of 318.72 mg/kg. This study concludes that CO emission factor is highest for wood pellets, CO2 is highest for switchgrass and CH4 is negligible for all feedstocks except for wood pellets, which is about 0.374 mg/kg at the end of 11-day storage at 40 °C. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle MV and LV Residential Grid Impact of Combined Slow and Fast Charging of Electric Vehicles
Energies 2015, 8(3), 1760-1783; doi:10.3390/en8031760
Received: 16 December 2014 / Revised: 15 February 2015 / Accepted: 17 February 2015 / Published: 3 March 2015
Cited by 6 | PDF Full-text (1095 KB) | HTML Full-text | XML Full-text
Abstract
This article investigates the combined low voltage (LV) and medium voltage (MV) residential grid impact for slow and fast electric vehicle (EV) charging, for an increasing local penetration rate and for different residential slow charging strategies. A realistic case study for a Flemish
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This article investigates the combined low voltage (LV) and medium voltage (MV) residential grid impact for slow and fast electric vehicle (EV) charging, for an increasing local penetration rate and for different residential slow charging strategies. A realistic case study for a Flemish urban distribution grid is used, for which three residential slow charging strategies are modeled: uncoordinated charging, residential off-peak charging, and EV-based peak shaving. For each slow charging strategy, the EV hosting capacity is determined, with and without the possibility of fast charging, while keeping the grid within its operating limits. The results show that the distribution grid impact is much less sensitive to the presence of fast charging compared to the slow charging strategy. EV-based peak shaving results in the lowest grid impact, allowing for the highest EV hosting capacity. Residential off-peak charging has the highest grid impact, due the load synchronization effect that occurs, resulting in the lowest EV hosting capacity. Therefore, the EV users should be incentivized to charge their EVs in a more grid-friendly manner when the local EV penetration rate becomes significant, as this increases the EV hosting capacity much more than the presence of fast charging decreases it. Full article
Open AccessArticle Microgrid Stability Controller Based on Adaptive Robust Total SMC
Energies 2015, 8(3), 1784-1801; doi:10.3390/en8031784
Received: 19 December 2014 / Revised: 14 February 2015 / Accepted: 25 February 2015 / Published: 4 March 2015
Cited by 9 | PDF Full-text (928 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a microgrid stability controller (MSC) in order to provide existing distributed generation units (DGs) the additional functionality of working in islanding mode without changing their control strategies in grid-connected mode and to enhance the stability of the microgrid. Microgrid operating
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This paper presents a microgrid stability controller (MSC) in order to provide existing distributed generation units (DGs) the additional functionality of working in islanding mode without changing their control strategies in grid-connected mode and to enhance the stability of the microgrid. Microgrid operating characteristics and mathematical models of the MSC indicate that the system is inherently nonlinear and time-variable. Therefore, this paper proposes an adaptive robust total sliding-mode control (ARTSMC) system for the MSC. It is proved that the ARTSMC system is insensitive to parametric uncertainties and external disturbances. The MSC provides fast dynamic response and robustness to the microgrid. When the system is operating in grid-connected mode, it is able to improve the controllability of the exchanged power between the microgrid and the utility grid, while smoothing the DGs’ output power. When the microgrid is operating in islanded mode, it provides voltage and frequency support, while guaranteeing seamless transition between the two operation modes. Simulation and experimental results show the effectiveness of the proposed approach. Full article
(This article belongs to the Special Issue Microgrids)
Open AccessArticle Evaluation of Novel Inoculation Strategies for Solid State Anaerobic Digestion of Yam Peelings in Low-Tech Digesters
Energies 2015, 8(3), 1802-1816; doi:10.3390/en8031802
Received: 23 December 2014 / Revised: 9 February 2015 / Accepted: 15 February 2015 / Published: 4 March 2015
Cited by 1 | PDF Full-text (806 KB) | HTML Full-text | XML Full-text
Abstract
The operation of household scale anaerobic digesters is typically based on diluted animal dung, requiring stabled livestock and adequate water availability. This excludes many rural households in low-income countries from the benefits of a domestic biogas digester. Solid state anaerobic digestion (SSAD) can
[...] Read more.
The operation of household scale anaerobic digesters is typically based on diluted animal dung, requiring stabled livestock and adequate water availability. This excludes many rural households in low-income countries from the benefits of a domestic biogas digester. Solid state anaerobic digestion (SSAD) can be operated with low process water demands, but the technology involves operational challenges, as e.g., risk of process acidification or low degradation rates. This study aimed at developing simple methods to perform SSAD of yam peelings in low-tech applications by testing different inoculation strategies and evaluating the necessity of dung addition as a supportive biomass. In initial lab scale trials 143 ± 4 mL CH4/g VS (volatile solids) were obtained from a mixture of yam peelings and dung digested in a multi-layer-inoculated batch reactor. In a consecutive incubation cycle in which adapted inoculum was applied, bottom inoculated digesters loaded without dung reached a yield of 140 ± 16 mL CH4/g VS. This indicates that SSAD of yam peelings is possible with simple inoculation methods and dung addition is unnecessary after microbial adaptation. A comparison with a conventional fixed dome digester indicated that SSAD can reduce process water demand and the digester volume necessary to supply a given biogas demand. Full article
Open AccessArticle Changes in Carbon Electrode Morphology Affect Microbial Fuel Cell Performance with Shewanella oneidensis MR-1
Energies 2015, 8(3), 1817-1829; doi:10.3390/en8031817
Received: 19 November 2014 / Revised: 8 January 2015 / Accepted: 11 February 2015 / Published: 4 March 2015
Cited by 5 | PDF Full-text (2262 KB) | HTML Full-text | XML Full-text
Abstract
The formation of biofilm-electrodes is crucial for microbial fuel cell current production because optimal performance is often associated with thick biofilms. However, the influence of the electrode structure and morphology on biofilm formation is only beginning to be investigated. This study provides insight
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The formation of biofilm-electrodes is crucial for microbial fuel cell current production because optimal performance is often associated with thick biofilms. However, the influence of the electrode structure and morphology on biofilm formation is only beginning to be investigated. This study provides insight on how changing the electrode morphology affects current production of a pure culture of anode-respiring bacteria. Specifically, an analysis of the effects of carbon fiber electrodes with drastically different morphologies on biofilm formation and anode respiration by a pure culture (Shewanella oneidensis MR-1) were examined. Results showed that carbon nanofiber mats had ~10 fold higher current than plain carbon microfiber paper and that the increase was not due to an increase in electrode surface area, conductivity, or the size of the constituent material. Cyclic voltammograms reveal that electron transfer from the carbon nanofiber mats was biofilm-based suggesting that decreasing the diameter of the constituent carbon material from a few microns to a few hundred nanometers is beneficial for electricity production solely because the electrode surface creates a more relevant mesh for biofilm formation by Shewanella oneidensis MR-1. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
Open AccessArticle Balancing Control Strategy for Li-Ion Batteries String Based on Dynamic Balanced Point
Energies 2015, 8(3), 1830-1847; doi:10.3390/en8031830
Received: 20 November 2014 / Revised: 23 January 2015 / Accepted: 6 February 2015 / Published: 4 March 2015
Cited by 6 | PDF Full-text (626 KB) | HTML Full-text | XML Full-text
Abstract
The Li-ion battery is becoming the optimal choice for the Electric Vehicle’s (EV) power supply. In order to protect the Li-ion battery from charging damage and to prolong the battery’s life, a special control strategy based on the dynamic balanced point along with
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The Li-ion battery is becoming the optimal choice for the Electric Vehicle’s (EV) power supply. In order to protect the Li-ion battery from charging damage and to prolong the battery’s life, a special control strategy based on the dynamic balanced point along with a non-dissipative equalizer is presented. The main focus of the proposed control strategy is to insure that the individual cell of a battery pack will be rapidly, efficiently and simultaneously balanced, by adjusting equalizing current of each cell dynamically. In this paper, a model of a four series connected Li-ion batteries pack has been established to evaluate the proposed control strategy. Superior performance is demonstrated by the simulation and experiment. Full article
Open AccessArticle A Linearized Large Signal Model of an LCL-Type Resonant Converter
Energies 2015, 8(3), 1848-1864; doi:10.3390/en8031848
Received: 10 January 2015 / Revised: 27 February 2015 / Accepted: 27 February 2015 / Published: 5 March 2015
Cited by 3 | PDF Full-text (689 KB) | HTML Full-text | XML Full-text
Abstract
In this work, an LCL-type resonant dc/dc converter with a capacitive output filter is modeled in two stages. In the first high-frequency ac stage, all ac signals are decomposed into two orthogonal vectors in a synchronous rotating d–q frame using multi-frequency modeling. In
[...] Read more.
In this work, an LCL-type resonant dc/dc converter with a capacitive output filter is modeled in two stages. In the first high-frequency ac stage, all ac signals are decomposed into two orthogonal vectors in a synchronous rotating d–q frame using multi-frequency modeling. In the dc stage, all dc quantities are represented by their average values with average state-space modeling. A nonlinear two-stage model is then created by means of a non-linear link. By aligning the transformer voltage on the d-axis, the nonlinear link can be eliminated, and the whole converter can be modeled by a single set of linear state-space equations. Furthermore, a feedback control scheme can be formed according to the steady-state solutions. Simulation and experimental results have proven that the resulted model is good for fast simulation and state variable estimation. Full article
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Open AccessArticle Nanoparticle Filtration Characteristics of Advanced Metal Foam Media for a Spark Ignition Direct Injection Engine in Steady Engine Operating Conditions and Vehicle Test Modes
Energies 2015, 8(3), 1865-1881; doi:10.3390/en8031865
Received: 18 November 2014 / Revised: 13 February 2015 / Accepted: 28 February 2015 / Published: 9 March 2015
Cited by 6 | PDF Full-text (1909 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the particle formation and reduction characteristics at the engine-out position, after a three-way catalyst (TWC) and a metal foam gasoline particulate filter (GPF), were evaluated for a gasoline direct-injection (GDI) engine under part-load operating conditions. The vehicle tests were performed
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In this study, the particle formation and reduction characteristics at the engine-out position, after a three-way catalyst (TWC) and a metal foam gasoline particulate filter (GPF), were evaluated for a gasoline direct-injection (GDI) engine under part-load operating conditions. The vehicle tests were performed under the Federal Test Procedure-75 (FTP-75) and the Highway Fuel Economy Test (HWFET) modes. Particle number (PN) concentrations, size distributions, and the filtering efficiency with the GPF were evaluated with a condensation particle counter (CPC) and a differential mobility spectrometer (DMS500). Under steady engine operating conditions, the PN concentrations at the engine-out position were 9.7 × 105–2.5 × 106 N/cc. While, the PN concentrations after the GPF were 9.2 × 104–3.5 × 105 N/cc, and the PN was reduced by 77%–96%. The PN filtering efficiency with the GPF-GDI vehicle reached approximately 58% in the FTP-75 and 62% in the HWFET mode. The PN concentration of the GPF-GDI vehicle was significantly reduced to 3.95 × 1011 N/km for the FTP-75 and 8.86 × 1010 N/km for the HWFET mode. The amount of nucleation mode particles below 23 nm was substantially reduced with the GPF-GDI vehicle. The fuel economy, CO2, and regulated emissions of the GPF-GDI vehicle were equivalent to those of the base GDI vehicle under the vehicle certification modes. Full article
Open AccessArticle Experimental and Numerical Investigation of Termination Impedance Effects in Wireless Power Transfer via Metamaterial
Energies 2015, 8(3), 1882-1895; doi:10.3390/en8031882
Received: 8 December 2014 / Revised: 16 February 2015 / Accepted: 26 February 2015 / Published: 9 March 2015
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Abstract
This paper presents an investigation of the transmitted power in a wireless power transfer system that employs a metamaterial. Metamaterials are a good means to transfer power wirelessly, as they are composed of multiple inductively-coupled resonators. The system can be designed and matched
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This paper presents an investigation of the transmitted power in a wireless power transfer system that employs a metamaterial. Metamaterials are a good means to transfer power wirelessly, as they are composed of multiple inductively-coupled resonators. The system can be designed and matched simply through magneto-inductive wave theory, particularly when the receiver inductor is located at the end of the metamaterial line. However, the power distribution changes significantly in terms of transmitted power, efficiency and frequency if the receiver inductor slides along the line. In this paper, the power distribution and transfer efficiency are analysed, studying the effects of a termination impedance in the last cell of the metamaterial and improving the system performance for the resonant frequency and for any position of the receiver inductor. Furthermore, a numerical characterisation is presented in order to support experimental tests and to predict the performance of a metamaterial composed of spiral inductor cells with very good accuracy. Full article
(This article belongs to the Special Issue Wireless Power Transfer)
Open AccessArticle Hierarchical Load Tracking Control of a Grid-Connected Solid Oxide Fuel Cell for Maximum Electrical Efficiency Operation
Energies 2015, 8(3), 1896-1916; doi:10.3390/en8031896
Received: 11 December 2014 / Revised: 12 February 2015 / Accepted: 4 March 2015 / Published: 11 March 2015
Cited by 1 | PDF Full-text (1184 KB) | HTML Full-text | XML Full-text
Abstract
Based on the benchmark solid oxide fuel cell (SOFC) dynamic model for power system studies and the analysis of the SOFC operating conditions, the nonlinear programming (NLP) optimization method was used to determine the maximum electrical efficiency of the grid-connected SOFC subject to
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Based on the benchmark solid oxide fuel cell (SOFC) dynamic model for power system studies and the analysis of the SOFC operating conditions, the nonlinear programming (NLP) optimization method was used to determine the maximum electrical efficiency of the grid-connected SOFC subject to the constraints of fuel utilization factor, stack temperature and output active power. The optimal operating conditions of the grid-connected SOFC were obtained by solving the NLP problem considering the power consumed by the air compressor. With the optimal operating conditions of the SOFC for the maximum efficiency operation obtained at different active power output levels, a hierarchical load tracking control scheme for the grid-connected SOFC was proposed to realize the maximum electrical efficiency operation with the stack temperature bounded. The hierarchical control scheme consists of a fast active power control and a slower stack temperature control. The active power control was developed by using a decentralized control method. The efficiency of the proposed hierarchical control scheme was demonstrated by case studies using the benchmark SOFC dynamic model. Full article
(This article belongs to the Special Issue Microgrids)
Open AccessArticle Ex-Post Critical Evaluations of Energy Policies in Malaysia from 1970 to 2010: A Historical Institutionalism Perspective
Energies 2015, 8(3), 1936-1957; doi:10.3390/en8031936
Received: 20 January 2015 / Revised: 17 February 2015 / Accepted: 28 February 2015 / Published: 12 March 2015
Cited by 1 | PDF Full-text (686 KB) | HTML Full-text | XML Full-text
Abstract
Ex-post evaluations of energy policies in Malaysia between 1970 and 2010 were conducted. The developments of energy policies in Malaysia were traced from the early 1970s with the introduction of the country’s first energy-related policy all the way to 2010 with the country’s
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Ex-post evaluations of energy policies in Malaysia between 1970 and 2010 were conducted. The developments of energy policies in Malaysia were traced from the early 1970s with the introduction of the country’s first energy-related policy all the way to 2010 with the country’s first endeavour towards a biobased energy system. Analyses revealed that many of the policies were either: (1) directly responding to changes in global/domestic socioeconomic and political events, or (2) provided visions to guide developments of the energy sector in alignment with the country’s growth agenda. Critical examinations of the country’s actual energy consumptions during these 40 years were also conducted to evaluate the efficacy of these energy-related policies. Three noteworthy successes in Malaysia’s energy landscape are: (1) the formation of PETRONAS as the national oil and gas company; (2) reduction of country’s over-reliance on oil as a single source of energy by significantly growing the production and use of natural gas in a short span of time; and (3) creation of a thriving oil and gas value chain and ecosystem in the country. However, the country is still critically dependent on scarce petroleum resources, despite having an abundance of renewable reserves. Progress towards renewable energy has been too little and too slow. Full article
Open AccessArticle Slit Wall and Heat Transfer Effect on the Taylor Vortex Flow
Energies 2015, 8(3), 1958-1974; doi:10.3390/en8031958
Received: 30 November 2014 / Revised: 3 February 2015 / Accepted: 3 March 2015 / Published: 12 March 2015
Cited by 4 | PDF Full-text (1787 KB) | HTML Full-text | XML Full-text
Abstract
The Taylor vortex flow in the plain model with a constant temperature gradient effect was studied by experimental measurement, and the preliminary features of Taylor vortex flow affected by heat transfer process were obtained. This flow field in the plain model was also
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The Taylor vortex flow in the plain model with a constant temperature gradient effect was studied by experimental measurement, and the preliminary features of Taylor vortex flow affected by heat transfer process were obtained. This flow field in the plain model was also studied by numerical simulation. The reliability of numerical simulation was verified by comparing the numerical results with the experimental ones. To study the slit wall effect on this flow regime under the same temperature gradient conditions, another three models with different slit numbers (6, 9 and 12) were considered. The vortex pairs were found to have a motion along the axial direction. Because of the existence of the temperature gradient, the axial flow in the annulus gap was enhanced, but the radial velocity near the inner cylinder was found to be weakened. The heat flux generated by the inner cylinder was also compared among different models, and it was found that the heat flux generated by the 6-slit model was increased by 4.5% compared to that of the plain model, and the 12-slit model generated the maximum heat flux, which has the best heat transfer ability. Full article
Open AccessArticle Energy’s Shadow Price and Energy Efficiency in China: A Non-Parametric Input Distance Function Analysis
Energies 2015, 8(3), 1975-1989; doi:10.3390/en8031975
Received: 10 November 2014 / Revised: 12 January 2015 / Accepted: 3 March 2015 / Published: 13 March 2015
Cited by 4 | PDF Full-text (1150 KB) | HTML Full-text | XML Full-text
Abstract
This paper extends prior research on energy inefficiency in China by utilizing a unique shadow price framework allocation in 30 Chinese provinces. We estimate the shadow price for energy input using the framework of production, and use the ratio of the shadow price
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This paper extends prior research on energy inefficiency in China by utilizing a unique shadow price framework allocation in 30 Chinese provinces. We estimate the shadow price for energy input using the framework of production, and use the ratio of the shadow price to the market price to describe energy utilization. Using Chinese provincial-level data from 1998 to 2011, the results of the analysis reveal that shadow prices in China have grown rapidly during the sample period, which signifies that China has improved its performance in energy utilization since 1998. However, there are eighteen provinces whose shadow prices are lower than market prices. This result suggests that energy utilization is at a low level in these provinces and can be improved by a reallocation of inputs. Full article
(This article belongs to the Special Issue Energy Policy and Climate Change) Printed Edition available
Open AccessArticle Impact of Organic Loading Rate on Psychrophilic Anaerobic Digestion of Solid Dairy Manure
Energies 2015, 8(3), 1990-2007; doi:10.3390/en8031990
Received: 21 November 2014 / Revised: 24 February 2015 / Accepted: 3 March 2015 / Published: 13 March 2015
Cited by 4 | PDF Full-text (522 KB) | HTML Full-text | XML Full-text
Abstract
Increasing the feed total solids to anaerobic digester improves the process economics and decreases the volume of liquid effluent from current wet anaerobic digestion. The objective of this study was to develop a novel psychrophilic (20 °C) anaerobic digestion technology of undiluted cow
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Increasing the feed total solids to anaerobic digester improves the process economics and decreases the volume of liquid effluent from current wet anaerobic digestion. The objective of this study was to develop a novel psychrophilic (20 °C) anaerobic digestion technology of undiluted cow feces (total solids of 11%–16%). Two sets of duplicate laboratory-scale sequence batch bioreactors have been operated at organic loading rates (OLR) of 6.0 to 8.0 g total chemical oxygen demand (TCOD) kg−1 inoculum day−1 (d−1) during 210 days. The results demonstrated that the process is feasible at treatment cycle length (TCL) of 21 days; however, the quality of cow feces rather than the OLR had a direct influence on the specific methane yield (SMY). The SMY ranged between 124.5 ± 1.4 and 227.9 ± 4.8 normalized liter (NL) CH4 kg−1 volatile solids (VS) fed d−1. Substrate-to-inoculum mass ratio (SIR) was 0.63 ± 0.05, 0.90 ± 0.09, and 1.06 ± 0.07 at OLR of 6.0, 7.0, and 8.0 g TCOD kg−1 inoculum d−1, respectively. No volatile fatty acids (VFAs) accumulation has been observed which indicated that hydrolysis was the rate limiting step and VFAs have been consumed immediately. Bioreactors performance consistency in terms of the level of SMYs, VFAs concentrations at end of the TCL, pH stability and volatile solids reduction indicates a stable and reproducible process during the entire operation. Full article
(This article belongs to the collection Bioenergy and Biofuel)
Open AccessArticle New TA Index-Based Rollover Prevention System for Electric Vehicles
Energies 2015, 8(3), 2008-2031; doi:10.3390/en8032008
Received: 20 November 2014 / Revised: 12 February 2015 / Accepted: 13 February 2015 / Published: 13 March 2015
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Abstract
In addition to clean transportation and energy savings, electric vehicles can inherently offer better performance in the field of active safety and dynamic stability control, thanks to the superior fast and accurate control characteristics of electric motors. With the novel wheel status parameter
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In addition to clean transportation and energy savings, electric vehicles can inherently offer better performance in the field of active safety and dynamic stability control, thanks to the superior fast and accurate control characteristics of electric motors. With the novel wheel status parameter TA for electric vehicles proposed by the authors in an earlier publication, a new TA index (TAI)-based rollover prevention method is presented in this paper to improve the driving performance of EVs equipped with in-wheel motors. A three-level electric vehicle control structure is used to analyze the effective control steps for rollover prevention with the newly proposed TAI method. The simulation is conducted using an in-house developed electric vehicle dynamic model. The simulation results prove the feasibility of using TAI to detect rollover. The experiment uses an electric vehicle equipped with four in-wheel motors in the authors’ research lab. The vehicle parameter and performance data are imported to CarSim, which is industrial standard vehicle dynamic analysis software to run the rollover test. The experimental results also demonstrate that TAI is an effective method of rollover prevention. Full article
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; doi:10.3390/en8032032
Received: 6 January 2015 / Revised: 18 February 2015 / Accepted: 28 February 2015 / Published: 13 March 2015
Cited by 3 | 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,
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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
Open AccessArticle Integration of a Water Scrubbing Technique and Two-Stage Pressurized Anaerobic Digestion in One Process
Energies 2015, 8(3), 2048-2065; doi:10.3390/en8032048
Received: 23 December 2014 / Revised: 13 February 2015 / Accepted: 15 February 2015 / Published: 13 March 2015
Cited by 5 | 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
Open AccessArticle Radiological Impacts and Regulation of Rare Earth Elements in Non-Nuclear Energy Production
Energies 2015, 8(3), 2066-2081; doi: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 Fabrication and Test of an Air-Breathing Microfluidic Fuel Cell
Energies 2015, 8(3), 2082-2096; doi:10.3390/en8032082
Received: 18 January 2015 / Revised: 23 February 2015 / Accepted: 5 March 2015 / Published: 16 March 2015
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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
Open AccessArticle Thermo-Economic Evaluation of Organic Rankine Cycles for Geothermal Power Generation Using Zeotropic Mixtures
Energies 2015, 8(3), 2097-2124; doi:10.3390/en8032097
Received: 30 January 2015 / Revised: 4 March 2015 / Accepted: 11 March 2015 / Published: 17 March 2015
Cited by 16 | 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))
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; doi:10.3390/en8032125
Received: 3 November 2014 / Accepted: 12 March 2015 / Published: 18 March 2015
Cited by 6 | 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
Open AccessArticle Load Frequency Control in Isolated Micro-Grids with Electrical Vehicles Based on Multivariable Generalized Predictive Theory
Energies 2015, 8(3), 2145-2164; doi:10.3390/en8032145
Received: 16 October 2014 / Accepted: 4 March 2015 / Published: 18 March 2015
Cited by 15 | 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
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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)
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; doi:10.3390/en8032165
Received: 8 October 2014 / Revised: 24 December 2014 / Accepted: 3 March 2015 / Published: 19 March 2015
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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)
Open AccessArticle Estimation of CO2 Transport Costs in South Korea Using a Techno-Economic Model
Energies 2015, 8(3), 2176-2196; doi:10.3390/en8032176
Received: 16 December 2014 / Revised: 5 March 2015 / Accepted: 16 March 2015 / Published: 19 March 2015
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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
Open AccessArticle Experimental Analysis of Cool Traditional Solar Shading Systems for Residential Buildings
Energies 2015, 8(3), 2197-2210; doi:10.3390/en8032197
Received: 9 February 2015 / Revised: 10 March 2015 / Accepted: 12 March 2015 / Published: 20 March 2015
Cited by 10 | 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
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; doi:10.3390/en8032211
Received: 3 November 2014 / Revised: 4 March 2015 / Accepted: 12 March 2015 / Published: 20 March 2015
Cited by 2 | 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
Open AccessArticle Modeling Innovative Power Take-Off Based on Double-Acting Hydraulic Cylinders Array for Wave Energy Conversion
Energies 2015, 8(3), 2230-2267; doi:10.3390/en8032230
Received: 28 January 2015 / Revised: 27 February 2015 / Accepted: 2 March 2015 / Published: 20 March 2015
Cited by 2 | 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
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; doi:10.3390/en8032268
Received: 12 October 2014 / Revised: 28 January 2015 / Accepted: 16 March 2015 / Published: 23 March 2015
Cited by 9 | 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 AccessReview Heat Recovery from High Temperature Slags: A Review of Chemical Methods
Energies 2015, 8(3), 1917-1935; doi:10.3390/en8031917
Received: 3 December 2014 / Revised: 13 January 2015 / Accepted: 5 March 2015 / Published: 12 March 2015
Cited by 20 | PDF Full-text (652 KB) | HTML Full-text | XML Full-text
Abstract
Waste heat recovery from high temperature slags represents the latest potential way to remarkably reduce the energy consumption and CO2 emissions of the steel industry. The molten slags, in the temperature range of 1723–1923 K, carry large amounts of high quality energy.
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Waste heat recovery from high temperature slags represents the latest potential way to remarkably reduce the energy consumption and CO2 emissions of the steel industry. The molten slags, in the temperature range of 1723–1923 K, carry large amounts of high quality energy. However, the heat recovery from slags faces several fundamental challenges, including their low thermal conductivity, inside crystallization, and discontinuous availability. During past decades, various chemical methods have been exploited and performed including methane reforming, coal and biomass gasification, and direct compositional modification and utilization of slags. These methods effectively meet the challenges mentioned before and help integrate the steel industry with other industrial sectors. During the heat recovery using chemical methods, slags can act as not only heat carriers but also as catalysts and reactants, which expands the field of utilization of slags. Fuel gas production using the waste heat accounts for the main R&D trend, through which the thermal heat in the slag could be transformed into high quality chemical energy in the fuel gas. Moreover, these chemical methods should be extended to an industrial scale to realize their commercial application, which is the only way by which the substantial energy in the slags could be extracted, i.e., amounting to 16 million tons of standard coal in China. Full article
(This article belongs to the Special Issue Recent Advances in Coal Combustion and Gasification)

Other

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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; doi: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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