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Energies, Volume 8, Issue 1 (January 2015) , Pages 1-683

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Open AccessCorrection
Correction: Jastrzebski, R.P.; Smirnov, A.; Mystkowski, A.; Pyrhönen, O. Cascaded Position-Flux Controller for an AMB System Operating at Zero Bias. Energies 2014, 7, 3561–3575
Energies 2015, 8(1), 682-683; https://doi.org/10.3390/en8010682
Received: 24 September 2014 / Accepted: 22 December 2014 / Published: 20 January 2015
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Abstract
The authors wish to make the following corrections to this paper [1]: Figure 7 on page 3573 should be changed from:[...] Full article
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Open AccessArticle
Mechanism Analysis and Experimental Validation of Employing Superconducting Magnetic Energy Storage to Enhance Power System Stability
Energies 2015, 8(1), 656-681; https://doi.org/10.3390/en8010656
Received: 18 November 2014 / Revised: 22 December 2014 / Accepted: 12 January 2015 / Published: 20 January 2015
Cited by 4 | Viewed by 2842 | PDF Full-text (1474 KB) | HTML Full-text | XML Full-text
Abstract
This paper investigates the mechanism analysis and the experimental validation of employing superconducting magnetic energy storage (SMES) to enhance power system stability. The models of the SMES device and the single-machine infinite-bus (SMIB) system with SMES are deduced. Based on the model of [...] Read more.
This paper investigates the mechanism analysis and the experimental validation of employing superconducting magnetic energy storage (SMES) to enhance power system stability. The models of the SMES device and the single-machine infinite-bus (SMIB) system with SMES are deduced. Based on the model of the SMIB system with SMES, the action mechanism of SMES on a generator is analyzed. The analysis takes the impact of SMES location and the system operating point into consideration, as well. Based on the mechanism analysis, the P-controller and Q-controller are designed utilizing the phase compensation method to improve the damping of the SMIB system. The influence of factors, such as SMES location, transmission system reactance, the dynamic characteristics of SMES and the system operating point, on the damping improvement of SMES, is investigated through root locus analysis. The simulation results of the SMIB test system verify the analysis conclusions and controller design method. The laboratory results of the 150-kJ/100-kW high-temperature SMES (HT-SMES) device validate that the SMES device can effectively enhance the damping, as well as the transient stability of the power system. Full article
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Open AccessArticle
Determination of Methane and Carbon Dioxide Formation Rate Constants for Semi-Continuously Fed Anaerobic Digesters
Energies 2015, 8(1), 645-655; https://doi.org/10.3390/en8010645
Received: 3 December 2014 / Accepted: 13 January 2015 / Published: 16 January 2015
Cited by 7 | Viewed by 2687 | PDF Full-text (511 KB) | HTML Full-text | XML Full-text
Abstract
To optimize commercial-scale biogas production, it is important to evaluate the performance of each microbial step in the anaerobic process. Hydrolysis and methanogenesis are usually the rate-limiting steps during digestion of organic waste and by-products. By measuring biogas production and methane concentrations on-line [...] Read more.
To optimize commercial-scale biogas production, it is important to evaluate the performance of each microbial step in the anaerobic process. Hydrolysis and methanogenesis are usually the rate-limiting steps during digestion of organic waste and by-products. By measuring biogas production and methane concentrations on-line in a semi-continuously fed reactor, gas kinetics can be evaluated. In this study, the rate constants of the fermentative hydrolysis step (kc) and the methanogenesis step (km) were determined and evaluated in a continuously stirred tank laboratory-scale reactor treating food and slaughterhouse waste and glycerin. A process additive containing Fe2+, Co2+ and Ni2+ was supplied until day 89, after which Ni2+ was omitted. The omission resulted in a rapid decline in the methanogenesis rate constant (km) to 70% of the level observed when Ni2+ was present, while kc remained unaffected. This suggests that Ni2+ mainly affects the methanogenic rather than the hydrolytic microorganisms in the system. However, no effect was initially observed when using conventional process monitoring parameters such as biogas yield and volatile fatty acid concentration. Hence, formation rate constants can reveal additional information on process performance and km can be used as a complement to conventional process monitoring tools for semi-continuously fed anaerobic digesters. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle
Life Cycle Assessment of Biochar versus Metal Catalysts Used in Syngas Cleaning
Energies 2015, 8(1), 621-644; https://doi.org/10.3390/en8010621
Received: 24 September 2014 / Accepted: 10 December 2014 / Published: 15 January 2015
Cited by 5 | Viewed by 2507 | PDF Full-text (803 KB) | HTML Full-text | XML Full-text
Abstract
Biomass gasification has the potential to produce renewable fuels, chemicals and power at large utility scale facilities. In these plants catalysts would likely be used to reform and clean the generated biomass syngas. Traditional catalysts are made from transition metals, while catalysts made [...] Read more.
Biomass gasification has the potential to produce renewable fuels, chemicals and power at large utility scale facilities. In these plants catalysts would likely be used to reform and clean the generated biomass syngas. Traditional catalysts are made from transition metals, while catalysts made from biochar are being studied. A life cycle assessment (LCA) study was performed to analyze the sustainability, via impact assessments, of producing a metal catalyst versus a dedicated biochar catalyst. The LCA results indicate that biochar has a 93% reduction in greenhouse gas (GHG) emissions and requires 95.7% less energy than the metal catalyst to produce. The study also estimated that biochar production would also have fewer impacts on human health (e.g., carcinogens and respiratory impacts) than the production of a metal catalyst. The possible disadvantage of biochar production in the ecosystem quality is due mostly to its impacts on agricultural land occupation. Sensitivity analysis was carried out to assess environmental impacts of variability in the two production systems. In the metal catalyst manufacture, the extraction and production of nickel (Ni) had significant negative effects on the environmental impacts. For biochar production, low moisture content (MC, 9%) and high yield type (8 tons/acre) switchgrass appeared more sustainable. Full article
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Open AccessArticle
Energy-Saving Lipid Extraction from Wet Euglena gracilis by the Low-Boiling-Point Solvent Dimethyl Ether
Energies 2015, 8(1), 610-620; https://doi.org/10.3390/en8010610
Received: 4 November 2014 / Accepted: 8 January 2015 / Published: 15 January 2015
Cited by 8 | Viewed by 2742 | PDF Full-text (418 KB) | HTML Full-text | XML Full-text
Abstract
We tested a wet extraction method for lipid extraction from Euglena gracilis water slurry at 0.51 MPa and 20 °C using liquefied dimethyl ether (DME). The yields, proximate analyses, elemental composition, and molecular weight distribution properties of the extracts from E. gracilis and [...] Read more.
We tested a wet extraction method for lipid extraction from Euglena gracilis water slurry at 0.51 MPa and 20 °C using liquefied dimethyl ether (DME). The yields, proximate analyses, elemental composition, and molecular weight distribution properties of the extracts from E. gracilis and the remaining residues obtained by DME extraction were compared with those of the extracts obtained by hexane Soxhlet extraction. Full article
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Open AccessReview
The Socio-Demographic and Psychological Predictors of Residential Energy Consumption: A Comprehensive Review
Energies 2015, 8(1), 573-609; https://doi.org/10.3390/en8010573
Received: 23 October 2014 / Accepted: 11 December 2014 / Published: 15 January 2015
Cited by 56 | Viewed by 4350 | PDF Full-text (334 KB) | HTML Full-text | XML Full-text
Abstract
This article provides a comprehensive review of theory and research on the individual-level predictors of household energy usage. Drawing on literature from across the social sciences, we examine two broad categories of variables that have been identified as potentially important for explaining variability [...] Read more.
This article provides a comprehensive review of theory and research on the individual-level predictors of household energy usage. Drawing on literature from across the social sciences, we examine two broad categories of variables that have been identified as potentially important for explaining variability in energy consumption and conservation: socio-demographic factors (e.g., income, employment status, dwelling type/size, home ownership, household size, stage of family life cycle) and psychological factors (e.g., beliefs and attitudes, motives and intentions, perceived behavioral control, cost-benefit appraisals, personal and social norms). Despite an expanding literature, we find that empirical evidence of the impact of these variables has been far from consistent and conclusive to date. Such inconsistency poses challenges for drawing generalizable conclusions, and underscores the complexity of consumer behavior in this domain. In this article, we propose that a multitude of factors—whether directly, indirectly, or in interaction—influence how householders consume and conserve energy. Theory, research and practice can be greatly advanced by understanding what these factors are, and how, when, where, why and for whom they operate. We conclude by outlining some important practical implications for policymakers and directions for future research. Full article
(This article belongs to the Special Issue Energy Policy and Climate Change) Printed Edition available
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Open AccessArticle
Power Quality Disturbances Recognition Based on a Multiresolution Generalized S-Transform and a PSO-Improved Decision Tree
Energies 2015, 8(1), 549-572; https://doi.org/10.3390/en8010549
Received: 30 September 2014 / Accepted: 7 January 2015 / Published: 15 January 2015
Cited by 14 | Viewed by 2335 | PDF Full-text (2080 KB) | HTML Full-text | XML Full-text
Abstract
In a microgrid, the distributed generators (DG) can power the user loads directly. As a result, power quality (PQ) events are more likely to affect the users. This paper proposes a Multiresolution Generalized S-transform (MGST) approach to improve the ability of analyzing and [...] Read more.
In a microgrid, the distributed generators (DG) can power the user loads directly. As a result, power quality (PQ) events are more likely to affect the users. This paper proposes a Multiresolution Generalized S-transform (MGST) approach to improve the ability of analyzing and monitoring the power quality in a microgrid. Firstly, the time-frequency distribution characteristics of different types of disturbances are analyzed. Based on the characteristics, the frequency domain is segmented into three frequency areas. After that, the width factor of the window function in the S-transform is set in different frequency areas. MGST has different time-frequency resolution in each frequency area to satisfy the recognition requirements of different disturbances in each frequency area. Then, a rule-based decision tree classifier is designed. In addition, particle swarm optimization (PSO) is applied to extract the applicable features. Finally, the proposed method is compared with some others. The simulation experiments show that the new approach has better accuracy and noise immunity. Full article
(This article belongs to the Special Issue Microgrids)
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Open AccessArticle
Theoretical Exploration of Various Lithium Peroxide Crystal Structures in a Li-Air Battery
Energies 2015, 8(1), 529-548; https://doi.org/10.3390/en8010529
Received: 11 November 2014 / Accepted: 6 January 2015 / Published: 14 January 2015
Cited by 9 | Viewed by 3069 | PDF Full-text (2149 KB) | HTML Full-text | XML Full-text
Abstract
We describe a series of metastable Li2O2 crystal structures involving different orientations and displacements of the O22− peroxy ions based on the known Li2O2 crystal structure. Within the vicinity of the chemical potential ΔG ~ [...] Read more.
We describe a series of metastable Li2O2 crystal structures involving different orientations and displacements of the O22− peroxy ions based on the known Li2O2 crystal structure. Within the vicinity of the chemical potential ΔG ~ 0.20 eV/Li from the thermodynamic ground state of the Li2O2 crystal structure (i.e., Föppl structure), all of these newly found metastable Li2O2 crystal structures are found to be insulating and high-k materials, and they have a common unique signature of an O22− O-O vibration mode (ω ~ 799–865 cm−1), which is in the range of that commonly observed in Li-air battery experiments, regardless of the random O22− orientations and the symmetry in the crystal lattice. From XRD patterns analysis, the commercially available Li2O2 powder is confirmed to be the thermodynamic ground state Föppl-like structure. However, for Li2O2 compounds that are grown electrochemically under the environment of Li-O2 cells, we found that the XRD patterns alone are not sufficient for structural identification of these metastable Li2O2 crystalline phases due to the poor crystallinity of the sample. In addition, the commonly known Raman signal of O22− vibration mode is also found to be insufficient to validate the possible existence of these newly predicted Li2O2 crystal structures, as all of them similarly share the similar O22− vibration mode. However considering that the discharge voltage in most Li-O2 cells are typically several tenths of an eV below the thermodynamic equilibrium for the formation of ground state Föppl structure, the formation of these metastable Li2O2 crystal structures appears to be thermodynamically feasible. Full article
(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)
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Open AccessArticle
Hybrid Statistical Testing for Nuclear Material Accounting Data and/or Process Monitoring Data in Nuclear Safeguards
Energies 2015, 8(1), 501-528; https://doi.org/10.3390/en8010501
Received: 13 November 2014 / Accepted: 15 December 2014 / Published: 13 January 2015
Cited by 2 | Viewed by 2353 | PDF Full-text (781 KB) | HTML Full-text | XML Full-text
Abstract
The aim of nuclear safeguards is to ensure that special nuclear material is used for peaceful purposes. Historically, nuclear material accounting (NMA) has provided the quantitative basis for monitoring for nuclear material loss or diversion, and process monitoring (PM) data is collected by [...] Read more.
The aim of nuclear safeguards is to ensure that special nuclear material is used for peaceful purposes. Historically, nuclear material accounting (NMA) has provided the quantitative basis for monitoring for nuclear material loss or diversion, and process monitoring (PM) data is collected by the operator to monitor the process. PM data typically support NMA in various ways, often by providing a basis to estimate some of the in-process nuclear material inventory. We develop options for combining PM residuals and NMA residuals (residual = measurement − prediction), using a hybrid of period-driven and data-driven hypothesis testing. The modified statistical tests can be used on time series of NMA residuals (the NMA residual is the familiar material balance), or on a combination of PM and NMA residuals. The PM residuals can be generated on a fixed time schedule or as events occur. Full article
(This article belongs to the Special Issue Advances in Nuclear Reactor and Fuel Cycle Technologies)
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Open AccessArticle
A Thermal Runaway Simulation on a Lithium Titanate Battery and the Battery Module
Energies 2015, 8(1), 490-500; https://doi.org/10.3390/en8010490
Received: 28 November 2014 / Accepted: 7 January 2015 / Published: 13 January 2015
Cited by 44 | Viewed by 3855 | PDF Full-text (970 KB) | HTML Full-text | XML Full-text
Abstract
Based on the electrochemical and thermal model, a coupled electro-thermal runaway model was developed and implemented using finite element methods. The thermal decomposition reactions when the battery temperature exceeds the material decomposition temperature were embedded into the model. The temperature variations of a [...] Read more.
Based on the electrochemical and thermal model, a coupled electro-thermal runaway model was developed and implemented using finite element methods. The thermal decomposition reactions when the battery temperature exceeds the material decomposition temperature were embedded into the model. The temperature variations of a lithium titanate battery during a series of charge-discharge cycles under different current rates were simulated. The results of temperature and heat generation rate demonstrate that the greater the current, the faster the battery temperature is rising. Furthermore, the thermal influence of the overheated cell on surrounding batteries in the module was simulated, and the variation of temperature and heat generation during thermal runaway was obtained. It was found that the overheated cell can induce thermal runaway in other adjacent cells within 3 mm distance in the battery module if the accumulated heat is not dissipated rapidly. Full article
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Open AccessArticle
Wind Power Prediction Considering Nonlinear Atmospheric Disturbances
Energies 2015, 8(1), 475-489; https://doi.org/10.3390/en8010475
Received: 11 November 2014 / Accepted: 5 January 2015 / Published: 13 January 2015
Cited by 16 | Viewed by 2050 | PDF Full-text (365 KB) | HTML Full-text | XML Full-text
Abstract
This paper considers the effect of nonlinear atmospheric disturbances on wind power prediction. A Lorenz system is introduced as an atmospheric disturbance model. Three new improved wind forecasting models combined with a Lorenz comprehensive disturbance are put forward in this study. Firstly, we [...] Read more.
This paper considers the effect of nonlinear atmospheric disturbances on wind power prediction. A Lorenz system is introduced as an atmospheric disturbance model. Three new improved wind forecasting models combined with a Lorenz comprehensive disturbance are put forward in this study. Firstly, we define the form of the Lorenz disturbance variable and the wind speed perturbation formula. Then, different artificial neural network models are used to verify the new idea and obtain better wind speed predictions. Finally we separately use the original and improved wind speed series to predict the related wind power. This proves that the corrected wind speed provides higher precision wind power predictions. This research presents a totally new direction in the wind prediction field and has profound theoretical research value and practical guiding significance. Full article
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Open AccessArticle
Anaerobic Digestion and Biogas Potential: Simulation of Lab and Industrial-Scale Processes
Energies 2015, 8(1), 454-474; https://doi.org/10.3390/en8010454
Received: 2 October 2014 / Accepted: 31 December 2014 / Published: 13 January 2015
Cited by 10 | Viewed by 3014 | PDF Full-text (1416 KB) | HTML Full-text | XML Full-text
Abstract
In this study, a simulation was carried out using BioWin 3.1 to test the capability of the software to predict the biogas potential for two different anaerobic systems. The two scenarios included: (1) a laboratory-scale batch reactor; and (2) an industrial-scale anaerobic continuous [...] Read more.
In this study, a simulation was carried out using BioWin 3.1 to test the capability of the software to predict the biogas potential for two different anaerobic systems. The two scenarios included: (1) a laboratory-scale batch reactor; and (2) an industrial-scale anaerobic continuous lagoon digester. The measured data related to the operating conditions, the reactor design parameters and the chemical properties of influent wastewater were entered into BioWin. A sensitivity analysis was carried out to identify the sensitivity of the most important default parameters in the software’s models. BioWin was then calibrated by matching the predicted data with measured data and used to simulate other parameters that were unmeasured or deemed uncertain. In addition, statistical analyses were carried out using evaluation indices, such as the coefficient of determination (R-squared), the correlation coefficient (r) and its significance (p-value), the general standard deviation (SD) and the Willmott index of agreement, to evaluate the agreement between the software prediction and the measured data. The results have shown that after calibration, BioWin can be used reliably to simulate both small-scale batch reactors and industrial-scale digesters with a mean absolute percentage error (MAPE) of less than 10% and very good values of the indexes. Furthermore, by changing the default parameters in BioWin, which is a way of calibrating the models in the software, as well, this may provide information about the performance of the digester. Furthermore, the results of this study showed there may be an over estimation for biogas generated from industrial-scale digesters. More sophisticated analytical devices may be required for reliable measurements of biogas quality and quantity. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessReview
Recent Advances in the Use of Sodium Borohydride as a Solid State Hydrogen Store
Energies 2015, 8(1), 430-453; https://doi.org/10.3390/en8010430
Received: 22 October 2014 / Accepted: 15 December 2014 / Published: 13 January 2015
Cited by 32 | Viewed by 3010 | PDF Full-text (817 KB) | HTML Full-text | XML Full-text
Abstract
The development of new practical hydrogen storage materials with high volumetric and gravimetric hydrogen densities is necessary to implement fuel cell technology for both mobile and stationary applications. NaBH4, owing to its low cost and high hydrogen density (10.6 wt%), has [...] Read more.
The development of new practical hydrogen storage materials with high volumetric and gravimetric hydrogen densities is necessary to implement fuel cell technology for both mobile and stationary applications. NaBH4, owing to its low cost and high hydrogen density (10.6 wt%), has received extensive attention as a promising hydrogen storage medium. However, its practical use is hampered by its high thermodynamic stability and slow hydrogen exchange kinetics. Recent developments have been made in promoting H2 release and tuning the thermodynamics of the thermal decomposition of solid NaBH4. These conceptual advances offer a positive outlook for using NaBH4-based materials as viable hydrogen storage carriers for mobile applications. This review summarizes contemporary progress in this field with a focus on the fundamental dehydrogenation and rehydrogenation pathways and properties and on material design strategies towards improved kinetics and thermodynamics such as catalytic doping, nano-engineering, additive destabilization and chemical modification. Full article
(This article belongs to the Special Issue Hydrides: Fundamentals and Applications) Printed Edition available
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Open AccessArticle
Development of a Photosynthetic Microbial Electrochemical Cell (PMEC) Reactor Coupled with Dark Fermentation of Organic Wastes: Medium Term Perspectives
Energies 2015, 8(1), 399-429; https://doi.org/10.3390/en8010399
Received: 29 August 2014 / Accepted: 16 December 2014 / Published: 13 January 2015
Cited by 10 | Viewed by 4112 | PDF Full-text (1311 KB) | HTML Full-text | XML Full-text
Abstract
In this article the concept, the materials and the exploitation potential of a photosynthetic microbial electrochemical cell for the production of hydrogen driven by solar power are investigated. In a photosynthetic microbial electrochemical cell, which is based on photosynthetic microorganisms confined to an [...] Read more.
In this article the concept, the materials and the exploitation potential of a photosynthetic microbial electrochemical cell for the production of hydrogen driven by solar power are investigated. In a photosynthetic microbial electrochemical cell, which is based on photosynthetic microorganisms confined to an anode and heterotrophic bacteria confined to a cathode, water is split by bacteria hosted in the anode bioactive film. The generated electrons are conveyed through external “bio-appendages” developed by the bacteria to transparent nano-pillars made of indium tin oxide (ITO), Fluorine-doped tin oxide (FTO) or other conducting materials, and then transferred to the cathode. On the other hand, the generated protons diffuse to the cathode via a polymer electrolyte membrane, where they are reduced by the electrons by heterotrophic bacteria growing attached to a similar pillared structure as that envisaged for the anode and supplemented with a specific low cost substrate (e.g., organic waste, anaerobic digestion outlet). The generated oxygen is released to the atmosphere or stored, while the produced pure hydrogen leaves the electrode through the porous layers. In addition, the integration of the photosynthetic microbial electrochemical cell system with dark fermentation as acidogenic step of anaerobic digester, which is able to produce additional H2, and the use of microbial fuel cell, feed with the residues of dark fermentation (mainly volatile fatty acids), to produce the necessary extra-bias for the photosynthetic microbial electrochemical cell is here analyzed to reveal the potential benefits to this novel integrated technology. Full article
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Open AccessEditorial
Acknowledgement to Reviewers of Energies in 2014
Energies 2015, 8(1), 387-398; https://doi.org/10.3390/en8010387
Received: 12 January 2015 / Accepted: 12 January 2015 / Published: 12 January 2015
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Abstract
The editors of Energies would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2014:[...] Full article
Open AccessArticle
Altering Kinetic Energy Entrainment in Large Eddy Simulations of Large Wind Farms Using Unconventional Wind Turbine Actuator Forcing
Energies 2015, 8(1), 370-386; https://doi.org/10.3390/en8010370
Received: 30 October 2014 / Accepted: 30 December 2014 / Published: 6 January 2015
Cited by 16 | Viewed by 3080 | PDF Full-text (4252 KB) | HTML Full-text | XML Full-text
Abstract
In this study, horizontally periodic large eddy simulations (LES) are utilized to study turbulent atmospheric boundary-layer flow over wind turbines in the far-downstream portion of a large wind farm where the wakes have merged and the flow is fully developed. In an attempt [...] Read more.
In this study, horizontally periodic large eddy simulations (LES) are utilized to study turbulent atmospheric boundary-layer flow over wind turbines in the far-downstream portion of a large wind farm where the wakes have merged and the flow is fully developed. In an attempt to increase power generation by enhancing the mean kinetic energy (MKE) entrainment to the wind turbines, hypothetical synthetic forcing is applied to the flow at the turbine rotor locations. The synthetic forcing is not meant to represent any existing devices or control schemes, but rather acts as a proof of concept to inform future designs. The turbines are modeled using traditional actuator disks, and the unconventional synthetic forcing is applied in the vertical direction with the magnitude and direction dependent on the instantaneous velocity fluctuation at the rotor disk; in one set of LES meant to enhance the vertical entrainment of MKE, a downward force is prescribed in conjunction with a positive axial velocity fluctuation, whereas a negative axial velocity fluctuation results in an upward force. The magnitude of the forcing is proportional to the instantaneous thrust force with prefactors ranging from 0.1 to 1. The synthetic vertical forcing is found to have a significant effect on the power generated by the wind farm. Consistent with previous findings, the MKE flux to the level of the turbines is found to vary along with the total power produced by the wind turbine array. The reverse strategy of downward forcing of slow axial velocity flow is found to have almost no effect on the power output or entrainment. Several of the scenarios tested, e.g., where the vertical force is of similar magnitude to the horizontal thrust, would be very difficult to implement in practice, but the simulations serve the purpose of identifying trends and bounds on possible power increases from flow modifications through action at the turbine rotor. Full article
(This article belongs to the collection Wind Turbines) Printed Edition available
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Open AccessArticle
Synchronising Energy Harvesting and Data Packets in a Wireless Sensor
Energies 2015, 8(1), 356-369; https://doi.org/10.3390/en8010356
Received: 20 November 2014 / Accepted: 26 December 2014 / Published: 5 January 2015
Cited by 26 | Viewed by 2454 | PDF Full-text (177 KB) | HTML Full-text | XML Full-text
Abstract
We consider a wireless sensor node that gathers energy through harvesting and reaps data through sensing. The node has a wireless transmitter that sends out a data packet whenever there is at least one “energy packet” and one “data packet”, where an energy [...] Read more.
We consider a wireless sensor node that gathers energy through harvesting and reaps data through sensing. The node has a wireless transmitter that sends out a data packet whenever there is at least one “energy packet” and one “data packet”, where an energy packet represents the amount of accumulated energy at the node that can allow the transmission of a data packet. We show that such a system is unstable when both the energy storage space and the data backlog buffer approach infinity, and we obtain the stable stationary solution when both buffers are finite. We then show that if a single energy packet is not sufficient to transmit a data packet, there are conditions under which the system is stable, and we provide the explicit expression for the joint probability distribution of the number of energy and data packets in the system. Since the two flows of energy and data can be viewed as flows that are instantaneously synchronised, this paper also provides a mathematical analysis of a fundamental problem in computer science related to the stability of the “join” synchronisation primitive. Full article
(This article belongs to the Special Issue Green IT and IT for Smart Energy Savings)
Open AccessArticle
Simulation of Standby Efficiency Improvement for a Line Level Control Resonant Converter Based on Solar Power Systems
Energies 2015, 8(1), 338-355; https://doi.org/10.3390/en8010338
Received: 13 September 2014 / Accepted: 22 December 2014 / Published: 5 January 2015
Cited by 2 | Viewed by 3272 | PDF Full-text (871 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a new scheme to improve the standby efficiency of the high-power half-bridge line level control (LLC) resonant converter. This new circuit is applicable to improving the efficiency of the renewable energy generation system in distributed power systems. The main purpose [...] Read more.
This paper proposes a new scheme to improve the standby efficiency of the high-power half-bridge line level control (LLC) resonant converter. This new circuit is applicable to improving the efficiency of the renewable energy generation system in distributed power systems. The main purpose is to achieve high-efficiency solar and wind power and stable output under different load conditions. In comparison with the traditional one, this novel method can improve standby efficiency at standby. The system characteristics of this proposed method have been analyzed through detailed simulations, which prove its feasibility. Full article
(This article belongs to the Special Issue Next Generation of Photovoltaic (PV) Technology)
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Open AccessArticle
Hydrogen Storage in Boron Nitride and Carbon Nanomaterials
Energies 2015, 8(1), 319-337; https://doi.org/10.3390/en8010319
Received: 10 September 2014 / Accepted: 26 December 2014 / Published: 31 December 2014
Cited by 13 | Viewed by 3785 | PDF Full-text (4965 KB) | HTML Full-text | XML Full-text
Abstract
Boron nitride (BN) nanomaterials were synthesized from LaB6 and Pd/boron powder, and the hydrogen storage was investigated by differential thermogravimetric analysis, which showed possibility of hydrogen storage of 1–3 wt%. The hydrogen gas storage in BN and carbon (C) clusters was also [...] Read more.
Boron nitride (BN) nanomaterials were synthesized from LaB6 and Pd/boron powder, and the hydrogen storage was investigated by differential thermogravimetric analysis, which showed possibility of hydrogen storage of 1–3 wt%. The hydrogen gas storage in BN and carbon (C) clusters was also investigated by molecular orbital calculations, which indicated possible hydrogen storage of 6.5 and 4.9 wt%, respectively. Chemisorption calculation was also carried out for B24N24 cluster with changing endohedral elements in BN cluster to compare the bonding energy at nitrogen and boron, which showed that Li is a suitable element for hydrogenation to the BN cluster. The BN cluster materials would store H2 molecule easier than carbon fullerene materials, and its stability for high temperature would be good. Molecular dynamics calculations showed that a H2 molecule remains stable in a C60 cage at 298 K and 0.1 MPa, and that pressures over 5 MPa are needed to store H2 molecules in the C60 cage. Full article
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Open AccessArticle
Characterization of Anaerobic Degradability and Kinetics of Harvested Submerged Aquatic Weeds Used for Nutrient Phytoremediation
Energies 2015, 8(1), 304-318; https://doi.org/10.3390/en8010304
Received: 25 November 2014 / Accepted: 26 December 2014 / Published: 31 December 2014
Cited by 16 | Viewed by 2687 | PDF Full-text (490 KB) | HTML Full-text | XML Full-text
Abstract
In this study, eight different submerged aquatic species were screened by batch biochemical methane potential and anaerobic degradability tests to identify a promising/suitable feedstock. Kinetics of the best-screened substrate were studied in a mesophilic semi-continuous experiment. The aquatic species Myriophyllum aquaticum, Egeria [...] Read more.
In this study, eight different submerged aquatic species were screened by batch biochemical methane potential and anaerobic degradability tests to identify a promising/suitable feedstock. Kinetics of the best-screened substrate were studied in a mesophilic semi-continuous experiment. The aquatic species Myriophyllum aquaticum, Egeria densa and Potamogeton perfoliatus showed relatively higher methane yields of over 400 NmL/g-VS (volatile solids). Semi-continuous operation was carried out by feeding E. densa for over 400 days. The achieved results were 33%–53% chemical oxygen demand (COD) reduction and methane yield of 126–231 NmL/g-VS with a short hydraulic retention time (HRT). Additionally, the NH4+ and PO43− releases from the biomass to water were found to be low (18%–27% and 2.5%–3.9%) throughout the experiment. Hydrolysis was the limiting step in the digestion of E. densa, regardless of changes in HRT (15–45 days). The acid-phase model indicated that the hydrolysis rate constant (kh) of E. densa was 0.058 one/day, which was one third lower the kh value of food waste, but quite similar to cow manure. Full article
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Open AccessArticle
Crop Management Effects on the Energy and Carbon Balances of Maize Stover-Based Ethanol Production
Energies 2015, 8(1), 278-303; https://doi.org/10.3390/en8010278
Received: 19 September 2014 / Accepted: 23 December 2014 / Published: 31 December 2014
Cited by 1 | Viewed by 2480 | PDF Full-text (1168 KB) | HTML Full-text | XML Full-text
Abstract
This study was conducted to identify the crop management options—the combinations of various cultivars, irrigation amounts, planting dates, and soils—that would maximize the energy sustainability and eco-friendliness of maize (Zea mays L.) stover-based ethanol production systems in the Mississippi Delta. Stover yields [...] Read more.
This study was conducted to identify the crop management options—the combinations of various cultivars, irrigation amounts, planting dates, and soils—that would maximize the energy sustainability and eco-friendliness of maize (Zea mays L.) stover-based ethanol production systems in the Mississippi Delta. Stover yields simulated with CERES-Maize were used to compute net energy value (NEV) and carbon credit balance (CCB), the indicators of sustainability and eco-friendliness of ethanol production, respectively, for various scenarios. As the results showed, deeper soils with higher water holding capacities had larger NEV and CCB values. Both NEV and CCB had sigmoid relationships with irrigation amount and planting date and could be maximized by planting the crop during the optimum planting window. Stover yield had positive effects on NEV and CCB, whereas travel distance had negative. The influence of stover yield was larger than that of travel distance, indicating that increasing feedstock yields should be emphasized over reducing travel distance. The NEV and CCB values indicated that stover-based ethanol production in the Mississippi Delta is sustainable and environmentally friendly. The study demonstrated that the energy sustainability and eco-friendliness of maize stover-based ethanol production could be increased with alternative crop management options. Full article
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Open AccessArticle
Determining the Interruptible Load with Strategic Behavior in a Competitive Electricity Market
Energies 2015, 8(1), 257-277; https://doi.org/10.3390/en8010257
Received: 29 September 2014 / Accepted: 24 December 2014 / Published: 30 December 2014
Cited by 7 | Viewed by 2320 | PDF Full-text (1034 KB) | HTML Full-text | XML Full-text
Abstract
In a deregulated market, independent system operators meet power balance based on supply and demand bids to maximize social welfare. Since electricity markets are typically oligopolies, players with market power may withhold capacity to maximize profit. Such exercise of market power can lead [...] Read more.
In a deregulated market, independent system operators meet power balance based on supply and demand bids to maximize social welfare. Since electricity markets are typically oligopolies, players with market power may withhold capacity to maximize profit. Such exercise of market power can lead to various problems, including increased electricity prices, and hence lower social welfare. Here we propose an approach to maximize social welfare and prevent the exercising of market power by means of interruptible loads in a competitive market environment. Our approach enables management of the market power by analyzing the benefit to the companies of capacity withdrawal and scheduling resources with interruptible loads. Our formulation shows that we can prevent power companies and demand-resource owners from exercising market powers. The oligopolistic conditions are described using the Cournot model to reflect the capacity withdrawal in electricity markets. The numerical results confirm the effectiveness of proposed method, via a comparison of perfect competition and oligopoly scenarios. Our approach provides reductions in market-clearing prices, increases in social welfare, and more equal distribution of surpluses between players. Full article
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Open AccessArticle
A Dynamic Economic Dispatch Model Incorporating Wind Power Based on Chance Constrained Programming
Energies 2015, 8(1), 233-256; https://doi.org/10.3390/en8010233
Received: 30 September 2014 / Accepted: 18 December 2014 / Published: 29 December 2014
Cited by 8 | Viewed by 2726 | PDF Full-text (817 KB) | HTML Full-text | XML Full-text
Abstract
In order to maintain the stability and security of the power system, the uncertainty and intermittency of wind power must be taken into account in economic dispatch (ED) problems. In this paper, a dynamic economic dispatch (DED) model based on chance constrained programming [...] Read more.
In order to maintain the stability and security of the power system, the uncertainty and intermittency of wind power must be taken into account in economic dispatch (ED) problems. In this paper, a dynamic economic dispatch (DED) model based on chance constrained programming is presented and an improved particle swarm optimization (PSO) approach is proposed to solve the problem. Wind power is regarded as a random variable and is included in the chance constraint. New formulation of up and down spinning reserve constraints are presented under expectation meaning. The improved PSO algorithm combines a feasible region adjustment strategy with a hill climbing search operation based on the basic PSO. Simulations are performed under three distinct test systems with different generators. Results show that both the proposed DED model and the improved PSO approach are effective. Full article
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Open AccessArticle
Optimal Scheduling of Domestic Appliances via MILP
Energies 2015, 8(1), 217-232; https://doi.org/10.3390/en8010217
Received: 20 August 2014 / Accepted: 12 November 2014 / Published: 29 December 2014
Cited by 26 | Viewed by 2679 | PDF Full-text (501 KB) | HTML Full-text | XML Full-text
Abstract
This paper analyzes a consumption scheduling mechanism for domestic appliances within a home area network. The aim of the proposed scheduling is to minimize the total energy price paid by the consumer and to reduce power peaks in order to achieve a balanced [...] Read more.
This paper analyzes a consumption scheduling mechanism for domestic appliances within a home area network. The aim of the proposed scheduling is to minimize the total energy price paid by the consumer and to reduce power peaks in order to achieve a balanced daily load schedule. An exact and computationally efficient mixed-integer linear programming (MILP) formulation of the problem is presented. This model is verified by several problem instances. Realistic scenarios based on the real price tariffs commercially available in the Czech Republic are calculated. The results obtained by solving the optimization problem are compared with a simulation of the ripple control service currently used by many domestic consumers in the Czech Republic. Full article
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Open AccessReview
A Numerical and Graphical Review of Energy Storage Technologies
Energies 2015, 8(1), 172-216; https://doi.org/10.3390/en8010172
Received: 18 November 2014 / Accepted: 12 December 2014 / Published: 29 December 2014
Cited by 47 | Viewed by 5927 | PDF Full-text (2668 KB) | HTML Full-text | XML Full-text
Abstract
More effective energy production requires a greater penetration of storage technologies. This paper takes a looks at and compares the landscape of energy storage devices. Solutions across four categories of storage, namely: mechanical, chemical, electromagnetic and thermal storage are compared on the basis [...] Read more.
More effective energy production requires a greater penetration of storage technologies. This paper takes a looks at and compares the landscape of energy storage devices. Solutions across four categories of storage, namely: mechanical, chemical, electromagnetic and thermal storage are compared on the basis of energy/power density, specific energy/power, efficiency, lifespan, cycle life, self-discharge rates, capital energy/power costs, scale, application, technical maturity as well as environmental impact. It’s noted that virtually every storage technology is seeing improvements. This paper provides an overview of some of the problems with existing storage systems and identifies some key technologies that hold promise. Full article
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Open AccessArticle
A Novel Constant-Pressure Pumped Hydro Combined with Compressed Air Energy Storage System
Energies 2015, 8(1), 154-171; https://doi.org/10.3390/en8010154
Received: 28 August 2014 / Accepted: 19 December 2014 / Published: 26 December 2014
Cited by 14 | Viewed by 3691 | PDF Full-text (838 KB) | HTML Full-text | XML Full-text
Abstract
As intermittent renewable energy is receiving increasing attention, the combination of intermittent renewable energy with large-scale energy storage technology is considered as an important technological approach for the wider application of wind power and solar energy. Pumped hydro combined with compressed air energy [...] Read more.
As intermittent renewable energy is receiving increasing attention, the combination of intermittent renewable energy with large-scale energy storage technology is considered as an important technological approach for the wider application of wind power and solar energy. Pumped hydro combined with compressed air energy storage system (PHCA) is one of the energy storage systems that not only integrates the advantages but also overcomes the disadvantages of compressed air energy storage (CAES) systems and pumped hydro energy storage systems to solve the problem of energy storage in China’s arid regions. Aiming at the variable working conditions of PHCA system technology, this study proposes a new constant-pressure PHCA. The most significant characteristics of this system were that the water pump and hydroturbine work under stable conditions and this improves the working efficiency of the equipment without incurring an energy loss. In addition, the constant-pressure PHCA system was subjected to energy and exergy analysis, in expectation of exploring an attractive solution for the large-scale storage of existing intermittent renewable energy. Full article
(This article belongs to the Special Issue Sustainable Energy Innovation: Strategies to Accelerate Progress)
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Open AccessFeature PaperArticle
The Role of Energy Quality in Shaping Long-Term Energy Intensity in Europe
Energies 2015, 8(1), 133-153; https://doi.org/10.3390/en8010133
Received: 11 November 2014 / Accepted: 12 December 2014 / Published: 26 December 2014
Cited by 3 | Viewed by 3086 | PDF Full-text (1207 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
On the European aggregate level there is an inverted-U curve for long-term energy intensity. In the 19th century aggregate European energy intensity rose, followed by a declining trend during the 20th century. This article discusses the possible explanations for the declining trend during [...] Read more.
On the European aggregate level there is an inverted-U curve for long-term energy intensity. In the 19th century aggregate European energy intensity rose, followed by a declining trend during the 20th century. This article discusses the possible explanations for the declining trend during the 20th century and explores the role of energy quality as expressed in energy prices. For the first time a complete set of national energy retail prices covering two centuries has been constructed and used for Britain, while the energy price data previously available for Sweden until 2000 has been updated to 2009. This allows us to explore the role of energy quality in shaping long-term energy intensity. We find no relation between energy quality and energy intensity in the 19th century, while energy quality may have stimulated the declining energy intensity in Europe over the 20th century, but is not the sole or even main reason for the decline. Rather, increased economic efficiency in the use of energy services seems to have been the main driver for the decline after 1970, presumably driven by the information and communication technology. Full article
(This article belongs to the Special Issue Energy Transitions and Economic Change)
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Open AccessArticle
A New Energy-Absorbing Device for Motion Suppression in Deep-Sea Floating Platforms
Energies 2015, 8(1), 111-132; https://doi.org/10.3390/en8010111
Received: 28 September 2014 / Accepted: 11 December 2014 / Published: 25 December 2014
Cited by 8 | Viewed by 2625 | PDF Full-text (664 KB) | HTML Full-text | XML Full-text
Abstract
Deep-sea floating platforms are one of the most important large structures for ocean energy exploitation. A new energy-absorbing device named S-shaped Tuned Liquid Column Damper (TLCD) has been invented for the suppression of the horizontal motion and vertical in-plane rotation of a deep-sea [...] Read more.
Deep-sea floating platforms are one of the most important large structures for ocean energy exploitation. A new energy-absorbing device named S-shaped Tuned Liquid Column Damper (TLCD) has been invented for the suppression of the horizontal motion and vertical in-plane rotation of a deep-sea floating platform. A conventional tuned liquid column damper has a U-shaped water tunnel to absorb the excessive energy of the main structure. The application of U-shaped dampers in deep-sea floating platforms is difficult due to the restriction of a large horizontal length. A novel S-shaped damper is proposed to retain the same amount of liquid using a shorter S-shaped tunnel. Theoretical and experimental works are conducted and prove that an S-shaped damper needs less than half the horizontal length to provide the same suppression as a U-shaped damper. A coupling calculation model is proposed and followed by the sensitivity analysis. The study demonstrates the applicability of the novel S-shaped damper for the motion suppression in deep-sea floating platforms. Full article
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Open AccessArticle
Design, Optimization and Energetic Efficiency of Producing Hydrogen-Rich Gas from Biomass Steam Gasification
Energies 2015, 8(1), 94-110; https://doi.org/10.3390/en8010094
Received: 24 October 2014 / Accepted: 11 December 2014 / Published: 25 December 2014
Cited by 8 | Viewed by 2929 | PDF Full-text (756 KB) | HTML Full-text | XML Full-text
Abstract
In this article, the conceptual design of biomass steam gasification (BSG) processes using raw oil palm (ROP) and torrefied oil palm (TOP) are examined in an Aspen Plus simulator. Through thermodynamic analysis, it is verified that the BSG process with torrefied feedstock can [...] Read more.
In this article, the conceptual design of biomass steam gasification (BSG) processes using raw oil palm (ROP) and torrefied oil palm (TOP) are examined in an Aspen Plus simulator. Through thermodynamic analysis, it is verified that the BSG process with torrefied feedstock can effectively enhance the hydrogen yield. When the heat recovery design is added into the BSG process, the system energetic efficiency (SEE) is significantly improved. Finally, an optimization algorithm with respect to SEE and hydrogen yield is solved, and the optimum operating conditions are validated by simulations. Full article
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Open AccessArticle
Real-Time Estimation of Power System Frequency Using a Three-Level Discrete Fourier Transform Method
Energies 2015, 8(1), 79-93; https://doi.org/10.3390/en8010079
Received: 21 October 2014 / Accepted: 17 December 2014 / Published: 24 December 2014
Cited by 9 | Viewed by 2651 | PDF Full-text (1345 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a three-level discrete Fourier transform (DFT) method to provide an accurate estimate of power system frequency in real time. The first level decomposes a power system signal into two orthogonal cosine- and sine-filtered signals. The second and third levels are [...] Read more.
This paper proposes a three-level discrete Fourier transform (DFT) method to provide an accurate estimate of power system frequency in real time. The first level decomposes a power system signal into two orthogonal cosine- and sine-filtered signals. The second and third levels are used to determine the amplitude ratio of the cosine- and sine-filtered signals without encountering the zero-crossing problem and with an increase in ability to suppress harmonics and inter-harmonics. The performance of the three-level DFT method is evaluated using computer-simulated signals with harmonics and inter-harmonics. The three-level DFT method is also implemented on a digital signal processor (DSP)-based hardware prototype, and its performance in the hardware implementation is evaluated using a real-time digital simulator (RTDS). The evaluation results show that the three-level DFT method can achieve real-time estimation of power system frequency with satisfactory performance. Full article
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