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Energies, Volume 5, Issue 4 (April 2012), Pages 862-1291

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Research

Open AccessArticle Microwave-Assisted Transesterification of Macroalgae
Energies 2012, 5(4), 862-871; doi:10.3390/en5040862
Received: 22 February 2012 / Revised: 19 March 2012 / Accepted: 22 March 2012 / Published: 26 March 2012
Cited by 8 | PDF Full-text (394 KB) | HTML Full-text | XML Full-text
Abstract
Nowadays microwave radiation is being researched to produce biodiesel from different raw materials due to the many advantages that this technology presents compared to traditional transesterification, such as shorter reaction times and less amount of heat energy to obtain biodiesel. The aim [...] Read more.
Nowadays microwave radiation is being researched to produce biodiesel from different raw materials due to the many advantages that this technology presents compared to traditional transesterification, such as shorter reaction times and less amount of heat energy to obtain biodiesel. The aim of this research was to explore the possibility of carrying out the microwave-assisted transesterification of macroalgae and compare the results with the traditional transesterification. For that reason, some experiences were conducted using sunflower oil and macroalgae as raw material. Based on the obtained results, the best conditions for microwave-assisted transesterification reaction were macroalgae to methanol ratio of 1:15 (wt/vol), sodium hydroxide concentration of 2 wt % and reaction time of 3 min. Full article
(This article belongs to the Special Issue Algae Fuel)
Open AccessArticle Life Cycle Greenhouse Gas Emissions from Electricity Generation: A Comparative Analysis of Australian Energy Sources
Energies 2012, 5(4), 872-897; doi:10.3390/en5040872
Received: 10 November 2011 / Revised: 12 March 2012 / Accepted: 15 March 2012 / Published: 26 March 2012
Cited by 16 | PDF Full-text (550 KB) | HTML Full-text | XML Full-text
Abstract
Electricity generation is one of the major contributors to global greenhouse gas emissions. Transitioning the World’s energy economy to a lower carbon future will require significant investment in a variety of cleaner technologies, including renewables and nuclear power. In the short term, [...] Read more.
Electricity generation is one of the major contributors to global greenhouse gas emissions. Transitioning the World’s energy economy to a lower carbon future will require significant investment in a variety of cleaner technologies, including renewables and nuclear power. In the short term, improving the efficiency of fossil fuel combustion in energy generation can provide an important contribution. Availability of life cycle GHG intensity data will allow decision-makers to move away from overly simplistic assertions about the relative merits of certain fuels, and focus on the complete picture, especially the critical roles of technology selection and application of best practice. This analysis compares the life-cycle greenhouse gas (GHG) intensities per megawatt-hour (MWh) of electricity produced for a range of Australian and other energy sources, including coal, conventional liquefied natural gas (LNG), coal seam gas LNG, nuclear and renewables, for the Australian export market. When Australian fossil fuels are exported to China, life cycle greenhouse gas emission intensity in electricity production depends to a significant degree on the technology used in combustion. LNG in general is less GHG intensive than black coal, but the gap is smaller for gas combusted in open cycle gas turbine plant (OCGT) and for LNG derived from coal seam gas (CSG). On average, conventional LNG burned in a conventional OCGT plant is approximately 38% less GHG intensive over its life cycle than black coal burned in a sub-critical plant, per MWh of electricity produced. However, if OCGT LNG combustion is compared to the most efficient new ultra-supercritical coal power, the GHG intensity gap narrows considerably. Coal seam gas LNG is approximately 13–20% more GHG intensive across its life cycle, on a like-for like basis, than conventional LNG. Upstream fugitive emissions from CSG (assuming best practice gas extraction techniques) do not materially alter the life cycle GHG intensity rankings, such is the dominance of end-use combustion, but application of the most recent estimates of the 20-year global warming potential (GWP) increases the contribution of fugitives considerably if best practice fugitives management is not assumed. However, if methane leakage approaches the elevated levels recently reported in some US gas fields (circa 4% of gas production) and assuming a 20-year methane GWP, the GHG intensity of CSG-LNG generation is on a par with sub-critical coal-fired generation. The importance of applying best practice to fugitives management in Australia’s emerging natural gas industry is evident. When exported to China for electricity production, LNG was found to be 22–36 times more GHG intensive than wind and concentrated solar thermal (CST) power and 13–21 times more GHG intensive than nuclear power which, even in the post-Fukushima world, continues to be a key option for global GHG reduction. Full article
Open AccessArticle Direct Observation of THF Hydrate Formation in Porous Microstructure Using Magnetic Resonance Imaging
Energies 2012, 5(4), 898-910; doi:10.3390/en5040898
Received: 27 December 2011 / Revised: 20 March 2012 / Accepted: 23 March 2012 / Published: 5 April 2012
Cited by 9 | PDF Full-text (775 KB) | HTML Full-text | XML Full-text
Abstract
The porous microstructure of hydrates governs the mechanical strength of the hydrate-bearing sediment. To investigate the growth law and microstructure of hydrates in porous media, the growth process of tetrahydrofuran (THF) hydrate under different concentration of THF solution is directly observed using [...] Read more.
The porous microstructure of hydrates governs the mechanical strength of the hydrate-bearing sediment. To investigate the growth law and microstructure of hydrates in porous media, the growth process of tetrahydrofuran (THF) hydrate under different concentration of THF solution is directly observed using Magnetic Resonance Imaging (MRI). The images show that the THF hydrate grows as different models under different concentration of THF solution (19%, 11.4% and 5.7% by weight) at 1 °C. When the concentration is 19% (stoichiometric molar ratio of THF/H2O = 1:17), the THF hydrate grows as cementing model. However, with the decreasing concentration of THF, the growth model transfers from cementing model to floating model. The results show that the growth of the THF hydrate was influenced by the dissolved quantity of THF in the water. The extension of the observed behavior to methane hydrate could have implications in understanding their role in seafloor and permafrost stability. Full article
(This article belongs to the Special Issue Natural Gas Hydrate 2011)
Open AccessArticle Comparative Experimental Analysis of the Thermal Performance of Evacuated Tube Solar Water Heater Systems With and Without a Mini-Compound Parabolic Concentrating (CPC) Reflector(C < 1)
Energies 2012, 5(4), 911-924; doi:10.3390/en5040911
Received: 17 January 2012 / Revised: 24 February 2012 / Accepted: 22 March 2012 / Published: 10 April 2012
Cited by 10 | PDF Full-text (247 KB) | HTML Full-text | XML Full-text
Abstract
Evacuated tube solar water heater systems are widely used in China due to their high thermal efficiency, simple construction requirements, and low manufacturing costs. CPC evacuated tube solar water heaters with a geometrical concentration ratio C of less than one are rare. [...] Read more.
Evacuated tube solar water heater systems are widely used in China due to their high thermal efficiency, simple construction requirements, and low manufacturing costs. CPC evacuated tube solar water heaters with a geometrical concentration ratio C of less than one are rare. A comparison of the experimental rig of evacuated tube solar water heater systems with and without a mini-CPC reflector was set up, with a series of experiments done in Hefei (31°53'N, 117°15'E), China. The first and second laws of thermodynamics were used to analyze and contrast their thermal performance. The water in the tank was heated from 26.9 to 55, 65, 75, 85, and 95 °C. Two types of solar water heater systems were used, and the data gathered for two days were compared. The results show that when attaining low temperature water, the evacuated tube solar water heater system without a mini-CPC reflector has higher thermal and exergy efficiencies than the system with a mini-CPC reflector, including the average and immediate values. On the other hand, when attaining high temperature water, the system with a mini-CPC reflector has higher thermal and exergy efficiencies than the other one. The comparison presents the advantages of evacuated tube solar water heater systems with and without a mini-CPC reflector, which can be offered as a reference when choosing which solar water system to use for actual applications. Full article
Open AccessArticle Characteristics of CO2 Hydrate Formation and Dissociation in Glass Beads and Silica Gel
Energies 2012, 5(4), 925-937; doi:10.3390/en5040925
Received: 9 February 2012 / Revised: 21 March 2012 / Accepted: 6 April 2012 / Published: 16 April 2012
Cited by 4 | PDF Full-text (374 KB) | HTML Full-text | XML Full-text
Abstract
CO2 hydrate formation and dissociation is crucial for hydrate-based CO2 capture and storage. Experimental and calculated phase equilibrium conditions of carbon dioxide (CO2) hydrate in porous medium were investigated in this study. Glass beads were used to form [...] Read more.
CO2 hydrate formation and dissociation is crucial for hydrate-based CO2 capture and storage. Experimental and calculated phase equilibrium conditions of carbon dioxide (CO2) hydrate in porous medium were investigated in this study. Glass beads were used to form the porous medium. The experimental data were generated using a graphical method. The results indicated the decrease of pore size resulted in the increase of the equilibrium pressure of CO2 hydrate. Magnetic resonance imaging (MRI) was used to investigate the priority formation site of CO2 hydrate in different porous media, and the results showed that the hydrate form firstly in BZ-02 glass beads under the same pressure and temperature. An improved model was used to predict CO2 hydrate equilibrium conditions, and the predictions showed good agreement with experimental measurements. Full article
(This article belongs to the Special Issue Natural Gas Hydrate 2011)
Open AccessArticle H Based Control for Load Mitigation in Wind Turbines
Energies 2012, 5(4), 938-967; doi:10.3390/en5040938
Received: 25 January 2012 / Revised: 20 March 2012 / Accepted: 31 March 2012 / Published: 17 April 2012
Cited by 20 | PDF Full-text (1023 KB) | HTML Full-text | XML Full-text
Abstract
This article demonstrates a strategy to design multivariable and multi-objective controllers based on the H norm reduction applied to a wind turbine. The wind turbine model has been developed in the GH Bladed software and it is based on a 5 [...] Read more.
This article demonstrates a strategy to design multivariable and multi-objective controllers based on the H norm reduction applied to a wind turbine. The wind turbine model has been developed in the GH Bladed software and it is based on a 5 MW wind turbine defined in the Upwind European project. The designed control strategy works in the above rated power production zone and performs generator speed control and load reduction on the drive train and tower. In order to do this, two robust H MISO (Multi-Input Single-Output) controllers have been developed. These controllers generate collective pitch angle and generator torque set-point values to achieve the imposed control objectives. Linear models obtained in GH Bladed 4.0 are used, but the control design methodology can be used with linear models obtained from any other modelling package. Controllers are designed by setting out a mixed sensitivity problem, where some notch filters are also included in the controller dynamics. The obtained H controllers have been validated in GH Bladed and an exhaustive analysis has been carried out to calculate fatigue load reduction on wind turbine components, as well as to analyze load mitigation in some extreme cases. The analysis compares the proposed control strategy based on H controllers to a baseline control strategy designed using the classical control methods implemented on the present wind turbines. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Analysis of the Induction and Wake Evolution of an Offshore Floating Wind Turbine
Energies 2012, 5(4), 968-1000; doi:10.3390/en5040968
Received: 3 February 2012 / Revised: 29 March 2012 / Accepted: 9 April 2012 / Published: 17 April 2012
Cited by 15 | PDF Full-text (14236 KB) | HTML Full-text | XML Full-text
Abstract
The degrees-of-freedom associated with offshore floating wind turbines (OFWTs) result in a more dynamic flow field. The resulting aerodynamic loads may be significantly influenced by these motions via perturbations in the evolving wake. This is of great interest in terms of OFWT [...] Read more.
The degrees-of-freedom associated with offshore floating wind turbines (OFWTs) result in a more dynamic flow field. The resulting aerodynamic loads may be significantly influenced by these motions via perturbations in the evolving wake. This is of great interest in terms of OFWT design, placement and simulation. This study presents free vortex wake method (FVM) simulations of the NREL 5-MW wind turbine of a variety of platforms, operating in a range of wind speeds synthesized platform motion time series. Motion-induced wake perturbations are observed to affect induction. Transitions between windmill and propeller states are also observed. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Design Specifications for the Hanstholm WEPTOS Wave Energy Converter
Energies 2012, 5(4), 1001-1017; doi:10.3390/en5041001
Received: 14 February 2012 / Revised: 9 April 2012 / Accepted: 9 April 2012 / Published: 18 April 2012
Cited by 7 | PDF Full-text (1263 KB) | HTML Full-text | XML Full-text
Abstract
The WEPTOS wave energy converter (WEC) is a novel device that combines an established and efficient wave energy absorbing mechanism with a smart structure, which can regulate the amount of incoming wave energy and reduce loads in extreme wave conditions. This adjustable [...] Read more.
The WEPTOS wave energy converter (WEC) is a novel device that combines an established and efficient wave energy absorbing mechanism with a smart structure, which can regulate the amount of incoming wave energy and reduce loads in extreme wave conditions. This adjustable A-shaped slack-moored and floating structure absorbs the energy of the waves through a multitude of rotors. The shape of the rotors is based on the renowned Salter’s Duck. On each leg, the rotors pivot around a common axle, through which the rotors transfer the absorbed power to a common power take off system. The study investigates the required capacity of the power take off (PTO) system and the structural forces on a WEPTOS WEC prototype, intended for installation at Hanstholm (Denmark), based on large scale experimental tests using a highly realistic laboratory model of the complete device. The results hereof includes the rotational speed and transmitted torque (and hereby power) to the PTO system using different PTO control strategies, the impact of fluctuations of the available mechanical power and the effect of limiting the PTO capacity on the annual energy production. Acquisition of structural forces includes mooring forces and structural bending moments in both production and extreme wave conditions, illustrating that the regulation of the angle in the A shape ensures that extreme forces on the structure can be kept in the same order of magnitude as in production conditions. Full article
Open AccessArticle Portfolio Value at Risk Estimate for Crude Oil Markets: A Multivariate Wavelet Denoising Approach
Energies 2012, 5(4), 1018-1043; doi:10.3390/en5041018
Received: 13 February 2012 / Revised: 5 April 2012 / Accepted: 12 April 2012 / Published: 18 April 2012
Cited by 8 | PDF Full-text (696 KB) | HTML Full-text | XML Full-text
Abstract
In the increasingly globalized economy these days, the major crude oil markets worldwide are seeing higher level of integration, which results in higher level of dependency and transmission of risks among different markets. Thus the risk of the typical multi-asset crude oil [...] Read more.
In the increasingly globalized economy these days, the major crude oil markets worldwide are seeing higher level of integration, which results in higher level of dependency and transmission of risks among different markets. Thus the risk of the typical multi-asset crude oil portfolio is influenced by dynamic correlation among different assets, which has both normal and transient behaviors. This paper proposes a novel multivariate wavelet denoising based approach for estimating Portfolio Value at Risk (PVaR). The multivariate wavelet analysis is introduced to analyze the multi-scale behaviors of the correlation among different markets and the portfolio volatility behavior in the higher dimensional time scale domain. The heterogeneous data and noise behavior are addressed in the proposed multi-scale denoising based PVaR estimation algorithm, which also incorporatesthe mainstream time series to address other well known data features such as autocorrelation and volatility clustering. Empirical studies suggest that the proposed algorithm outperforms the benchmark ExponentialWeighted Moving Average (EWMA) and DCC-GARCH model, in terms of conventional performance evaluation criteria for the model reliability. Full article
Open AccessArticle Simulation of the Effect of Water Temperature on Domestic Biomass Boiler Performance
Energies 2012, 5(4), 1044-1061; doi:10.3390/en5041044
Received: 27 February 2012 / Revised: 23 March 2012 / Accepted: 11 April 2012 / Published: 19 April 2012
Cited by 3 | PDF Full-text (1556 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a methodology to simulate the combustion of fixed beds of biomass particles using computational fluid dynamics (CFD) techniques. The models presented were used in the simulation of a domestic pellet boiler working under operating conditions and the model predictions [...] Read more.
This paper presents a methodology to simulate the combustion of fixed beds of biomass particles using computational fluid dynamics (CFD) techniques. The models presented were used in the simulation of a domestic pellet boiler working under operating conditions and the model predictions were compared with measurements of heat transfer, temperature and species concentration. The same procedure was then used to simulate the same domestic boiler working with different values of water temperature and the influence of water temperature variations on the main variables was analyzed. Full article
Open AccessArticle Supercritical Transesterification of Palm Oil and Hydrated Ethanol in a Fixed Bed Reactor with a CaO/Al2O3 Catalyst
Energies 2012, 5(4), 1062-1080; doi:10.3390/en5041062
Received: 11 January 2012 / Revised: 2 April 2012 / Accepted: 6 April 2012 / Published: 19 April 2012
Cited by 3 | PDF Full-text (443 KB) | HTML Full-text | XML Full-text
Abstract
Biodiesel production from palm oil and hydrated ethanol in a fixed bed reactor using CaO/Al2O3 as the catalyst was investigated and optimized using response surface methodology. The investigated parameters were temperature, pressure, ethanol/palm oil molar ratio, residence time and [...] Read more.
Biodiesel production from palm oil and hydrated ethanol in a fixed bed reactor using CaO/Al2O3 as the catalyst was investigated and optimized using response surface methodology. The investigated parameters were temperature, pressure, ethanol/palm oil molar ratio, residence time and total mass flow rate. The approach was divided into two parts, a preliminary study using broad scale changes over a reasonable range of the above operating parameters and then, using this data to select a narrower range, a finer scale study to optimize the selected narrower operating parameters from the preliminary study. The resultant biodiesel obtained under the optimal conditions (285 °C, 20 MPa, 30:1 ethanol/oil molar ratio, 2 g/min flow rate and 4.85 min residence time) was measured for 11 fuel properties following the International Biodiesel Standard (EN14214), and was found to comply with this International Standard. Moreover, ZnO/Al2O3 and La2O3/Al2O3 catalysts were tested for their activity and stability. Although the La2O3/Al2O3 catalyst had a slightly higher initial activity than that of CaO/Al2O3, it is some 800-fold more expensive. Therefore, the CaO/Al2O3 catalyst has a greater industrial potential than La2O3/Al2O3, when comparing together the technical and economic benefits. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2012)
Figures

Open AccessArticle Canonical Correlation Between Partial Discharges and Gas Formation in Transformer Oil Paper Insulation
Energies 2012, 5(4), 1081-1097; doi:10.3390/en5041081
Received: 1 February 2012 / Revised: 26 March 2012 / Accepted: 11 April 2012 / Published: 19 April 2012
Cited by 3 | PDF Full-text (882 KB) | HTML Full-text | XML Full-text
Abstract
Dissolved gas analysis (DGA) has been widely applied to diagnose internal faults in transformer insulation systems. However, the accuracy of DGA technique is limited because of the lack of positive correlation of the fault-identifying gases with faults found in power transformers. This [...] Read more.
Dissolved gas analysis (DGA) has been widely applied to diagnose internal faults in transformer insulation systems. However, the accuracy of DGA technique is limited because of the lack of positive correlation of the fault-identifying gases with faults found in power transformers. This paper presents a laboratory study on the correlation between oil dissolved gas formation and partial discharge (PD) statistical parameters. Canonical correlation analysis (CCA) is employed to explore the underlying correlation and to extract principal feature parameters and gases in the development of different PD defects. This study is aimed to provide more information in assisting the separation, classification and identification of PD defects, which might improve the existing transformer dissolved gas analysis (DGA) schemes. An application of a novel ratio method for discharge diagnosis is proposed. The evaluation of DGA data both in laboratory and actual transformers proves the effectiveness of the method and the correlation investigation. Full article
(This article belongs to the Special Issue Electrical Power and Energy Systems)
Open AccessArticle Estimation of State of Charge of Lithium-Ion Batteries Used in HEV Using Robust Extended Kalman Filtering
Energies 2012, 5(4), 1098-1115; doi:10.3390/en5041098
Received: 17 February 2012 / Revised: 27 March 2012 / Accepted: 11 April 2012 / Published: 19 April 2012
Cited by 24 | PDF Full-text (460 KB) | HTML Full-text | XML Full-text
Abstract
A robust extended Kalman filter (EKF) is proposed as a method for estimation of the state of charge (SOC) of lithium-ion batteries used in hybrid electric vehicles (HEVs). An equivalent circuit model of the battery, including its electromotive force (EMF) hysteresis characteristics [...] Read more.
A robust extended Kalman filter (EKF) is proposed as a method for estimation of the state of charge (SOC) of lithium-ion batteries used in hybrid electric vehicles (HEVs). An equivalent circuit model of the battery, including its electromotive force (EMF) hysteresis characteristics and polarization characteristics is used. The effect of the robust EKF gain coefficient on SOC estimation is analyzed, and an optimized gain coefficient is determined to restrain battery terminal voltage from fluctuating. Experimental and simulation results are presented. SOC estimates using the standard EKF are compared with the proposed robust EKF algorithm to demonstrate the accuracy and precision of the latter for SOC estimation. Full article
(This article belongs to the Special Issue Vehicle to Grid)
Open AccessArticle Look-Ahead Energy Management of a Grid-Connected Residential PV System with Energy Storage under Time-Based Rate Programs
Energies 2012, 5(4), 1116-1134; doi:10.3390/en5041116
Received: 5 March 2012 / Revised: 10 April 2012 / Accepted: 10 April 2012 / Published: 19 April 2012
Cited by 10 | PDF Full-text (413 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents look-ahead energy management system for a grid-connected residential photovoltaic (PV) system with battery under critical peak pricing for electricity, enabling effective and proactive participation of consumers in the Smart Grid’s demand response. In the proposed system, the PV is [...] Read more.
This paper presents look-ahead energy management system for a grid-connected residential photovoltaic (PV) system with battery under critical peak pricing for electricity, enabling effective and proactive participation of consumers in the Smart Grid’s demand response. In the proposed system, the PV is the primary energy source with the battery for storing (or retrieving) excessive (or stored) energy to pursue the lowest possible electricity bill but it is grid-tied to secure electric power delivery. Premise energy management scheme with an accurate yet practical load forecasting capability based on a Kalman filter is designed to increase the predictability in controlling the power flows among these power system components and the controllable electric appliances in the premise. The case studies with various operating scenarios demonstrate the validity of the proposed system and significant cost savings through operating the energy management scheme. Full article
Open AccessArticle The Effect of Additional Mooring Chains on the Motion Performance of a Floating Wind Turbine with a Tension Leg Platform
Energies 2012, 5(4), 1135-1149; doi:10.3390/en5041135
Received: 22 February 2012 / Revised: 5 April 2012 / Accepted: 6 April 2012 / Published: 20 April 2012
Cited by 9 | PDF Full-text (1048 KB) | HTML Full-text | XML Full-text
Abstract
In this study, two types of floating offshore wind turbine (FOWT) systems were proposed: a traditional tension leg platform (TLP) type and a new TLP type with additional mooring chains. They were both based on the National Renewable Energy Laboratory 5 MW [...] Read more.
In this study, two types of floating offshore wind turbine (FOWT) systems were proposed: a traditional tension leg platform (TLP) type and a new TLP type with additional mooring chains. They were both based on the National Renewable Energy Laboratory 5 MW offshore wind turbine model. Taking the coupled effect of dynamic response of the top wind turbine, tower support structure and lower mooring system into consideration, not only were the 1/60 scale model tests for the two floating wind turbine systems done in HIT’s wind-wave tunnel according to the typical design conditions in IEC61400-3 code, but also the numerical simulations corresponding to the scaled model tests were performed by advanced numerical tools. As a result, the numerical results displayed good agreement with the test data. Moreover, the additional mooring chains could play an active role in reducing the surge displacement, surge acceleration and typical tension leg force responses of the FOWT system, which is very beneficial for ensuring the good operational performance and the safety of the FOWT system. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Optimal Coordination of Automatic Line Switches for Distribution Systems
Energies 2012, 5(4), 1150-1174; doi:10.3390/en5041150
Received: 20 February 2012 / Revised: 31 March 2012 / Accepted: 17 April 2012 / Published: 23 April 2012
Cited by 1 | PDF Full-text (419 KB) | HTML Full-text | XML Full-text
Abstract
For the Taiwan Power Company (Taipower), the margins of coordination times between the lateral circuit breakers (LCB) of underground 4-way automatic line switches and the protection equipment of high voltage customers are often too small. This could lead to sympathy tripping by [...] Read more.
For the Taiwan Power Company (Taipower), the margins of coordination times between the lateral circuit breakers (LCB) of underground 4-way automatic line switches and the protection equipment of high voltage customers are often too small. This could lead to sympathy tripping by the feeder circuit breaker (FCB) of the distribution feeder and create difficulties in protection coordination between upstream and downstream protection equipment, identification of faults, and restoration operations. In order to solve the problem, it is necessary to reexamine the protection coordination between LCBs and high voltage customers’ protection equipment, and between LCBs and FCBs, in order to bring forth new proposals for settings and operations. This paper applies linear programming to optimize the protection coordination of protection devices, and proposes new time current curves (TCCs) for the overcurrent (CO) and low-energy overcurrent (LCO) relays used in normally open distribution systems by performing simulations in the Electrical Transient Analyzer Program (ETAP) environment. The simulation results show that the new TCCs solve the coordination problems among high voltage customer, lateral, feeder, bus-interconnection, and distribution transformer. The new proposals also satisfy the requirements of Taipower on protection coordination of the distribution feeder automation system (DFAS). Finally, the authors believe that the system configuration, operation experience, and relevant criteria mentioned in this paper may serve as valuable references for other companies or utilities when building DFAS of their own. Full article
Open AccessArticle A Fuzzy Logic Global Power Management Strategy for Hybrid Electric Vehicles Based on a Permanent Magnet Electric Variable Transmission
Energies 2012, 5(4), 1175-1198; doi:10.3390/en5041175
Received: 30 January 2012 / Revised: 9 April 2012 / Accepted: 12 April 2012 / Published: 23 April 2012
Cited by 14 | PDF Full-text (1275 KB) | HTML Full-text | XML Full-text
Abstract
The major contribution of this paper is to propose a Fuzzy Logic Global Power Management Strategy for Hybrid Electric Vehicles (HEVs) that are driven by the PM-EVT (PM machine—Electric Variable Transmission) powertrain, such that the PM-EVT will have superior advantages over other [...] Read more.
The major contribution of this paper is to propose a Fuzzy Logic Global Power Management Strategy for Hybrid Electric Vehicles (HEVs) that are driven by the PM-EVT (PM machine—Electric Variable Transmission) powertrain, such that the PM-EVT will have superior advantages over other types of powertrains, including the current Toyota Prius powertrain for series-parallel HEVs. This has been investigated throughout three aspects. The first is the optimum power splitting between the Internal Combustion Engine (ICE) and the PM-EVT. The second is maximizing the vehicle’s energy capture during the braking process. Finally, sustaining the State of Charge (SOC) of the battery is adopted by a robust ON/OFF controller of the ICE. These goals have been accomplished by developing three fuzzy logic (FL) controllers. The FL controllers are designed based on the state of charge of the battery, vehicle’s velocity, traction torque, and the vehicle’s requested power. The integration of the studied system is accomplished via the Energetic Macroscopic Representation (EMR) simulation model strategy based on the software Matlab/Simulink. The PM-EVT based HEV system with the proposed power management strategy is validated by comparing to the Toyota Prius HEV. The vehicle’s performances have been analyzed throughout a combined long-trip driving cycle that represents the normal and the worst operating conditions. The simulation results show that global control system is effective to control the engine’s operating points within the highest efficiency region, exploiting of EVT machines for capturing maximum braking energy, as well as to sustain the SOC of the battery while satisfy the drive ability. The proposed control strategy for the studied HEVs sounds interesting and feasible as supported by a large amount of simulation results. Full article
Open AccessArticle The Effects of Particle Size, Different Corn Stover Components, and Gas Residence Time on Torrefaction of Corn Stover
Energies 2012, 5(4), 1199-1214; doi:10.3390/en5041199
Received: 20 February 2012 / Revised: 31 March 2012 / Accepted: 17 April 2012 / Published: 23 April 2012
Cited by 20 | PDF Full-text (648 KB) | HTML Full-text | XML Full-text
Abstract
Large scale biofuel production will be possible only if significant quantities of biomass feedstock can be stored, transported, and processed in an economic and sustainable manner. Torrefaction has the potential to significantly reduce the cost of transportation, storage, and downstream processing through [...] Read more.
Large scale biofuel production will be possible only if significant quantities of biomass feedstock can be stored, transported, and processed in an economic and sustainable manner. Torrefaction has the potential to significantly reduce the cost of transportation, storage, and downstream processing through the improvement of physical and chemical characteristics of biomass. The main objective of this study was to investigate the effects of particle size, plant components, and gas residence time on the production of torrefied corn (Zea mays) stover. Different particle sizes included 0.85 mm and 20 mm. Different stover components included ground corn stover, whole corn stalk, stalk shell and pith, and corn cob shell. Three different purge gas residence times were employed to assess the effects of interaction of volatiles and torrefied biomass. Elemental analyses were performed on all of the samples, and the data obtained was used to estimate the energy contents and energy yields of different torrefied biomass samples. Particle density, elemental composition, and fiber composition of raw biomass fractions were also determined. Stalk pith torrefied at 280 °C and stalk shell torrefied at 250 °C had highest and lowest dry matter loss, of about 44% and 13%, respectively. Stalk pith torrefied at 250 °C had lowest energy density of about 18–18.5 MJ/kg, while cob shell torrefied at 280 °C had the highest energy density of about 21.5 MJ/kg. The lowest energy yield, at 59%, was recorded for stalk pith torrefied at 280 °C, whereas cob and stalk shell torrefied at 250 °C had highest energy yield at 85%. These differences were a consequence of the differences in particle densities, hemicellulose quantities, and chemical properties of the original biomass samples. Gas residence time did not have a significant effect on the aforementioned parameters. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2012)
Open AccessArticle Repeated-Batch Ethanol Production from Sweet Sorghum Juice by Saccharomyces cerevisiae Immobilized on Sweet Sorghum Stalks
Energies 2012, 5(4), 1215-1228; doi:10.3390/en5041215
Received: 4 January 2012 / Revised: 5 April 2012 / Accepted: 12 April 2012 / Published: 23 April 2012
Cited by 13 | PDF Full-text (346 KB) | HTML Full-text | XML Full-text
Abstract
Sweet sorghum stalks were used as a low cost carrier for immobilization of Saccharomyces cerevisiae NP 01 to produce ethanol from sweet sorghum juice. The effects on ethanol production of carrier size (6 × 6 × 6 to 20 × 20 × [...] Read more.
Sweet sorghum stalks were used as a low cost carrier for immobilization of Saccharomyces cerevisiae NP 01 to produce ethanol from sweet sorghum juice. The effects on ethanol production of carrier size (6 × 6 × 6 to 20 × 20 × 20 mm3) and initial cell concentrations (5 × 107 to 2 × 108 cells mL−1) for cell immobilization were investigated. The ethanol production medium was the juice containing 230 g L−1 of total sugar without nutrient supplementation. The fermentations were carried out under static conditions in 500-mL air-locked Erlenmeyer flasks at 30 °C. The results showed that the optimum size of sorghum stalk pieces for repeated-batch ethanol production was 6 × 6 × 6 mm3, while the optimum initial cell concentration for the immobilization was 1.0 × 108 cells mL−1. The immobilized yeast under these conditions could be used for at least eight successive batches without any losses of ethanol production efficiencies. The average ethanol concentration, productivity and yield of the eight successive batches were 99.28 ± 3.53 g L−1, 1.36 ± 0.05 g L−1 h−1 and 0.47 ± 0.03 g g−1, respectively. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2012)
Open AccessArticle Field Experiments of PV-Thermal Collectors for Residential Application in Bangkok
Energies 2012, 5(4), 1229-1244; doi:10.3390/en5041229
Received: 6 February 2012 / Revised: 25 March 2012 / Accepted: 11 April 2012 / Published: 23 April 2012
Cited by 3 | PDF Full-text (626 KB) | HTML Full-text | XML Full-text
Abstract
This study presents experimental results on Photovoltaic-thermal (PVT) solar systems, the commercial photovoltaic (PV) panels used as solar absorbers in PVT collectors, which are amorphous and multi-crystalline silicon. Testing was done with outdoor experiments in the climate of Bangkok corresponding to energy [...] Read more.
This study presents experimental results on Photovoltaic-thermal (PVT) solar systems, the commercial photovoltaic (PV) panels used as solar absorbers in PVT collectors, which are amorphous and multi-crystalline silicon. Testing was done with outdoor experiments in the climate of Bangkok corresponding to energy consumption behavior of medium size Thai families. The experimental results show that the thermal recovery of amorphous silicon PVT collector is almost the same as that of multi-crystalline silicon PVT collectors while electricity generation of multi crystalline silicon PVT is 1.2 times as much as that of amorphous silicon PVT. The maximum of heat gain from the PVT systems were obtained in March in summer. It was found that PVT collectors of unit area annually produced 1.1 × 103 kWh/m2 .year of heat and 55–83 kWh/m2.year of electricity, respectively. The results show that annual average solar factor of hot water supply is 0.45 for unit collector area. Economical evaluation based on energy costs in Thailand was conducted, which estimated the payback time would be 7 and 14 years for a-Si PVT and mc-Si PV, respectively. Full article
Open AccessArticle A Low-Carbon Dispatch Model in a Wind Power Integrated System Considering Wind Speed Forecasting and Energy-Environmental Efficiency
Energies 2012, 5(4), 1245-1270; doi:10.3390/en5041245
Received: 9 March 2012 / Revised: 11 April 2012 / Accepted: 13 April 2012 / Published: 24 April 2012
Cited by 6 | PDF Full-text (472 KB) | HTML Full-text | XML Full-text
Abstract
This paper introduces the “Energy-Environmental Efficiency” concept of building a low-carbon dispatch model of wind-incorporated power systems from the perspective of environmental protection and low-carbon dispatch promotion based on the existing economic environmental dispatch. A rolling auto-regressive and moving-average model is adopted [...] Read more.
This paper introduces the “Energy-Environmental Efficiency” concept of building a low-carbon dispatch model of wind-incorporated power systems from the perspective of environmental protection and low-carbon dispatch promotion based on the existing economic environmental dispatch. A rolling auto-regressive and moving-average model is adopted to forecast wind speeds for the next 24 h and reduce the disadvantages brought about to the power system dispatch by wind speed fluctuations. A fuzzy satisfaction-maximizing approach is employed to convert the multi-objective decision-making problem in the low-carbon dispatch model into a single nonlinear one. Particle swarm optimization with a simulated annealing algorithm hybrid is used for better solutions. Simulation results show that the energy-environmental efficiency concept benefits the optimization of the proposed power system dispatch, and the proposed low-carbon dispatch model is reasonable and practical. Full article
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Open AccessArticle An Integrated Performance Evaluation Model for the Photovoltaics Industry
Energies 2012, 5(4), 1271-1291; doi:10.3390/en5041271
Received: 22 February 2012 / Revised: 9 April 2012 / Accepted: 16 April 2012 / Published: 24 April 2012
Cited by 14 | PDF Full-text (249 KB) | HTML Full-text | XML Full-text
Abstract
Global warming is causing damaging changes to climate around the World. For environmental protection and natural resource scarcity, alternative forms of energy, such as wind energy, fire energy, hydropower energy, geothermal energy, solar energy, biomass energy, ocean power and natural gas, are [...] Read more.
Global warming is causing damaging changes to climate around the World. For environmental protection and natural resource scarcity, alternative forms of energy, such as wind energy, fire energy, hydropower energy, geothermal energy, solar energy, biomass energy, ocean power and natural gas, are gaining attention as means of meeting global energy demands. Due to Japan’s nuclear plant disaster in March 2011, people are demanding a good alternative energy resource, which not only produces zero or little air pollutants and greenhouse gases, but also with a high safety level to protect the World. Solar energy, which depends on an infinite resource, the sun, is one of the most promising renewable energy sources from the perspective of environmental sustainability. Currently, the manufacturing cost of solar cells is still very high, and the power conversion efficiency is low. Therefore, photovoltaics (PV) firms must continue to invest in research and development, commit to product differentiation, achieve economies of scale, and consider the possibility of vertical integration, in order to strengthen their competitiveness and to acquire the maximum benefit from the PV market. This research proposes a performance evaluation model by integrating analytic hierarchy process (AHP) and data envelopment analysis (DEA) to assess the current business performance of PV firms. AHP is applied to obtain experts’ opinions on the importance of the factors, and DEA is used to determine which firms are efficient. A case study is performed on the crystalline silicon PV firms in Taiwan. The findings shall help the firms determine their strengths and weaknesses and provide directions for future improvements in business operations. Full article

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