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Energies, Volume 6, Issue 3 (March 2013), Pages 1181-1801

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Open AccessArticle Improved Control Strategy for DFIG Wind Turbines for Low Voltage Ride Through
Energies 2013, 6(3), 1181-1197; doi:10.3390/en6031181
Received: 20 November 2012 / Revised: 20 February 2013 / Accepted: 20 February 2013 / Published: 25 February 2013
Cited by 9 | PDF Full-text (717 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents an improved control strategy for both the rotor side converter (RSC) and grid side converter (GSC) of a doubly fed induction generator (DFIG)-based wind turbine (WT) system to enhance the low voltage ride through (LVRT) capability. Within the proposed [...] Read more.
This paper presents an improved control strategy for both the rotor side converter (RSC) and grid side converter (GSC) of a doubly fed induction generator (DFIG)-based wind turbine (WT) system to enhance the low voltage ride through (LVRT) capability. Within the proposed control strategy, the RSC control introduces transient feed-forward compensation terms to mitigate the high frequency harmonic components and reduce the surge in the rotor currents. The proposed GSC control scheme also introduces a compensation term reflecting the instantaneous variation of the output power of the rotor side converter with consideration of the instantaneous power of grid filter impendence to keep the dc-link voltage nearly constant during the grid faults. To provide precise control, non-ideal proportional resonant (PR) controllers for both the RSC and GSC current regulation are employed to further improve dynamic performance. Simulations performed in Matlab/Simulink verify the effectiveness of the proposed control strategy. Full article
(This article belongs to the Special Issue Wind Turbines 2013)
Open AccessArticle Experimental and Numerical Study on the Thermal Performance of a Water/Steam Cavity Receiver
Energies 2013, 6(3), 1198-1216; doi:10.3390/en6031198
Received: 26 September 2012 / Revised: 7 December 2012 / Accepted: 24 January 2013 / Published: 25 February 2013
Cited by 1 | PDF Full-text (1619 KB) | HTML Full-text | XML Full-text
Abstract
An experimental platform was designed and built for testing the thermal performance of a water/steam cavity receiver. The experimental platform was utilized to investigate the start-up performance and operation characteristics of the receiver. The electrical heating mode was chosen to simulate the [...] Read more.
An experimental platform was designed and built for testing the thermal performance of a water/steam cavity receiver. The experimental platform was utilized to investigate the start-up performance and operation characteristics of the receiver. The electrical heating mode was chosen to simulate the non-uniform distribution of heat flux on the surface of absorber tubes inside the cavity. During start-up the temperature rise rate and the mass flow rate are considered as control variables. A couple of start-up curves under different working pressures were finally obtained. The results showed that the receiver performed at relatively low thermal efficiencies. The main reason for the low thermal efficiency was attributed to the low steam mass flow rate, which causes a high proportional heat loss. In order to study the relationship between thermal efficiency and mass flow rate, a computational model for evaluating the thermal performance of a cavity receiver was built and verified. This model couples three aspects of heat transfer: the radiative heat transfer inside the receiver, the flow boiling heat transfer inside the absorber tubes and the convection heat transfer around the receiver. The water/steam cavity receiver of the experimental platform was studied numerically. The curve of thermal efficiency versus mass flow rate was obtained to show that the thermal efficiency increases with increasing mass flow rate within a certain range, and the increase is more remarkable at low mass flow rates. The purpose of the present study was to determine an appropriate mass flow rate for the receiver of the experimental platform to ensure its efficient operation. Full article
(This article belongs to the Special Issue Combined Heat and Power – Strategy and Practice)
Open AccessArticle The Influence of Allocation on the Carbon Footprint of Electricity Production from Waste Gas, a Case Study for Blast Furnace Gas
Energies 2013, 6(3), 1217-1232; doi:10.3390/en6031217
Received: 14 December 2012 / Revised: 19 February 2013 / Accepted: 22 February 2013 / Published: 1 March 2013
Cited by 3 | PDF Full-text (1223 KB) | HTML Full-text | XML Full-text
Abstract
Producing electricity from waste gas is an after treatment for waste gas while recovering the energy content. This paper addresses the methodology to calculate the effect that waste gas energy recovery has on lowering the impact of climate change. Greenhouse gases are [...] Read more.
Producing electricity from waste gas is an after treatment for waste gas while recovering the energy content. This paper addresses the methodology to calculate the effect that waste gas energy recovery has on lowering the impact of climate change. Greenhouse gases are emitted while burning the waste gas. However, a thorough study should include the production of the feedstock as well as the production of the infrastructure. A framework is developed to calculate the environmental impact of electricity production from waste gas with a life cycle approach. The present paper has a twofold purpose: to assess the climate change impact of generating electricity with blast furnace gas (BFG) as a waste gas from the steel industry; and to establish a sensitivity assessment of the environmental implications of different allocation rules. Full article
Open AccessArticle Characteristics of Methane Hydrate Formation in Artificial and Natural Media
Energies 2013, 6(3), 1233-1249; doi:10.3390/en6031233
Received: 20 December 2012 / Revised: 29 January 2013 / Accepted: 4 February 2013 / Published: 1 March 2013
Cited by 3 | PDF Full-text (733 KB) | HTML Full-text | XML Full-text
Abstract
The formation of methane hydrate in two significantly different media was investigated, using silica gel as an artificial medium and loess as a natural medium. The methane hydrate formation was observed through the depletion of water in the matrix, measured via the [...] Read more.
The formation of methane hydrate in two significantly different media was investigated, using silica gel as an artificial medium and loess as a natural medium. The methane hydrate formation was observed through the depletion of water in the matrix, measured via the matrix potential and the relationship between the matrix potential and the water content was determined using established equations. The velocity of methane hydrate nucleation slowed over the course of the reaction, as it relied on water transfer to the hydrate surfaces with lower Gibbs free energy after nucleation. Significant differences in the reactions in the two types of media arose from differences in the water retention capacity and lithology of media due to the internal surface area and pore size distributions. Compared with methane hydrate formation in silica gel, the reaction in loess was much slower and formed far less methane hydrate. The results of this study will advance the understanding of how the properties of the environment affect the formation of gas hydrates in nature. Full article
Open AccessArticle Development of Specific Rules for the Application of Life Cycle Assessment to Carbon Capture and Storage
Energies 2013, 6(3), 1250-1265; doi:10.3390/en6031250
Received: 2 November 2012 / Revised: 1 February 2013 / Accepted: 20 February 2013 / Published: 4 March 2013
Cited by 8 | PDF Full-text (210 KB) | HTML Full-text | XML Full-text
Abstract
Carbon Capture and Storage (CCS) is a very innovative and promising solution for greenhouse gases (GHG) reduction, i.e., capturing carbon dioxide (CO2) at its source and storing it indefinitely to avoid its release to the atmosphere. This paper investigates [...] Read more.
Carbon Capture and Storage (CCS) is a very innovative and promising solution for greenhouse gases (GHG) reduction, i.e., capturing carbon dioxide (CO2) at its source and storing it indefinitely to avoid its release to the atmosphere. This paper investigates a set of key issues in the development of specific rules for the application of Life Cycle Assessment (LCA) to CCS. The following LCA-based information are addressed in this work: definition of service type, definition of functional unit, definition of system boundaries, choice of allocation rules, choice of selected Life Cycle Inventory (LCI) results or other selected parameters for description of environmental performance. From a communication perspective, the specific rules defined in this study have been developed coherently with the requirements of a type III environment label scheme, the International EPD® System, according to the ISO 14025 standard. Full article
Open AccessArticle Balancing Fiscal, Energy, and Environmental Concerns: Analyzing the Policy Options for California’s Energy and Economic Future
Energies 2013, 6(3), 1266-1297; doi:10.3390/en6031266
Received: 6 December 2012 / Revised: 24 January 2013 / Accepted: 16 February 2013 / Published: 4 March 2013
PDF Full-text (1053 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This study estimates the fiscal, energy, and environmental tradeoffs involved in supplying California’s future energy needs. An integrated framework is developed whereby an econometric forecasting system of California energy demand is coupled with engineering-economic models of energy supply, and economic impacts are [...] Read more.
This study estimates the fiscal, energy, and environmental tradeoffs involved in supplying California’s future energy needs. An integrated framework is developed whereby an econometric forecasting system of California energy demand is coupled with engineering-economic models of energy supply, and economic impacts are estimated using input-output models of the California economy. A baseline scenario in which California relies on imported electricity to meet future demand is then compared against various energy supply development scenarios over the forecast horizon (2012–2035). The results indicate that if California implements its renewable portfolio standard (RPS), there will be a substantial net cost in terms of value added, employment, and state tax revenues because the economic benefits of building capacity are outweighed by higher energy prices. Although carbon emissions fall, the cost per ton of avoided emissions is well above market prices. Building out natural gas fired generation capacity also leads to losses compared to the baseline, although the impacts are relatively minor. Meanwhile, a strategy of replacing imported crude oil and natural gas with domestic production using indigenous resources increases gross state product, employment, and tax revenues, with minimal impact on carbon emissions. This option could, therefore, help mitigate the costs of California meeting its RPS commitment. Full article
Open AccessArticle Performance Analysis of a District Heating System
Energies 2013, 6(3), 1298-1313; doi:10.3390/en6031298
Received: 5 December 2012 / Revised: 15 January 2013 / Accepted: 20 February 2013 / Published: 4 March 2013
Cited by 2 | PDF Full-text (700 KB) | HTML Full-text | XML Full-text
Abstract
Lowering the exergy content of heat required for heating purposes decreases the primary energy consumption. District heating systems are often an important link between facilities that generate heat with low exergy content and consumers. Exergetic efficiency of heat distribution is an important [...] Read more.
Lowering the exergy content of heat required for heating purposes decreases the primary energy consumption. District heating systems are often an important link between facilities that generate heat with low exergy content and consumers. Exergetic efficiency of heat distribution is an important performance criterion in heat supply to consumers. It can serve as a criterion for optimization, towards a more sustainable distribution-network design and operation. This paper presents a methodology for an exergy-based distribution-network analysis in a district heating system. Criteria for performance evaluations are defined. They can be used to evaluate heat supply to different points in the network, or individual system components. A case study is performed on an existing district heating system. Energetic and exergetic efficiencies of supply lines are analyzed. Exergy destructions and exergy losses are studied. Large differences in efficiency of heat supply to different points in the network are discovered. Over-dimensioned parameters of the distribution network are investigated. Full article
Open AccessArticle Harmonic Current Predictors for Wind Turbines
Energies 2013, 6(3), 1314-1328; doi:10.3390/en6031314
Received: 21 October 2012 / Revised: 21 December 2012 / Accepted: 22 February 2013 / Published: 4 March 2013
Cited by 4 | PDF Full-text (636 KB) | HTML Full-text | XML Full-text
Abstract
The harmonic impact caused by wind turbines should be carefully investigated before wind turbines are interconnected. However, the harmonic currents of wind turbines are not easily predicted due to the variations of wind speed. If the harmonic current outputs can be predicted [...] Read more.
The harmonic impact caused by wind turbines should be carefully investigated before wind turbines are interconnected. However, the harmonic currents of wind turbines are not easily predicted due to the variations of wind speed. If the harmonic current outputs can be predicted accurately, the harmonic impact of wind turbines and wind farms for power grids can be analyzed efficiently. Therefore, this paper analyzes the harmonic current characteristics of wind turbines and investigates the feasibility of developing harmonic current predictors. Field measurement, data sorting, and analysis are conducted for wind turbines. Two harmonic current predictors are proposed based on the measured harmonic data. One is the Auto-Regressive and Moving Average (ARMA)-based harmonic current predictor, which can be used for real-time prediction. The other is the stochastic harmonic current predictor considering the probability density distributions of harmonic currents. It uses the measured harmonic data to establish the probability density distributions of harmonic currents at different wind speeds, and then uses them to implement a long-term harmonic current prediction. Test results use the measured data to validate the forecast ability of these two harmonic current predictors. The ARMA-based predictor obtains poor performance on some harmonic orders due to the stochastic characteristics of harmonic current caused by the variations of wind speed. Relatively, the prediction results of stochastic harmonic current predictor show that the harmonic currents of a wind turbine in long-term operation can be effectively analyzed by the established probability density distributions. Therefore, the proposed stochastic harmonic current predictor is helpful in predicting and analyzing the possible harmonic problems during the operation of wind turbines and wind farms. Full article
Open AccessArticle Load Forecast Model Switching Scheme for Improved Robustnessto Changes in Building Energy Consumption Patterns
Energies 2013, 6(3), 1329-1343; doi:10.3390/en6031329
Received: 4 January 2013 / Revised: 27 January 2013 / Accepted: 26 February 2013 / Published: 5 March 2013
Cited by 5 | PDF Full-text (2527 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a new, accurate load forecasting technique robust to fluctuations due to unusual load behavioral changes in buildings, i.e., the potential for small commercial buildings with heterogeneous stores. The proposed scheme is featured with two functional components: data classification by [...] Read more.
This paper presents a new, accurate load forecasting technique robust to fluctuations due to unusual load behavioral changes in buildings, i.e., the potential for small commercial buildings with heterogeneous stores. The proposed scheme is featured with two functional components: data classification by daily characteristics and automatic forecast model switching. The scheme extracts daily characteristics of the input load data and arranges the load data into weekday and weekend data. Forecasting is conducted based on a selected model among ARMAX (autoregressive moving average with exogenous variable) models with the processed input data. Kalman filtering is applied to estimate model parameters. The model-switching scheme monitors the accumulated error and substitutes a backup load model for the currently working model, when the accumulated error exceeds a threshold value, to reduce the increased bias error due to the change in the consumption pattern. This switching reinforces the limited performance of parameter estimation given a fixed structure and, thus, forecasting capability. The study results demonstrate that the proposed scheme is reasonably accurate and even robust to changes in the electricity use patterns. It should help improve the performance for building control systems for energy efficiency. Full article
(This article belongs to the Special Issue Hybrid Advanced Techniques for Forecasting in Energy Sector)
Open AccessArticle Evaluation of Various Technologies for Wave Energy Conversion in the Portuguese Nearshore
Energies 2013, 6(3), 1344-1364; doi:10.3390/en6031344
Received: 7 December 2012 / Revised: 6 February 2013 / Accepted: 18 February 2013 / Published: 5 March 2013
Cited by 40 | PDF Full-text (1127 KB) | HTML Full-text | XML Full-text
Abstract
The objective of the present work is to perform an evaluation of the performance provided by various technologies for wave energy conversion in the Portuguese continental coastal environment. The wave climate in the target area is first analyzed using the results from [...] Read more.
The objective of the present work is to perform an evaluation of the performance provided by various technologies for wave energy conversion in the Portuguese continental coastal environment. The wave climate in the target area is first analyzed using the results from three years of simulations with a wave prediction system based on numerical models. Based on the above data, diagrams for the bivariate distributions of the sea states occurrences, defined by the significant wave height and the energy period, are designed for both winters and whole years. On this basis, the output of five different technologies for the conversion of wave energy is assessed in some relevant locations from the Portuguese nearshore. According to the results obtained, the Portuguese continental coastal environment appears to be appropriate for the wave energy extraction. At the same time, the present work shows that the output of the wave energy conversion devices does not depend only on the average wave energy but is also dependent on the distribution of the wave energy among the sea states of different periods. For this reason, a good agreement between the characteristics of the power matrices of the wave energy converters operating in a certain place and the diagrams for the bivariate distributions of the sea states occurrences corresponding to the considered location represents a key issue in selecting the most appropriate technology for wave energy conversion. Full article
(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)
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Open AccessArticle Design and Performance of an Innovative Four-Bed, Three-Stage Adsorption Cycle
Energies 2013, 6(3), 1365-1384; doi:10.3390/en6031365
Received: 19 December 2012 / Revised: 4 February 2013 / Accepted: 18 February 2013 / Published: 5 March 2013
Cited by 3 | PDF Full-text (682 KB) | HTML Full-text | XML Full-text
Abstract
The design of a four-bed three-stage adsorption cycle has been proposed to reduce the volume of the six-bed three-stage adsorption cycle. A simulation model for the proposed innovative cycle was developed to analyse the influence of cycle time on the system performance [...] Read more.
The design of a four-bed three-stage adsorption cycle has been proposed to reduce the volume of the six-bed three-stage adsorption cycle. A simulation model for the proposed innovative cycle was developed to analyse the influence of cycle time on the system performance identifying the specific cooling power (SCP) and coefficient of performance (COP). A particle swarm optimization (PSO) technique was used to optimize the cycle time enabling us to maximize the SCP. PSO results showed that the optimal cycle time was decreased with heat source temperature and SCP value was proportional to heat source temperature. It was found that the proposed cycle could be driven by waste heat as low as 40 °C, along with coolant at 30 °C. Comparative study of optimized result indicated that the proposed cycle increased the performance significantly over a whole range of temperatures from 40 to 70 °C and reduced two adsorbent beds, compared to the six-bed three-stage cycle. Full article
Open AccessArticle Short-Term Load Forecasting for Microgrids Based on Artificial Neural Networks
Energies 2013, 6(3), 1385-1408; doi:10.3390/en6031385
Received: 28 November 2012 / Revised: 18 February 2013 / Accepted: 20 February 2013 / Published: 5 March 2013
Cited by 22 | PDF Full-text (1090 KB) | HTML Full-text | XML Full-text
Abstract
Electricity is indispensable and of strategic importance to national economies. Consequently, electric utilities make an effort to balance power generation and demand in order to offer a good service at a competitive price. For this purpose, these utilities need electric load forecasts [...] Read more.
Electricity is indispensable and of strategic importance to national economies. Consequently, electric utilities make an effort to balance power generation and demand in order to offer a good service at a competitive price. For this purpose, these utilities need electric load forecasts to be as accurate as possible. However, electric load depends on many factors (day of the week, month of the year, etc.), which makes load forecasting quite a complex process requiring something other than statistical methods. This study presents an electric load forecast architectural model based on an Artificial Neural Network (ANN) that performs Short-Term Load Forecasting (STLF). In this study, we present the excellent results obtained, and highlight the simplicity of the proposed model. Load forecasting was performed in a geographic location of the size of a potential microgrid, as microgrids appear to be the future of electric power supply. Full article
(This article belongs to the Special Issue Hybrid Advanced Techniques for Forecasting in Energy Sector)
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Open AccessArticle Energy Production and Regional Economic Growth in China: A More Comprehensive Analysis Using a Panel Model
Energies 2013, 6(3), 1409-1420; doi:10.3390/en6031409
Received: 31 December 2012 / Revised: 30 January 2013 / Accepted: 17 February 2013 / Published: 5 March 2013
Cited by 5 | PDF Full-text (381 KB) | HTML Full-text | XML Full-text
Abstract
China has witnessed a fast economic growth in the recent two decades. However, the heavy energy exploitation seems to show a negative relation to regional economic growth. Thus, the issue is whether the energy production is a curse or blessing for the [...] Read more.
China has witnessed a fast economic growth in the recent two decades. However, the heavy energy exploitation seems to show a negative relation to regional economic growth. Thus, the issue is whether the energy production is a curse or blessing for the regional economic growth in China. The present study deploys a comprehensive approach to rigorously prove the validity of a proposed panel data model that includes a second generation panel unit root test and panel cointegration and a spatial panel model. The results from the second generation panel unit root test and panel cointegration allowing for cross-sectional dependences show the differenced series are stationary and there exists a cointegration relationship among these variables for all sub-regions. The results from the spatial panel data model support the conjecture of the spatial dependent and show that there is a “resource curse” only for the Western region and Central region in China. Full article
Open AccessArticle A Novel Routing Algorithm for Power Line Communication over a Low-voltage Distribution Network in a Smart Grid
Energies 2013, 6(3), 1421-1438; doi:10.3390/en6031421
Received: 29 November 2012 / Revised: 28 January 2013 / Accepted: 21 February 2013 / Published: 5 March 2013
Cited by 3 | PDF Full-text (481 KB) | HTML Full-text | XML Full-text
Abstract
A novel artificial cobweb routing algorithm (ACRA) for routing the tree-type physical topology of a low-voltage distribution network in a smart grid is proposed and analyzed in this paper. The establishment, maintenance and reconstruction of the route are presented. The artificial cobweb [...] Read more.
A novel artificial cobweb routing algorithm (ACRA) for routing the tree-type physical topology of a low-voltage distribution network in a smart grid is proposed and analyzed in this paper. The establishment, maintenance and reconstruction of the route are presented. The artificial cobweb routing algorithm is shown to have broad general applicability for power line communication. To provide a theoretical foundation for further research, the communication delay of the network is calculated accurately. Simulation analysis of the communication delay and throughputs, which were based on Opnet14.5, demonstrate the accuracy of the theoretical calculation. For the performance evaluation of ACRA, a test-bed that includes PLC nodes with the ACRA is set up in a noisy environment. Experimental results show the feasibility of the ACRA algorithm. These indicate that ACRA is effective for guaranteeing Quality of Service (QoS) and reliability in power line communication. Full article
(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)
Open AccessArticle Pareto Optimal Reconfiguration of Power Distribution Systems Using a Genetic Algorithm Based on NSGA-II
Energies 2013, 6(3), 1439-1455; doi:10.3390/en6031439
Received: 17 December 2012 / Revised: 2 February 2013 / Accepted: 19 February 2013 / Published: 6 March 2013
Cited by 18 | PDF Full-text (510 KB) | HTML Full-text | XML Full-text
Abstract
Reconfiguration, by exchanging the functional links between the elements of the system, represents one of the most important measures which can improve the operational performance of a distribution system. The authors propose an original method, aiming at achieving such optimization through the [...] Read more.
Reconfiguration, by exchanging the functional links between the elements of the system, represents one of the most important measures which can improve the operational performance of a distribution system. The authors propose an original method, aiming at achieving such optimization through the reconfiguration of distribution systems taking into account various criteria in a flexible and robust approach. The novelty of the method consists in: the criteria for optimization are evaluated on active power distribution systems (containing distributed generators connected directly to the main distribution system and microgrids operated in grid-connected mode); the original formulation (Pareto optimality) of the optimization problem and an original genetic algorithm (based on NSGA-II) to solve the problem in a non-prohibitive execution time. The comparative tests performed on test systems have demonstrated the accuracy and promptness of the proposed algorithm. Full article
Open AccessArticle Forecasting Energy CO2 Emissions Using a Quantum Harmony Search Algorithm-Based DMSFE Combination Model
Energies 2013, 6(3), 1456-1477; doi:10.3390/en6031456
Received: 7 January 2013 / Revised: 14 February 2013 / Accepted: 28 February 2013 / Published: 6 March 2013
Cited by 6 | PDF Full-text (658 KB) | HTML Full-text | XML Full-text
Abstract
he accurate forecasting of carbon dioxide (CO2) emissions from fossil fuel energy consumption is a key requirement for making energy policy and environmental strategy. In this paper, a novel quantum harmony search (QHS) algorithm-based discounted mean square forecast error (DMSFE) [...] Read more.
he accurate forecasting of carbon dioxide (CO2) emissions from fossil fuel energy consumption is a key requirement for making energy policy and environmental strategy. In this paper, a novel quantum harmony search (QHS) algorithm-based discounted mean square forecast error (DMSFE) combination model is proposed. In the DMSFE combination forecasting model, almost all investigations assign the discounting factor (β) arbitrarily since β varies between 0 and 1 and adopt one value for all individual models and forecasting periods. The original method doesn’t consider the influences of the individual model and the forecasting period. This work contributes by changing β from one value to a matrix taking the different model and the forecasting period into consideration and presenting a way of searching for the optimal β values by using the QHS algorithm through optimizing the mean absolute percent error (MAPE) objective function. The QHS algorithm-based optimization DMSFE combination forecasting model is established and tested by forecasting CO2 emission of the World top‒5 CO2 emitters. The evaluation indexes such as MAPE, root mean squared error (RMSE) and mean absolute error (MAE) are employed to test the performance of the presented approach. The empirical analyses confirm the validity of the presented method and the forecasting accuracy can be increased in a certain degree. Full article
Open AccessArticle A Co-Powered Biomass and Concentrated Solar Power Rankine Cycle Concept for Small Size Combined Heat and Power Generation
Energies 2013, 6(3), 1478-1496; doi:10.3390/en6031478
Received: 17 November 2012 / Revised: 11 January 2013 / Accepted: 25 February 2013 / Published: 6 March 2013
Cited by 3 | PDF Full-text (699 KB) | HTML Full-text | XML Full-text
Abstract
The present work investigates the matching of an advanced small scale Combined Heat and Power (CHP) Rankine cycle plant with end-user thermal and electric load. The power plant consists of a concentrated solar power field co-powered by a biomass furnace to produce [...] Read more.
The present work investigates the matching of an advanced small scale Combined Heat and Power (CHP) Rankine cycle plant with end-user thermal and electric load. The power plant consists of a concentrated solar power field co-powered by a biomass furnace to produce steam in a Rankine cycle, with a CHP configuration. A hotel was selected as the end user due to its high thermal to electric consumption ratio. The power plant design and its operation were modelled and investigated by adopting transient simulations with an hourly distribution. The study of the load matching of the proposed renewable power technology and the final user has been carried out by comparing two different load tracking scenarios, i.e., the thermal and the electric demands. As a result, the power output follows fairly well the given load curves, supplying, on a selected winter day, about 50 GJ/d of thermal energy and the 6 GJ/d of electric energy, with reduced energy dumps when matching the load. Full article
Open AccessArticle Analysis and Performance Comparison of Different Power Conditioning Systems for SMES-Based Energy Systems in Wind Turbines
Energies 2013, 6(3), 1527-1553; doi:10.3390/en6031527
Received: 20 November 2012 / Revised: 19 February 2013 / Accepted: 1 March 2013 / Published: 6 March 2013
Cited by 5 | PDF Full-text (718 KB) | HTML Full-text | XML Full-text
Abstract
Suitability of energy systems based on Superconducting Magnetic Energy Storage (SMES) has been widely tested in the field of wind energy, being able to supply power in cases such as low wind speeds or voltage dips, and to store energy when there [...] Read more.
Suitability of energy systems based on Superconducting Magnetic Energy Storage (SMES) has been widely tested in the field of wind energy, being able to supply power in cases such as low wind speeds or voltage dips, and to store energy when there are surpluses. This article analyzes and compares the performance of three SMES-based systems that differ in the topology of power converter: a two-level Voltage Source Converter (VSC), a three-level VSC and a two-level Current Source Converter (CSC). Their performance has been improved by means of an appropriate modulation strategy. To obtain a high reliability and accuracy, a co-simulation between MATLAB/Simulink® (running the control system) and PSIM® (running the power system) has been executed. Full article
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Open AccessArticle A Novel Pumped Hydro Combined with Compressed Air Energy Storage System
Energies 2013, 6(3), 1554-1567; doi:10.3390/en6031554
Received: 21 December 2012 / Revised: 10 February 2013 / Accepted: 18 February 2013 / Published: 11 March 2013
Cited by 6 | PDF Full-text (1079 KB) | HTML Full-text | XML Full-text
Abstract
A novel pumped hydro combined with compressed air energy storage (PHCA) system is proposed in this paper to resolve the problems of bulk energy storage in the wind power generation industry over an area in China, which is characterised by drought and [...] Read more.
A novel pumped hydro combined with compressed air energy storage (PHCA) system is proposed in this paper to resolve the problems of bulk energy storage in the wind power generation industry over an area in China, which is characterised by drought and water shortages. Thermodynamic analysis of the energy storage system, which focuses on the pre-set pressure, storage volume capacity, water air volume ratio, pump performance, and water turbine performance of the storage system, is also presented. This paper discovers how such parameters affect the performance of the whole system. The ideal performance of this novel system has the following advantages: a simple, highly effective and low cost structure, which is comparable to the efficiency of a traditional pumped hydro storage system. Research results show a great solution to the current storage constraints encountered in the development of the wind power industry in China, which have been widely recognised as a bottleneck in the wind energy storage industry. Full article
Open AccessArticle Catalytic Upgrading of Bio-Oil by Reacting with Olefins and Alcohols over Solid Acids: Reaction Paths via Model Compound Studies
Energies 2013, 6(3), 1568-1589; doi:10.3390/en6031568
Received: 5 January 2013 / Revised: 1 February 2013 / Accepted: 26 February 2013 / Published: 11 March 2013
Cited by 7 | PDF Full-text (338 KB) | HTML Full-text | XML Full-text
Abstract
Catalytic refining of bio-oil by reacting with olefin/alcohol over solid acids can convert bio-oil to oxygen-containing fuels. Reactivities of groups of compounds typically present in bio-oil with 1-octene (or 1-butanol) were studied at 120 °C/3 h over Dowex50WX2, Amberlyst15, Amberlyst36, silica sulfuric [...] Read more.
Catalytic refining of bio-oil by reacting with olefin/alcohol over solid acids can convert bio-oil to oxygen-containing fuels. Reactivities of groups of compounds typically present in bio-oil with 1-octene (or 1-butanol) were studied at 120 °C/3 h over Dowex50WX2, Amberlyst15, Amberlyst36, silica sulfuric acid (SSA) and Cs2.5H0.5PW12O40 supported on K10 clay (Cs2.5/K10, 30 wt. %). These compounds include phenol, water, acetic acid, acetaldehyde, hydroxyacetone, d-glucose and 2-hydroxymethylfuran. Mechanisms for the overall conversions were proposed. Other olefins (1,7-octadiene, cyclohexene, and 2,4,4-trimethylpentene) and alcohols (iso-butanol) with different activities were also investigated. All the olefins and alcohols used were effective but produced varying product selectivities. A complex model bio-oil, synthesized by mixing all the above-stated model compounds, was refined under similar conditions to test the catalyst’s activity. SSA shows the highest hydrothermal stability. Cs2.5/K10 lost most of its activity. A global reaction pathway is outlined. Simultaneous and competing esterification, etherfication, acetal formation, hydration, isomerization and other equilibria were involved. Synergistic interactions among reactants and products were determined. Acid-catalyzed olefin hydration removed water and drove the esterification and acetal formation equilibria toward ester and acetal products. Full article
Open AccessArticle Understanding the Mechanism of Cypress Liquefaction in Hot-Compressed Water through Characterization of Solid Residues
Energies 2013, 6(3), 1590-1603; doi:10.3390/en6031590
Received: 26 November 2012 / Revised: 4 February 2013 / Accepted: 28 February 2013 / Published: 11 March 2013
Cited by 19 | PDF Full-text (360 KB) | HTML Full-text | XML Full-text
Abstract
The mechanism of hydrothermal liquefaction of cypress was investigated by examining the effects of temperature and retention time on the characteristics of the solid residues remaining after liquefaction. The solid residues were divided into acid-soluble and acid-insoluble residues. Results showed the polymerization [...] Read more.
The mechanism of hydrothermal liquefaction of cypress was investigated by examining the effects of temperature and retention time on the characteristics of the solid residues remaining after liquefaction. The solid residues were divided into acid-soluble and acid-insoluble residues. Results showed the polymerization reactions also mainly occurred at low temperatures. The reactive fragments transformed into acid-insoluble solid residue in the form of carbon and oxygen through polymerization reactions. The process of cellulose degradation consists of two steps: an initial hydrolysis of the more solvent- accessible amorphous region and a later hydrolytic attack on the crystalline portion. Hemicelluloses were decomposed into small compounds during the initial stage of the cypress liquefaction process, and then these compounds may rearrange through polymerization to form acid-insoluble solid residues above 240 °C. The higher heating value of the solid residues obtained from liquefaction at 260–300 °C was 23.4–26.3 MJ/kg, indicating that they were suitable for combustion as a solid fuel. Full article
Open AccessArticle Impact of Furfural on Rapid Ethanol Production Using a Membrane Bioreactor
Energies 2013, 6(3), 1604-1617; doi:10.3390/en6031604
Received: 9 January 2013 / Revised: 26 February 2013 / Accepted: 1 March 2013 / Published: 11 March 2013
Cited by 9 | PDF Full-text (444 KB) | HTML Full-text | XML Full-text
Abstract
A membrane bioreactor was developed to counteract the inhibition effect of furfural in ethanol production. Furfural, a major inhibitor in lignocellulosic hydrolyzates, is a highly toxic substance which is formed from pentose sugars released during the acidic degradation of lignocellulosic materials. Continuous [...] Read more.
A membrane bioreactor was developed to counteract the inhibition effect of furfural in ethanol production. Furfural, a major inhibitor in lignocellulosic hydrolyzates, is a highly toxic substance which is formed from pentose sugars released during the acidic degradation of lignocellulosic materials. Continuous cultivations with complete cell retention were performed at a high dilution rate of 0.5 h−1. Furfural was added directly into the bioreactor by pulse injection or by addition into the feed medium to obtain furfural concentrations ranging from 0.1 to 21.8 g L−1. At all pulse injections of furfural, the yeast was able to convert the furfural very rapidly by in situ detoxification. When injecting 21.8 g L−1 furfural to the cultivation, the yeast converted it by a specific conversion rate of 0.35 g g−1 h−1. At high cell density, Saccharomyces cerevisiae could tolerate very high furfural levels without major changes in the ethanol production. During the continuous cultures when up to 17.0 g L−1 furfural was added to the inlet medium, the yeast successfully produced ethanol, whereas an increase of furfural to 18.6 and 20.6 g L−1 resulted in a rapidly decreasing ethanol production and accumulation of sugars in the permeate. This study show that continuous ethanol fermentations by total cell retention in a membrane bioreactor has a high furfural tolerance and can conduct rapid in situ detoxification of medium containing high furfural concentrations. Full article
Open AccessArticle Dried Spent Yeast and Its Hydrolysate as Nitrogen Supplements for Single Batch and Repeated-Batch Ethanol Fermentation from Sweet Sorghum Juice
Energies 2013, 6(3), 1618-1631; doi:10.3390/en6031618
Received: 2 October 2012 / Revised: 18 February 2013 / Accepted: 25 February 2013 / Published: 11 March 2013
Cited by 3 | PDF Full-text (267 KB) | HTML Full-text | XML Full-text
Abstract
Dried spent yeast (DSY) and its hydrolysate (DSYH) were used as low-cost nitrogen supplements to improve ethanol production from sweet sorghum juice by Saccharomyces cerevisiae NP01 under very high gravity (VHG) fermentation (280 g·L−1 of total sugar) conditions. The supplemented DSY [...] Read more.
Dried spent yeast (DSY) and its hydrolysate (DSYH) were used as low-cost nitrogen supplements to improve ethanol production from sweet sorghum juice by Saccharomyces cerevisiae NP01 under very high gravity (VHG) fermentation (280 g·L−1 of total sugar) conditions. The supplemented DSY and DSYH concentrations were 11, 16 and 21 g·L−1, corresponding to a yeast extract nitrogen content of 6, 9 and 12 g·L−1, respectively. The initial yeast cell concentration for ethanol fermentation was approximately 5 × 107 cells·mL−1. The fermentation was carried out in single batch mode at 30 °C in 1-L air-locked bottles with an agitation rate of 100 rpm. Ethanol production from the juice with and without yeast extract (9 g·L−1) was also performed as control treatments. The results showed that DSY at 21 g·L−1gave the highest ethanol concentration (PE, 107 g·L−1) and yield (Yp/s, 0.47 g·g−1). The use of DSYH at the same DSY concentration improved ethanol productivity (Qp), but not PE and Yp/s. The ethanol production efficiencies of the juice under DSY and DSYH supplementations were markedly higher than those without nutrient supplementation. However, the PE and Qp values of the juice containing 21 g·L−1 of DSY was approximately 7 g·L−1 and 0.62 g·L−1·h−1 lower than those under the presence of yeast extract (9 g·L−1), respectively. At the end of the single batch fermentation under the optimum DSY concentration, the sugar consumption was approximately 80%. Therefore in the repeated-batch fermentation, the initial total sugar was reduced to 240 g·L−1. The results showed that the system could be carried out at least 20 successive batches with the average PE, Yp/s and Qp of 95 g·L−1, 0.46 g·g−1 and 1.45 g·L−1·h−1, respectively. Full article
Open AccessArticle Percolation Theory in Solid Oxide Fuel Cell Composite Electrodes with a Mixed Electronic and Ionic Conductor
Energies 2013, 6(3), 1632-1656; doi:10.3390/en6031632
Received: 6 December 2012 / Revised: 26 February 2013 / Accepted: 6 March 2013 / Published: 11 March 2013
Cited by 7 | PDF Full-text (1698 KB) | HTML Full-text | XML Full-text
Abstract
Percolation theory is generalized to predict the effective properties of specific solid oxide fuel cell composite electrodes, which consist of a pure ion conducting material (e.g., YSZ or GDC) and a mixed electron and ion conducting material (e.g., LSCF, LSCM or CeO [...] Read more.
Percolation theory is generalized to predict the effective properties of specific solid oxide fuel cell composite electrodes, which consist of a pure ion conducting material (e.g., YSZ or GDC) and a mixed electron and ion conducting material (e.g., LSCF, LSCM or CeO2). The investigated properties include the probabilities of an LSCF particle belonging to the electron and ion conducting paths, percolated three-phase-boundary electrochemical reaction sites, which are based on different assumptions, the exposed LSCF surface electrochemical reaction sites and the revised expressions for the inter-particle ionic conductivities among LSCF and YSZ materials. The effects of the microstructure parameters, such as the volume fraction of the LSCF material, the particle size distributions of both the LSCF and YSZ materials (i.e., the mean particle radii and the non-dimensional standard deviations, which represent the particle size distributions) and the porosity are studied. Finally, all of the calculated results are presented in non-dimensional forms to provide generality for practical application. Based on these results, the relevant properties can be easily evaluated, and the microstructure parameters and intrinsic properties of each material are specified. Full article
Open AccessCommunication A Demonstration of Carbon-Assisted Water Electrolysis
Energies 2013, 6(3), 1657-1668; doi:10.3390/en6031657
Received: 19 December 2012 / Revised: 22 February 2013 / Accepted: 5 March 2013 / Published: 11 March 2013
Cited by 5 | PDF Full-text (298 KB) | HTML Full-text | XML Full-text
Abstract
It is shown that carbon fuel cell technology can be combined with that of high temperature steam electrolysis by the incorporation of carbon fuel at the cell anode, with the resulting reduction of the required electrolysis voltage by around 1 V. The [...] Read more.
It is shown that carbon fuel cell technology can be combined with that of high temperature steam electrolysis by the incorporation of carbon fuel at the cell anode, with the resulting reduction of the required electrolysis voltage by around 1 V. The behaviour of the cell current density and applied voltage are shown to be connected with the threshold of electrolysis and the main features are compared with theoretical results from the literature. The advantage arises from the avoidance of efficiency losses associated with electricity generation using thermal cycles, as well as the natural separation of the carbon dioxide product stream for subsequent processing. Full article
Open AccessArticle Li-Ion Battery Charging with a Buck-Boost Power Converter for a Solar Powered Battery Management System
Energies 2013, 6(3), 1669-1699; doi:10.3390/en6031669
Received: 26 November 2012 / Revised: 16 February 2013 / Accepted: 5 March 2013 / Published: 11 March 2013
Cited by 6 | PDF Full-text (1970 KB) | HTML Full-text | XML Full-text
Abstract
This paper analyzes and simulates the Li-ion battery charging process for a solar powered battery management system. The battery is charged using a non-inverting synchronous buck-boost DC/DC power converter. The system operates in buck, buck-boost, or boost mode, according to the supply [...] Read more.
This paper analyzes and simulates the Li-ion battery charging process for a solar powered battery management system. The battery is charged using a non-inverting synchronous buck-boost DC/DC power converter. The system operates in buck, buck-boost, or boost mode, according to the supply voltage conditions from the solar panels. Rapid changes in atmospheric conditions or sunlight incident angle cause supply voltage variations. This study develops an electrochemical-based equivalent circuit model for a Li-ion battery. A dynamic model for the battery charging process is then constructed based on the Li-ion battery electrochemical model and the buck-boost power converter dynamic model. The battery charging process forms a system with multiple interconnections. Characteristics, including battery charging system stability margins for each individual operating mode, are analyzed and discussed. Because of supply voltage variation, the system can switch between buck, buck-boost, and boost modes. The system is modeled as a Markov jump system to evaluate the mean square stability of the system. The MATLAB based Simulink piecewise linear electric circuit simulation tool is used to verify the battery charging model. Full article
Open AccessArticle Mitigation of Asymmetrical Grid Faults in Induction Generator-Based Wind Turbines Using Constant Power Load
Energies 2013, 6(3), 1700-1717; doi:10.3390/en6031700
Received: 11 October 2012 / Revised: 24 January 2013 / Accepted: 27 February 2013 / Published: 12 March 2013
Cited by 3 | PDF Full-text (515 KB) | HTML Full-text | XML Full-text
Abstract
Constant power loads (CPLs), interfaced through active rectifiers can be used for improving the stability of induction generator (IG)-based wind turbines under balanced grid voltage dips by providing the reactive power. Under asymmetrical grid faults, the negative sequence voltage produces additional generator [...] Read more.
Constant power loads (CPLs), interfaced through active rectifiers can be used for improving the stability of induction generator (IG)-based wind turbines under balanced grid voltage dips by providing the reactive power. Under asymmetrical grid faults, the negative sequence voltage produces additional generator torque oscillations and reduces the lifetime of the installed equipment. This article explores the possibility of using a CPL for mitigation of unbalanced voltage dips in an AC distribution system in addition to consuming a constant active power. Unbalanced fault mitigation as an ancillary service by the load itself could greatly increase the stability and performance of the overall power system. A CPL control structure, capable of controlling the positive and negative sequence of the grid voltage is suggested. The simulation results clearly indicate the effects of compensating the positive and negative sequence of the grid voltage on the performance of IG based wind turbines. The maximum Fault Ride Through (FRT) enhancement has been given priority and is done by the compensation of positive sequence voltage. The remaining CPL current capacity is used to compensate the negative sequence voltage in order to reduce the additional torque ripples in the IG. Full article
(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)
Open AccessArticle Experimental Investigation on the Performance of a Compressed-Air Driven Piston Engine
Energies 2013, 6(3), 1731-1745; doi:10.3390/en6031731
Received: 3 December 2012 / Revised: 7 March 2013 / Accepted: 8 March 2013 / Published: 12 March 2013
Cited by 12 | PDF Full-text (1548 KB) | HTML Full-text | XML Full-text
Abstract
This study presents an experimental investigation of a piston engine driven by compressed air. The compressed air engine was a modified 100 cm3 internal combustion engine obtained from a motorcycle manufacturer. The experiments in this study used a test bench to [...] Read more.
This study presents an experimental investigation of a piston engine driven by compressed air. The compressed air engine was a modified 100 cm3 internal combustion engine obtained from a motorcycle manufacturer. The experiments in this study used a test bench to examine the power performance and pressure/temperature variations of the compressed air engine at pressures ranging from 5 to 9 bar (absolute pressure). The engine was modified from a 4-stroke to a 2-stroke engine using a cam system driven by a crankshaft and the intake and exhaust valves have a small lift due to this modification. The highest power output of 0.95 kW was obtained at 9 bar and 1320 rpm. The highest torque of 9.99 N·m occurred at the same pressure, but at 465 rpm. The pressure-volume (P-V) diagram shows that cylinder pressure gradually increases after the intake valve opens because of the limited lift movement of the intake valve. Similar situations occurred during the exhaust process, restricting the power output of the compressed air engine. The pressure and temperature variation of the air at engine inlet and outlet were recorded during the experiment. The outlet pressure increased from 1.5 bar at 500 rpm to 2.25 bar at 2000 rpm, showing the potential of recycling the compressed air energy by attaching additional cylinders (split-cycle engine). A temperature decrease (from room temperature to 17 °C) inside the cylinder was observed. It should be noted that pressures higher than that currently employed can result in lower temperatures and this can cause poor lubrication and sealing issues. The current design of a compressed air engine, which uses a conventional cam mechanism for intake and exhaust, has limited lift movement during operation, and has a restricted flow rate and power output. Fast valve actuation and a large lift are essential for improving the performance of the current compressed air engine. This study presents a power output examination with the pressure and temperature measurements of a piston-type compressed air engine to be installed in compact vehicles as the main or auxiliary power system. Full article
Open AccessArticle Intake Manifold Boosting of Turbocharged Spark-Ignited Engines
Energies 2013, 6(3), 1746-1763; doi:10.3390/en6031746
Received: 5 February 2013 / Revised: 5 March 2013 / Accepted: 8 March 2013 / Published: 13 March 2013
Cited by 2 | PDF Full-text (514 KB) | HTML Full-text | XML Full-text
Abstract
Downsizing and turbocharging is a widely used approach to reduce the fuel consumption of spark ignited engines while retaining the maximum power output. However, a substantial loss in drivability must be expected due to the occurrence of the so-called turbo lag. The [...] Read more.
Downsizing and turbocharging is a widely used approach to reduce the fuel consumption of spark ignited engines while retaining the maximum power output. However, a substantial loss in drivability must be expected due to the occurrence of the so-called turbo lag. The turbo lag results from the additional inertia that the turbocharger adds to the system. Supplying air by an additional valve, the boost valve, to the intake manifold can be used to overcome the turbo lag. This turbo lag compensationmethod is referred to as intakemanifold boosting. The aims of this study are to show the effectiveness of intake manifold boosting on a turbocharged spark-ignited engine and to show that intake manifold boosting can be used as an enabler of strong downsizing. Guidelines for the dimensioning of the boost valve are given and a control strategy is presented. The trade-off between additional fuel consumption and the consumption of pressurized air during the turbo lag compensation is discussed. For a load step at 2000 rpm the rise time can be reduced from 2.8 s to 124ms, requiring 11.8 g of pressurized air. The transient performance is verified experimentally by means of load steps at various engine speeds to various engine loads. Full article
Figures

Open AccessArticle Efficiency of Edible Agriculture in Canada and the U.S. Over the Past Three and Four Decades
Energies 2013, 6(3), 1764-1793; doi:10.3390/en6031764
Received: 17 January 2013 / Revised: 7 March 2013 / Accepted: 8 March 2013 / Published: 19 March 2013
Cited by 7 | PDF Full-text (398 KB) | HTML Full-text | XML Full-text
Abstract
We examine technological progress in the US and Canada to answer the question: has the efficiency (e.g., the edible energy efficiency, or EEE) for producing agricultural products in the US and Canada increased in recent decades? Specifically, we determined the energy efficiency [...] Read more.
We examine technological progress in the US and Canada to answer the question: has the efficiency (e.g., the edible energy efficiency, or EEE) for producing agricultural products in the US and Canada increased in recent decades? Specifically, we determined the energy efficiency of agriculture at the farm gate in recent decades by dividing the outputs (the total annual crop and animal output in energy units minus the feed used for animal production and the grain used for ethanol production) by the energy inputs: all the energy used by the nation to produce food (the energy used to generate and apply the fertilizer, pesticides, seed and to operate machinery) minus the energy inputs to produce grain for ethanol. Our data comes primarily from national and international agricultural censuses. Our study found that the energy efficiency of US agriculture has more than doubled from 0.8:1 in 1970 to 2.2:1 by 2000, then increased more slowly to 2.3:1 by 2009. The energy efficiency of the agricultural sector in Canada has not changed appreciably since 1980, and has varied about a mean of 2:1 from 1981 to 2009. Our study found that EEE improvements in the US could be attributable in part to advancements in crop production per hectare, and lower direct fuel consumption, but also a greater proportion of less energy-intensive corn and changes to the diet of livestock (e.g., increased use of meals and other by-products which have increased the availability of grain). Thus increases due to technological progress alone for the last several decades appear small, less than one percent a year. Full article
Open AccessArticle Production of Bioethanol from Carrot Pomace Using the Thermotolerant Yeast Kluyveromyces marxianus
Energies 2013, 6(3), 1794-1801; doi:10.3390/en6031794
Received: 8 October 2012 / Revised: 20 December 2012 / Accepted: 8 March 2013 / Published: 21 March 2013
Cited by 2 | PDF Full-text (357 KB) | HTML Full-text | XML Full-text
Abstract
Carrot pomace, a major agricultural waste from the juice industry, was used as a feedstock for bioethanol production by fermentation with the thermotolerant yeast Kluyveromyces marxianus. Treatment of the carrot pomace with AccelleraseTM 1000 and pectinase at 50 °C for [...] Read more.
Carrot pomace, a major agricultural waste from the juice industry, was used as a feedstock for bioethanol production by fermentation with the thermotolerant yeast Kluyveromyces marxianus. Treatment of the carrot pomace with AccelleraseTM 1000 and pectinase at 50 °C for 84 h, resulted in conversion of 42% of its mass to fermentable sugars, mainly glucose, fructose, and sucrose. Simultaneous saccharification and fermentation (SSF) at 42 °C was performed on 10% (w/v) carrot pomace; the concentration of ethanol reached 18 g/L and the yield of ethanol from carrot pomace was 0.18 g/g. The highest ethanol concentration of 37 g/L was observed with an additional charge of 10% supplemented to the original 10% of carrot pomace after 12 h; the corresponding yield was 0.185 g/g. Our results clearly demonstrated the potential of combining a SSF process with thermotolerant yeast for the production of bioethanol using carrot pomace as a feedstock. Full article

Review

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Open AccessReview 2002–2012: 10 Years of Research Progress in Horizontal-Axis Marine Current Turbines
Energies 2013, 6(3), 1497-1526; doi:10.3390/en6031497
Received: 30 November 2012 / Revised: 13 February 2013 / Accepted: 26 February 2013 / Published: 6 March 2013
Cited by 17 | PDF Full-text (243 KB) | HTML Full-text | XML Full-text
Abstract
Research in marine current energy, including tidal and ocean currents, has undergone significant growth in the past decade. The horizontal-axis marine current turbine is one of the machines used to harness marine current energy, which appears to be the most technologically and [...] Read more.
Research in marine current energy, including tidal and ocean currents, has undergone significant growth in the past decade. The horizontal-axis marine current turbine is one of the machines used to harness marine current energy, which appears to be the most technologically and economically viable one at this stage. A number of large-scale marine current turbines rated at more than 1 MW have been deployed around the World. Parallel to the development of industry, academic research on horizontal-axis marine current turbines has also shown positive growth. This paper reviews previous research on horizontal-axis marine current turbines and provides a concise overview for future researchers who might be interested in horizontal-axis marine current turbines. The review covers several main aspects, such as: energy assessment, turbine design, wakes, generators, novel modifications and environmental impact. Future trends for research on horizontal-axis marine current turbines are also discussed. Full article
(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)
Open AccessReview Preparation and Doping Mode of Doped LiMn2O4 for Li-Ion Batteries
Energies 2013, 6(3), 1718-1730; doi:10.3390/en6031718
Received: 5 January 2013 / Revised: 2 March 2013 / Accepted: 6 March 2013 / Published: 12 March 2013
Cited by 20 | PDF Full-text (246 KB) | HTML Full-text | XML Full-text
Abstract
Spinel LiMn2O4 is an appealing candidate cathode material for Li-ion rechargeable batteries, but it suffers from severe capacity fading, especially at higher temperature (55 °C) during discharging/charging. In recent years, many attempts have been made to synthesize modified LiMn [...] Read more.
Spinel LiMn2O4 is an appealing candidate cathode material for Li-ion rechargeable batteries, but it suffers from severe capacity fading, especially at higher temperature (55 °C) during discharging/charging. In recent years, many attempts have been made to synthesize modified LiMn2O4. This paper reviews the recent research on the preparation and doping modes of doped LiMn2O4 for modifying the LiMn2O4. We firstly compared preparation methods for doped spinel LiMn2O4, such as solid state reactions and solution synthetic methods. Then we mainly discuss doping modes reported in recent years, such as bulk doping, surface doping and combined doping. A comparison of different doping modes is also provided. The research shows that the multiple-ion doping and combined doping modes of LiMn2O4 used in Li-ion battery are excellent for improving different aspects of the electrochemical performance which holds great promise in the future. From this paper, we also can see that spinel LiMnO4 as an attractive candidate cathode material for Li-ion batteries. Full article
(This article belongs to the Special Issue Li-ion Batteries and Energy Storage Devices)

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