Energies

243 KiB

Open AccessCorrection

Correction: Legros Arnaud, Guillaume Ludovic, Diny Mouad, Zaïdi Hamid and Lemort Vincent. Comparison and Impact of Waste Heat Recovery Technologies on Passenger Car Fuel Consumption in a Normalized Driving Cycle. Energies 2014, 7, 5273–5290

by Arnaud Legros, Ludovic Guillaume, Mouad Diny, Hamid Zaïdi and Vincent Lemort

Energies 2014, 7(10), 6823-6824; https://doi.org/10.3390/en7106823 - 23 Oct 2014

Cited by 1 | Viewed by 4772

Abstract

We have found the following error in the authors’ information in this article, which was recently published in Energies [1]. On page 5273, the names of the authors are incorrect; they should be changed from:[...] Full article

5513 KiB

Open AccessArticle

Insight into Rotational Effects on a Wind Turbine Blade Using Navier–Stokes Computations

by Iván Herráez, Bernhard Stoevesandt and Joachim Peinke

Energies 2014, 7(10), 6798-6822; https://doi.org/10.3390/en7106798 - 21 Oct 2014

Cited by 47 | Viewed by 9116

Abstract

Rotational effects are known to influence severely the aerodynamic performance of the inboard region of rotor blades. The underlying physical mechanisms are however far from being well understood. The present work addresses this problem using Reynolds averaged Navier–Stokes computations and experimental results of [...] Read more.

Rotational effects are known to influence severely the aerodynamic performance of the inboard region of rotor blades. The underlying physical mechanisms are however far from being well understood. The present work addresses this problem using Reynolds averaged Navier–Stokes computations and experimental results of the MEXICO (Model Experiments in Controlled Conditions) rotor. Four axisymmetric inflow cases with wind speeds ranging from pre-stall to post-stall conditions are computed and compared with pressure and particle image velocimetry (PIV) experimental data, obtaining, in general, consistent results. At low angles of attack, the aerodynamic behavior of all of the studied blade sections resembles the one from the corresponding 2D airfoils. However, at high angles of attack, rotational effects lead to stall delay and/or lift enhancement at inboard positions. Such effects are shown to occur only in the presence of significant radial flows. Interestingly, the way in which rotational effects influence the aerodynamics of the MEXICO blades differs qualitatively in certain aspects from the descriptions found in the literature about this topic. The presented results provide new insights that are useful for the development of advanced and physically-sound correction models. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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457 KiB

Open AccessArticle

Study on the Optimal Charging Strategy for Lithium-Ion Batteries Used in Electric Vehicles

by Shuo Zhang, Chengning Zhang, Rui Xiong and Wei Zhou

Energies 2014, 7(10), 6783-6797; https://doi.org/10.3390/en7106783 - 21 Oct 2014

Cited by 40 | Viewed by 8446

Abstract

The charging method of lithium-ion batteries used in electric vehicles (EVs) significantly affects its commercial application. This paper aims to make three contributions to the existing literature. (1) In order to achieve an efficient charging strategy for lithium-ion batteries with shorter charging time [...] Read more.

The charging method of lithium-ion batteries used in electric vehicles (EVs) significantly affects its commercial application. This paper aims to make three contributions to the existing literature. (1) In order to achieve an efficient charging strategy for lithium-ion batteries with shorter charging time and lower charring loss, the trade-off problem between charging loss and charging time has been analyzed in details through the dynamic programing (DP) optimization algorithm; (2) To reduce the computation time consumed during the optimization process, we have proposed a database based optimization approach. After off-line calculation, the simulation results can be applied to on-line charge; (3) The novel database-based DP method is proposed and the simulation results illustrate that this method can effectively find the suboptimal charging strategies under a certain balance between the charging loss and charging time. Full article

(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)

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855 KiB

Open AccessArticle

A Zero Input Current Ripple ZVS/ZCS Boost Converter with Boundary-Mode Control

by Ching-Ming Lai, Ming-Ji Yang and Shih-Kun Liang

Energies 2014, 7(10), 6765-6782; https://doi.org/10.3390/en7106765 - 20 Oct 2014

Cited by 13 | Viewed by 8260

Abstract

In this paper, in order to achieve zero ripple conditions, the use of a ripple mirror (RM) circuit for the boost converter is proposed. The operation modes are studied and steady-state analyses performed to show the merits of the proposed converter. It is [...] Read more.

In this paper, in order to achieve zero ripple conditions, the use of a ripple mirror (RM) circuit for the boost converter is proposed. The operation modes are studied and steady-state analyses performed to show the merits of the proposed converter. It is found that the proposed RM circuit technique can provide much better flexibility than the two-phase interleaved boost converter for locating the zero ripple operating point in the design stage. In addition, the choice of using a boundary-mode control is mainly based on the consideration of achieving both ZVS (zero voltage switching)/ZCS (zero current switching) soft-switching and constant on-time control for the converter. To verify the performance of the proposed converter, a 48 V input and 200 W/200 V output prototype is constructed. Experimental results verify the effectiveness of the proposed converter. Full article

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Graphical abstract

810 KiB

Open AccessArticle

Assessment of Energy, Environmental and Economic Performance of a Solar Desiccant Cooling System with Different Collector Types

by Giovanni Angrisani, Carlo Roselli, Maurizio Sasso and Francesco Tariello

Energies 2014, 7(10), 6741-6764; https://doi.org/10.3390/en7106741 - 20 Oct 2014

Cited by 23 | Viewed by 7243

Abstract

Desiccant-based air handling units can achieve reductions in greenhouse gas emissions and energy savings with respect to conventional air conditioning systems. Benefits are maximized when they interact with renewable energy technologies, such as solar collectors. In this work, experimental tests and data derived [...] Read more.

Desiccant-based air handling units can achieve reductions in greenhouse gas emissions and energy savings with respect to conventional air conditioning systems. Benefits are maximized when they interact with renewable energy technologies, such as solar collectors. In this work, experimental tests and data derived from scientific and technical literature are used to implement a model of a solar desiccant cooling system, considering three different collector technologies (air, flat-plate and evacuated collectors). Simulations were then performed to compare the energy, environmental and economic performance of the system with those of a desiccant-based unit where regeneration thermal energy is supplied by a natural gas boiler, and with those of a conventional air-handling unit. The only solution that allows achieving the economic feasibility of the solar desiccant cooling unit consists of 16 m² of evacuated solar collectors. This is able to obtain, with respect to the reference system, a reduction of primary energy consumption and of the equivalent CO₂ emissions of 50.2% and 49.8%, respectively, but with a payback time of 20 years. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International e-Conference on Energies — Whither Energy Conversion? Present Trends, Current Problems and Realistic Future Solutions)

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968 KiB

Open AccessArticle

A Novel Modeling of Molten-Salt Heat Storage Systems in Thermal Solar Power Plants

by Rogelio Peón Menéndez, Juan Á. Martínez, Miguel J. Prieto, Lourdes Á. Barcia and Juan M. Martín Sánchez

Energies 2014, 7(10), 6721-6740; https://doi.org/10.3390/en7106721 - 17 Oct 2014

Cited by 24 | Viewed by 10922 | Correction

Abstract

Many thermal solar power plants use thermal oil as heat transfer fluid, and molten salts as thermal energy storage. Oil absorbs energy from sun light, and transfers it to a water-steam cycle across heat exchangers, to be converted into electric energy by means [...] Read more.

Many thermal solar power plants use thermal oil as heat transfer fluid, and molten salts as thermal energy storage. Oil absorbs energy from sun light, and transfers it to a water-steam cycle across heat exchangers, to be converted into electric energy by means of a turbogenerator, or to be stored in a thermal energy storage system so that it can be later transferred to the water-steam cycle. The complexity of these thermal solar plants is rather high, as they combine traditional engineering used in power stations (water-steam cycle) or petrochemical (oil piping), with the new solar (parabolic trough collector) and heat storage (molten salts) technologies. With the engineering of these plants being relatively new, regulation of the thermal energy storage system is currently achieved in manual or semiautomatic ways, controlling its variables with proportional-integral-derivative (PID) regulators. This makes the overall performance of these plants non optimal. This work focuses on energy storage systems based on molten salt, and defines a complete model of the process. By defining such a model, the ground for future research into optimal control methods will be established. The accuracy of the model will be determined by comparing the results it provides and those measured in the molten-salt heat storage system of an actual power plant. Full article

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Open AccessArticle

Seismic Velocity/Temperature Correlations and a Possible New Geothermometer: Insights from Exploration of a High-Temperature Geothermal System on Montserrat, West Indies

by Graham Alexander Ryan and Eylon Shalev

Energies 2014, 7(10), 6689-6720; https://doi.org/10.3390/en7106689 - 17 Oct 2014

Cited by 13 | Viewed by 8008

Abstract

In 2013, two production wells were drilled into a geothermal reservoir on Montserrat, W.I. (West Indies) Drilling results confirmed the main features of a previously developed conceptual model. The results confirm that below ~220 °C there is a negative correlation between reservoir temperature [...] Read more.

In 2013, two production wells were drilled into a geothermal reservoir on Montserrat, W.I. (West Indies) Drilling results confirmed the main features of a previously developed conceptual model. The results confirm that below ~220 °C there is a negative correlation between reservoir temperature and seismic velocity anomaly. However, above ~220 °C there is a positive correlation. We hypothesise that anomalous variations in seismic velocity within the reservoir are controlled to first order by the hydrothermal mineral assemblage. This study suggests a new geophysical thermometer which can be used to estimate temperatures in three dimensions with unprecedented resolution and to indicate the subsurface fluid pathways which are the target of geothermal exploitation. Full article

(This article belongs to the Special Issue Geothermal Energy: Delivering on the Global Potential)

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2967 KiB

Open AccessArticle

Electromagnetic Analysis and Design of Switched Reluctance Double-Rotor Machine for Hybrid Electric Vehicles

by Shouliang Han, Shumei Cui, Liwei Song and Ching Chuen Chan

Energies 2014, 7(10), 6665-6688; https://doi.org/10.3390/en7106665 - 16 Oct 2014

Cited by 9 | Viewed by 7872

Abstract

The double-rotor machine is a kind of multiple input and output electromechanical energy transducer with two electrical ports and two mechanical ports, which is an ideal transmission system for hybrid electric vehicles and has a series of advantages such as integration of power [...] Read more.

The double-rotor machine is a kind of multiple input and output electromechanical energy transducer with two electrical ports and two mechanical ports, which is an ideal transmission system for hybrid electric vehicles and has a series of advantages such as integration of power and energy, high efficiency and compaction. In this paper, a switched reluctance double-rotor machine (SRDRM) is proposed for hybrid electric vehicles, while no conductor or PM in the middle rotor. This machine not only inherits the merits of switched reluctance machine, such as simple salient rotor structure, high reliability and wide speed range, but also can avoid the outer rotor’s cooling problem effectively. By using an equivalent magnetic circuit model, the function of middle rotor yoke is analyzed. Electromagnetic analyses of the SRDRM are performed with analytical calculations and 2-D finite element methods, including the effects of main parameters on performance. Finally, a 4.4 kW prototype machine is designed and manufactured, and the tests are performed, which validate the proposed design method. Full article

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384 KiB

Open AccessArticle

Methods for Risk-Based Planning of O&M of Wind Turbines

by Jannie Sønderkær Nielsen and John Dalsgaard Sørensen

Energies 2014, 7(10), 6645-6664; https://doi.org/10.3390/en7106645 - 16 Oct 2014

Cited by 47 | Viewed by 8256

Abstract

In order to make wind energy more competitive, the big expenses for operation and maintenance must be reduced. Consistent decisions that minimize the expected costs can be made based on risk-based methods. Such methods have been implemented for maintenance planning for oil and [...] Read more.

In order to make wind energy more competitive, the big expenses for operation and maintenance must be reduced. Consistent decisions that minimize the expected costs can be made based on risk-based methods. Such methods have been implemented for maintenance planning for oil and gas structures, but for offshore wind turbines, the conditions are different and the methods need to be adjusted accordingly. This paper gives an overview of various approaches to solve the decision problem: methods with decision rules based on observed variables, a method with decision rules based on the probability of failure, a method based on limited memory influence diagrams and a method based on the partially observable Markov decision process. The methods with decision rules based on observed variables are easy to use, but can only take the most recent observation into account, when a decision is made. The other methods can take more information into account, and especially, the method based on the Markov decision process is very flexible and accurate. A case study shows that the Markov decision process and decision rules based on the probability of failure are equally good and give lower costs compared to decision rules based on observed variables. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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1037 KiB

Open AccessArticle

Real-Time Wavelet-Based Coordinated Control of Hybrid Energy Storage Systems for Denoising and Flattening Wind Power Output

by Tran Thai Trung, Seon-Ju Ahn, Joon-Ho Choi, Seok-Il Go and Soon-Ryul Nam

Energies 2014, 7(10), 6620-6644; https://doi.org/10.3390/en7106620 - 16 Oct 2014

Cited by 31 | Viewed by 8552

Abstract

Since the penetration level of wind energy is continuously increasing, the negative impact caused by the fluctuation of wind power output needs to be carefully managed. This paper proposes a novel real-time coordinated control algorithm based on a wavelet transform to mitigate both [...] Read more.

Since the penetration level of wind energy is continuously increasing, the negative impact caused by the fluctuation of wind power output needs to be carefully managed. This paper proposes a novel real-time coordinated control algorithm based on a wavelet transform to mitigate both short-term and long-term fluctuations by using a hybrid energy storage system (HESS). The short-term fluctuation is eliminated by using an electric double-layer capacitor (EDLC), while the wind-HESS system output is kept constant during each 10-min period by a Ni-MH battery (NB). State-of-charge (SOC) control strategies for both EDLC and NB are proposed to maintain the SOC level of storage within safe operating limits. A ramp rate limitation (RRL) requirement is also considered in the proposed algorithm. The effectiveness of the proposed algorithm has been tested by using real time simulation. The simulation model of the wind-HESS system is developed in the real-time digital simulator (RTDS)/RSCAD environment. The proposed algorithm is also implemented as a user defined model of the RSCAD. The simulation results demonstrate that the HESS with the proposed control algorithm can indeed assist in dealing with the variation of wind power generation. Moreover, the proposed method shows better performance in smoothing out the fluctuation and managing the SOC of battery and EDLC than the simple moving average (SMA) based method. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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2726 KiB

Open AccessArticle

Control Strategies to Smooth Short-Term Power Fluctuations in Large Photovoltaic Plants Using Battery Storage Systems

by Javier Marcos, Iñigo De la Parra, Miguel García and Luis Marroyo

Energies 2014, 7(10), 6593-6619; https://doi.org/10.3390/en7106593 - 16 Oct 2014

Cited by 116 | Viewed by 11024

Abstract

The variations in irradiance produced by changes in cloud cover can cause rapid fluctuations in the power generated by large photovoltaic (PV) plants. As the PV power share in the grid increases, such fluctuations may adversely affect power quality and reliability. Thus, energy [...] Read more.

The variations in irradiance produced by changes in cloud cover can cause rapid fluctuations in the power generated by large photovoltaic (PV) plants. As the PV power share in the grid increases, such fluctuations may adversely affect power quality and reliability. Thus, energy storage systems (ESS) are necessary in order to smooth power fluctuations below the maximum allowable. This article first proposes a new control strategy (step-control), to improve the results in relation to two state-of-the-art strategies, ramp-rate control and moving average. It also presents a method to quantify the storage capacity requirements according to the three different smoothing strategies and for different PV plant sizes. Finally, simulations shows that, although the moving-average (MA) strategy requires the smallest capacity, it presents more losses (2–3 times more) and produces a much higher number of cycles over the ESS (around 10 times more), making it unsuitable with storage technologies as lithium-ion. The step-control shown as a better option in scenery with exigent ramp restrictions (around 2%/min) and distributed generation against the ramp-rate control in all ESS key aspects: 20% less of capacity, up to 30% less of losses and a 40% less of ageing. All the simulations were based on real PV production data, taken every 5 s in the course of one year (2012) from a number of systems with power outputs ranging from 550 kW to 40 MW. Full article

(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)

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1490 KiB

Open AccessArticle

Modeling and Control of a Parallel Waste Heat Recovery System for Euro-VI Heavy-Duty Diesel Engines

by Emanuel Feru, Frank Willems, Bram De Jager and Maarten Steinbuch

Energies 2014, 7(10), 6571-6592; https://doi.org/10.3390/en7106571 - 14 Oct 2014

Cited by 62 | Viewed by 8770

Abstract

This paper presents the modeling and control of a waste heat recovery systemfor a Euro-VI heavy-duty truck engine. The considered waste heat recovery system consists of two parallel evaporators with expander and pumps mechanically coupled to the engine crankshaft. Compared to previous work, [...] Read more.

This paper presents the modeling and control of a waste heat recovery systemfor a Euro-VI heavy-duty truck engine. The considered waste heat recovery system consists of two parallel evaporators with expander and pumps mechanically coupled to the engine crankshaft. Compared to previous work, the waste heat recovery system modeling is improved by including evaporator models that combine the finite difference modeling approach with a moving boundary one. Over a specific cycle, the steady-state and dynamic temperature prediction accuracy improved on average by 2% and 7%. From a control design perspective, the objective is to maximize the waste heat recovery system output power.However, for safe system operation, the vapor state needs to be maintained before the expander under highly dynamic engine disturbances. To achieve this, a switching model predictive control strategy is developed. The proposed control strategy performance is demonstrated using the high-fidelity waste heat recovery system model subject to measured disturbances from an Euro-VI heavy-duty diesel engine. Simulations are performed usinga cold-start World Harmonized Transient cycle that covers typical urban, rural and highway driving conditions. The model predictive control strategy provides 15% more time in vaporand recovered thermal energy than a classical proportional-integral (PI) control strategy. In the case that the model is accurately known, the proposed control strategy performance can be improved by 10% in terms of time in vapor and recovered thermal energy. This is demonstrated with an offline nonlinear model predictive control strategy. Full article

(This article belongs to the Special Issue Waste Heat Recovery—Strategy and Practice)

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646 KiB

Open AccessArticle

Does a Change in Price of Fuel Affect GDP Growth? An Examination of the U.S. Data from 1950–2013

by Michael Aucott and Charles Hall

Energies 2014, 7(10), 6558-6570; https://doi.org/10.3390/en7106558 - 14 Oct 2014

Cited by 20 | Viewed by 14715

Abstract

We examined data on fuel consumption and costs for the years 1950 through 2013, along with economic and population data, to determine the percent of U.S. gross domestic product (GDP) spent each year on fuels, including fossil fuels and nuclear ore, and the [...] Read more.

We examined data on fuel consumption and costs for the years 1950 through 2013, along with economic and population data, to determine the percent of U.S. gross domestic product (GDP) spent each year on fuels, including fossil fuels and nuclear ore, and the growth of the economy. We found that these variables are inversely correlated. This suggests that the availability and cost of energy is a significant determinant of economic performance. We believe this relation is consistent with analyses based on the energy return on investment (EROI) concept in that increasingly scarce, and hence expensive, fuels are a drag on economic growth. The best-fitting linear equation relating the percent of GDP (energy cost share) and year-over-year (YoY) GDP change variables suggests that a threshold exists in the vicinity of 4%; if the percent of GDP spent on fuels is greater than this, poorer economic performance has been likely. Currently, about 5% of GDP is spent on fuels; most of this is for liquids. Continued weak economic performance appears likely unless improvements in energy efficiency, on the order of a factor of 3 for liquid fuels, and/or a more rapid adoption of renewable or nuclear energy sources can be achieved, provided that the EROI of these new sources proves to be sufficiently high. Full article

(This article belongs to the Special Issue Energy Transitions and Economic Change)

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428 KiB

Open AccessArticle

Development and Characterization of an Electrically Rechargeable Zinc-Air Battery Stack

by Hongyun Ma, Baoguo Wang, Yongsheng Fan and Weichen Hong

Energies 2014, 7(10), 6549-6557; https://doi.org/10.3390/en7106549 - 13 Oct 2014

Cited by 45 | Viewed by 10261

Abstract

An electrically rechargeable zinc-air battery stack consisting of three single cells in series was designed using a novel structured bipolar plate with air-breathing holes. Alpha-MnO₂ and LaNiO₃ severed as the catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction [...] Read more.

An electrically rechargeable zinc-air battery stack consisting of three single cells in series was designed using a novel structured bipolar plate with air-breathing holes. Alpha-MnO₂ and LaNiO₃ severed as the catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The anodic and cathodic polarization and individual cell voltages were measured at constant charge-discharge (C-D) current densities indicating a uniform voltage profile for each single cell. One hundred C-D cycles were carried out for the stack. The results showed that, over the initial 10 cycles, the average C-D voltage gap was about 0.94 V and the average energy efficiency reached 89.28% with current density charging at 15 mA·cm⁻² and discharging at 25 mA·cm⁻². The total increase in charging voltage over the 100 C-D cycles was ~1.56% demonstrating excellent stability performance. The stack performance degradation was analyzed by galvanostatic electrochemical impedance spectroscopy. The charge transfer resistance of ORR increased from 1.57 to 2.21 Ω and that of Zn/Zn²⁺ reaction increased from 0.21 to 0.34 Ω after 100 C-D cycles. The quantitative analysis guided the potential for the optimization of both positive and negative electrodes to improve the cycle life of the cell stack. Full article

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5485 KiB

Open AccessArticle

Transient Thunderstorm Downbursts and Their Effects on Wind Turbines

by Hieu H. Nguyen and Lance Manuel

Energies 2014, 7(10), 6527-6548; https://doi.org/10.3390/en7106527 - 13 Oct 2014

Cited by 11 | Viewed by 7249

Abstract

The International Electrotechnical Commission (IEC) Standard 61400-1 for the design of wind turbines does not explicitly address site-specific conditions associated with anomalous atmospheric events or conditions. Examples of off-standard atmospheric conditions include thunderstorm downbursts, hurricanes, tornadoes, low-level jets, etc. The simulation of thunderstorm [...] Read more.

The International Electrotechnical Commission (IEC) Standard 61400-1 for the design of wind turbines does not explicitly address site-specific conditions associated with anomalous atmospheric events or conditions. Examples of off-standard atmospheric conditions include thunderstorm downbursts, hurricanes, tornadoes, low-level jets, etc. The simulation of thunderstorm downbursts and associated loads on a utility-scale wind turbine is the focus of this study. Since the problem has not received sufficient attention, especially in terms of design, we thus focus in this paper on practical aspects. A wind field model that incorporates component non-turbulent and turbulent parts is described and employed in inflow simulations. The non-turbulent part is based on an available analytical model with some modifications, while the turbulent part is simulated as a stochastic process using standard turbulence power spectral density functions and coherence functions whose defining parameters are related to the downburst characteristics such as the storm translation velocity. Available information on recorded downbursts is used to define two storm scenarios that are studied. Rotor loads are generated using stochastic simulation of the aeroelastic response of a model of a utility-scale 5-MW turbine. An illustrative single storm simulation and the associated turbine response are used to discuss load characteristics and to highlight storm-related and environmental parameters of interest. Extensive simulations for two downbursts are then conducted while varying the storm’s location and track relative to the turbine. Results suggest that wind turbine yaw and pitch control systems clearly influence overall system response. Results also highlight the important effects of both the turbulence as well as the downburst mean wind profiles on turbine extreme loads. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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1795 KiB

Open AccessArticle

Opportunities for Energy Crop Production Based on Subfield Scale Distribution of Profitability

by Ian J. Bonner, Kara G. Cafferty, David J. Muth, Jr., Mark D. Tomer, David E. James, Sarah A. Porter and Douglas L. Karlen

Energies 2014, 7(10), 6509-6526; https://doi.org/10.3390/en7106509 - 13 Oct 2014

Cited by 41 | Viewed by 8086

Abstract

Incorporation of dedicated herbaceous energy crops into row crop landscapes is a promising means to supply an expanding biofuel industry while benefiting soil and water quality and increasing biodiversity. Despite these positive traits, energy crops remain largely unaccepted due to concerns over their [...] Read more.

Incorporation of dedicated herbaceous energy crops into row crop landscapes is a promising means to supply an expanding biofuel industry while benefiting soil and water quality and increasing biodiversity. Despite these positive traits, energy crops remain largely unaccepted due to concerns over their practicality and cost of implementation. This paper presents a case study for Hardin County, Iowa, to demonstrate how subfield decision making can be used to target candidate areas for conversion to energy crop production. Estimates of variability in row crop production at a subfield level are used to model the economic performance of corn (Zea mays L.) grain and the environmental impacts of corn stover collection using the Landscape Environmental Analysis Framework (LEAF). The strategy used in the case study integrates switchgrass (Panicum virgatum L.) into subfield landscape positions where corn grain is modeled to return a net economic loss. Results show that switchgrass integration has the potential to increase sustainable biomass production from 48% to 99% (depending on the rigor of conservation practices applied to corn stover collection), while also improving field level profitability of corn. Candidate land area is highly sensitive to grain price (0.18 to 0.26 $·kg⁻¹) and dependent on the acceptable subfield net loss for corn production (ranging from 0 to −1000 $·ha⁻¹) and the ability of switchgrass production to meet or exceed this return. This work presents the case that switchgrass may be economically incorporated into row crop landscapes when management decisions are applied at a subfield scale within field areas modeled to have a negative net profit with current management practices. Full article

(This article belongs to the Special Issue Renewable Energy for Agriculture)

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2457 KiB

Open AccessArticle

Prognostics of Lithium-Ion Batteries Based on Battery Performance Analysis and Flexible Support Vector Regression

by Shuai Wang, Lingling Zhao, Xiaohong Su and Peijun Ma

Energies 2014, 7(10), 6492-6508; https://doi.org/10.3390/en7106492 - 10 Oct 2014

Cited by 72 | Viewed by 8960

Abstract

Accurate prediction of the remaining useful life (RUL) of lithium-ion batteries is important for battery management systems. Traditional empirical data-driven approaches for RUL prediction usually require multidimensional physical characteristics including the current, voltage, usage duration, battery temperature, and ambient temperature. From [...] Read more.

Accurate prediction of the remaining useful life (RUL) of lithium-ion batteries is important for battery management systems. Traditional empirical data-driven approaches for RUL prediction usually require multidimensional physical characteristics including the current, voltage, usage duration, battery temperature, and ambient temperature. From a capacity fading analysis of lithium-ion batteries, it is found that the energy efficiency and battery working temperature are closely related to the capacity degradation, which account for all performance metrics of lithium-ion batteries with regard to the RUL and the relationships between some performance metrics. Thus, we devise a non-iterative prediction model based on flexible support vector regression (F-SVR) and an iterative multi-step prediction model based on support vector regression (SVR) using the energy efficiency and battery working temperature as input physical characteristics. The experimental results show that the proposed prognostic models have high prediction accuracy by using fewer dimensions for the input data than the traditional empirical models. Full article

(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)

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707 KiB

Open AccessArticle

Voltage Control Scheme with Distributed Generation and Grid Connected Converter in a DC Microgrid

by Jong-Chan Choi, Ho-Yong Jeong, Jin-Young Choi, Dong-Jun Won, Seon-Ju Ahn and Seung-il Moon

Energies 2014, 7(10), 6477-6491; https://doi.org/10.3390/en7106477 - 10 Oct 2014

Cited by 27 | Viewed by 5640

Abstract

Direct Current (DC) microgrids are expected to become larger due to the rapid growth of DC energy sources and power loads. As the scale of the system expends, the importance of voltage control will be increased to operate power systems stably. Many studies [...] Read more.

Direct Current (DC) microgrids are expected to become larger due to the rapid growth of DC energy sources and power loads. As the scale of the system expends, the importance of voltage control will be increased to operate power systems stably. Many studies have been performed on voltage control methods in a DC microgrid, but most of them focused only on a small scale microgrid, such as a building microgrid. Therefore, a new control method is needed for a middle or large scale DC microgrid. This paper analyzes voltage drop problems in a large DC microgrid and proposes a cooperative voltage control scheme with a distributed generator (DG) and a grid connected converter (GCC). For the voltage control with DGs, their location and capacity should be considered for economic operation in the systems. Accordingly, an optimal DG allocation algorithm is proposed to minimize the capacity of a DG for voltage control in DC microgrids. The proposed methods are verified with typical load types by a simulation using MATLAB and PSCAD/EMTDC. Full article

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657 KiB

Open AccessArticle

Performance Evaluation of an Anti-Lock Braking System for Electric Vehicles with a Fuzzy Sliding Mode Controller

by Jingang Guo, Xiaoping Jian and Guangyu Lin

Energies 2014, 7(10), 6459-6476; https://doi.org/10.3390/en7106459 - 9 Oct 2014

Cited by 58 | Viewed by 16448

Abstract

Traditional friction braking torque and motor braking torque can be used in braking for electric vehicles (EVs). A sliding mode controller (SMC) based on the exponential reaching law for the anti-lock braking system (ABS) is developed to maintain the optimal slip value. Parameter [...] Read more.

Traditional friction braking torque and motor braking torque can be used in braking for electric vehicles (EVs). A sliding mode controller (SMC) based on the exponential reaching law for the anti-lock braking system (ABS) is developed to maintain the optimal slip value. Parameter optimizing is applied to the reaching law by fuzzy logic control (FLC). A regenerative braking algorithm, in which the motor torque is taken full advantage of, is adopted to distribute the braking force between the motor braking and the hydraulic braking. Simulations were carried out with Matlab/Simulink. By comparing with a conventional Bang-bang ABS controller, braking stability and passenger comfort is improved with the proposed SMC controller, and the chatting phenomenon is reduced effectively with the parameter optimizing by FLC. With the increasing proportion of the motor braking torque, the tracking of the slip ratio is more rapid and accurate. Furthermore, the braking distance is shortened and the conversion energy is enhanced. Full article

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996 KiB

Open AccessArticle

An Improved Genetic Algorithm for Optimal Stationary Energy Storage System Locating and Sizing

by Bin Wang, Zhongping Yang, Fei Lin and Wei Zhao

Energies 2014, 7(10), 6434-6458; https://doi.org/10.3390/en7106434 - 9 Oct 2014

Cited by 56 | Viewed by 9225

Abstract

The application of a stationary ultra-capacitor energy storage system (ESS) in urban rail transit allows for the recuperation of vehicle braking energy for increasing energy savings as well as for a better vehicle voltage profile. This paper aims to obtain the best energy [...] Read more.

The application of a stationary ultra-capacitor energy storage system (ESS) in urban rail transit allows for the recuperation of vehicle braking energy for increasing energy savings as well as for a better vehicle voltage profile. This paper aims to obtain the best energy savings and voltage profile by optimizing the location and size of ultra-capacitors. This paper firstly raises the optimization objective functions from the perspectives of energy savings, regenerative braking cancellation and installation cost, respectively. Then, proper mathematical models of the DC (direct current) traction power supply system are established to simulate the electrical load-flow of the traction supply network, and the optimization objections are evaluated in the example of a Chinese metro line. Ultimately, a methodology for optimal ultra-capacitor energy storage system locating and sizing is put forward based on the improved genetic algorithm. The optimized result shows that certain preferable and compromised schemes of ESSs’ location and size can be obtained, acting as a compromise between satisfying better energy savings, voltage profile and lower installation cost. Full article

(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)

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1154 KiB

Open AccessArticle

A Real-Time Sliding Mode Control for a Wind Energy System Based on a Doubly Fed Induction Generator

by Oscar Barambones, Jose A. Cortajarena, Patxi Alkorta and Jose M. Gonzalez De Durana

Energies 2014, 7(10), 6412-6433; https://doi.org/10.3390/en7106412 - 9 Oct 2014

Cited by 28 | Viewed by 7737

Abstract

In this paper, a real time sliding mode control scheme for a variable speed wind turbine that incorporates a doubly feed induction generator is described. In this design, the so-called vector control theory is applied, in order to simplify the system electrical equations. [...] Read more.

In this paper, a real time sliding mode control scheme for a variable speed wind turbine that incorporates a doubly feed induction generator is described. In this design, the so-called vector control theory is applied, in order to simplify the system electrical equations. The proposed control scheme involves a low computational cost and therefore can be implemented in real-time applications using a low cost Digital Signal Processor (DSP). The stability analysis of the proposed sliding mode controller under disturbances and parameter uncertainties is provided using the Lyapunov stability theory. A new experimental platform has been designed and constructed in order to analyze the real-time performance of the proposed controller in a real system. Finally, the experimental validation carried out in the experimental platform shows; on the one hand that the proposed controller provides high-performance dynamic characteristics, and on the other hand that this scheme is robust with respect to the uncertainties that usually appear in the real systems. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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928 KiB

Open AccessArticle

Experimental Investigation and Discussion on the Mechanical Endurance Limit of Nafion Membrane Used in Proton Exchange Membrane Fuel Cell

by Yang Xiao and Chongdu Cho

Energies 2014, 7(10), 6401-6411; https://doi.org/10.3390/en7106401 - 9 Oct 2014

Cited by 24 | Viewed by 7552

Abstract

As a solution of high efficiency and clean energy, fuel cell technologies, especially proton exchange membrane fuel cell (PEMFC), have caught extensive attention. However, after decades of development, the performances of PEMFCs are far from achieving the target from the Department of Energy [...] Read more.

As a solution of high efficiency and clean energy, fuel cell technologies, especially proton exchange membrane fuel cell (PEMFC), have caught extensive attention. However, after decades of development, the performances of PEMFCs are far from achieving the target from the Department of Energy (DOE). Thus, further understanding of the degradation mechanism is needed to overcome this obstacle. Due to the importance of proton exchange membrane in a PEMFC, the degradation of the membrane, such as hygrothermal aging effect on its properties, are particularly necessary. In this work, a thick membrane (Nafion N117), which is always used as an ionic polymer for the PEMFCs, has been analyzed. Experimental investigation is performed for understanding the mechanical endurance of the bare membranes under different loading conditions. Tensile tests are conducted to compare the mechanical property evolution of two kinds of bare-membrane specimens including the dog-bone and the deeply double edge notched (DDEN) types. Both dog-bone and DDEN specimens were subjected to a series of degradation tests with different cycling times and wide humidity ranges. The tensile tests are repeated for both kinds of specimens to assess the strain-stress relations. Furthermore, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Scanning electron microscope (SEM) observation and water absorption measurement were conducted to speculate the cause of this variation. The initial cracks along with the increasing of bound water content were speculated as the primary cause. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International e-Conference on Energies — Whither Energy Conversion? Present Trends, Current Problems and Realistic Future Solutions)

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458 KiB

Open AccessArticle

Performance Evaluation of a Continuous Operation Adsorption Chiller Powered by Solar Energy Using Silica Gel and Water as the Working Pair

by Hassan Zohair Hassan

Energies 2014, 7(10), 6382-6400; https://doi.org/10.3390/en7106382 - 9 Oct 2014

Cited by 17 | Viewed by 5772

Abstract

In the present study, dynamic analysis and performance evaluation of a solar-powered continuous operation adsorption chiller are introduced. The adsorption chiller uses silica gel and water as the working pair. The developed mathematical model represents the heat and mass transfer within the reactor [...] Read more.

In the present study, dynamic analysis and performance evaluation of a solar-powered continuous operation adsorption chiller are introduced. The adsorption chiller uses silica gel and water as the working pair. The developed mathematical model represents the heat and mass transfer within the reactor coupled with the energy balance of the collector plate and the glass cover. Moreover, a non-equilibrium adsorption kinetic model is taken into account by using the linear driving force equation. The variation of solar radiation, wind speed, and atmospheric temperature along a complete cycle are considered for a more realistic simulation. Based on the case studied and the baseline parameters, the chiller is found to acquire a coefficient of performance of 0.402. The average thermal efficiency of the solar collector is estimated to be 62.96% and the average total efficiency approaches a value of 50.91%. Other performance parameters obtained are 363.8 W and 1.82 W/kg for the cooling capacity and the specific cooling power of the chiller, respectively. Furthermore, every 1 kg of silica gel inside the adsorption reactor produces a daily chilled water mass of 3 kg at a temperature of 10 ◦C. In addition, the cooling system harnesses 25.35% of the total available solar radiation and converts it to a cooling effect. Full article

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Development of Natural Gas Fired Combined Cycle Plant for Tri-Generation of Power, Cooling and Clean Water Using Waste Heat Recovery: Techno-Economic Analysis

by Gowtham Mohan, Sujata Dahal, Uday Kumar, Andrew Martin and Hamid Kayal

Energies 2014, 7(10), 6358-6381; https://doi.org/10.3390/en7106358 - 8 Oct 2014

Cited by 37 | Viewed by 13094

Abstract

Tri-generation is one of the most efficient ways for maximizing the utilization of available energy. Utilization of waste heat (flue gases) liberated by the Al-Hamra gas turbine power plant is analyzed in this research work for simultaneous production of: (a) electricity by combining [...] Read more.

Tri-generation is one of the most efficient ways for maximizing the utilization of available energy. Utilization of waste heat (flue gases) liberated by the Al-Hamra gas turbine power plant is analyzed in this research work for simultaneous production of: (a) electricity by combining steam rankine cycle using heat recovery steam generator (HRSG); (b) clean water by air gap membrane distillation (AGMD) plant; and (c) cooling by single stage vapor absorption chiller (VAC). The flue gases liberated from the gas turbine power cycle is the prime source of energy for the tri-generation system. The heat recovered from condenser of steam cycle and excess heat available at the flue gases are utilized to drive cooling and desalination cycles which are optimized based on the cooling energy demands of the villas. Economic and environmental benefits of the tri-generation system in terms of cost savings and reduction in carbon emissions were analyzed. Energy efficiency of about 82%–85% is achieved by the tri-generation system compared to 50%–52% for combined cycles. Normalized carbon dioxide emission per MW·h is reduced by 51.5% by implementation of waste heat recovery tri-generation system. The tri-generation system has a payback period of 1.38 years with cumulative net present value of $66 million over the project life time. Full article

(This article belongs to the Special Issue Waste Heat Recovery—Strategy and Practice)

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1440 KiB

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New Power Quality Analysis Method Based on Chaos Synchronization and Extension Neural Network

by Meng-Hui Wang and Her-Terng Yau

Energies 2014, 7(10), 6340-6357; https://doi.org/10.3390/en7106340 - 8 Oct 2014

Cited by 15 | Viewed by 7602

Abstract

A hybrid method comprising a chaos synchronization (CS)-based detection scheme and an Extension Neural Network (ENN) classification algorithm is proposed for power quality monitoring and analysis. The new method can detect minor changes in signals of the power systems. Likewise, prominent characteristics of [...] Read more.

A hybrid method comprising a chaos synchronization (CS)-based detection scheme and an Extension Neural Network (ENN) classification algorithm is proposed for power quality monitoring and analysis. The new method can detect minor changes in signals of the power systems. Likewise, prominent characteristics of system signal disturbance can be extracted by this technique. In the proposed approach, the CS-based detection method is used to extract three fundamental characteristics of the power system signal and an ENN-based clustering scheme is then applied to detect the state of the signal, i.e., normal, voltage sag, voltage swell, interruption or harmonics. The validity of the proposed method is demonstrated by means of simulations given the use of three different chaotic systems, namely Lorenz, New Lorenz and Sprott. The simulation results show that the proposed method achieves a high detection accuracy irrespective of the chaotic system used or the presence of noise. The proposed method not only achieves higher detection accuracy than existing methods, but also has low computational cost, an improved robustness toward noise, and improved scalability. As a result, it provides an ideal solution for the future development of hand-held power quality analyzers and real-time detection devices. Full article

(This article belongs to the Special Issue Microgrids)

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3001 KiB

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Powering-up Wireless Sensor Nodes Utilizing Rechargeable Batteries and an Electromagnetic Vibration Energy Harvesting System

by Salar Chamanian, Sajjad Baghaee, Hasan Ulusan, Özge Zorlu, Haluk Külah and Elif Uysal-Biyikoglu

Energies 2014, 7(10), 6323-6339; https://doi.org/10.3390/en7106323 - 2 Oct 2014

Cited by 27 | Viewed by 8923

Abstract

This paper presents a wireless sensor node (WSN) system where an electromagnetic (EM) energy harvester is utilized for charging its rechargeable batteries while the system is operational. The capability and the performance of an in-house low-frequency EM energy harvester for charging rechargeable NiMH [...] Read more.

This paper presents a wireless sensor node (WSN) system where an electromagnetic (EM) energy harvester is utilized for charging its rechargeable batteries while the system is operational. The capability and the performance of an in-house low-frequency EM energy harvester for charging rechargeable NiMH batteries were experimentally verified in comparison to a regular battery charger. Furthermore, the power consumption of MicaZ motes, used as the WSN, was evaluated in detail for different operation conditions. The battery voltage and current were experimentally monitored during the operation of the MicaZ sensor node equipped with the EM vibration energy harvester. A compact (24.5 cm³) in-house EM energy harvester provides approximately 65 µA charging current to the batteries when excited by 0.4 g acceleration at 7.4 Hz. It has been shown that the current demand of the MicaZ mote can be compensated for by the energy harvester for a specific low-power operation scenario, with more than a 10-fold increase in the battery lifetime. The presented results demonstrate the autonomous operation of the WSN, with the utilization of a vibration-based energy harvester. Full article

(This article belongs to the Special Issue Green IT and IT for Smart Energy Savings)

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659 KiB

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Fast Frequency Response Capability of Photovoltaic Power Plants: The Necessity of New Grid Requirements and Definitions

by Claudia Rahmann and Alfredo Castillo

Energies 2014, 7(10), 6306-6322; https://doi.org/10.3390/en7106306 - 30 Sep 2014

Cited by 133 | Viewed by 13038

Abstract

In recent years, only a small number of publications have been presented addressing power system stability with the increased use of large-scale photovoltaic (PV) generation around the world. The focus of these publications was on classical stability problems, such as transient and small [...] Read more.

In recent years, only a small number of publications have been presented addressing power system stability with the increased use of large-scale photovoltaic (PV) generation around the world. The focus of these publications was on classical stability problems, such as transient and small signal stability, without considering frequency stability. Nevertheless, with increased PV generation, its effects on system frequency response during contingencies can no longer be ignored, especially in the case of weakly interconnected networks or isolated power systems. This paper addresses the impacts of large scale PV generation on the frequency stability of power systems. The positive effects of deloaded PV power plants (PV-PPs) able to support system frequency recovery during the initial seconds after major contingencies are also examined. Because this type of frequency support is not covered by current definitions, a new terminology is proposed that includes the frequency response of inertia-less generation units immediately after major power imbalances. We refer to this type of frequency support as fast frequency response (FFR). Finally, a discussion is also presented regarding the applicability and pertinence of frequency-related grid requirements for PV-PPs in the case of real power systems. The investigation is based on the isolated power system of northern Chile. The obtained results indicate that in the case of major power imbalances, no significant effects arise on the system frequency response until PV penetration levels exceed approximately 20%. From a system security perspective, the problems arise for PV penetration levels of approximately 50%, in which case, the frequency response capability in PV-PPs would be justified during certain hours of the year. Full article

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1786 KiB

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Non-Destructive Analysis of Degradation Mechanisms in Cycle-Aged Graphite/LiCoO₂ Batteries

by Liqiang Zhang, Lixin Wang, Chao Lyu, Junfu Li and Jun Zheng

Energies 2014, 7(10), 6282-6305; https://doi.org/10.3390/en7106282 - 29 Sep 2014

Cited by 35 | Viewed by 8335

Abstract

Non-destructive analysis of degradation mechanisms can be very beneficial for the prognostics and health management (PHM) study of lithium-ion batteries. In this paper, a type of graphite/LiCoO₂ battery was cycle aged at high ambient temperature, then 25 parameters of the multi-physics model [...] Read more.

Non-destructive analysis of degradation mechanisms can be very beneficial for the prognostics and health management (PHM) study of lithium-ion batteries. In this paper, a type of graphite/LiCoO₂ battery was cycle aged at high ambient temperature, then 25 parameters of the multi-physics model were identified. Nine key parameters degraded with the cycle life, and they were treated as indicators of battery degradation. Accordingly, the degradation mechanism was discussed by using the multi-physics model and key parameters, and the reasons for capacity fade and the internal resistance increase were analyzed in detail. All evidence indicates that the formation reaction of the solid electrolyte interface (SEI) film is the main cause of battery degradation at high ambient temperature. Full article

(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)

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867 KiB

Open AccessArticle

LCA Study of Oleaginous Bioenergy Chains in a Mediterranean Environment

by Daniele Cocco, Paola A. Deligios, Luigi Ledda, Leonardo Sulas, Adriana Virdis and Gianluca Carboni

Energies 2014, 7(10), 6258-6281; https://doi.org/10.3390/en7106258 - 29 Sep 2014

Cited by 30 | Viewed by 6629

Abstract

This paper reports outcomes of life cycle assessments (LCAs) of three different oleaginous bioenergy chains (oilseed rape, Ethiopian mustard and cardoon) under Southern Europe conditions. Accurate data on field practices previously collected during a three-year study at two sites were used. The vegetable [...] Read more.

This paper reports outcomes of life cycle assessments (LCAs) of three different oleaginous bioenergy chains (oilseed rape, Ethiopian mustard and cardoon) under Southern Europe conditions. Accurate data on field practices previously collected during a three-year study at two sites were used. The vegetable oil produced by oleaginous seeds was used for power generation in medium-speed diesel engines while the crop residues were used in steam power plants. For each bioenergy chain, the environmental impact related to cultivation, transportation of agricultural products and industrial conversion for power generation was evaluated by calculating cumulative energy demand, acidification potential and global warming potential. For all three bioenergy chains, the results of the LCA study show a considerable saving of primary energy (from 70 to 86 GJ·ha⁻¹) and greenhouse gas emissions (from 4.1 to 5.2 t CO₂·ha⁻¹) in comparison to power generation from fossil fuels, although the acidification potential of these bioenergy chains may be twice that of conventional power generation. In addition, the study highlights that land use changes due to the cultivation of the abovementioned crops reduce soil organic content and therefore worsen and increase greenhouse gas emissions for all three bioenergy chains. The study also demonstrates that the exploitation of crop residues for energy production greatly contributes to managing environmental impact of the three bioenergy chains. Full article

(This article belongs to the Special Issue Renewable Energy for Agriculture)

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682 KiB

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Multi-Objective Planning of Multi-Type Distributed Generation Considering Timing Characteristics and Environmental Benefits

by Yajing Gao, Jianpeng Liu, Jin Yang, Haifeng Liang and Jiancheng Zhang

Energies 2014, 7(10), 6242-6257; https://doi.org/10.3390/en7106242 - 29 Sep 2014

Cited by 31 | Viewed by 6485

Abstract

This paper presents a novel approach to multi-type distributed generation (DG) planning based on the analysis of investment and income brought by grid-connected DG. Firstly, the timing characteristics of loads and DG outputs, as well as the environmental benefits of DG are analyzed. [...] Read more.

This paper presents a novel approach to multi-type distributed generation (DG) planning based on the analysis of investment and income brought by grid-connected DG. Firstly, the timing characteristics of loads and DG outputs, as well as the environmental benefits of DG are analyzed. Then, on the basis of the classification of daily load sequences, the typical daily load sequence and the typical daily output sequence of DG per unit capacity can be computed. The proposed planning model takes the location, capacity and types of DG into account as optimization variables. An improved adaptive genetic algorithm is proposed to solve the model. Case studies have been carried out on the IEEE 14-node distribution system to verify the feasibility and effectiveness of the proposed method and model. Full article

(This article belongs to the Collection Smart Grid)

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Energies, Volume 7, Issue 10 (October 2014) – 31 articles , Pages 6225-6824

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