Energies

4446 KiB

Open AccessArticle

A Study on the Power Generation Capacity of Piezoelectric Energy Harvesters with Different Fixation Modes and Adjustment Methods

by Zhixiang Li, Gongbo Zhou, Zhencai Zhu and Wei Li

Energies 2016, 9(2), 98; https://doi.org/10.3390/en9020098 - 19 Feb 2016

Cited by 20 | Viewed by 6061

Abstract

The power generation capacity of piezoelectric energy harvesters (PEHs) is not only related to the properties of the piezoelectric material, the vibration magnitude and the subsequent conditioning circuit, but also to the fixation modes and adjustment methods. In this paper, a commercial piezoelectric [...] Read more.

The power generation capacity of piezoelectric energy harvesters (PEHs) is not only related to the properties of the piezoelectric material, the vibration magnitude and the subsequent conditioning circuit, but also to the fixation modes and adjustment methods. In this paper, a commercial piezoelectric ceramic plate (PCP) in simply supported beam fixation mode and cantilever beam fixation mode were analyzed through finite element simulations and experiments, and furthermore, two ways of adjusting the natural frequency of PCP are studied and compared. As a result, some guidelines are proposed for the application of PCPs according to the simulation and experimental results which showed that: (1) the simply supported beam fixation mode is suitable for environments in which the exciting frequency exceeds 50 Hz, while the cantilever beam fixation mode fits the circumstance where the exciting frequency is below 50 Hz; (2) the maximum generation power a PCP produces in simply supported beam fixation mode is larger than that in cantilever beam fixation mode; (3) adjusting the weight of the mass block affixed on the PCP can change the natural frequency of PCP more efficiently than length-width ratio does. Full article

(This article belongs to the Special Issue Waste Energy Harvesting)

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4630 KiB

Open AccessArticle

Exploitation Contradictions Concerning Multi-Energy Resources among Coal, Gas, Oil, and Uranium: A Case Study in the Ordos Basin (Western North China Craton and Southern Side of Yinshan Mountains)

by Xiaowei Feng, Nong Zhang, Xiaoting Chen, Lianyuan Gong, Chuangxin Lv and Yu Guo

Energies 2016, 9(2), 119; https://doi.org/10.3390/en9020119 - 19 Feb 2016

Cited by 19 | Viewed by 8741

Abstract

The particular “rich coal, meager oil, and deficient gas” energy structure of China determines its high degree of dependence on coal resources. After over 100 years of high-intensity mining activities in Northeast China, East Region, and the Southern Region, coal mining in these [...] Read more.

The particular “rich coal, meager oil, and deficient gas” energy structure of China determines its high degree of dependence on coal resources. After over 100 years of high-intensity mining activities in Northeast China, East Region, and the Southern Region, coal mining in these areas is facing a series of serious problems, which force China’s energy exploitation map to be rewritten. New energy bases will move to the western and northern regions in the next few years. However, overlapping phenomena of multiple resources are frequently encountered. Previous exploitation mainly focused on coal mining, which destroys many mutualistic and accompanying resources, such as uranium, gas, and oil. Aiming at solving this unscientific development mode, this research presents a case study in the Ordos Basin, where uranium, coal, and gas/oil show a three-dimensional overlapping phenomenon along the vertical downward direction. The upper uranium and lower coal situation in this basin is remarkable; specifically, coal mining disturbs the overlaying aquifer, thus requiring the uranium to be leached first. The technical approach must be sufficiently reliable to avoid the leakage of radioactive elements in subsequent coal mining procedures. Hence, the unbalanced injection and extraction of uranium mining is used to completely eradicate the discharged emissions to the environment. The gas and oil are typically not extracted because of their deep occurrence strata and their overlapping phenomenon with coal seams. Use of the integrated coal and gas production method is recommended, and relevant fracturing methods to increase the gas migrating degree in the strata are also introduced. The results and recommendations in this study are applicable in some other areas with similarities. Full article

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35703 KiB

Open AccessArticle

Structural Reliability of Plain Bearings for Wave Energy Converter Applications

by Simon Ambühl, Morten Kramer and John Dalsgaard Sørensen

Energies 2016, 9(2), 118; https://doi.org/10.3390/en9020118 - 19 Feb 2016

Cited by 4 | Viewed by 6389

Abstract

The levelized cost of energy (LCOE) from wave energy converters (WECs) needs to be decreased in order to be able to become competitive with other renewable electricity sources. Probabilistic reliability methods can be used to optimize the structure of WECs. Optimization is often [...] Read more.

The levelized cost of energy (LCOE) from wave energy converters (WECs) needs to be decreased in order to be able to become competitive with other renewable electricity sources. Probabilistic reliability methods can be used to optimize the structure of WECs. Optimization is often performed for critical structural components, like welded details, bolts or bearings. This paper considers reliability studies with a focus on plain bearings available from stock for the Wavestar device, which exists at the prototype level. The Wavestar device is a point absorber WEC. The plan is to mount a new power take-off (PTO) system consisting of a discrete displacement cylinder (DDC), which will allow different hydraulic cycles to operate at constant pressure levels. This setup increases the conversion efficiency, as well as decouples the electricity production from the pressure variations within the hydraulic cycle when waves are passing. The new PTO system leads to different load characteristics at the floater itself compared to the actual setup where the turbine/generator is directly coupled to the fluctuating hydraulic pressure within the PTO system. This paper calculates the structural reliability of the different available plain bearings planned to be mounted at the new PTO system based on a probabilistic approach, and the paper gives suggestions for fulfilling the minimal target reliability levels. The considered failure mode in this paper is the brittle fatigue failure of plain bearings. The performed sensitivity analysis shows that parameters defining the initial crack size have a big impact on the resulting reliability of the plain bearing. Full article

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2427 KiB

Open AccessArticle

Performance Analysis of a Grid-connected High Concentrating Photovoltaic System under Practical Operation Conditions

by Zhe Mi, Jikun Chen, Nuofu Chen, Yiming Bai, Wenwang Wu, Rui Fu and Hu Liu

Energies 2016, 9(2), 117; https://doi.org/10.3390/en9020117 - 19 Feb 2016

Cited by 10 | Viewed by 5079

Abstract

High concentrating photovoltaic (HCPV) is a promising technique for the practical commercial utilization of solar energy. However, the performance of a HCPV system is significantly influenced by environmental parameters such as solar direct normal irradiance (DNI) level and environmental temperature. This paper analyzes [...] Read more.

High concentrating photovoltaic (HCPV) is a promising technique for the practical commercial utilization of solar energy. However, the performance of a HCPV system is significantly influenced by environmental parameters such as solar direct normal irradiance (DNI) level and environmental temperature. This paper analyzes the performance of a 9 kW_p grid-connected HCPV system in Kunming (Yunnan, China), during practical field operations over an entire year, and discusses how the environmental parameters influence the performance from both the energy conversion and power inversion perspective. Large variations in the performance of the HCPV system have been observed for different months, due to the respective changes in the environmental parameters. The DNI level has been found to be a dominant parameter that mainly determines the amount of energy production as well as the performance ratio of the HCPV system. The environmental temperature and wind velocity have less influence on the system performance ratio than expected. Based on the performance of the present HCPV system, a quantified correlation between the output power and the direct normal irradiance has been derived, which provides guidelines for both the cogent application and the modeling of HCPV techniques for grid-connected power generation. Full article

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1080 KiB

Open AccessArticle

The Value of Lost Load for Sectoral Load Shedding Measures: The German Case with 51 Sectors

by Aaron Praktiknjo

Energies 2016, 9(2), 116; https://doi.org/10.3390/en9020116 - 19 Feb 2016

Cited by 22 | Viewed by 8745

Abstract

The transition of the German electricity system towards a renewable, nuclear free and increasingly fluctuating power generation raises concerns about supply security. A possible contribution to solve this issue might lie in demand response or load shedding measures. The goal of our work [...] Read more.

The transition of the German electricity system towards a renewable, nuclear free and increasingly fluctuating power generation raises concerns about supply security. A possible contribution to solve this issue might lie in demand response or load shedding measures. The goal of our work is to monetarily quantify the consequences of power interruptions. The focus lies on power interruption costs in 51 economic sectors. Two input-output models are proposed to estimate the Value of Lost Load for each sector. The first does not take inter-linkages of the sectors and possible cascading effects on interruption costs into account. The second model is a new and innovative approach which is based on the Ghosh Input-Output model and which accounts for these effects. We assume that the first model is adequate to assess shorter power interruptions, whereas the second model might be more appropriate when estimating costs of longer interruptions. Full article

(This article belongs to the Special Issue Applied Energy System Modeling 2015)

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4098 KiB

Open AccessArticle

Synthesis and Characterization of Sulfonated Poly(Phenylene) Containing a Non-Planar Structure and Dibenzoyl Groups

by Hohyoun Jang, Sabuj Chandra Sutradhar, Jiho Yoo, Jaeseong Ha, Jaeseung Pyo, Chaekyun Lee, Taewook Ryu and Whangi Kim

Energies 2016, 9(2), 115; https://doi.org/10.3390/en9020115 - 18 Feb 2016

Cited by 16 | Viewed by 5806

Abstract

Polymers for application as sulfonated polyphenylene membranes were prepared by nickel-catalyzed carbon-carbon coupling reaction of bis(4-chlorophenyl)-1,2-diphenylethylene (BCD) and 1,4-dichloro-2,5-dibenzoylbenzene (DCBP). Conjugated cis/trans isomer (BCD) had a non-planar conformation containing four peripheral aromatic rings that facilitate the formation of π–π interactions. 1,4-Dichloro-2,5-dibenzoylbenzene was synthesized [...] Read more.

Polymers for application as sulfonated polyphenylene membranes were prepared by nickel-catalyzed carbon-carbon coupling reaction of bis(4-chlorophenyl)-1,2-diphenylethylene (BCD) and 1,4-dichloro-2,5-dibenzoylbenzene (DCBP). Conjugated cis/trans isomer (BCD) had a non-planar conformation containing four peripheral aromatic rings that facilitate the formation of π–π interactions. 1,4-Dichloro-2,5-dibenzoylbenzene was synthesized from the oxidation reaction of 2,5-dichloro-p-xylene, followed by Friedel-Crafts reaction with benzene. DCBP monomer had good reactivity in polymerization affecting the activity of benzophenone as an electron-withdrawing group. The polyphenylene was sulfonated using concentrated sulfuric acid. These polymers without any ether linkages on the polymer backbone were protected from nucleophilic attack by hydrogen peroxide, hydroxide anion, and radicals generated by polymer electrolyte membrane fuel cell (PEMFC) operation systems. The mole fraction of the sulfonic acid groups was controlled by varying the mole ratio of bis(4-chlorophenyl)-1,2-diphenylethylene in the copolymer. In comparison with Nafion 211^® membrane, these SBCDCBP membranes showed ion exchange capacity (IEC) ranging from 1.04 to 2.07 meq./g, water uptake from 36.5% to 69.4%, proton conductivity from 58.7 to 101.9 mS/cm, and high thermal stability. Full article

(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells 2016)

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7197 KiB

Open AccessArticle

A New Fluctuation Index: Characteristics and Application to Hydro-Wind Systems

by Xianxun Wang, Yadong Mei, Hao Cai and Xiangyu Cong

Energies 2016, 9(2), 114; https://doi.org/10.3390/en9020114 - 18 Feb 2016

Cited by 28 | Viewed by 6644

Abstract

Hydro-wind system output fluctuations are the primary factors used to assess the effects of hydropower on power companies compensating for wind power intermittency. Considering that most fluctuation indices can only characterize one aspect of fluctuations, namely, the quantitative or contour variations, we present [...] Read more.

Hydro-wind system output fluctuations are the primary factors used to assess the effects of hydropower on power companies compensating for wind power intermittency. Considering that most fluctuation indices can only characterize one aspect of fluctuations, namely, the quantitative or contour variations, we present a new index that uses the standard deviation (SD) and rotation angle to detect the quantitative variations and contour changes, respectively. Herein, the new index is compared with commonly used indices, specifically, the first-order difference, SD, and Richards-Baker flashiness indices. The results of tests performed using various processes and disposals show that: (1) when dealing with the process by moving average, repeating or overlay disposal, the new index performs comparably to the other indices, while when dealing with the process by zooming disposal, it more fully describes the fluctuation characteristics by taking both quantitative and contour variations into consideration; (2) when the new index is used to characterize the hydro-wind output fluctuations with different resources and capacities, the outcomes coincide with the mechanisms of hydro-wind systems. This study presents a new way to characterize the fluctuation of hydro-wind output. Full article

(This article belongs to the Special Issue Hydropower)

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2426 KiB

Open AccessArticle

Ice Storage Air-Conditioning System Simulation with Dynamic Electricity Pricing: A Demand Response Study

by Chi-Chun Lo, Shang-Ho Tsai and Bor-Shyh Lin

Energies 2016, 9(2), 113; https://doi.org/10.3390/en9020113 - 18 Feb 2016

Cited by 37 | Viewed by 7652

Abstract

This paper presents an optimal dispatch model of an ice storage air-conditioning system for participants to quickly and accurately perform energy saving and demand response, and to avoid the over contact with electricity price peak. The schedule planning for an ice storage air-conditioning [...] Read more.

This paper presents an optimal dispatch model of an ice storage air-conditioning system for participants to quickly and accurately perform energy saving and demand response, and to avoid the over contact with electricity price peak. The schedule planning for an ice storage air-conditioning system of demand response is mainly to transfer energy consumption from the peak load to the partial-peak or off-peak load. Least Squares Regression (LSR) is used to obtain the polynomial function for the cooling capacity and the cost of power consumption with a real ice storage air-conditioning system. Based on the dynamic electricity pricing, the requirements of cooling loads, and all technical constraints, the dispatch model of the ice-storage air-conditioning system is formulated to minimize the operation cost. The Improved Ripple Bee Swarm Optimization (IRBSO) algorithm is proposed to solve the dispatch model of the ice storage air-conditioning system in a daily schedule on summer. Simulation results indicate that reasonable solutions provide a practical and flexible framework allowing the demand response of ice storage air-conditioning systems to demonstrate the optimization of its energy savings and operational efficiency and offering greater energy efficiency. Full article

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1951 KiB

Open AccessArticle

Feasibility Assessment of Using Power Plant Waste Heat in Large Scale Horticulture Facility Energy Supply Systems

by Min Gyung Yu and Yujin Nam

Energies 2016, 9(2), 112; https://doi.org/10.3390/en9020112 - 18 Feb 2016

Cited by 13 | Viewed by 6350

Abstract

Recently, the Korean government has been carrying out projects to construct several large scale horticulture facilities. However, it is difficult for an energy supply to operate stably and economically with only a conventional fossil fuel boiler system. For this reason, several unused energy [...] Read more.

Recently, the Korean government has been carrying out projects to construct several large scale horticulture facilities. However, it is difficult for an energy supply to operate stably and economically with only a conventional fossil fuel boiler system. For this reason, several unused energy sources have become attractive and it was found that power plant waste heat has the greatest potential for application in this scenario. In this study, we performed a feasibility assessment of power plant waste heat as an energy source for horticulture facilities. As a result, it was confirmed that there was a sufficient amount of energy potential for the use of waste heat to supply energy to the assumed area. In Dangjin, an horticultural area of 500 ha could be constructed by utilizing 20% of the energy reserves. In Hadong, a horticulture facility can be set up to be 260 ha with 7.4% of the energy reserves. In Youngdong, an assumed area of 65 ha could be built utilizing about 19% of the energy reserves. Furthermore, the payback period was calculated in order to evaluate the economic feasibility compared with a conventional system. The initial investment costs can be recovered by the approximately 83% reduction in the annual operating costs. Full article

(This article belongs to the Special Issue Energy Conservation in Infrastructures)

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3191 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Review of Modeling Bioelectrochemical Systems: Engineering and Statistical Aspects

by Shuai Luo, Hongyue Sun, Qingyun Ping, Ran Jin and Zhen He

Energies 2016, 9(2), 111; https://doi.org/10.3390/en9020111 - 18 Feb 2016

Cited by 64 | Viewed by 11614

Abstract

Bioelectrochemical systems (BES) are promising technologies to convert organic compounds in wastewater to electrical energy through a series of complex physical-chemical, biological and electrochemical processes. Representative BES such as microbial fuel cells (MFCs) have been studied and advanced for energy recovery. Substantial experimental [...] Read more.

Bioelectrochemical systems (BES) are promising technologies to convert organic compounds in wastewater to electrical energy through a series of complex physical-chemical, biological and electrochemical processes. Representative BES such as microbial fuel cells (MFCs) have been studied and advanced for energy recovery. Substantial experimental and modeling efforts have been made for investigating the processes involved in electricity generation toward the improvement of the BES performance for practical applications. However, there are many parameters that will potentially affect these processes, thereby making the optimization of system performance hard to be achieved. Mathematical models, including engineering models and statistical models, are powerful tools to help understand the interactions among the parameters in BES and perform optimization of BES configuration/operation. This review paper aims to introduce and discuss the recent developments of BES modeling from engineering and statistical aspects, including analysis on the model structure, description of application cases and sensitivity analysis of various parameters. It is expected to serves as a compass for integrating the engineering and statistical modeling strategies to improve model accuracy for BES development. Full article

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2873 KiB

Open AccessArticle

Dynamic Analysis of Wind Turbine Gearbox Components

by Mingming Zhao and Jinchen Ji

Energies 2016, 9(2), 110; https://doi.org/10.3390/en9020110 - 17 Feb 2016

Cited by 33 | Viewed by 8792

Abstract

This paper studies the dynamic response of a wind turbine gearbox under different excitation conditions. The proposed 4 degree-of-freedom (DOF) dynamic model takes into account the key factors such as the time-varying mesh stiffness, bearing stiffness, damping, static transmission error and gear backlash. [...] Read more.

This paper studies the dynamic response of a wind turbine gearbox under different excitation conditions. The proposed 4 degree-of-freedom (DOF) dynamic model takes into account the key factors such as the time-varying mesh stiffness, bearing stiffness, damping, static transmission error and gear backlash. Both the external excitation due to wind and the internal excitation due to the static transmission error are included to represent the gearbox excitation conditions. With the help of the time history and frequency spectrum, the dynamic responses of wind turbine gearbox components are investigated by using the numerical integration method. This paper explains under which conditions the fretting corrosion, as one of the wind turbine gearbox failure modes, may occur. Furthermore, it is observed that the external excitation fluctuation has large influence on the dynamic responses of both the gears and bearings. Full article

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778 KiB

Open AccessArticle

Wind Speed Prediction Using a Univariate ARIMA Model and a Multivariate NARX Model

by Erasmo Cadenas, Wilfrido Rivera, Rafael Campos-Amezcua and Christopher Heard

Energies 2016, 9(2), 109; https://doi.org/10.3390/en9020109 - 17 Feb 2016

Cited by 243 | Viewed by 13396

Abstract

Two on step ahead wind speed forecasting models were compared. A univariate model was developed using a linear autoregressive integrated moving average (ARIMA). This method’s performance is well studied for a large number of prediction problems. The other is a multivariate model developed [...] Read more.

Two on step ahead wind speed forecasting models were compared. A univariate model was developed using a linear autoregressive integrated moving average (ARIMA). This method’s performance is well studied for a large number of prediction problems. The other is a multivariate model developed using a nonlinear autoregressive exogenous artificial neural network (NARX). This uses the variables: barometric pressure, air temperature, wind direction and solar radiation or relative humidity, as well as delayed wind speed. Both models were developed from two databases from two sites: an hourly average measurements database from La Mata, Oaxaca, Mexico, and a ten minute average measurements database from Metepec, Hidalgo, Mexico. The main objective was to compare the impact of the various meteorological variables on the performance of the multivariate model of wind speed prediction with respect to the high performance univariate linear model. The NARX model gave better results with improvements on the ARIMA model of between 5.5% and 10. 6% for the hourly database and of between 2.3% and 12.8% for the ten minute database for mean absolute error and mean squared error, respectively. Full article

(This article belongs to the Special Issue Forecasting Methods and Measurements of Forecasting Errors for Renewable Energy Sources)

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6080 KiB

Open AccessArticle

Performance and Feasibility Study of a Standing Column Well (SCW) System Using a Deep Geothermal Well

by Jeong-Heum Cho, Yujin Nam and Hyoung-Chan Kim

Energies 2016, 9(2), 108; https://doi.org/10.3390/en9020108 - 17 Feb 2016

Cited by 12 | Viewed by 7117

Abstract

Deep geothermal heat pump systems have considerable energy saving potential for heating and cooling systems that use stable ground temperature and groundwater as their heat sources. However, deep geothermal systems have several limitations for real applications such as a very high installation cost [...] Read more.

Deep geothermal heat pump systems have considerable energy saving potential for heating and cooling systems that use stable ground temperature and groundwater as their heat sources. However, deep geothermal systems have several limitations for real applications such as a very high installation cost and a lack of recognition as heating and cooling systems. In this study, we performed a feasibility assessment of a Standing Column Well (SCW) system using a deep geothermal well, based on a real-scale experiment in Korea. The results showed that the temperature of the heat source increased up to 42.04 °C in the borehole after the heating experiment, which is about 30 °C higher than that of normal shallow geothermal wells. Furthermore, the coefficient of performance (COP) of the heat pump during 3 months of operation was 5.8, but the system COP was only 3.6 due to the relatively high electric consumption of the pump. Moreover, the payback period of the system using a deep well for controlled horticulture in a glass greenhouse was calculated as 6 years compared with using a diesel boiler system. Full article

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6609 KiB

Open AccessArticle

Coordinated Voltage Control in Distribution Network with the Presence of DGs and Variable Loads Using Pareto and Fuzzy Logic

by José Raúl Castro, Maarouf Saad, Serge Lefebvre, Dalal Asber and Laurent Lenoir

Energies 2016, 9(2), 107; https://doi.org/10.3390/en9020107 - 17 Feb 2016

Cited by 11 | Viewed by 5505

Abstract

This paper presents an efficient algorithm to solve the multi-objective (MO) voltage control problem in distribution networks. The proposed algorithm minimizes the following three objectives: voltage variation on pilot buses, reactive power production ratio deviation, and generator voltage deviation. This work leverages two [...] Read more.

This paper presents an efficient algorithm to solve the multi-objective (MO) voltage control problem in distribution networks. The proposed algorithm minimizes the following three objectives: voltage variation on pilot buses, reactive power production ratio deviation, and generator voltage deviation. This work leverages two optimization techniques: fuzzy logic to find the optimum value of the reactive power of the distributed generation (DG) and Pareto optimization to find the optimal value of the pilot bus voltage so that this produces lower losses under the constraints that the voltage remains within established limits. Variable loads and DGs are taken into account in this paper. The algorithm is tested on an IEEE 13-node test feeder and the results show the effectiveness of the proposed model. Full article

(This article belongs to the Special Issue Distributed Renewable Generation)

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921 KiB

Open AccessEditor’s ChoiceArticle

Recovery of Bio-Oil from Industrial Food Waste by Liquefied Dimethyl Ether for Biodiesel Production

by Kiyoshi Sakuragi, Peng Li, Maromu Otaka and Hisao Makino

Energies 2016, 9(2), 106; https://doi.org/10.3390/en9020106 - 17 Feb 2016

Cited by 34 | Viewed by 9504

Abstract

The development of new energy sources has become particularly important from the perspective of energy security and environmental protection. Therefore, the utilization of waste resources such as industrial food wastes (IFWs) in energy production is expected. The central research institute of electric power [...] Read more.

The development of new energy sources has become particularly important from the perspective of energy security and environmental protection. Therefore, the utilization of waste resources such as industrial food wastes (IFWs) in energy production is expected. The central research institute of electric power industry (CRIEPI, Tokyo, Japan) has recently developed an energy-saving oil-extraction technique involving the use of liquefied dimethyl ether (DME), which is an environmentally friendly solvent. In this study, three common IFWs (spent coffee grounds, soybean, and rapeseed cakes) were evaluated with respect to oil yield for biodiesel fuel (BDF) production by the DME extraction method. The coffee grounds were found to contain 16.8% bio-oil, whereas the soybean and rapeseed cakes contained only approximately 0.97% and 2.6% bio-oil, respectively. The recovered oils were qualitatively analysed by gas chromatography-mass spectrometry. The properties of fatty acid methyl esters derived from coffee oil, such as kinematic viscosity, pour point, and higher heating value (HHV), were also determined. Coffee grounds had the highest oil content and could be used as biofuel. In addition, the robust oil extraction capability of DME indicates that it may be a favourable alternative to conventional oil extraction solvents. Full article

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973 KiB

Open AccessArticle

Evaluation of Strategies to Reducing Traction Energy Consumption of Metro Systems Using an Optimal Train Control Simulation Model

by Shuai Su, Tao Tang and Yihui Wang

Energies 2016, 9(2), 105; https://doi.org/10.3390/en9020105 - 12 Feb 2016

Cited by 83 | Viewed by 12205

Abstract

Increasing attention is being paid to the energy efficiency in metro systems to reduce the operational cost and to advocate the sustainability of railway systems. Classical research has studied the energy-efficient operational strategy and the energy-efficient system design separately to reduce the traction [...] Read more.

Increasing attention is being paid to the energy efficiency in metro systems to reduce the operational cost and to advocate the sustainability of railway systems. Classical research has studied the energy-efficient operational strategy and the energy-efficient system design separately to reduce the traction energy consumption. This paper aims to combine the operational strategies and the system design by analyzing how the infrastructure and vehicle parameters of metro systems influence the operational traction energy consumption. Firstly, a solution approach to the optimal train control model is introduced, which is used to design the Optimal Train Control Simulator(OTCS). Then, based on the OTCS, the performance of some important energy-efficient system design strategies is investigated to reduce the trains’ traction energy consumption, including reduction of the train mass, improvement of the kinematic resistance, the design of the energy-saving gradient, increasing the maximum traction and braking forces, introducing regenerative braking and timetable optimization. As for these energy-efficient strategies, the performances are finally evaluated using the OTCS with the practical operational data of the Beijing Yizhuang metro line. The proposed approach gives an example to quantitatively analyze the energy reduction of different strategies in the system design procedure, which may help the decision makers to have an overview of the energy-efficient performances and then to make decisions by balancing the costs and the benefits. Full article

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730 KiB

Open AccessArticle

Influence of Electrode Density on the Performance of Li-Ion Batteries: Experimental and Simulation Results

by Jelle Smekens, Rahul Gopalakrishnan, Nils Van den Steen, Noshin Omar, Omar Hegazy, Annick Hubin and Joeri Van Mierlo

Energies 2016, 9(2), 104; https://doi.org/10.3390/en9020104 - 12 Feb 2016

Cited by 49 | Viewed by 16066

Abstract

Lithium-ion battery (LIB) technology further enabled the information revolution by powering smartphones and tablets, allowing these devices an unprecedented performance against reasonable cost. Currently, this battery technology is on the verge of carrying the revolution in road transport and energy storage of renewable [...] Read more.

Lithium-ion battery (LIB) technology further enabled the information revolution by powering smartphones and tablets, allowing these devices an unprecedented performance against reasonable cost. Currently, this battery technology is on the verge of carrying the revolution in road transport and energy storage of renewable energy. However, to fully succeed in the latter, a number of hurdles still need to be taken. Battery performance and lifetime constitute a bottleneck for electric vehicles as well as stationary electric energy storage systems to penetrate the market. Electrochemical battery models are one of the engineering tools which could be used to enhance their performance. These models can help us optimize the cell design and the battery management system. In this study, we evaluate the ability of the Porous Electrode Theory (PET) to predict the effect of changing positive electrode density in the overall performance of Li-ion battery cells. It can be concluded that Porous Electrode Theory (PET) is capable of predicting the difference in cell performance due to a changing positive electrode density. Full article

(This article belongs to the Special Issue Advances in Plug-in Hybrid Vehicles and Hybrid Vehicles)

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1549 KiB

Open AccessArticle

Maximum Power Point Tracking and Harmonic Reducing Control Method for Generator-Based Exercise Equipment

by Meng-Hui Wang, Mei-Ling Huang and Wei-Jhe Jiang

Energies 2016, 9(2), 103; https://doi.org/10.3390/en9020103 - 11 Feb 2016

Cited by 5 | Viewed by 4761

Abstract

This study uses a sliding mode control (SMC) in a generator-based exercise equipment (GBEE) with nonlinear P-V characteristic curves. A P-V characteristics curve can be influenced by varying the pedaling speed of the generator. The traditional maximum power point [...] Read more.

This study uses a sliding mode control (SMC) in a generator-based exercise equipment (GBEE) with nonlinear P-V characteristic curves. A P-V characteristics curve can be influenced by varying the pedaling speed of the generator. The traditional maximum power point tracking (MPPT) control method is used with perturb and observe algorithms (P&O), extremum seeking control (ESC), etc. However, these control methods are not robust enough for control. SMC is created by two pattern methods for robustness control, approaching and sliding conditions. However, SMC allows infinite high-frequency switching of the sign function. If the sign function is used to switch the converter, it will cause the converter and switch life to be cut short, and also to form high frequency noise. Therefore, this study proposes an extension theory for an intelligent control method that will effectively improve conversion efficiency and responsiveness. This study compares generator input current waveforms for fast Fourier transform (FFT) for three different control methods. Finally, using simulation validates the stability and FFT analysis with power simulation (PSIM) software. The results of upgrading overall efficiency are about a 5% increase in efficiency and a faster response speed of about 0.5 s. The amount of generator input current harmonic is greatly reduced. Full article

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4677 KiB

Open AccessArticle

Analysis of the Potential for Use of Floating Photovoltaic Systems on Mine Pit Lakes: Case Study at the Ssangyong Open-Pit Limestone Mine in Korea

by Jinyoung Song and Yosoon Choi

Energies 2016, 9(2), 102; https://doi.org/10.3390/en9020102 - 10 Feb 2016

Cited by 104 | Viewed by 10901

Abstract

Recently, the mining industry has introduced renewable energy technologies to resolve power supply problems at mines operating in polar regions or other remote areas, and to foster substitute industries, able to benefit from abandoned sites of exhausted mines. However, little attention has been [...] Read more.

Recently, the mining industry has introduced renewable energy technologies to resolve power supply problems at mines operating in polar regions or other remote areas, and to foster substitute industries, able to benefit from abandoned sites of exhausted mines. However, little attention has been paid to the potential placement of floating photovoltaic (PV) systems operated on mine pit lakes because it was assumed that the topographic characteristics of open-pit mines are unsuitable for installing any type of PV systems. This study analyzed the potential of floating PV systems on a mine pit lake in Korea to break this misconception. Using a fish-eye lens camera and digital elevation models, a shading analysis was performed to identify the area suitable for installing a floating PV system. The layout of the floating PV system was designed in consideration of the optimal tilt angle and array spacing of the PV panels. The System Advisor Model (SAM) by National Renewable Energy Laboratory, USA, was used to conduct energy simulations based on weather data and the system design. The results indicated that the proposed PV system could generate 971.57 MWh/year. The economic analysis (accounting for discount rate and a 20-year operational lifetime) showed that the net present value would be $897,000 USD, and a payback period of about 12.3 years. Therefore, we could know that the economic effect of the floating PV system on the mine pit lake is relatively higher than that of PV systems in the other abandoned mines in Korea. The annual reduction of greenhouse gas emissions was analyzed and found to be 471.21 tCO₂/year, which is twice the reduction effect achieved by forest restoration of an abandoned mine site. The economic feasibility of a floating PV system on a pit lake of an abandoned mine was thus established, and may be considered an efficient reuse option for abandoned mines. Full article

(This article belongs to the Special Issue Selected Papers from 5th Asia-Pacific Forum on Renewable Energy)

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3314 KiB

Open AccessEditor’s ChoiceArticle

Design and Analysis of Electrical Distribution Networks and Balancing Markets in the UK: A New Framework with Applications

by Vijayanarasimha Hindupur Pakka and Richard Mark Rylatt

Energies 2016, 9(2), 101; https://doi.org/10.3390/en9020101 - 9 Feb 2016

Cited by 13 | Viewed by 9486

Abstract

We present a framework for the design and simulation of electrical distribution systems and short term electricity markets specific to the UK. The modelling comprises packages relating to the technical and economic features of the electrical grid. The first package models the medium/low [...] Read more.

We present a framework for the design and simulation of electrical distribution systems and short term electricity markets specific to the UK. The modelling comprises packages relating to the technical and economic features of the electrical grid. The first package models the medium/low distribution networks with elements such as transformers, voltage regulators, distributed generators, composite loads, distribution lines and cables. This model forms the basis for elementary analysis such as load flow and short circuit calculations and also enables the investigation of effects of integrating distributed resources, voltage regulation, resource scheduling and the like. The second part of the modelling exercise relates to the UK short term electricity market with specific features such as balancing mechanism and bid-offer strategies. The framework is used for investigating methods of voltage regulation using multiple control technologies, to demonstrate the effects of high penetration of wind power on balancing prices and finally use these prices towards achieving demand response through aggregated prosumers. Full article

(This article belongs to the Special Issue Multi-Disciplinary Perspectives on Energy and Sustainable Development)

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3638 KiB

Open AccessArticle

Joint Estimation of the Electric Vehicle Power Battery State of Charge Based on the Least Squares Method and the Kalman Filter Algorithm

by Xiangwei Guo, Longyun Kang, Yuan Yao, Zhizhen Huang and Wenbiao Li

Energies 2016, 9(2), 100; https://doi.org/10.3390/en9020100 - 8 Feb 2016

Cited by 69 | Viewed by 7935

Abstract

An estimation of the power battery state of charge (SOC) is related to the energy management, the battery cycle life and the use cost of electric vehicles. When a lithium-ion power battery is used in an electric vehicle, the SOC displays [...] Read more.

An estimation of the power battery state of charge (SOC) is related to the energy management, the battery cycle life and the use cost of electric vehicles. When a lithium-ion power battery is used in an electric vehicle, the SOC displays a very strong time-dependent nonlinearity under the influence of random factors, such as the working conditions and the environment. Hence, research on estimating the SOC of a power battery for an electric vehicle is of great theoretical significance and application value. In this paper, according to the dynamic response of the power battery terminal voltage during a discharging process, the second-order RC circuit is first used as the equivalent model of the power battery. Subsequently, on the basis of this model, the least squares method (LS) with a forgetting factor and the adaptive unscented Kalman filter (AUKF) algorithm are used jointly in the estimation of the power battery SOC. Simulation experiments show that the joint estimation algorithm proposed in this paper has higher precision and convergence of the initial value error than a single AUKF algorithm. Full article

(This article belongs to the Special Issue Electrochemical Energy Storage - 2015)

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3471 KiB

Open AccessArticle

One-Dimensional Modeling of an Entrained Coal Gasification Process Using Kinetic Parameters

by Moonkyeong Hwang, Eunhye Song and Juhun Song

Energies 2016, 9(2), 99; https://doi.org/10.3390/en9020099 - 6 Feb 2016

Cited by 11 | Viewed by 5569

Abstract

A one-dimensional reactor model was developed to simulate the performance of an entrained flow gasifier under various operating conditions. The model combined the plug flow reactor (PFR) model with the well-stirred reactor (WSR) model. Reaction kinetics was considered together with gas diffusion for [...] Read more.

A one-dimensional reactor model was developed to simulate the performance of an entrained flow gasifier under various operating conditions. The model combined the plug flow reactor (PFR) model with the well-stirred reactor (WSR) model. Reaction kinetics was considered together with gas diffusion for the solid-phase reactions in the PFR model, while equilibrium was considered for the gas-phase reactions in the WSR model. The differential and algebraic equations of mass balance and energy balance were solved by a robust ODE solver, i.e., an semi-implicit Runge–Kutta method, and by a nonlinear algebraic solver, respectively. The computed gasifier performance was validated against experimental data from the literature. The difference in product gas concentration from the equilibrium model, and the underlying mechanisms were discussed further. The optimal condition was found after parameter studies were made for various operating conditions. Full article

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1618 KiB

Open AccessArticle

Performance Evaluation of Palm Oil-Based Biodiesel Combustion in an Oil Burner

by Abdolsaeid Ganjehkaviri, Mohammad Nazri Mohd Jaafar, Seyed Ehsan Hosseini and Anas Basri Musthafa

Energies 2016, 9(2), 97; https://doi.org/10.3390/en9020097 - 4 Feb 2016

Cited by 52 | Viewed by 7669

Abstract

This paper presents an experimental investigation of the combustion characteristics of palm methyl ester (PME), also known as palm oil-based biodiesel, in an oil burner system. The performance of conventional diesel fuel (CDF) and various percentages of diesel blended with palm oil-based biodiesel [...] Read more.

This paper presents an experimental investigation of the combustion characteristics of palm methyl ester (PME), also known as palm oil-based biodiesel, in an oil burner system. The performance of conventional diesel fuel (CDF) and various percentages of diesel blended with palm oil-based biodiesel is also studied to evaluate their performance. The performance of the various fuels is evaluated based on the temperature profile of the combustor’s wall and emissions, such as nitrogen oxides (NO_x) and carbon monoxide (CO). The combustion experiments were conducted using three different oil burner nozzles (1.25, 1.50 and 1.75 USgal/h) under lean (equivalence ratio (Φ) = 0.8), stoichiometric (Φ = 1) and rich fuel (Φ = 1.2) ratio conditions. The results show that the rate of emission formation decreases as the volume percent of palm biodiesel in a blend increases. PME combustion tests present a lower temperature inside the chamber compared to CDF combustion. High rates of NO_x formation occur under lean mixture conditions with the presence of high nitrogen and sufficient temperature, whereas high CO occurs for rich mixtures with low oxygen presence. Full article

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10081 KiB

Open AccessArticle

Elimination of the Inrush Current Phenomenon Associated with Single-Phase Offline UPS Systems

by Syed Sabir Hussain Bukhari, Shahid Atiq and Byung-il Kwon

Energies 2016, 9(2), 96; https://doi.org/10.3390/en9020096 - 4 Feb 2016

Cited by 13 | Viewed by 7479

Abstract

Critical load applications always rely on UPS systems to uphold continuous power during abnormal grid conditions. In case of any power disruption, an offline UPS system starts powering the load to avoid blackout. However, this process can root the momentous inrush current for [...] Read more.

Critical load applications always rely on UPS systems to uphold continuous power during abnormal grid conditions. In case of any power disruption, an offline UPS system starts powering the load to avoid blackout. However, this process can root the momentous inrush current for the transformer installed before the load. The consequences of inrush current can be the reduction of output voltage and tripping of protective devices of the UPS system. Furthermore, it can also damage the sensitive load and decrease the transformer’s lifetime. To prevent the inrush current, and to avoid its disruptive effects, this research suggests an offline UPS system based on a current regulated inverter that eliminates the inrush current while powering the transformer coupled loads. A detailed comparative analysis of the conventional and proposed topologies is presented and the experiment was performed by using a small prototype to validate the performance, and operation of the proposed topology. Full article

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6658 KiB

Open AccessArticle

Simulation of Wind Speed in the Ventilation Tunnel for Surge Tanks in Transient Processes

by Jiandong Yang, Huang Wang, Wencheng Guo, Weijia Yang and Wei Zeng

Energies 2016, 9(2), 95; https://doi.org/10.3390/en9020095 - 3 Feb 2016

Cited by 5 | Viewed by 5764

Abstract

Hydroelectric power plants’ open-type surge tanks may be built in mountains subject to the provision of atmospheric air. Hence, a ventilation tunnel is indispensable. The air flow in the ventilation tunnel is associated with the fluctuation of water-level in the surge tank. There [...] Read more.

Hydroelectric power plants’ open-type surge tanks may be built in mountains subject to the provision of atmospheric air. Hence, a ventilation tunnel is indispensable. The air flow in the ventilation tunnel is associated with the fluctuation of water-level in the surge tank. There is a great relationship between the wind speed and the safe use and project investment of ventilation tunnels. To obtain the wind speed in a ventilation tunnel for a surge tank during transient processes, this article adopts the one-dimensional numerical simulation method and establishes a mathematical model of a wind speed by assuming the boundary conditions of air discharge for a surge tank. Thereafter, the simulation of wind speed in a ventilation tunnel, for the case of a surge tank during transient processes, is successfully realized. Finally, the effective mechanism of water-level fluctuation in a surge tank and the shape of the ventilation tunnel (including length, sectional area and dip angle) for the wind speed distribution and the change process are discovered. On the basis of comparison between the simulation results of 1D and 3D computational fluid dynamics (CFD), the results indicate that the one-dimensional simulation method as proposed in this article can be used to accurately simulate the wind speed in the ventilation tunnel of a surge tank during transient processes. The wind speed fluctuations can be superimposed by using the low frequency mass wave (i.e., fundamental wave) and the high frequency elastic wave (i.e., harmonic wave). The water-level fluctuation in a surge tank and the sectional area of the ventilation tunnel mainly affect the amplitude of fundamental and harmonic waves. The period of a fundamental wave can be determined from the water-level fluctuations. The length of the ventilation tunnel has an effect on the period and amplitude of harmonic waves, whereas the dip angle influences the amplitude of harmonic waves. Full article

(This article belongs to the Special Issue Hydropower)

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3611 KiB

Open AccessReview

Overcoming the Fundamental Limit: Combustion of a Hydrogen-Oxygen Mixture in Micro- and Nano-Bubbles

by Vitaly Svetovoy, Alexander Postnikov, Ilia Uvarov, Remco Sanders and Gijs Krijnen

Energies 2016, 9(2), 94; https://doi.org/10.3390/en9020094 - 3 Feb 2016

Cited by 21 | Viewed by 9415

Abstract

Combustion reactions quench in small volumes due to fast heat escape via the volume boundary. Nevertheless, the reaction between hydrogen and oxygen was observed in nano- and micro-bubbles. The bubbles containing a mixture of gases were produced in microsystems using electrochemical decomposition of [...] Read more.

Combustion reactions quench in small volumes due to fast heat escape via the volume boundary. Nevertheless, the reaction between hydrogen and oxygen was observed in nano- and micro-bubbles. The bubbles containing a mixture of gases were produced in microsystems using electrochemical decomposition of water with a fast switching of voltage polarity. In this paper, we review our experimental results on the reaction in micro- and nano-bubbles and provide their physical interpretation. Experiments were performed using microsystems of different designs. The process was observed with a stroboscope and with a vibrometer. The latter was used to measure the gas concentration in the electrolyte and to monitor pressure in a reaction chamber covered with a flexible membrane. Information on the temperature was extracted from the Faraday current in the electrolyte. Since the direct observation of the combustion is complicated by the small size and short time scale of the events, special attention is paid to the signatures of the reaction. The mechanism of the reaction is not yet clear, but it is obvious that the process is surface dominated and happens without significant temperature increase. Full article

(This article belongs to the Special Issue Micro Combustor)

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1542 KiB

Open AccessArticle

Quantitative Model and Metrics of Electrical Grids’ Resilience Evaluated at a Power Distribution Level

by Alexis Kwasinski

Energies 2016, 9(2), 93; https://doi.org/10.3390/en9020093 - 3 Feb 2016

Cited by 114 | Viewed by 10519

Abstract

This paper presents a framework to systematically measure and assess power grids’ resilience with a focus on performance as perceived by customers at the power distribution level. The proposed framework considers an analogous measure of availability as a basic metric for resilience and [...] Read more.

This paper presents a framework to systematically measure and assess power grids’ resilience with a focus on performance as perceived by customers at the power distribution level. The proposed framework considers an analogous measure of availability as a basic metric for resilience and defines other key resilience-related concepts and metrics, such as resistance and brittleness. This framework also provides a measurement for the degree of functional dependency of loads on power grids and demonstrates how the concepts of resilience and dependency are inherently related. It also discusses the implications of considering human-centered processes as fundamental constituting components of infrastructure systems. Thanks to its quantitative nature, the proposed resilience framework enables the creation of tools to evaluate power grids’ performance as a lifeline and to assess the effects of plans for optimal electrical power infrastructure deployment and operation. The discussion is supported by practical examples and empirical records from field damage assessments conducted after recent notable natural disasters. Full article

(This article belongs to the Special Issue Resilience of Energy Systems)

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956 KiB

Open AccessArticle

Potential Biogas Production from Artichoke Byproducts in Sardinia, Italy

by Fabio De Menna, Remo Alessio Malagnino, Matteo Vittuari, Giovanni Molari, Giovanna Seddaiu, Paola A. Deligios, Stefania Solinas and Luigi Ledda

Energies 2016, 9(2), 92; https://doi.org/10.3390/en9020092 - 2 Feb 2016

Cited by 30 | Viewed by 6097

Abstract

The paper aims at evaluating the potential biogas production, both in terms of CH₄ and theoretical energy potential, from globe artichoke agricultural byproducts in Sardinia. Field data about the productivity of byproducts were collected on five artichoke varieties cultivated in Sardinia, to [...] Read more.

The paper aims at evaluating the potential biogas production, both in terms of CH₄ and theoretical energy potential, from globe artichoke agricultural byproducts in Sardinia. Field data about the productivity of byproducts were collected on five artichoke varieties cultivated in Sardinia, to assess the biomethane production of their aboveground non-food parts (excluding the head). Moreover, secondary data from previous studies and surveys at regional scale were collected to evaluate the potential biogas production of the different districts. Fresh globe artichoke residues yielded, on average, 292.2 Nm³·t_DOM⁻¹, with dissimilarities among cultivars. Fresh samples were analyzed in two series: (a) wet basis; and (b) wet basis with catalytic enzymes application. Enzymes proved to have some beneficial effects in terms of anticipated biomethane availability. At the regional level, ab. 20 × 10⁶ Nm³ CH₄ could be produced, corresponding to the 60% of current installed capacity. However, districts potentials show some differences, depending on the specific biomass partitioning and on the productivity of cultivated varieties. Regional assessments should encompass the sensitiveness of results to agro-economic variables and the economic impacts of globe artichoke residue use in the current regional biogas sector. Full article

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748 KiB

Open AccessArticle

Probability Density Function Characterization for Aggregated Large-Scale Wind Power Based on Weibull Mixtures

by Emilio Gómez-Lázaro, María C. Bueso, Mathieu Kessler, Sergio Martín-Martínez, Jie Zhang, Bri-Mathias Hodge and Angel Molina-García

Energies 2016, 9(2), 91; https://doi.org/10.3390/en9020091 - 2 Feb 2016

Cited by 25 | Viewed by 6878

Abstract

The Weibull probability distribution has been widely applied to characterize wind speeds for wind energy resources. Wind power generation modeling is different, however, due in particular to power curve limitations, wind turbine control methods, and transmission system operation requirements. These differences are even [...] Read more.

The Weibull probability distribution has been widely applied to characterize wind speeds for wind energy resources. Wind power generation modeling is different, however, due in particular to power curve limitations, wind turbine control methods, and transmission system operation requirements. These differences are even greater for aggregated wind power generation in power systems with high wind penetration. Consequently, models based on one-Weibull component can provide poor characterizations for aggregated wind power generation. With this aim, the present paper focuses on discussing Weibull mixtures to characterize the probability density function (PDF) for aggregated wind power generation. PDFs of wind power data are firstly classified attending to hourly and seasonal patterns. The selection of the number of components in the mixture is analyzed through two well-known different criteria: the Akaike information criterion (AIC) and the Bayesian information criterion (BIC). Finally, the optimal number of Weibull components for maximum likelihood is explored for the defined patterns, including the estimated weight, scale, and shape parameters. Results show that multi-Weibull models are more suitable to characterize aggregated wind power data due to the impact of distributed generation, variety of wind speed values and wind power curtailment. Full article

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4402 KiB

Open AccessArticle

Optimization of Fuel Consumption and Emissions for Auxiliary Power Unit Based on Multi-Objective Optimization Model

by Yongpeng Shen, Zhendong He, Dongqi Liu and Binjie Xu

Energies 2016, 9(2), 90; https://doi.org/10.3390/en9020090 - 2 Feb 2016

Cited by 10 | Viewed by 8831

Abstract

Auxiliary power units (APUs) are widely used for electric power generation in various types of electric vehicles, improvements in fuel economy and emissions of these vehicles directly depend on the operating point of the APUs. In order to balance the conflicting goals of [...] Read more.

Auxiliary power units (APUs) are widely used for electric power generation in various types of electric vehicles, improvements in fuel economy and emissions of these vehicles directly depend on the operating point of the APUs. In order to balance the conflicting goals of fuel consumption and emissions reduction in the process of operating point choice, the APU operating point optimization problem is formulated as a constrained multi-objective optimization problem (CMOP) firstly. The four competing objectives of this CMOP are fuel-electricity conversion cost, hydrocarbon (HC) emissions, carbon monoxide (CO) emissions and nitric oxide (NO x ) emissions. Then, the multi-objective particle swarm optimization (MOPSO) algorithm and weighted metric decision making method are employed to solve the APU operating point multi-objective optimization model. Finally, bench experiments under New European driving cycle (NEDC), Federal test procedure (FTP) and high way fuel economy test (HWFET) driving cycles show that, compared with the results of the traditional fuel consumption single-objective optimization approach, the proposed multi-objective optimization approach shows significant improvements in emissions performance, at the expense of a slight drop in fuel efficiency. Full article

(This article belongs to the Special Issue Advances in Plug-in Hybrid Vehicles and Hybrid Vehicles)

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Energies, Volume 9, Issue 2 (February 2016) – 55 articles

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