Energies

Editorial

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20 pages, 644 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Energies in 2015

by Energies Editorial Office

MDPI AG, Klybeckstrasse 64, CH-4057 Basel, Switzerland

Energies 2016, 9(1), 64; https://doi.org/10.3390/en9010064 - 21 Jan 2016

Viewed by 6763

Abstract

The editors of energies would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2015. Full article

Research

Jump to: Editorial, Review, Other

18 pages, 4089 KiB

Open AccessArticle

A New Fast Peak Current Controller for Transient Voltage Faults for Power Converters

by Jesús Muñoz-Cruzado-Alba^1,*, Javier Villegas-Núñez^1,‡, José Alberto Vite-Frías^1,‡ and Juan Manuel Carrasco Solís^2,‡

¹ R & D Department, GPTech, Av. Camas N26, Bollullos de la Mitacion 41703, Spain

² Electronics Engineering Department, Seville University, Av. de los Descubrimientos S/N, Seville 41092, Spain

^‡ These authors contributed equally to this work.

Energies 2016, 9(1), 1; https://doi.org/10.3390/en9010001 - 22 Dec 2015

Cited by 11 | Viewed by 5813

Abstract

Power converters are the basic unit for the transient voltage fault ride through capability for most renewable distributed generators (DGs). When a transient fault happens, the grid voltage will drop suddenly and probably will also suffer a phase-jump event as well. State-of-the-art voltage [...] Read more.

Power converters are the basic unit for the transient voltage fault ride through capability for most renewable distributed generators (DGs). When a transient fault happens, the grid voltage will drop suddenly and probably will also suffer a phase-jump event as well. State-of-the-art voltage fault control techniques regulate the current injected during the grid fault. However, the beginning of the fault could be too fast for the inner current control loops of the inverter, and transient over-current would be expected. In order to avoid the excessive peak current of the methods presented in the literature, a new fast peak current control (FPCC) technique is proposed. Controlling the peak current magnitude avoids undesirable disconnection of the distributed generator in a fault state and improves the life expectancy of the converter. Experimental and simulation tests with high power converters provide the detailed behaviour of the method with excellent results. Full article

(This article belongs to the Special Issue Selected Papers from 15 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2015))

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23 pages, 3302 KiB

Open AccessArticle

Reconfiguration of Urban Photovoltaic Arrays Using Commercial Devices

by Sergio Ignacio Serna-Garcés^1,*

, Juan David Bastidas-Rodríguez²

and Carlos Andrés Ramos-Paja³

¹ Departamento de Electrónica y Telecomunicaciones, Instituto Tecnológico Metropolitano, Cra. 31 No. 54-10, Medellín 050013, Colombia

² Escuela de Ingenierías Eléctrica, Electrónica y de Telecomunicaciones, Universidad Industrial de Santander, Cra. 27 Calle 9, Bucaramanga 680002, Colombia

³ Departamento de Energía Eléctrica y Automática, Universidad Nacional de Colombia, Cra. 80 No. 65-223, Medellín 050041, Colombia

Energies 2016, 9(1), 2; https://doi.org/10.3390/en9010002 - 22 Dec 2015

Cited by 17 | Viewed by 7280

Abstract

A recent approach to mitigate the adverse effects of photovoltaic (PV) arrays operating under mismatching conditions is the dynamic electrical reconfiguration of the PV panels. This paper introduces a procedure to determine the best configuration of a PV array connected in a series-parallel [...] Read more.

A recent approach to mitigate the adverse effects of photovoltaic (PV) arrays operating under mismatching conditions is the dynamic electrical reconfiguration of the PV panels. This paper introduces a procedure to determine the best configuration of a PV array connected in a series-parallel structure without using complex mathematical models. Such a procedure uses the experimental current vs. voltage curves of the PV panels, which are composed of multiple PV modules, to construct the power vs. voltage curves of all of the possible configurations to identify the optimal one. The main advantage of this method is the low computational effort required to reconstruct the power vs. voltage curves of the array. This characteristic enables one to implement the proposed solution using inexpensive embedded devices, which are widely adopted in industrial applications. The proposed method, and its embedded implementation, were tested using a hardware-in-the-loop simulation of the PV system. Finally, the real-time operation and benefits of the proposed solution are illustrated using a practical example based on commercial devices. Full article

(This article belongs to the Special Issue Nano-Structured Solar Cells)

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20 pages, 852 KiB

Open AccessEditor’s ChoiceArticle

Wind Turbine Fault Detection through Principal Component Analysis and Statistical Hypothesis Testing

by Francesc Pozo^*

and Yolanda Vidal

Control, Dynamics and Applications (CoDAlab), Departament de Matemàtiques, Escola Universitària d’Enginyeria Tècnica Industrial de Barcelona (EUETIB), Universitat Politècnica de Catalunya (UPC), Comte d’Urgell, 187, Barcelona 08036, Spain

Energies 2016, 9(1), 3; https://doi.org/10.3390/en9010003 - 23 Dec 2015

Cited by 60 | Viewed by 8208

Abstract

This paper addresses the problem of online fault detection of an advanced wind turbine benchmark under actuators (pitch and torque) and sensors (pitch angle measurement) faults of different type: fixed value, gain factor, offset and changed dynamics. The fault detection scheme starts by [...] Read more.

This paper addresses the problem of online fault detection of an advanced wind turbine benchmark under actuators (pitch and torque) and sensors (pitch angle measurement) faults of different type: fixed value, gain factor, offset and changed dynamics. The fault detection scheme starts by computing the baseline principal component analysis (PCA) model from the healthy or undamaged wind turbine. Subsequently, when the structure is inspected or supervised, new measurements are obtained are projected into the baseline PCA model. When both sets of data—the baseline and the data from the current wind turbine—are compared, a statistical hypothesis testing is used to make a decision on whether or not the wind turbine presents some damage, fault or misbehavior. The effectiveness of the proposed fault-detection scheme is illustrated by numerical simulations on a well-known large offshore wind turbine in the presence of wind turbulence and realistic fault scenarios. The obtained results demonstrate that the proposed strategy provides and early fault identification, thereby giving the operators sufficient time to make more informed decisions regarding the maintenance of their machines. Full article

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14 pages, 3386 KiB

Open AccessArticle

A Numerical Study on System Performance of Groundwater Heat Pumps

by Jinsang Kim¹ and Yujin Nam^2,*

¹ Blue Economy Strategy Institute, Suite 911, 55 Digital-Ro 34-Gil, Seoul 08378, Korea

² Department of Architectural Engineering, Pusan National University, Jangjun-2 Dong, Busan 609-735, Korea

Energies 2016, 9(1), 4; https://doi.org/10.3390/en9010004 - 23 Dec 2015

Cited by 19 | Viewed by 6499

Abstract

Groundwater heat pumps have energy saving potential where the groundwater resources are sufficient. System Coefficients of Performance (COPs) are measurements of performance of groundwater heat pump systems. In this study, the head and power of submersible pumps, heat pump units, piping, and heat [...] Read more.

Groundwater heat pumps have energy saving potential where the groundwater resources are sufficient. System Coefficients of Performance (COPs) are measurements of performance of groundwater heat pump systems. In this study, the head and power of submersible pumps, heat pump units, piping, and heat exchangers are expressed as polynomial equations, and these equations are solved numerically to determine the system performance. Regression analysis is used to find the coefficients of the polynomial equations from a catalog of performance data. The cooling and heating capacities of water-to-water heat pumps are determined using Energy Plus. Results show that system performance drops as the water level drops, and the lowest flow rates generally achieve the highest system performance. The system COPs are used to compare the system performance of various system configurations. The groundwater pumping level and temperature provide the greatest effects on the system performance of groundwater heat pumps along with the submersible pumps and heat exchangers. The effects of groundwater pumping levels, groundwater temperatures, and the heat transfer coefficient in heat exchanger on the system performance are given and compared. This analysis needs to be included in the design process of groundwater heat pump systems, possibly with analysis tools that include a wide range of performance data. Full article

(This article belongs to the Special Issue Advanced Heating and Cooling Techniques)

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16 pages, 3066 KiB

Open AccessArticle

Energy Management Strategy for Microgrids by Using Enhanced Bee Colony Optimization

by Whei-Min Lin¹, Chia-Sheng Tu¹ and Ming-Tang Tsai^2,*

¹ Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung 807, Taiwan

² Department of Electrical Engineering, Cheng-Shiu University, Kaohsiung 833, Taiwan

Energies 2016, 9(1), 5; https://doi.org/10.3390/en9010005 - 23 Dec 2015

Cited by 75 | Viewed by 6994

Abstract

This paper presents a microgrid (MG) energy management strategy by considering renewable energy and battery storage systems. Renewable energy, including wind power generation and solar power generation, is integrated into the distribution network, for which is formulated the optimal dispatch model of mixed-power [...] Read more.

This paper presents a microgrid (MG) energy management strategy by considering renewable energy and battery storage systems. Renewable energy, including wind power generation and solar power generation, is integrated into the distribution network, for which is formulated the optimal dispatch model of mixed-power generation by considering the charging/discharging scheduling of battery storage systems. The MG system has an electrical link for power exchange between the MG and the utility during different hours of the day. Based on the time-of-use (TOU) and all technical constraints, an enhanced bee colony optimization (EBCO) is proposed to solve the daily economic dispatch of MG systems. In the EBCO procedure, the self-adaption repulsion factor is embedded in the bee swarm of the BCO in order to improve the behavior patterns of each bee swarm and increase its search efficiency and accuracy in high dimensions. Different modifications in moving patterns of EBCO are proposed to search the feasible space more effectively. EBCO is used for economic energy management of grid-connected and stand-alone scenarios, and the results are compared to those in previous algorithms. In either grid-connected or stand-alone scenarios, an optimal MG scheduling dispatch is achieved using micro-turbines, renewable energy and battery storage systems. Results show that the proposed method is feasible, robust and more effective than many previously-developed algorithms. Full article

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21 pages, 3827 KiB

Open AccessArticle

Heuristic Optimization of Consumer Electricity Costs Using a Generic Cost Model

by Chris Ogwumike^*, Michael Short^*

and Fathi Abugchem

School of Science and Engineering, Teesside University, Middlesbrough TS1 3BA, UK

Energies 2016, 9(1), 6; https://doi.org/10.3390/en9010006 - 23 Dec 2015

Cited by 30 | Viewed by 6954

Abstract

Many new demand response strategies are emerging for energy management in smart grids. Real-Time Energy Pricing (RTP) is one important aspect of consumer Demand Side Management (DSM), which encourages consumers to participate in load scheduling. This can help reduce peak demand and improve [...] Read more.

Many new demand response strategies are emerging for energy management in smart grids. Real-Time Energy Pricing (RTP) is one important aspect of consumer Demand Side Management (DSM), which encourages consumers to participate in load scheduling. This can help reduce peak demand and improve power system efficiency. The use of Intelligent Decision Support Systems (IDSSs) for load scheduling has become necessary in order to enable consumers to respond to the changing economic value of energy across different hours of the day. The type of scheduling problem encountered by a consumer IDSS is typically NP-hard, which warrants the search for good heuristics with efficient computational performance and ease of implementation. This paper presents an extensive evaluation of a heuristic scheduling algorithm for use in a consumer IDSS. A generic cost model for hourly pricing is utilized, which can be configured for traditional on/off peak pricing, RTP, Time of Use Pricing (TOUP), Two-Tier Pricing (2TP) and combinations thereof. The heuristic greedily schedules controllable appliances to minimize smart appliance energy costs and has a polynomial worst-case computation time. Extensive computational experiments demonstrate the effectiveness of the algorithm and the obtained results indicate the gaps between the optimal achievable costs are negligible. Full article

(This article belongs to the Special Issue Selected Papers from 15 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2015))

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20 pages, 3976 KiB

Open AccessArticle

Hybrid Wind Speed Prediction Based on a Self-Adaptive ARIMAX Model with an Exogenous WRF Simulation

by Erdong Zhao¹, Jing Zhao^2,*, Liwei Liu¹, Zhongyue Su³ and Ning An⁴

¹ School of Economics and Management, North China Electric Power University, Beijing 102206, China

² School of Mathematics and Statistics, Lanzhou University, Lanzhou 730000, China

³ College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China

⁴ Gerontechnology Lab, School of Computer and Information, Hefei University of Technology, Hefei 230009, China

Energies 2016, 9(1), 7; https://doi.org/10.3390/en9010007 - 24 Dec 2015

Cited by 25 | Viewed by 7369

Abstract

Wind speed forecasting is difficult not only because of the influence of atmospheric dynamics but also for the impossibility of providing an accurate prediction with traditional statistical forecasting models that work by discovering an inner relationship within historical records. This paper develops a [...] Read more.

Wind speed forecasting is difficult not only because of the influence of atmospheric dynamics but also for the impossibility of providing an accurate prediction with traditional statistical forecasting models that work by discovering an inner relationship within historical records. This paper develops a self-adaptive (SA) auto-regressive integrated moving average with exogenous variables (ARIMAX) model that is optimized very-short-term by the chaotic particle swarm optimization (CPSO) algorithm, known as the SA-ARIMA-CPSO approach, for wind speed prediction. The ARIMAX model chooses the wind speed result from the Weather Research and Forecasting (WRF) simulation as an exogenous input variable. Further, an SA strategy is applied to the ARIMAX process. When new information is available, the model process can be updated adaptively with parameters optimized by the CPSO algorithm. The proposed SA-ARIMA-CPSO approach enables the forecasting process to update training information and model parameters intelligently and adaptively. As tested using the 15-min wind speed data collected from a wind farm in Northern China, the improved method has the best performance compared with several other models. Full article

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27 pages, 8232 KiB

Open AccessArticle

Error Assessment of Solar Irradiance Forecasts and AC Power from Energy Conversion Model in Grid-Connected Photovoltaic Systems

by Gianfranco Chicco^1,*

, Valeria Cocina¹

, Paolo Di Leo¹, Filippo Spertino¹

and Alessandro Massi Pavan²

¹ Energy Department, Politecnico di Torino, corso Duca degli Abruzzi 24, Torino 10129, Italy

² Department of Engineering and Architecture, University of Trieste, Via Valerio 10, Trieste 34127, Italy

Energies 2016, 9(1), 8; https://doi.org/10.3390/en9010008 - 24 Dec 2015

Cited by 27 | Viewed by 7492

Abstract

Availability of effective estimation of the power profiles of photovoltaic systems is essential for studying how to increase the share of intermittent renewable sources in the electricity mix of many countries. For this purpose, weather forecasts, together with historical data of the meteorological [...] Read more.

Availability of effective estimation of the power profiles of photovoltaic systems is essential for studying how to increase the share of intermittent renewable sources in the electricity mix of many countries. For this purpose, weather forecasts, together with historical data of the meteorological quantities, provide fundamental information. The weak point of the forecasts depends on variable sky conditions, when the clouds successively cover and uncover the solar disc. This causes remarkable positive and negative variations in the irradiance pattern measured at the photovoltaic (PV) site location. This paper starts from 1 to 3 days-ahead solar irradiance forecasts available during one year, with a few points for each day. These forecasts are interpolated to obtain more irradiance estimations per day. The estimated irradiance data are used to classify the sky conditions into clear, variable or cloudy. The results are compared with the outcomes of the same classification carried out with the irradiance measured in meteorological stations at two real PV sites. The occurrence of irradiance spikes in “broken cloud” conditions is identified and discussed. From the measured irradiance, the Alternating Current (AC) power injected into the grid at two PV sites is estimated by using a PV energy conversion model. The AC power errors resulting from the PV model with respect to on-site AC power measurements are shown and discussed. Full article

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

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16 pages, 6611 KiB

Open AccessArticle

Empirical Validation of a Thermal Model of a Complex Roof Including Phase Change Materials

by Stéphane Guichard^1,*, Frédéric Miranville², Dimitri Bigot²

, Bruno Malet-Damour²

, Teddy Libelle² and Harry Boyer²

¹ Research Institute in Innovation and Business Sciences (IRISE) Laboratory/Superior Industrial Center Study (CESI)-Reunion Chamber of Commerce and Industry (CCIR)/Regional Centre for the Innovation and Transfer of Technologies (CRITT), The CESI engineering school, Campus Pro—CCIR 65 rue du Père Lafosse-Boîte n°4, Saint-Pierre 97410, France

² Physics and Mathematical Engineering Laboratory for Energy, Environment and Building (PIMENT), University of Reunion, 117, rue du Général Ailleret Le Tampon 97430, France

Energies 2016, 9(1), 9; https://doi.org/10.3390/en9010009 - 24 Dec 2015

Cited by 7 | Viewed by 5990

Abstract

This paper deals with the empirical validation of a building thermal model of a complex roof including a phase change material (PCM). A mathematical model dedicated to PCMs based on the heat apparent capacity method was implemented in a multi-zone building simulation code, [...] Read more.

This paper deals with the empirical validation of a building thermal model of a complex roof including a phase change material (PCM). A mathematical model dedicated to PCMs based on the heat apparent capacity method was implemented in a multi-zone building simulation code, the aim being to increase the understanding of the thermal behavior of the whole building with PCM technologies. In order to empirically validate the model, the methodology is based both on numerical and experimental studies. A parametric sensitivity analysis was performed and a set of parameters of the thermal model has been identified for optimization. The use of the generic optimization program called GenOpt^® coupled to the building simulation code enabled to determine the set of adequate parameters. We first present the empirical validation methodology and main results of previous work. We then give an overview of GenOpt^® and its coupling with the building simulation code. Finally, once the optimization results are obtained, comparisons of the thermal predictions with measurements are found to be acceptable and are presented. Full article

(This article belongs to the Special Issue PCM Applications in Building Energy)

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18 pages, 6253 KiB

Open AccessArticle

Design and Control of a 3 kW Wireless Power Transfer System for Electric Vehicles

by Zhenshi Wang^1,2, Xuezhe Wei^2,* and Haifeng Dai^1,2

¹ Clean Energy Automotive Engineering Center, Tongji University, No. 4800, Caoan Road, Shanghai 201804, China

² School of Automotive Studies, Tongji University, No. 4800, Caoan Road, Shanghai 201804, China

Energies 2016, 9(1), 10; https://doi.org/10.3390/en9010010 - 24 Dec 2015

Cited by 51 | Viewed by 10157

Abstract

This paper aims to study a 3 kW wireless power transfer system for electric vehicles. First, the LCL-LCL topology and LC-LC series topology are analyzed, and their transfer efficiencies under the same transfer power are compared. The LC-LC series topology is validated to [...] Read more.

This paper aims to study a 3 kW wireless power transfer system for electric vehicles. First, the LCL-LCL topology and LC-LC series topology are analyzed, and their transfer efficiencies under the same transfer power are compared. The LC-LC series topology is validated to be more efficient than the LCL-LCL topology and thus is more suitable for the system design. Then a novel q-Zsource-based online power regulation method which employs a unique impedance network (two pairs of inductors and capacitors) to couple the cascaded H Bridge to the power source is proposed. By controlling the shoot-through state of the H Bridge, the charging current can be adjusted, and hence, transfer power. Finally, a prototype is implemented, which can transfer 3 kW wirelessly with ~95% efficiency over a 20 cm transfer distance. Full article

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15 pages, 3743 KiB

Open AccessArticle

A Power Prediction Method for Photovoltaic Power Plant Based on Wavelet Decomposition and Artificial Neural Networks

by Honglu Zhu¹

, Xu Li^1,*, Qiao Sun², Ling Nie², Jianxi Yao¹ and Gang Zhao³

¹ School of Renewable Energy, North China Electric Power University, Beijing 102206, China

² Beijing Guodiantong Network Technology Co., Ltd., Beijing 100070, China

³ School of Electronic Engineering, Xidian University, Xian 710071, China

Energies 2016, 9(1), 11; https://doi.org/10.3390/en9010011 - 24 Dec 2015

Cited by 133 | Viewed by 9786

Abstract

The power prediction for photovoltaic (PV) power plants has significant importance for their grid connection. Due to PV power’s periodicity and non-stationary characteristics, traditional power prediction methods based on linear or time series models are no longer applicable. This paper presents a method [...] Read more.

The power prediction for photovoltaic (PV) power plants has significant importance for their grid connection. Due to PV power’s periodicity and non-stationary characteristics, traditional power prediction methods based on linear or time series models are no longer applicable. This paper presents a method combining the advantages of the wavelet decomposition (WD) and artificial neural network (ANN) to solve this problem. With the ability of ANN to address nonlinear relationships, theoretical solar irradiance and meteorological variables are chosen as the input of the hybrid model based on WD and ANN. The output power of the PV plant is decomposed using WD to separated useful information from disturbances. The ANNs are used to build the models of the decomposed PV output power. Finally, the outputs of the ANN models are reconstructed into the forecasted PV plant power. The presented method is compared with the traditional forecasting method based on ANN. The results shows that the method described in this paper needs less calculation time and has better forecasting precision. Full article

(This article belongs to the Special Issue Solar Photovoltaics Trilemma: Efficiencey, Stability and Cost Reduction)

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20 pages, 1558 KiB

Open AccessArticle

A Simple Operating Strategy of Small-Scale Battery Energy Storages for Energy Arbitrage under Dynamic Pricing Tariffs

by Enrico Telaretti^*, Mariano Ippolito and Luigi Dusonchet

Department of Energy, Information Engineering and Mathematical Models, University of Palermo, Viale delle Scienze, 90128, Palermo, Italy

Energies 2016, 9(1), 12; https://doi.org/10.3390/en9010012 - 25 Dec 2015

Cited by 40 | Viewed by 8276

Abstract

Price arbitrage involves taking advantage of an electricity price difference, storing electricity during low-prices times, and selling it back to the grid during high-prices periods. This strategy can be exploited by customers in presence of dynamic pricing schemes, such as hourly electricity prices, [...] Read more.

Price arbitrage involves taking advantage of an electricity price difference, storing electricity during low-prices times, and selling it back to the grid during high-prices periods. This strategy can be exploited by customers in presence of dynamic pricing schemes, such as hourly electricity prices, where the customer electricity cost may vary at any hour of day, and power consumption can be managed in a more flexible and economical manner, taking advantage of the price differential. Instead of modifying their energy consumption, customers can install storage systems to reduce their electricity bill, shifting the energy consumption from on-peak to off-peak hours. This paper develops a detailed storage model linking together technical, economic and electricity market parameters. The proposed operating strategy aims to maximize the profit of the storage owner (electricity customer) under simplifying assumptions, by determining the optimal charge/discharge schedule. The model can be applied to several kinds of storages, although the simulations refer to three kinds of batteries: lead-acid, lithium-ion (Li-ion) and sodium-sulfur (NaS) batteries. Unlike literature reviews, often requiring an estimate of the end-user load profile, the proposed operation strategy is able to properly identify the battery-charging schedule, relying only on the hourly price profile, regardless of the specific facility’s consumption, thanks to some simplifying assumptions in the sizing and the operation of the battery. This could be particularly useful when the customer load profile cannot be scheduled with sufficient reliability, because of the uncertainty inherent in load forecasting. The motivation behind this research is that storage devices can help to lower the average electricity prices, increasing flexibility and fostering the integration of renewable sources into the power system. Full article

(This article belongs to the Special Issue Control of Energy Storage)

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11 pages, 1887 KiB

Open AccessArticle

Generation of Hydrogen, Lignin and Sodium Hydroxide from Pulping Black Liquor by Electrolysis

by Guangzai Nong^*

, Zongwen Zhou and Shuangfei Wang^*

Institute of Light Industry and Food Engineering, Guangxi University, Nanning 530004, China

Energies 2016, 9(1), 13; https://doi.org/10.3390/en9010013 - 25 Dec 2015

Cited by 25 | Viewed by 7835

Abstract

Black liquor is generated in Kraft pulping of wood or non-wood raw material in pulp mills, and regarded as a renewable resource. The objective of this paper was to develop an effective means to remove the water pollutants by recovery of both lignin [...] Read more.

Black liquor is generated in Kraft pulping of wood or non-wood raw material in pulp mills, and regarded as a renewable resource. The objective of this paper was to develop an effective means to remove the water pollutants by recovery of both lignin and sodium hydroxide from black liquor, based on electrolysis. The treatment of a 1000 mL of black liquor (122 g/L solid contents) consumed 345.6 kJ of electric energy, and led to the generation of 30.7 g of sodium hydroxide, 0.82 g of hydrogen gas and 52.1 g of biomass solids. Therefore, the recovery ratios of elemental sodium and biomass solids are 80.4% and 76%, respectively. Treating black liquor by electrolysis is an environmentally friendly technology that can, in particular, be an alternative process in addressing the environmental issues of pulping waste liquor to the small-scale mills without black liquor recovery. Full article

(This article belongs to the Special Issue Organic Waste/Resources to Energy and Value added Product)

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15 pages, 4839 KiB

Open AccessEditor’s ChoiceArticle

Methods for Global Survey of Natural Gas Flaring from Visible Infrared Imaging Radiometer Suite Data

by Christopher D. Elvidge^1,*, Mikhail Zhizhin^2,3, Kimberly Baugh², Feng-Chi Hsu² and Tilottama Ghosh²

¹ Earth Observation Group, National Centers for Environmental Information, National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, CO 80205, USA

² Cooperative Institute for Research in the Environmental Sciences, University of Colorado, Boulder, CO 80303, USA

³ Russian Space Research Institute, Moscow 117997, Russia

Energies 2016, 9(1), 14; https://doi.org/10.3390/en9010014 - 25 Dec 2015

Cited by 302 | Viewed by 32627

Abstract

A set of methods are presented for the global survey of natural gas flaring using data collected by the National Aeronautics and Space Administration/National Oceanic and Atmospheric Administration NASA/NOAA Visible Infrared Imaging Radiometer Suite (VIIRS). The accuracy of the flared gas volume estimates [...] Read more.

A set of methods are presented for the global survey of natural gas flaring using data collected by the National Aeronautics and Space Administration/National Oceanic and Atmospheric Administration NASA/NOAA Visible Infrared Imaging Radiometer Suite (VIIRS). The accuracy of the flared gas volume estimates is rated at ±9.5%. VIIRS is particularly well suited for detecting and measuring the radiant emissions from gas flares through the collection of shortwave and near-infrared data at night, recording the peak radiant emissions from flares. In 2012, a total of 7467 individual flare sites were identified. The total flared gas volume is estimated at 143 (±13.6) billion cubic meters (BCM), corresponding to 3.5% of global production. While the USA has the largest number of flares, Russia leads in terms of flared gas volume. Ninety percent of the flared gas volume was found in upstream production areas, 8% at refineries and 2% at liquified natural gas (LNG) terminals. The results confirm that the bulk of natural gas flaring occurs in upstream production areas. VIIRS data can provide site-specific tracking of natural gas flaring for use in evaluating efforts to reduce and eliminate routine flaring. Full article

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19 pages, 7095 KiB

Open AccessArticle

Fumed Silica Nanoparticles Incorporated in Quaternized Poly(Vinyl Alcohol) Nanocomposite Membrane for Enhanced Power Densities in Direct Alcohol Alkaline Fuel Cells

by Selvaraj Rajesh Kumar¹

, Cheng-Hsin Juan¹, Guan-Ming Liao¹, Jia-Shiun Lin¹, Chun-Chen Yang²

, Wei-Ting Ma¹, Jiann-Hua You¹ and Shingjiang Jessie Lue^1,*

¹ Department of Chemical and Materials Engineering, Chang Gung University, Kwei-shan, Taoyuan 333, Taiwan

² Department of Chemical Engineering, Mingchi University of Technology, Tai-shan, New Taipei City 243, Taiwan

Energies 2016, 9(1), 15; https://doi.org/10.3390/en9010015 - 25 Dec 2015

Cited by 68 | Viewed by 7988

Abstract

A nanocomposite polymer membrane based on quaternized poly(vinyl alcohol)/fumed silica (QPVA/FS) was prepared via a quaternization process and solution casting method. The physico-chemical properties of the QPVA/FS membrane were investigated. Its high ionic conductivity was found to depend greatly on the concentration of [...] Read more.

A nanocomposite polymer membrane based on quaternized poly(vinyl alcohol)/fumed silica (QPVA/FS) was prepared via a quaternization process and solution casting method. The physico-chemical properties of the QPVA/FS membrane were investigated. Its high ionic conductivity was found to depend greatly on the concentration of fumed silica in the QPVA matrix. A maximum conductivity of 3.50 × 10⁻² S/cm was obtained for QPVA/5%FS at 60 °C when it was doped with 6 M KOH. The permeabilities of methanol and ethanol were reduced with increasing fumed silica content. Cell voltage and peak power density were analyzed as functions of fumed silica concentration, temperature, methanol and ethanol concentrations. A maximum power density of 96.8 mW/cm² was achieved with QPVA/5%FS electrolyte using 2 M methanol + 6 M KOH as fuel at 80 °C. A peak power density of 79 mW/cm² was obtained using the QPVA/5%FS electrolyte with 3 M ethanol + 5 M KOH as fuel. The resulting peak power densities are higher than the majority of published reports. The results confirm that QPVA/FS exhibits promise as a future polymeric electrolyte for use in direct alkaline alcoholic fuel cells. Full article

(This article belongs to the Special Issue Methanol and Alcohol Fuel Cells)

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12 pages, 2085 KiB

Open AccessArticle

Enhancing LVRT of DFIG by Using a Superconducting Current Limiter on Rotor Circuit

by Flávio Oliveira¹, Arthur Amorim²

, Lucas Encarnação²

, Jussara Fardin², Marcos Orlando³, Selênio Silva⁴ and Domingos Simonetti^2,*

¹ Department of Computer and Electronics, Federal University of Espírito Santo, São Mateus-ES 29932-540, Brazil

² Department of Electrical Engineering, Federal University of Espírito Santo, Vitória-ES 29075-910, Brazil

³ Department of Physics, Federal University of Espírito Santo, Vitória-ES 29075-910, Brazil

⁴ Department of Electrical Engineering, Federal University of Minas Gerais, Belo Horizonte-MG 31270-901, Brazil

Energies 2016, 9(1), 16; https://doi.org/10.3390/en9010016 - 25 Dec 2015

Cited by 18 | Viewed by 6124

Abstract

This paper have studied the dynamic of a 2.0 MW Doubly Fed Induction Generator (DFIG) during a severe voltage sag. Using the dynamic model of a DFIG, it was possible to determine the current, Electromagnetic Force and flux behavior during three-phase symmetrical voltage [...] Read more.

This paper have studied the dynamic of a 2.0 MW Doubly Fed Induction Generator (DFIG) during a severe voltage sag. Using the dynamic model of a DFIG, it was possible to determine the current, Electromagnetic Force and flux behavior during three-phase symmetrical voltage dip. Among the technologies of wind turbines the DFIG is widely employed; however, this machine is extremely susceptible to disturbances from the grid. In order to improve DFIG Low Voltage Ride-Through (LVRT), it is proposed a novel solution, using Superconducting Current Limiter (SCL) in two arrangements: one, the SCL is placed between the machine rotor and the rotor side converter (RSC), and another placed in the RSC DC-link. The proposal is validated through simulation using PSCAD™/EMTDC™ and according to requirements of specific regulations. The analysis ensure that both SCL arrangements behave likewise, and are effective in decrement the rotor currents during the disturbance. Full article

(This article belongs to the Special Issue Wind Turbine 2015)

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21 pages, 5099 KiB

Open AccessArticle

Optimal Allocation of Thermal-Electric Decoupling Systems Based on the National Economy by an Improved Conjugate Gradient Method

by Shuang Rong^1,*, Weixing Li^1,*, Zhimin Li¹, Yong Sun² and Taiyi Zheng²

¹ Department of Electrical Engineering, Harbin Institute of Technology, Harbin 150001, China

² State Grid Jilinsheng Electric Power Supply Company, Changchun 130021, China

Energies 2016, 9(1), 17; https://doi.org/10.3390/en9010017 - 29 Dec 2015

Cited by 15 | Viewed by 6161

Abstract

Aiming to relieve the large amount of wind power curtailment during the heating period in the North China region, a thermal-electric decoupling (TED) approach is proposed to both bring down the constraint of forced power output of combined heat and power plants and [...] Read more.

Aiming to relieve the large amount of wind power curtailment during the heating period in the North China region, a thermal-electric decoupling (TED) approach is proposed to both bring down the constraint of forced power output of combined heat and power plants and increase the electric load level during valley load times that assist the power grid in consuming more wind power. The operating principles of the thermal-electric decoupling approach is described, the mathematical model of its profits is developed, the constraint conditions of its operation are listed, also, an improved parallel conjugate gradient is utilized to bypass the saddle problem and accelerate the optimal speed. Numerical simulations are implemented and reveal an optimal allocation of TED which with a rated power of 280 MW and 185 MWh heat storage capacity are possible. This allocation of TED could bring approximately 16.9 billion Yuan of economic profit and consume more than 80% of the surplus wind energy which would be curtailed without the participation of TED. The results in this article verify the effectiveness of this method that could provide a referential guidance for thermal-electric decoupling system allocation in practice. Full article

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

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11 pages, 3983 KiB

Open AccessArticle

Performance Characteristics of a Modularized and Integrated PTC Heating System for an Electric Vehicle

by Yoon Hyuk Shin¹, Seungkyu Sim² and Sung Chul Kim^3,*

¹ Green Car Power System R&D Division, Korea Automotive Technology Institute, 74 Yongjung-Ri, Pungse-Myun, Dongnam-Gu, Chonan-Si, Chungnam 330-912, Korea

² Donga High Tech Company, Dongtangiheung-Road, Dongtan-Myeon, Hwaseong-Si, Gyunggi-Do 445-813, Korea

³ School of Mechanical Engineering, Yeungnam University, 280 Daehak-Ro, Gyeongsan, Gyeongbuk 712-749, Korea

Energies 2016, 9(1), 18; https://doi.org/10.3390/en9010018 - 28 Dec 2015

Cited by 31 | Viewed by 12486

Abstract

A modularized positive temperature coefficient heating system has controller-integrated heater modules. Such a heating system that uses a high-voltage power of 330 V was developed in the present study for use in electric vehicles. Four heater modules and one controller with an input [...] Read more.

A modularized positive temperature coefficient heating system has controller-integrated heater modules. Such a heating system that uses a high-voltage power of 330 V was developed in the present study for use in electric vehicles. Four heater modules and one controller with an input power of 5.6 kW were integrated in the modularized system, which was designed for improved heating power density and light weight compared to the conventional heating system, in which the controller is separated. We experimentally investigated the performance characteristics, namely, the heating capacity, energy efficiency, and pressure drop, of a prototype of the developed heating system and found it to have satisfactory performance. The findings of this study will contribute to the development of heating systems for electric vehicles. Full article

(This article belongs to the Special Issue Advanced Heating and Cooling Techniques)

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10 pages, 1255 KiB

Open AccessArticle

Noise Emission of a 200 kW Vertical Axis Wind Turbine

by Erik Möllerström^1,2,*

, Fredric Ottermo¹, Jonny Hylander¹ and Hans Bernhoff²

¹ School of Business, Engineering and Science, Halmstad University, Halmstad SE-301 18, Sweden

² Division for Electricity, Department of Engineering Sciences, Uppsala University, Uppsala SE-751 21, Sweden

Energies 2016, 9(1), 19; https://doi.org/10.3390/en9010019 - 29 Dec 2015

Cited by 43 | Viewed by 12826

Abstract

The noise emission from a vertical axis wind turbine (VAWT) has been investigated. A noise measurement campaign on a 200 kW straight-bladed VAWT has been conducted, and the result has been compared to a semi-empirical model for turbulent-boundary-layer trailing edge (TBL-TE) noise. The [...] Read more.

The noise emission from a vertical axis wind turbine (VAWT) has been investigated. A noise measurement campaign on a 200 kW straight-bladed VAWT has been conducted, and the result has been compared to a semi-empirical model for turbulent-boundary-layer trailing edge (TBL-TE) noise. The noise emission from the wind turbine was measured, at wind speed 8 m/s, 10 m above ground, to 96.2 dBA. At this wind speed, the turbine was stalling as it was run at a tip speed lower than optimal due to constructional constraints. The noise emission at a wind speed of 6 m/s, 10 m above ground was measured while operating at optimum tip speed and was found to be 94.1 dBA. A comparison with similar size horizontal axis wind turbines (HAWTs) indicates a noise emission at the absolute bottom of the range. Furthermore, it is clear from the analysis that the turbulent-boundary-layer trailing-edge noise, as modeled here, is much lower than the measured levels, which suggests that other mechanisms are likely to be important, such as inflow turbulence. Full article

(This article belongs to the Special Issue Wind Turbine 2015)

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22 pages, 1765 KiB

Open AccessArticle

A Robust Weighted Combination Forecasting Method Based on Forecast Model Filtering and Adaptive Variable Weight Determination

by Lianhui Li^1,†, Chunyang Mu^2,*,†, Shaohu Ding^1,*, Zheng Wang³, Runyang Mo^4,5 and Yongfeng Song^4,6

¹ College of Mechatronic Engineering, Beifang University of Nationalities, Yinchuan 750021, China

² State Key Laboratory of Robotics and System, Harbin Institute of Technology (HIT), Harbin 150001, China

³ State Grid Ningxia Electric Power Design Co. Ltd., Yinchuan 750001, China

⁴ School of Management, Qingdao Technological University, Qingdao 266520, China

⁵ College of Electrical &Information Engineering, Hunan University, Changsha 410082, China

⁶ College of Electrical Engineering and Information, Sichuan University, Chengdu 610065, China

^† These authors contributed equally to this work.

Energies 2016, 9(1), 20; https://doi.org/10.3390/en9010020 - 31 Dec 2015

Cited by 8 | Viewed by 5256

Abstract

Medium-and-long-term load forecasting plays an important role in energy policy implementation and electric department investment decision. Aiming to improve the robustness and accuracy of annual electric load forecasting, a robust weighted combination load forecasting method based on forecast model filtering and adaptive variable [...] Read more.

Medium-and-long-term load forecasting plays an important role in energy policy implementation and electric department investment decision. Aiming to improve the robustness and accuracy of annual electric load forecasting, a robust weighted combination load forecasting method based on forecast model filtering and adaptive variable weight determination is proposed. Similar years of selection is carried out based on the similarity between the history year and the forecast year. The forecast models are filtered to select the better ones according to their comprehensive validity degrees. To determine the adaptive variable weight of the selected forecast models, the disturbance variable is introduced into Immune Algorithm-Particle Swarm Optimization (IA-PSO) and the adaptive adjustable strategy of particle search speed is established. Based on the forecast model weight determined by improved IA-PSO, the weighted combination forecast of annual electric load is obtained. The given case study illustrates the correctness and feasibility of the proposed method. Full article

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19 pages, 1811 KiB

Open AccessArticle

Decomposing Industrial Energy-Related CO₂ Emissions in Yunnan Province, China: Switching to Low-Carbon Economic Growth

by Mingxiang Deng

, Wei Li^* and Yan Hu

State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China

Energies 2016, 9(1), 23; https://doi.org/10.3390/en9010023 - 4 Jan 2016

Cited by 29 | Viewed by 7195

Abstract

As a less-developed province that has been chosen to be part of a low-carbon pilot project, Yunnan faces the challenge of maintaining rapid economic growth while reducing CO₂ emissions. Understanding the drivers behind CO₂ emission changes can help decouple economic growth [...] Read more.

As a less-developed province that has been chosen to be part of a low-carbon pilot project, Yunnan faces the challenge of maintaining rapid economic growth while reducing CO₂ emissions. Understanding the drivers behind CO₂ emission changes can help decouple economic growth from CO₂ emissions. However, previous studies on the drivers of CO₂ emissions in less-developed regions that focus on both production and final demand have been seldom conducted. In this study, a structural decomposition analysis-logarithmic mean Divisia index (SDA-LMDI) model was developed to find the drivers behind the CO₂ emission changes during 1997–2012 in Yunnan, based on times series energy consumption and input-output data. The results demonstrated that the sharp rise in exports of high-carbon products from the metal processing and electricity sectors increased CO₂ emissions, during 2002–2007. Although increased investments in the construction sector also increased CO₂ emissions, during 2007–2012, the carbon intensity of Yunnan’s economy decreased substantially because the province vigorously developed hydropower and improved energy efficiency in energy-intensive sectors. Construction investments not only carbonized the GDP composition, but also formed a carbon-intensive production structure because of high-carbon supply chains. To further mitigate CO₂ emissions in Yunnan, measures should promote the development and application of clean energy and the formation of consumption-based economic growth. Full article

(This article belongs to the Special Issue Economics of Bioenergy 2015)

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20 pages, 3334 KiB

Open AccessArticle

Research on Heat Recovery Technology for Reducing the Energy Consumption of Dedicated Ventilation Systems: An Application to the Operating Model of a Laboratory

by Lian Zhang^1,2,* and Yu Feng Zhang¹

¹ School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China

² School of Electrical and Energy, Tianjin Sino-German Vocational Technical College, Tianjin 300350, China

Energies 2016, 9(1), 24; https://doi.org/10.3390/en9010024 - 4 Jan 2016

Cited by 11 | Viewed by 6005

Abstract

In this research, the application of heat pipes in the air handler dedicated to decoupling dehumidification from cooling to reduce energy consumption was simulated and investigated by simulations and experimental studies. The cooling load profiles and heat pipes with effectiveness of 0.45 and [...] Read more.

In this research, the application of heat pipes in the air handler dedicated to decoupling dehumidification from cooling to reduce energy consumption was simulated and investigated by simulations and experimental studies. The cooling load profiles and heat pipes with effectiveness of 0.45 and 0.6, respectively, were evaluated in achieving the desired space conditions and calculated hour by hour. The results demonstrated that for all examined cases, a heat pipe heat exchanger (HPHX) can be used to save over 80% of the energy during the hours of operation of air conditioning. The overall energy reduction rate was from 3.2% to 4.5% under air conditioning system conditions. It was found that the energy saving potential of a laboratory was higher than for other kinds of buildings. Therefore, the dedicated ventilation system combined with heat recovery technology can be efficiently applied to buildings, especially for laboratories in subtropical areas. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2016)

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20 pages, 5371 KiB

Open AccessArticle

A Fuzzy-Logic Power Management Strategy Based on Markov Random Prediction for Hybrid Energy Storage Systems

by Yanzi Wang¹, Weida Wang^1,*, Yulong Zhao¹, Lei Yang² and Wenjun Chen³

¹ National Key Laboratory of Vehicle Transmission, Beijing Institute of Technology, Beijing 100081, China

² Transmission System Section, Powertrain Department, Shanghai Automotive Industry Corporation Motor Commercial Vehicle Technical Center, Shanghai 200432, China

³ The Forth Branch Company, Inner Mongolia First Machinery Group Co. Ltd., Baotou 014032, China

Energies 2016, 9(1), 25; https://doi.org/10.3390/en9010025 - 4 Jan 2016

Cited by 67 | Viewed by 9546

Abstract

Over the last few years; issues regarding the use of hybrid energy storage systems (HESSs) in hybrid electric vehicles have been highlighted by the industry and in academic fields. This paper proposes a fuzzy-logic power management strategy based on Markov random prediction for [...] Read more.

Over the last few years; issues regarding the use of hybrid energy storage systems (HESSs) in hybrid electric vehicles have been highlighted by the industry and in academic fields. This paper proposes a fuzzy-logic power management strategy based on Markov random prediction for an active parallel battery-UC HESS. The proposed power management strategy; the inputs for which are the vehicle speed; the current electric power demand and the predicted electric power demand; is used to distribute the electrical power between the battery bank and the UC bank. In this way; the battery bank power is limited to a certain range; and the peak and average charge/discharge power of the battery bank and overall loss incurred by the whole HESS are also reduced. Simulations and scaled-down experimental platforms are constructed to verify the proposed power management strategy. The simulations and experimental results demonstrate the advantages; feasibility and effectiveness of the fuzzy-logic power management strategy based on Markov random prediction. Full article

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

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20 pages, 5943 KiB

Open AccessArticle

A Novel Geographical Information Systems Framework to Characterize Photovoltaic Deployment in the UK: Initial Evidence

by Paul Westacott^* and Chiara Candelise

Imperial College Centre for Energy Policy and Technology (ICEPT), Imperial College London, London SW7 1NA, UK

Energies 2016, 9(1), 26; https://doi.org/10.3390/en9010026 - 5 Jan 2016

Cited by 12 | Viewed by 6457

Abstract

Globally, deployment of grid-connected photovoltaics (PV) has increased dramatically in recent years. The UK has seen rapid uptake reaching over 500,000 installations totalling 2.8 GWp by 2013. PV can be installed in different market segments (domestic rooftop, non-domestic rooftop and ground-mounted “solar-farms”) covering [...] Read more.

Globally, deployment of grid-connected photovoltaics (PV) has increased dramatically in recent years. The UK has seen rapid uptake reaching over 500,000 installations totalling 2.8 GWp by 2013. PV can be installed in different market segments (domestic rooftop, non-domestic rooftop and ground-mounted “solar-farms”) covering a broad range of system sizes in a high number of locations. It is important to gain detailed understanding of what grid-connected PV deployment looks like (e.g., how it deployed across different geographic areas and market segments), and identify the major drivers behind it. This paper answers these questions by developing a novel geographical information systems (GIS)-framework—the United Kingdom Photovoltaics Database (UKPVD)—to analyze temporal and spatial PV deployment trends at high resolution across all market segments. Results show how PV deployment changed over time with the evolution of governmental PV policy support. Then spatial trends as function of local irradiation, rurality (as a proxy of building and population density) and building footprint (as a proxy for roof-area) are analyzed. We find in all market segments, PV deployment is strongly correlated with the level of policy support. Furthermore, all markets show a preference to deploy in rural areas and those with higher irradiation. Finally, local clustering of PV in all market segments was observed, revealing that PV is not spread evenly across areas. This work reveals the complex nature of PV deployment, both spatially and by market segment, reinforcing the need capture this through mapping. Full article

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12 pages, 5469 KiB

Open AccessArticle

Effects of Oxygen Content of Fuels on Combustion and Emissions of Diesel Engines

by Haiwen Song¹, Kelly Sison Quinton¹, Zhijun Peng^2,3,*, Hua Zhao⁴ and Nicos Ladommatos⁵

¹ Ford Motor Company, Dunton Technical Centre, Basildon SS15 6EE, UK

² Key State Lab of Engines, Tianjin University, Tianjin 300072, China

³ School of Engineering and Technology, University of Hertfordshire, Hatfield AL10 9AB, UK

⁴ School of Engineering and Design, Brunel University, Uxbridge UB8 3PH, UK

⁵ Department of Mechanical Engineering, University College London, London WC1E 6BT, UK

Energies 2016, 9(1), 28; https://doi.org/10.3390/en9010028 - 5 Jan 2016

Cited by 66 | Viewed by 9197

Abstract

Effects of oxygen content of fuels on combustion characteristics and emissions were investigated on both an optical single cylinder direct injection (DI) diesel engine and a multi-cylinder engine. Three fuels were derived from conventional diesel fuel (Finnish City diesel summer grade) by blending [...] Read more.

Effects of oxygen content of fuels on combustion characteristics and emissions were investigated on both an optical single cylinder direct injection (DI) diesel engine and a multi-cylinder engine. Three fuels were derived from conventional diesel fuel (Finnish City diesel summer grade) by blending Rapeseed Methyl Ester (RME) or Diglyme and Butyl-Diglyme of different quantities to make their oxygen content 3%, 3% and 9%, respectively. The experimental results with three tested fuels show that the fuel spray development was not affected apparently by the oxygenating. Compared with the base fuel, the ignition delay to pilot injection was shortened by 0%, 11% and 19% for three oxygenated fuels, respectively. The ignition delay to main injection was shortened by 10%, 19% and 38%, respectively. With regard to emissions, the smoke level was reduced by 24% to 90%, depending on fuel properties and engine running conditions. The penalties of increased NO_x emissions and fuel consumption were up to 19% and 24%, respectively. Full article

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20 pages, 3689 KiB

Open AccessArticle

Optimal Coordinated Control of Power Extraction in LES of a Wind Farm with Entrance Effects

by Jay P. Goit, Wim Munters

and Johan Meyers^*

Department of Mechanical Engineering, University of Leuven, Celestijnenlaan 300A, Leuven B3001, Belgium

Energies 2016, 9(1), 29; https://doi.org/10.3390/en9010029 - 6 Jan 2016

Cited by 50 | Viewed by 6963

Abstract

We investigate the use of optimal coordinated control techniques in large eddy simulations of wind farm boundary layer interaction with the aim of increasing the total energy extraction in wind farms. The individual wind turbines are considered as flow actuators, and their energy [...] Read more.

We investigate the use of optimal coordinated control techniques in large eddy simulations of wind farm boundary layer interaction with the aim of increasing the total energy extraction in wind farms. The individual wind turbines are considered as flow actuators, and their energy extraction is dynamically regulated in time, so as to optimally influence the flow field. We extend earlier work on wind farm optimal control in the fully-developed regime (Goit and Meyers 2015, J. Fluid Mech. 768, 5–50) to a ‘finite’ wind farm case, in which entrance effects play an important role. For the optimal control, a receding horizon framework is employed in which turbine thrust coefficients are optimized in time and per turbine. Optimization is performed with a conjugate gradient method, where gradients of the cost functional are obtained using adjoint large eddy simulations. Overall, the energy extraction is increased 7% by the optimal control. This increase in energy extraction is related to faster wake recovery throughout the farm. For the first row of turbines, the optimal control increases turbulence levels and Reynolds stresses in the wake, leading to better wake mixing and an inflow velocity for the second row that is significantly higher than in the uncontrolled case. For downstream rows, the optimal control mainly enhances the sideways mean transport of momentum. This is different from earlier observations by Goit and Meyers (2015) in the fully-developed regime, where mainly vertical transport was enhanced. Full article

(This article belongs to the Collection Wind Turbines)

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17 pages, 7796 KiB

Open AccessArticle

Phase Change Materials-Assisted Heat Flux Reduction: Experiment and Numerical Analysis

by Hussein J. Akeiber^1,*, Seyed Ehsan Hosseini^1,*, Mazlan A. Wahid¹, Hasanen M. Hussen² and Abdulrahman Th. Mohammad³

¹ High-Speed Reacting Flow Laboratory, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor 81310, Malaysia

² Machine and Mechanical Department, University of Technology, Baghdad 35023, Iraq

³ Baqubah Technical Institute, Middle Technical University, Baghdad 06800, Iraq

Energies 2016, 9(1), 30; https://doi.org/10.3390/en9010030 - 7 Jan 2016

Cited by 17 | Viewed by 7467

Abstract

Phase change materials (PCM) in the construction industry became attractive because of several interesting attributes, such as thermo-physical parameters, open air atmospheric condition usage, cost and the duty structure requirement. Thermal performance optimization of PCMs in terms of proficient storage of a large [...] Read more.

Phase change materials (PCM) in the construction industry became attractive because of several interesting attributes, such as thermo-physical parameters, open air atmospheric condition usage, cost and the duty structure requirement. Thermal performance optimization of PCMs in terms of proficient storage of a large amount of heat or cold in a finite volume remains a challenging task. Implementation of PCMs in buildings to achieve thermal comfort for a specific climatic condition in Iraq is our main focus. From this standpoint, the present paper reports the experimental and numerical results on the lowering of heat flux inside a residential building using PCM, which is composed of oil (40%) and wax (60%). This PCM (paraffin), being plentiful and cost-effective, is extracted locally from waste petroleum products in Iraq. Experiments are performed with two rooms of identical internal dimensions in the presence and absence of PCM. A two-dimensional numerical transient heat transfer model is developed and solved using the finite difference method. A relatively simple geometry is chosen to initially verify the numerical solution procedure by incorporating in the computer program two-dimensional elliptic flows. It is demonstrated that the heat flux inside the room containing PCM is remarkably lower than the one devoid of PCM. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2016)

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24 pages, 4050 KiB

Open AccessEditor’s ChoiceArticle

Assessing the Environmental Sustainability of Electricity Generation in Turkey on a Life Cycle Basis

by Burcin Atilgan and Adisa Azapagic^*

School of Chemical Engineering and Analytical Science, The University of Manchester, The Mill, Room C16, Sackville Street, Manchester M13 9PL, UK

Energies 2016, 9(1), 31; https://doi.org/10.3390/en9010031 - 7 Jan 2016

Cited by 47 | Viewed by 7818

Abstract

Turkey’s electricity mix is dominated by fossil fuels, but the country has ambitious future targets for renewable and nuclear energy. At present, environmental impacts of electricity generation in Turkey are unknown so this paper represents a first attempt to fill this knowledge gap. [...] Read more.

Turkey’s electricity mix is dominated by fossil fuels, but the country has ambitious future targets for renewable and nuclear energy. At present, environmental impacts of electricity generation in Turkey are unknown so this paper represents a first attempt to fill this knowledge gap. Taking a life cycle approach, the study considers eleven impacts from electricity generation over the period 1990–2014. All 516 power plants currently operational in Turkey are assessed: lignite, hard coal, natural gas, hydro, onshore wind and geothermal. The results show that the annual impacts from electricity have been going up steadily over the period, increasing by 2–9 times, with the global warming potential being higher by a factor of five. This is due to a four-fold increase in electricity demand and a growing share of fossil fuels. The impact trends per unit of electricity generated differ from those for the annual impacts, with only four impacts being higher today than in 1990, including the global warming potential. Most other impacts are lower from 35% to two times. These findings demonstrate the need for diversifying the electricity mix by increasing the share of domestically-abundant renewable resources, such as geothermal, wind, and solar energy. Full article

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20 pages, 7681 KiB

Open AccessArticle

Direct and Indirect Impacts of Vegetation on Building Comfort: A Comparative Study of Lawns, Green Walls and Green Roofs

by Laurent Malys^1,2, Marjorie Musy^1,2,*,† and Christian Inard^2,3,†

¹ L'Université Nantes Angers Le Mans, ensa Nantes, UMR CNRS 1563, Centre de REcherche Nantais Architecture Urbanité, 6 quai F. Mitterrand, Nantes 44000, France

² Institut de Recherche en Sciences et Techniques de la Ville, FR CNRS 2488, 1 rue de La Noé, Nantes 44000, France

³ Laboratoire des Sciences de l'Ingénieur pour l'Environnement, Université de La Rochelle, UMR CNRS 7356, Avenue M. Crépeau, 17042 La Rochelle Cedex 1, France

^† These authors contributed equally to this work.

Energies 2016, 9(1), 32; https://doi.org/10.3390/en9010032 - 7 Jan 2016

Cited by 37 | Viewed by 9457

Abstract

Following development and validation of the SOLENE-microclimat tool, the underlying model was used to compare the impacts of various “greening strategies” on buildings’ summer energy consumption and indoor comfort. This study distinguishes between direct and indirect impacts by successively implementing the test strategies [...] Read more.

Following development and validation of the SOLENE-microclimat tool, the underlying model was used to compare the impacts of various “greening strategies” on buildings’ summer energy consumption and indoor comfort. This study distinguishes between direct and indirect impacts by successively implementing the test strategies on both the studied building and surrounding ones; it also considers insulated vs. non-insulated buildings. Findings indicate that green walls have a direct effect on indoor comfort throughout the entire building, whereas the effect of green roofs is apparently primarily confined to the upper floor. Moreover, the indirect effect of a green wall is greater, mainly due to the drop in infrared emissions resulting from a lower surface temperature. It has also been proven that the indirect effects of green walls and surrounding lawns can help reduce the loads acting on a non-insulated building. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2016)

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17 pages, 1690 KiB

Open AccessArticle

Molecular Level Factors Affecting the Efficiency of Organic Chromophores for p-Type Dye Sensitized Solar Cells

by Svitlana Karamshuk¹, Stefano Caramori^2,*

, Norberto Manfredi¹

, Matteo Salamone¹, Riccardo Ruffo¹, Stefano Carli²

, Carlo A. Bignozzi² and Alessandro Abbotto^1,*

¹ Department of Materials Science and Milano-Bicocca Solar Energy Research Center—MIB-Solar, University of Milano-Bicocca, INSTM Unit, Via Cozzi 55, 20125 Milano, Italy

² Department of Chemistry, University of Ferrara, Via L. Borsari 46, 44121 Ferrara, Italy

Energies 2016, 9(1), 33; https://doi.org/10.3390/en9010033 - 7 Jan 2016

Cited by 16 | Viewed by 6873

Abstract

A series of mono- and di-branched donor-π-acceptor charge-separated dyes incorporating triphenylamine as a donor and either Dalton’s or benzothiadiazole group as strong acceptors was synthesized and its fundamental properties relevant to the sensitization of nanocrystalline NiO investigated. The dyes exhibited an intense visible [...] Read more.

A series of mono- and di-branched donor-π-acceptor charge-separated dyes incorporating triphenylamine as a donor and either Dalton’s or benzothiadiazole group as strong acceptors was synthesized and its fundamental properties relevant to the sensitization of nanocrystalline NiO investigated. The dyes exhibited an intense visible absorption band with a strong charge transfer character favorable to NiO sensitization, shifting the electron density from the donor to the acceptor branches. Nevertheless, the computed exciton binding energy is circa twice that of a common literature standard (P1), suggesting a more difficult charge separation. When tested in p-type dye-sensitized solar cells the dyes successfully sensitized NiO electrodes, with photocurrent densities about half than that of the reference compound. Being recombination kinetics comparable, the larger photocurrent generated by P1 agrees with the superior charge separation capability originating by its smaller exciton binding energy. Full article

(This article belongs to the Special Issue Dye Sensitized Solar Cells)

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17 pages, 2839 KiB

Open AccessArticle

Assessing the Potential of Plug-in Electric Vehicles in Active Distribution Networks

by Reza Ahmadi Kordkheili^1,*, Seyyed Ali Pourmousavi², Mehdi Savaghebi¹

, Josep M. Guerrero¹

and Mohammad Hashem Nehrir³

¹ Department of Energy Technology, Aalborg University, Pontoppidanstraede 101, Aalborg 9220, Denmark

² NEC Laboratories America Incorporations, Cupertino, CA 95014, USA

³ Electrical and computer engineering department, Montana State University, Bozeman, MT 59717, USA

Energies 2016, 9(1), 34; https://doi.org/10.3390/en9010034 - 7 Jan 2016

Cited by 17 | Viewed by 6494

Abstract

A multi-objective optimization algorithm is proposed in this paper to increase the penetration level of renewable energy sources (RESs) in distribution networks by intelligent management of plug-in electric vehicle (PEV) storage. The proposed algorithm is defined to manage the reverse power flow (PF) [...] Read more.

A multi-objective optimization algorithm is proposed in this paper to increase the penetration level of renewable energy sources (RESs) in distribution networks by intelligent management of plug-in electric vehicle (PEV) storage. The proposed algorithm is defined to manage the reverse power flow (PF) from the distribution network to the upstream electrical system. Furthermore, a charging algorithm is proposed within the proposed optimization in order to assure PEV owner’s quality of service (QoS). The method uses genetic algorithm (GA) to increase photovoltaic (PV) penetration without jeopardizing PEV owners’ (QoS) and grid operating limits, such as voltage level of the grid buses. The method is applied to a part of the Danish low voltage (LV) grid to evaluate its effectiveness and capabilities. Different scenarios have been defined and tested using the proposed method. Simulation results demonstrate the capability of the algorithm in increasing solar power penetration in the grid up to 50%, depending on the PEV penetration level and the freedom of the system operator in managing the available PEV storage. Full article

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14 pages, 4018 KiB

Open AccessArticle

A Viable Electrode Material for Use in Microbial Fuel Cells for Tropical Regions

by Felix Offei¹, Anders Thygesen^2,*

, Moses Mensah¹, Kwame Tabbicca¹, Dinesh Fernando³, Irina Petrushina⁴ and Geoffrey Daniel³

¹ Department of Chemical Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

² Center for Bioprocess Engineering, Department of Chemical and Biochemical Engineering, Technical University of Denmark, Søltofts Plads 229, Lyngby DK-2800, Denmark

³ Department of Forest Products, Swedish University of Agricultural Sciences, Uppsala SE-75651, Sweden

⁴ Department of Energy Conversion and Storage, Technical University of Denmark, Building 207, Lyngby DK-2800, Denmark

Energies 2016, 9(1), 35; https://doi.org/10.3390/en9010035 - 7 Jan 2016

Cited by 25 | Viewed by 6723

Abstract

Electrode materials are critical for microbial fuel cells (MFC) since they influence the construction and operational costs. This study introduces a simple and efficient electrode material in the form of palm kernel shell activated carbon (AC) obtained in tropical regions. The novel introduction [...] Read more.

Electrode materials are critical for microbial fuel cells (MFC) since they influence the construction and operational costs. This study introduces a simple and efficient electrode material in the form of palm kernel shell activated carbon (AC) obtained in tropical regions. The novel introduction of this material is also targeted at introducing an inexpensive and durable electrode material, which can be produced in rural communities to improve the viability of MFCs. The maximum voltage and power density obtained (under 1000 Ω load) using an H-shaped MFC with AC as both anode and cathode electrode material was 0.66 V and 1.74 W/m³, respectively. The power generated by AC was as high as 86% of the value obtained with the extensively used carbon paper. Scanning electron microscopy and Denaturing Gradient Gel Electrophoresis (DGGE) analysis of AC anode biofilms confirmed that electrogenic bacteria were present on the electrode surface for substrate oxidation and the formation of nanowires. Full article

(This article belongs to the Special Issue Microbial Fuel Cells: Power-up, Cost Reduction and Practical Application)

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24 pages, 4621 KiB

Open AccessArticle

Developing a New HSR Switching Node (SwitchBox) for Improving Traffic Performance in HSR Networks

by Nguyen Xuan Tien

and Jong Myung Rhee^*

Department of Information and Communications Engineering, Myongji University, 116 Myongji-ro, Yongin-si, Gyeonggi-do 449-728, Korea

Energies 2016, 9(1), 36; https://doi.org/10.3390/en9010036 - 8 Jan 2016

Cited by 6 | Viewed by 7058

Abstract

High availability is crucial for industrial Ethernet networks as well as Ethernet-based control systems such as automation networks and substation automation systems (SAS). Since standard Ethernet does not support fault tolerance capability, the high availability of Ethernet networks can be increased by using [...] Read more.

High availability is crucial for industrial Ethernet networks as well as Ethernet-based control systems such as automation networks and substation automation systems (SAS). Since standard Ethernet does not support fault tolerance capability, the high availability of Ethernet networks can be increased by using redundancy protocols. Various redundancy protocols for Ethernet networks have been developed and standardized, such as rapid spanning tree protocol (RSTP), media redundancy protocol (MRP), parallel redundancy protocol (PRP), high-availability seamless redundancy (HSR) and others. RSTP and MRP have switchover delay drawbacks. PRP provides zero recovery time, but requires a duplicate network infrastructure. HSR operation is similar to PRP, but HSR uses a single network. However, the standard HSR protocol is mainly applied to ring-based topologies and generates excessively unnecessary redundant traffic in the network. In this paper, we develop a new switching node for the HSR protocol, called SwitchBox, which is used in HSR networks in order to support any network topology and significantly reduce redundant network traffic, including unicast, multicast and broadcast traffic, compared with standard HSR. By using the SwitchBox, HSR not only provides seamless communications with zero switchover time in case of failure, but it is also easily applied to any network topology and significantly reduces unnecessary redundant traffic in HSR networks. Full article

(This article belongs to the Collection Smart Grid)

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14 pages, 912 KiB

Open AccessArticle

Model-Free Coordinated Control for MHTGR-Based Nuclear Steam Supply Systems

by Zhe Dong^1,2

¹ Institute of Nuclear and New Energy Technology (INET), Tsinghua University, Beijing 100084, China

² Collaborative Innovation Center of Advanced Nuclear Energy Technology of China, Beijing 100084, China

Energies 2016, 9(1), 37; https://doi.org/10.3390/en9010037 - 11 Jan 2016

Cited by 18 | Viewed by 5725

Abstract

The modular high temperature gas-cooled reactor (MHTGR) is a typical small modular reactor (SMR) that offers simpler, standardized and safer modular design by being factory built, requiring smaller initial capital investment, and having a shorter construction period. Thanks to its small size, the [...] Read more.

The modular high temperature gas-cooled reactor (MHTGR) is a typical small modular reactor (SMR) that offers simpler, standardized and safer modular design by being factory built, requiring smaller initial capital investment, and having a shorter construction period. Thanks to its small size, the MHTGRs could be beneficial in providing electric power to remote areas that are deficient in transmission or distribution and in generating local power for large population centers. Based on the multi-modular operation scheme, the inherent safety feature of the MHTGRs can be applicable to large nuclear plants of any desired power rating. The MHTGR-based nuclear steam supplying system (NSSS) is constituted by an MHTGR, a side-by-side arranged helical-coil once-through steam generator (OTSG) and some connecting pipes. Due to the side-by-side arrangement, there is a tight coupling effect between the MHTGR and OTSG. Moreover, there always exists the parameter perturbation of the NSSSs. Thus, it is meaningful to study the model-free coordinated control of MHTGR-based NSSSs for safe, stable, robust and efficient operation. In this paper, a new model-free coordinated control strategy that regulates the nuclear power, MHTGR outlet helium temperature and OTSG outlet overheated steam temperature by properly adjusting the control rod position, helium flowrate and feed-water flowrate is established for the MHTGR-based NSSSs. Sufficient conditions for the globally asymptotic closed-loop stability is given. Finally, numerical simulation results in the cases of large range power decrease and increase illustrate the satisfactory performance of this newly-developed model-free coordinated NSSS control law. Full article

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16 pages, 1387 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

What Do Capacity Deployment Rates Tell Us about the Efficiency of Electricity Generation from Renewable Energy Sources Support Measures in Greece?

by Sotiris Papadelis, Vasssilis Stavrakas and Alexandros Flamos^*

Department of Industrial Management and Technology, University of Piraeus, Karaoli & Dimitriou 80, Piraeus 18534, Greece

Energies 2016, 9(1), 38; https://doi.org/10.3390/en9010038 - 13 Jan 2016

Cited by 20 | Viewed by 7984

Abstract

The efficiency of fiscal support for electricity generation from renewable energy sources (RES-E) is a multifaceted notion that cannot be adequately described by a single metric. Efficiency is related to the ability of a policy measure to support deployment without creating negative feedback [...] Read more.

The efficiency of fiscal support for electricity generation from renewable energy sources (RES-E) is a multifaceted notion that cannot be adequately described by a single metric. Efficiency is related to the ability of a policy measure to support deployment without creating negative feedback effects. These negative effects may stem from saturation of the grid’s ability to absorb an increased amount of RES-E power, the inability of regulatory bodies to cope with the larger workload due to the increased number of projects requesting permits or from rent-seeking behavior. Furthermore, the primary rationale for feed-in tariffs (FITs) and other fiscal support schemes is that increased deployment of RES-E technologies will lead to reductions in costs and increases in efficiency. As a result, the efficiency of an RES-E support policy should be also judged by its ability to capitalize on cost reductions. Overall, we present an approach to facilitate ongoing assessments of the efficiency of support measures for RES-E deployment. We demonstrate the proposed approach using the FIT support policy in Greece as a case study. In particular, the RES-E support policy in Greece has been recently revised through tariff cuts and a moratorium on new production licenses. We aim to demonstrate that if publicly available data are appropriately monitored, a policy revision can take place in a timelier and less disruptive manner. Full article

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

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16 pages, 383 KiB

Open AccessArticle

Analysis of the Channel Influence to Power Line Communications Based on ITU-T G.9904 (PRIME)

by Asier Llano^1,*

, Itziar Angulo^2,†

, Pablo Angueira^2,†

, Txetxu Arzuaga^1,† and David De la Vega^2,†

¹ Engineering Department, Distribution Automation Solutions (DAS), ZIV, Parque Tecnológico 210, 48170 Zamudio, Spain

² Department of Communications Engineering, University of the Basque Country (UPV/EHU), Alameda Urquijo s/n, 48013 Bilbao, Spain

^† These authors contributed equally to this work.

Energies 2016, 9(1), 39; https://doi.org/10.3390/en9010039 - 12 Jan 2016

Cited by 16 | Viewed by 5761

Abstract

ITU-T G.9904 standard, also known as PoweRline Intelligent Metering Evolution (PRIME), is a Power Line Communications standard for advanced metering, grid control and asset monitoring defined by the International Telecommunication Union (ITU). In this paper, an analysis about how different characteristics of the [...] Read more.

ITU-T G.9904 standard, also known as PoweRline Intelligent Metering Evolution (PRIME), is a Power Line Communications standard for advanced metering, grid control and asset monitoring defined by the International Telecommunication Union (ITU). In this paper, an analysis about how different characteristics of the communication channel and types of noise might affect the system performance is carried out. This study is based on simulations of the PRIME physical layer using different channel characteristics and transmission parameters. The conclusions obtained are very valuable for better understanding the behavior of the ITU-T G.9904 (PRIME) standard in the field, allowing future improvements in deployment strategies and equipment design. Full article

(This article belongs to the Special Issue Smart Metering)

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14 pages, 1721 KiB

Open AccessArticle

A New Fault Location Approach for Acoustic Emission Techniques in Wind Turbines

by Carlos Quiterio Gómez Muñoz^*

and Fausto Pedro García Márquez

Ingenium Research Group, Department of Business Management, University of Castilla-La Mancha, Ciudad Real 13071, Spain

Energies 2016, 9(1), 40; https://doi.org/10.3390/en9010040 - 12 Jan 2016

Cited by 92 | Viewed by 8212

Abstract

The renewable energy industry is undergoing continuous improvement and development worldwide, wind energy being one of the most relevant renewable energies. This industry requires high levels of reliability, availability, maintainability and safety (RAMS) for wind turbines. The blades are critical components in wind [...] Read more.

The renewable energy industry is undergoing continuous improvement and development worldwide, wind energy being one of the most relevant renewable energies. This industry requires high levels of reliability, availability, maintainability and safety (RAMS) for wind turbines. The blades are critical components in wind turbines. The objective of this research work is focused on the fault detection and diagnosis (FDD) of the wind turbine blades. The FDD approach is composed of a robust condition monitoring system (CMS) and a novel signal processing method. CMS collects and analyses the data from different non-destructive tests based on acoustic emission. The acoustic emission signals are collected applying macro-fiber composite (MFC) sensors to detect and locate cracks on the surface of the blades. Three MFC sensors are set in a section of a wind turbine blade. The acoustic emission signals are generated by breaking a pencil lead in the blade surface. This method is used to simulate the acoustic emission due to a breakdown of the composite fibers. The breakdown generates a set of mechanical waves that are collected by the MFC sensors. A graphical method is employed to obtain a system of non-linear equations that will be used for locating the emission source. This work demonstrates that a fiber breakage in the wind turbine blade can be detected and located by using only three low cost sensors. It allows the detection of potential failures at an early stages, and it can also reduce corrective maintenance tasks and downtimes and increase the RAMS of the wind turbine. Full article

(This article belongs to the Special Issue Wind Turbine 2015)

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16 pages, 5022 KiB

Open AccessArticle

Enhanced Predictive Current Control of Three-Phase Grid-Tied Reversible Converters with Improved Switching Patterns

by Zhanfeng Song^1,*,†, Yanjun Tian^2,†, Zhe Chen² and Yanting Hu³

¹ Department of Electrical Engineering and Automation, Tianjin University, Tianjin 30072, China

² Department of Energy Technology, Aalborg University, Aalborg 9220, Denmark

³ Faculty of Science and Engineering, University of Chester, Chester CH1 4BJ, UK

^† These authors contributed equally to this work.

Energies 2016, 9(1), 41; https://doi.org/10.3390/en9010041 - 13 Jan 2016

Cited by 5 | Viewed by 5418

Abstract

A predictive current control strategy can realize flexible regulation of three-phase grid-tied converters based on system behaviour prediction and cost function minimization. However, when the predictive current control strategy with conventional switching patterns is adopted, the predicted duration time for voltage vectors turns [...] Read more.

A predictive current control strategy can realize flexible regulation of three-phase grid-tied converters based on system behaviour prediction and cost function minimization. However, when the predictive current control strategy with conventional switching patterns is adopted, the predicted duration time for voltage vectors turns out to be negative in some cases, especially under the conditions of bidirectional power flows and transient situations, leading to system performance deteriorations. This paper aims to clarify the real reason for this phenomenon under bidirectional power flows, i.e., rectifier mode and inverter mode, and, furthermore, seeks to propose effective solutions. A detailed analysis of instantaneous current variations under different conditions was conducted. An enhanced predictive current control strategy with improved switching patterns was then proposed. An experimental platform was built based on a commercial converter produced by Danfoss, and moreover, relative experiments were carried out, confirming the superiority of the proposed scheme. Full article

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

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11 pages, 1325 KiB

Open AccessArticle

Intermittent Very High Frequency Plasma Deposition on Microcrystalline Silicon Solar Cells Enabling High Conversion Efficiency

by Mitsuoki Hishida^1,*

, Takeyuki Sekimoto², Mitsuhiro Matsumoto³ and Akira Terakawa³

¹ Automotive & Industrial Systems Company, Panasonic Corporation, Kadoma, Osaka 571-8506, Japan

² Advanced Research Division, Panasonic Corporation, Seika, Kyoto 619-0237, Japan

³ Eco Solution Company, Panasonic Corporation, Kaizuka, Osaka 597-0094, Japan

Energies 2016, 9(1), 42; https://doi.org/10.3390/en9010042 - 13 Jan 2016

Cited by 2 | Viewed by 5258

Abstract

Stopping the plasma-enhanced chemical vapor deposition (PECVD) once and maintaining the film in a vacuum for 30 s were performed. This was done several times during the formation of a film of i-layer microcrystalline silicon (μc-Si:H) used in thin-film silicon tandem solar cells. [...] Read more.

Stopping the plasma-enhanced chemical vapor deposition (PECVD) once and maintaining the film in a vacuum for 30 s were performed. This was done several times during the formation of a film of i-layer microcrystalline silicon (μc-Si:H) used in thin-film silicon tandem solar cells. This process aimed to reduce defect regions which occur due to collision with neighboring grains as the film becomes thicker. As a result, high crystallinity (X_c) of μc-Si:H was obtained. Eventually, a solar cell using this process improved the conversion efficiency by 1.3% (0.14 points), compared with a normal-condition cell. In this paper, we propose an easy method to improve the conversion efficiency with PECVD. Full article

(This article belongs to the Special Issue Key Developments in Thin Film Solar Cells)

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19 pages, 1957 KiB

Open AccessArticle

Reliability Analysis and Overload Capability Assessment of Oil-Immersed Power Transformers

by Chen Wang¹

, Jie Wu^2,*, Jianzhou Wang³ and Weigang Zhao^4,5

¹ School of Mathematics and Statistics, Lanzhou University, Lanzhou 730000, China

² School of Mathematics and Computer Science, Northwest University for Nationalities, Lanzhou 730030, China

³ School of Statistics, Dongbei University of Finance and Economics, Dalian 116025, China

⁴ Center for Energy and Environmental Policy Research, Beijing Institute of Technology, Beijing 100081, China

⁵ School of Management and Economics, Beijing Institute of Technology, Beijing 100081, China

Energies 2016, 9(1), 43; https://doi.org/10.3390/en9010043 - 14 Jan 2016

Cited by 16 | Viewed by 6590

Abstract

Smart grids have been constructed so as to guarantee the security and stability of the power grid in recent years. Power transformers are a most vital component in the complicated smart grid network. Any transformer failure can cause damage of the whole power [...] Read more.

Smart grids have been constructed so as to guarantee the security and stability of the power grid in recent years. Power transformers are a most vital component in the complicated smart grid network. Any transformer failure can cause damage of the whole power system, within which the failures caused by overloading cannot be ignored. This research gives a new insight into overload capability assessment of transformers. The hot-spot temperature of the winding is the most critical factor in measuring the overload capacity of power transformers. Thus, the hot-spot temperature is calculated to obtain the duration running time of the power transformers under overloading conditions. Then the overloading probability is fitted with the mature and widely accepted Weibull probability density function. To guarantee the accuracy of this fitting, a new objective function is proposed to obtain the desired parameters in the Weibull distributions. In addition, ten different mutation scenarios are adopted in the differential evolutionary algorithm to optimize the parameter in the Weibull distribution. The final comprehensive overload capability of the power transformer is assessed by the duration running time as well as the overloading probability. Compared with the previous studies that take no account of the overloading probability, the assessment results obtained in this research are much more reliable. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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18 pages, 2672 KiB

Open AccessArticle

Screening Criteria and Considerations of Offshore Enhanced Oil Recovery

by Pan-Sang Kang^1,†

, Jong-Se Lim^1,*

and Chun Huh^2,†

¹ Department of Energy and Resources Engineering, Korea Maritime and Ocean University, Yeongdo-Gu, Busan 49112, Korea

² Department of Petroleum and Geosystems Engineering, The University of Texas at Austin, Austin, TX 78712-1585, USA

^† These authors contributed equally to this work.

Energies 2016, 9(1), 44; https://doi.org/10.3390/en9010044 - 14 Jan 2016

Cited by 55 | Viewed by 11217

Abstract

The application of enhanced oil recovery (EOR) in offshore oil fields has received significant attention due to the potentially enormous amount of recoverable oil. However, EOR application offshore is in its very early stage due to conditions that are more complex than onshore [...] Read more.

The application of enhanced oil recovery (EOR) in offshore oil fields has received significant attention due to the potentially enormous amount of recoverable oil. However, EOR application offshore is in its very early stage due to conditions that are more complex than onshore oil fields, owing to the unique parameters present offshore. Therefore, successful EOR applications in offshore oil fields require different screening criteria than those for conventional onshore applications. A comprehensive database for onshore applications of EOR processes together with a limited offshore EOR application database are analyzed in this paper, and the important parameters for successful offshore application are incorporated into the new EOR screening criteria. In this paper, screening criteria to determine acceptable EOR processes for offshore fields, including hydrocarbon gas miscible, CO₂ miscible, and polymer processes, are presented. Suggested screening criteria for these EOR processes comprise quantitative boundaries and qualitative considerations. Quantitative screening criteria are predominantly based on quantifiable data, such as oil and reservoir properties. Qualitative screening considerations mainly focus on the operational issues present offshore, including platform space constraints, limited disposal options, injectant availability, and flow assurance matters (including hydrate formation and difficulties in emulsion separation). Full article

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23 pages, 1072 KiB

Open AccessArticle

Matching of Energy Provisions in Multihop Wireless Infra-Structures

by Rui Teng^1,*, Huan-Bang Li¹, Ryu Miura¹, Tatsuya Yamazaki² and Peter Davis³

¹ National Institute of Information and Communications Technology, Yokosuka 239-0847, Japan

² Graduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan

³ Telecognix Corporation, Sakyo-ku, Kyoto 606-8314, Japan

Energies 2016, 9(1), 45; https://doi.org/10.3390/en9010045 - 14 Jan 2016

Cited by 3 | Viewed by 5413

Abstract

Recently there have been large advances in energy technologies for battery-operated systems, including green energy resources and high capacity batteries. The effective use of battery energy resources in wireless infrastructure networks to improve the versatility and reliability of wireless communications is an important [...] Read more.

Recently there have been large advances in energy technologies for battery-operated systems, including green energy resources and high capacity batteries. The effective use of battery energy resources in wireless infrastructure networks to improve the versatility and reliability of wireless communications is an important issue. Emerging applications of smart cities, Internet of Things (IoT), and emergency responses highly rely on the basic communication network infrastructures that enable ubiquitous network connections. However, energy consumption by nodes in a wireless infrastructure network depends on the transmissions of other nodes in the network. Considering this inter-dependence is necessary to achieve efficient provision of energy in wireless networks. This paper studies the issue of energy provision for wireless relay nodes in Wireless Multihop Infrastructures (WMI) assuming constraints on the total energy provision. We introduce a scheme of Energy Provision Matching (Matching-EP) for WMI which optimizes energy provision based on matching of energy provision with estimates of differentiated position-dependent energy consumption by wireless nodes distributed in the network. The evaluation results show that Matching-EP with 4%–34% improvement in energy matching degree enables 10%–40% improvement of the network lifetime, and 5%–40% improvement of packet delivery compared with conventional WMI networks. Full article

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20 pages, 4316 KiB

Open AccessArticle

Optimal Maintenance Management of Offshore Wind Farms

by Alberto Pliego Marugán¹, Fausto Pedro García Márquez^1,*

and Jesús María Pinar Pérez²

¹ Ingenium Research Group, Universidad Castilla-La Mancha, 13071 Ciudad Real, Spain

² CUNEF-Ingenium, Colegio Universitario de Estudios Financieros, 28040 Madrid, Spain

Energies 2016, 9(1), 46; https://doi.org/10.3390/en9010046 - 15 Jan 2016

Cited by 89 | Viewed by 10074

Abstract

Nowadays offshore wind energy is the renewable energy source with the highest growth. Offshore wind farms are composed of large and complex wind turbines, requiring a high level of reliability, availability, maintainability and safety (RAMS). Firms are employing robust remote condition monitoring systems [...] Read more.

Nowadays offshore wind energy is the renewable energy source with the highest growth. Offshore wind farms are composed of large and complex wind turbines, requiring a high level of reliability, availability, maintainability and safety (RAMS). Firms are employing robust remote condition monitoring systems in order to improve RAMS, considering the difficulty to access the wind farm. The main objective of this research work is to optimise the maintenance management of wind farms through the fault probability of each wind turbine. The probability has been calculated by Fault Tree Analysis (FTA) employing the Binary Decision Diagram (BDD) in order to reduce the computational cost. The fault tree presented in this paper has been designed and validated based on qualitative data from the literature and expert from important European collaborative research projects. The basic events of the fault tree have been prioritized employing the criticality method in order to use resources efficiently. Exogenous variables, e.g., weather conditions, have been also considered in this research work. The results provided by the dynamic probability of failure and the importance measures have been employed to develop a scheduled maintenance that contributes to improve the decision making and, consequently, to reduce the maintenance costs. Full article

(This article belongs to the Special Issue Wind Turbine 2015)

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18 pages, 3421 KiB

Open AccessArticle

Two-Dimensional Simulation of Mass Transfer in Unitized Regenerative Fuel Cells under Operation Mode Switching

by Lulu Wang¹, Hang Guo^1,2,*, Fang Ye¹ and Chongfang Ma¹

¹ Key Laboratory of Enhanced Heat Transfer and Energy Conservation, Ministry of Education and Beijing Key Laboratory of Heat Transfer and Energy Conversion, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, China

² Collaborative Innovation Center of Electric Vehicles in Beijing, Beijing 100081, China

Energies 2016, 9(1), 47; https://doi.org/10.3390/en9010047 - 15 Jan 2016

Cited by 28 | Viewed by 7024

Abstract

A two-dimensional, single-phase, isothermal, multicomponent, transient model is built to investigate the transport phenomena in unitized regenerative fuel cells (URFCs) under the condition of switching from the fuel cell (FC) mode to the water electrolysis (WE) mode. The model is coupled with an [...] Read more.

A two-dimensional, single-phase, isothermal, multicomponent, transient model is built to investigate the transport phenomena in unitized regenerative fuel cells (URFCs) under the condition of switching from the fuel cell (FC) mode to the water electrolysis (WE) mode. The model is coupled with an electrochemical reaction. The proton exchange membrane (PEM) is selected as the solid electrolyte of the URFC. The work is motivated by the need to elucidate the complex mass transfer and electrochemical process under operation mode switching in order to improve the performance of PEM URFC. A set of governing equations, including conservation of mass, momentum, species, and charge, are considered. These equations are solved by the finite element method. The simulation results indicate the distributions of hydrogen, oxygen, water mass fraction, and electrolyte potential response to the transient phenomena via saltation under operation mode switching. The hydrogen mass fraction gradients are smaller than the oxygen mass fraction gradients. The average mass fractions of the reactants (oxygen and hydrogen) and product (water) exhibit evident differences between each layer in the steady state of the FC mode. By contrast, the average mass fractions of the reactant (water) and products (oxygen and hydrogen) exhibit only slight differences between each layer in the steady state of the WE mode. Under either the FC mode or the WE mode, the duration of the transient state is only approximately 0.2 s. Full article

(This article belongs to the Special Issue Methanol and Alcohol Fuel Cells)

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15 pages, 2445 KiB

Open AccessArticle

Optimal Bidding Strategy for Renewable Microgrid with Active Network Management

by Seung Wan Kim¹, Jip Kim²

, Young Gyu Jin^3,* and Yong Tae Yoon¹

¹ Department of Electrical and Computer Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, Korea

² Power System Research Division, Korea Electrical Engineering & Science Research Institute, Bldg. 130, 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, Korea

³ Center for Advanced Power & Environmental Technology (APET), The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

Energies 2016, 9(1), 48; https://doi.org/10.3390/en9010048 - 15 Jan 2016

Cited by 16 | Viewed by 7607

Abstract

Active Network Management (ANM) enables a microgrid to optimally dispatch the active/reactive power of its Renewable Distributed Generation (RDG) and Battery Energy Storage System (BESS) units in real time. Thus, a microgrid with high penetration of RDGs can handle their uncertainties and variabilities [...] Read more.

Active Network Management (ANM) enables a microgrid to optimally dispatch the active/reactive power of its Renewable Distributed Generation (RDG) and Battery Energy Storage System (BESS) units in real time. Thus, a microgrid with high penetration of RDGs can handle their uncertainties and variabilities to achieve the stable operation using ANM. However, the actual power flow in the line connecting the main grid and microgrid may deviate significantly from the day-ahead bids if the bids are determined without consideration of the real-time adjustment through ANM, which will lead to a substantial imbalance cost. Therefore, this study proposes a formulation for obtaining an optimal bidding which reflects the change of power flow in the connecting line by real-time adjustment using ANM. The proposed formulation maximizes the expected profit of the microgrid considering various network and physical constraints. The effectiveness of the proposed bidding strategy is verified through the simulations with a 33-bus test microgrid. The simulation results show that the proposed bidding strategy improves the expected operating profit by reducing the imbalance cost to a greater degree compared to the basic bidding strategy without consideration of ANM. Full article

(This article belongs to the Special Issue Decentralized Management of Energy Streams in Smart Grids)

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11 pages, 4430 KiB

Open AccessArticle

Power Generation from Concentration Gradient by Reverse Electrodialysis in Dense Silica Membranes for Microfluidic and Nanofluidic Systems

by Sang Woo Lee, Hyun Jung Kim and Dong-Kwon Kim^*

Department of Mechanical Engineering, Ajou University, Suwon 443-749, Korea

Energies 2016, 9(1), 49; https://doi.org/10.3390/en9010049 - 15 Jan 2016

Cited by 41 | Viewed by 9836

Abstract

In this study, we investigate power generation by reverse electrodialysis in a dense silica membrane that is between two NaCl solutions with various combinations of concentrations. Each silica membrane is fabricated by depositing a silica layer on a porous alumina substrate via chemical [...] Read more.

In this study, we investigate power generation by reverse electrodialysis in a dense silica membrane that is between two NaCl solutions with various combinations of concentrations. Each silica membrane is fabricated by depositing a silica layer on a porous alumina substrate via chemical vapor deposition. The measured potential-current (V-I) characteristics of the silica membrane are used to obtain the transference number, diffusion potential, and electrical resistance. We develop empirical correlations for the transference number and the area-specific resistance, and present the results of power generation by reverse electrodialysis using the fabricated silica membranes. The highest measured power density is 0.98 mW/m². In addition, we develop a contour map of the power density as a function of NaCl concentrations on the basis of the empirical correlations. The contour map shows that a power output density of 1.2 mW/m² is achievable with the use of silica membranes and is sufficient to drive nanofluidic and microfluidic systems. The dense silica membrane has the potential for use in micro power generators in nanofluidic and microfluidic systems. Full article

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

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23 pages, 8426 KiB

Open AccessArticle

An Algorithm to Translate Building Topology in Building Information Modeling into Object-Oriented Physical Modeling-Based Building Energy Modeling

by WoonSeong Jeong

and JeongWook Son^*

Department of Architectural Engineering, Ewha Womans University, Seoul 120-750, Korea

Energies 2016, 9(1), 50; https://doi.org/10.3390/en9010050 - 18 Jan 2016

Cited by 22 | Viewed by 8803

Abstract

This paper presents an algorithm to translate building topology in an object-oriented architectural building model (Building Information Modeling, BIM) into an object-oriented physical-based energy performance simulation by using an object-oriented programming approach. Our algorithm demonstrates efficient mapping of building components in a BIM [...] Read more.

This paper presents an algorithm to translate building topology in an object-oriented architectural building model (Building Information Modeling, BIM) into an object-oriented physical-based energy performance simulation by using an object-oriented programming approach. Our algorithm demonstrates efficient mapping of building components in a BIM model into space boundary conditions in an object-oriented physical modeling (OOPM)-based building energy model, and the translation of building topology into space boundary conditions to create an OOPM model. The implemented command, TranslatingBuildingTopology, using an object-oriented programming approach, enables graphical representation of the building topology of BIM models and the automatic generation of space boundaries information for OOPM models. The algorithm and its implementation allow coherent object-mapping from BIM to OOPM and facilitate the definition of space boundaries information during model translation for building thermal simulation. In order to demonstrate our algorithm and its implementation, we conducted experiments with three test cases using the BESTEST 600 model. Our experiments show that our algorithm and its implementation enable building topology information to be automatically translated into space boundary information, and facilitates the reuse of BIM data into building thermal simulations without additional export or import processes. Full article

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21 pages, 1765 KiB

Open AccessArticle

A Lithium-Ion Battery Simulator Based on a Diffusion and Switching Overpotential Hybrid Model for Dynamic Discharging Behavior and Runtime Predictions

by Lan-Rong Dung^1,*

, Hsiang-Fu Yuan^2,*

, Jieh-Hwang Yen², Chien-Hua She³ and Ming-Han Lee¹

¹ Department of Electrical and Computer Engineering, National Chiao-Tung University, 1001 Ta-Hsueh Rd., Hsinchu 30010, Taiwan

² Institute of Electrical Control Engineering, National Chiao-Tung University, 1001 Ta-Hsueh Rd., Hsinchu 30010, Taiwan

³ MiTAC International Corp., No. 1, R & D 2nd Road, Hsinchu Science-Based Industrial Park, Hsinchu 30010, Taiwan

Energies 2016, 9(1), 51; https://doi.org/10.3390/en9010051 - 18 Jan 2016

Cited by 8 | Viewed by 9683

Abstract

A new battery simulator based on a hybrid model is proposed in this paper for dynamic discharging behavior and runtime predictions in existing electronic simulation environments, e.g., PSIM, so it can help power circuit designers to develop and optimize their battery-powered electronic systems. [...] Read more.

A new battery simulator based on a hybrid model is proposed in this paper for dynamic discharging behavior and runtime predictions in existing electronic simulation environments, e.g., PSIM, so it can help power circuit designers to develop and optimize their battery-powered electronic systems. The hybrid battery model combines a diffusion model and a switching overpotential model, which automatically switches overpotential resistance mode or overpotential voltage mode to accurately describe the voltage difference between battery electro-motive force (EMF) and terminal voltage. Therefore, this simulator can simply run in an electronic simulation software with less computational efforts and estimate battery performances by further considering nonlinear capacity effects. A linear extrapolation technique is adopted for extracting model parameters from constant current discharging tests, so the EMF hysteresis problem is avoided. For model validation, experiments and simulations in MATLAB and PSIM environments are conducted with six different profiles, including constant loads, an interrupted load, increasing and decreasing loads and a varying load. The results confirm the usefulness and accuracy of the proposed simulator. The behavior and runtime prediction errors can be as low as 3.1% and 1.2%, respectively. Full article

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27 pages, 2799 KiB

Open AccessArticle

Vibration Durability Testing of Nickel Manganese Cobalt Oxide (NMC) Lithium-Ion 18,650 Battery Cells

by James Michael Hooper^1,*

, James Marco¹, Gael Henri Chouchelamane² and Christopher Lyness²

¹ Warwick Manufacturing Group (WMG), University of Warwick, Coventry CV4 7AL, UK

² Jaguar Land Rover, Banbury Road, Warwick, Coventry CV35 0XJ, UK

Energies 2016, 9(1), 52; https://doi.org/10.3390/en9010052 - 19 Jan 2016

Cited by 54 | Viewed by 15757

Abstract

Electric vehicle (EV) manufacturers are employing cylindrical format cells in the construction of the vehicles’ battery systems. There is evidence to suggest that both the academic and industrial communities have evaluated cell degradation due to vibration and other forms of mechanical loading. The [...] Read more.

Electric vehicle (EV) manufacturers are employing cylindrical format cells in the construction of the vehicles’ battery systems. There is evidence to suggest that both the academic and industrial communities have evaluated cell degradation due to vibration and other forms of mechanical loading. The primary motivation is often the need to satisfy the minimum requirements for safety certification. However, there is limited research that quantifies the durability of the battery and in particular, how the cells will be affected by vibration that is representative of a typical automotive service life (e.g., 100,000 miles). This paper presents a study to determine the durability of commercially available 18,650 cells and quantifies both the electrical and mechanical vibration-induced degradation through measuring changes in cell capacity, impedance and natural frequency. The impact of the cell state of charge (SOC) and in-pack orientation is also evaluated. Experimental results are presented which clearly show that the performance of 18,650 cells can be affected by vibration profiles which are representative of a typical vehicle life. Consequently, it is recommended that EV manufacturers undertake vibration testing, as part of their technology selection and development activities to enhance the quality of EVs and to minimize the risk of in-service warranty claims. Full article

(This article belongs to the Collection Electric and Hybrid Vehicles Collection)

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16 pages, 2659 KiB

Open AccessArticle

A Carbon Price Forecasting Model Based on Variational Mode Decomposition and Spiking Neural Networks

by Guoqiang Sun^*

, Tong Chen^*

, Zhinong Wei, Yonghui Sun, Haixiang Zang

and Sheng Chen

College of Energy and Electrical Engineering, Hohai University, Nanjing 211100, China

Energies 2016, 9(1), 54; https://doi.org/10.3390/en9010054 - 19 Jan 2016

Cited by 117 | Viewed by 9117

Abstract

Accurate forecasting of carbon price is important and fundamental for anticipating the changing trends of the energy market, and, thus, to provide a valid reference for establishing power industry policy. However, carbon price forecasting is complicated owing to the nonlinear and non-stationary characteristics [...] Read more.

Accurate forecasting of carbon price is important and fundamental for anticipating the changing trends of the energy market, and, thus, to provide a valid reference for establishing power industry policy. However, carbon price forecasting is complicated owing to the nonlinear and non-stationary characteristics of carbon prices. In this paper, a combined forecasting model based on variational mode decomposition (VMD) and spiking neural networks (SNNs) is proposed. An original carbon price series is firstly decomposed into a series of relatively stable components through VMD to simplify the interference and coupling across characteristic information of different scales in the data. Then, a SNN forecasting model is built for each component, and the partial autocorrelation function (PACF) is used to determine the input variables for each SNN model. The final forecasting result for the original carbon price can be obtained by aggregating the forecasting results of all the components. Actual InterContinental Exchange (ICE) carbon price data is used for simulation, and comprehensive evaluation criteria are proposed for quantitative error evaluation. Simulation results and analysis suggest that the proposed VMD-SNN forecasting model outperforms conventional models in terms of forecasting accuracy and reliability. Full article

(This article belongs to the Special Issue Kernel Methods and Hybrid Evolutionary Algorithms in Energy Forecasting)

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12 pages, 1522 KiB

Open AccessArticle

A Hierarchical Approach Using Machine Learning Methods in Solar Photovoltaic Energy Production Forecasting

by Zhaoxuan Li^1,†, SM Mahbobur Rahman^1,†, Rolando Vega^2,* and Bing Dong¹

¹ Mechanical Engineering, University of Texas at San Antonio, San Antonio, TX 78249, USA

² Texas Sustainable Energy Research Institute, San Antonio, TX 78249, USA

^† These authors contributed equally to this work.

Energies 2016, 9(1), 55; https://doi.org/10.3390/en9010055 - 19 Jan 2016

Cited by 119 | Viewed by 13735

Abstract

We evaluate and compare two common methods, artificial neural networks (ANN) and support vector regression (SVR), for predicting energy productions from a solar photovoltaic (PV) system in Florida 15 min, 1 h and 24 h ahead of time. A hierarchical approach is proposed [...] Read more.

We evaluate and compare two common methods, artificial neural networks (ANN) and support vector regression (SVR), for predicting energy productions from a solar photovoltaic (PV) system in Florida 15 min, 1 h and 24 h ahead of time. A hierarchical approach is proposed based on the machine learning algorithms tested. The production data used in this work corresponds to 15 min averaged power measurements collected from 2014. The accuracy of the model is determined using computing error statistics such as mean bias error (MBE), mean absolute error (MAE), root mean square error (RMSE), relative MBE (rMBE), mean percentage error (MPE) and relative RMSE (rRMSE). This work provides findings on how forecasts from individual inverters will improve the total solar power generation forecast of the PV system. Full article

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

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15 pages, 3043 KiB

Open AccessArticle

Capacitor Voltage Ripple Suppression for Z-Source Wind Energy Conversion System

by Shoudao Huang, Yang Zhang^* and Zhikang Shuai

College of Electrical and Information Engineering, Hunan University, Changsha 410082, China

Energies 2016, 9(1), 56; https://doi.org/10.3390/en9010056 - 19 Jan 2016

Cited by 3 | Viewed by 5516

Abstract

This paper proposes an improved pulse-width modulation (PWM) strategy to reduce the capacitor voltage ripple in Z-source wind energy conversion system. In order to make sure that Z-source capacitor voltage has symmetrical maximum and minimum amplitudes in each active state, the shoot-through time [...] Read more.

This paper proposes an improved pulse-width modulation (PWM) strategy to reduce the capacitor voltage ripple in Z-source wind energy conversion system. In order to make sure that Z-source capacitor voltage has symmetrical maximum and minimum amplitudes in each active state, the shoot-through time is divided into six unequal parts. According to the active state and zero state, the shoot-through time is rearranged to match the charging time and discharging time of the Z-source capacitors. Theoretically, it is indicated that the voltage ripple of the Z-source capacitors can be reduced effectively by means of the proposed PWM scheme. Finally, simulation and experimental results are given to verify the performance of the presented method. Full article

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

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24 pages, 2572 KiB

Open AccessEditor’s ChoiceArticle

A Comparison of Energy Consumption Prediction Models Based on Neural Networks of a Bioclimatic Building

by Hamid R. Khosravani^1,2, María Del Mar Castilla^3,*

, Manuel Berenguel³

, Antonio E. Ruano^1,2

and Pedro M. Ferreira⁴

¹ Faculty of Science and Technology, University of Algarve, Campus Gambelas, Faro, Portugal

² Institute of Mechanical Engineering (IDMEC), Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal

³ Department of Computer Science, Automatic Control, Robotics and Mechatronics Research Group, University of Almería, Agrifood Campus of International Excellence (ceiA3), CIESOL, Joint Center University of Almería-CIEMAT, Almería, Spain

⁴ LaSIGE, Faculdade de Ciências, Universidade de Lisboa, Portugal

Energies 2016, 9(1), 57; https://doi.org/10.3390/en9010057 - 20 Jan 2016

Cited by 98 | Viewed by 10551

Abstract

Energy consumption has been increasing steadily due to globalization and industrialization. Studies have shown that buildings are responsible for the biggest proportion of energy consumption; for example in European Union countries, energy consumption in buildings represents around 40% of the total energy consumption. [...] Read more.

Energy consumption has been increasing steadily due to globalization and industrialization. Studies have shown that buildings are responsible for the biggest proportion of energy consumption; for example in European Union countries, energy consumption in buildings represents around 40% of the total energy consumption. In order to control energy consumption in buildings, different policies have been proposed, from utilizing bioclimatic architectures to the use of predictive models within control approaches. There are mainly three groups of predictive models including engineering, statistical and artificial intelligence models. Nowadays, artificial intelligence models such as neural networks and support vector machines have also been proposed because of their high potential capabilities of performing accurate nonlinear mappings between inputs and outputs in real environments which are not free of noise. The main objective of this paper is to compare a neural network model which was designed utilizing statistical and analytical methods, with a group of neural network models designed benefiting from a multi objective genetic algorithm. Moreover, the neural network models were compared to a naïve autoregressive baseline model. The models are intended to predict electric power demand at the Solar Energy Research Center (Centro de Investigación en Energía SOLar or CIESOL in Spanish) bioclimatic building located at the University of Almeria, Spain. Experimental results show that the models obtained from the multi objective genetic algorithm (MOGA) perform comparably to the model obtained through a statistical and analytical approach, but they use only 0.8% of data samples and have lower model complexity. Full article

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19 pages, 425 KiB

Open AccessArticle

Diesel-Minimal Combustion Control of a Natural Gas-Diesel Engine

by Florian Zurbriggen^*, Richard Hutter and Christopher Onder

Institute for Dynamic Systems and Control, ETH Zurich, Sonneggstrasse 3, Zurich 8092, Switzerland

Energies 2016, 9(1), 58; https://doi.org/10.3390/en9010058 - 19 Jan 2016

Cited by 22 | Viewed by 6618

Abstract

This paper investigates the combustion phasing control of natural gas-diesel engines. In this study, the combustion phasing is influenced by manipulating the start and the duration of the diesel injection. Instead of using both degrees of freedom to control the center of combustion [...] Read more.

This paper investigates the combustion phasing control of natural gas-diesel engines. In this study, the combustion phasing is influenced by manipulating the start and the duration of the diesel injection. Instead of using both degrees of freedom to control the center of combustion only, we propose a method that simultaneously controls the combustion phasing and minimizes the amount of diesel used. Minimizing the amount of diesel while keeping the center of combustion at a constant value is formulated as an optimization problem with an equality constraint. A combination of feedback control and extremum seeking is used to solve this optimization problem online. The necessity to separate the different time scales is discussed and a structure is proposed that facilitates this separation for this specific example. The proposed method is validated by experiments on a test bench. Full article

(This article belongs to the Special Issue Energy Efficient Actuators and Systems)

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19 pages, 3958 KiB

Open AccessArticle

Low Voltage Ride-Through Capability Solutions for Permanent Magnet Synchronous Wind Generators

by Victor F. Mendes^1,*, Frederico F. Matos^2,3, Silas Y. Liu², Allan F. Cupertino^2,4, Heverton A. Pereira^2,5 and Clodualdo V. De Sousa³

¹ Department of Electrical Engineering, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais 31270-010, Brazil

² Graduate Program in Electrical Engineering, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais 31270-901, Brazil

³ Department of Electrical Engineering, Federal University of Itajubá, Itabira, Minas Gerais 35903-087, Brazil

⁴ Department of Materials Engineering, Federal Center for Technological Education of Minas Gerais, Belo Horizonte, Minas Gerais 30421-169, Brazil

⁵ Department of Electrical Engineering, Federal University of Viçosa, Viçosa, Minas Gerais 36570-900, Brazil

Energies 2016, 9(1), 59; https://doi.org/10.3390/en9010059 - 20 Jan 2016

Cited by 30 | Viewed by 7619

Abstract

Due to the increasing number of wind power plants, several countries have modified their grid codes to include specific requirements for the connection of this technology to the power system. One of the requirements is the ride-through fault capability (RTFC), i.e., the [...] Read more.

Due to the increasing number of wind power plants, several countries have modified their grid codes to include specific requirements for the connection of this technology to the power system. One of the requirements is the ride-through fault capability (RTFC), i.e., the system capability to sustain operation during voltage sags. In this sense, the present paper intends to investigate the behavior of a full-converter wind generator with a permanent magnet synchronous machine during symmetrical and asymmetrical voltage sags. Two solutions to improve the low voltage ride-through capability (LVRT) of this technology are analyzed: discharging resistors (brake chopper) and resonant controllers (RCs). The design and limitations of these solutions and the others proposed in the literature are discussed. Experimental results in a 34 kW test bench, which represents a scaled prototype of a real 2 MW wind conversion system, are presented. Full article

(This article belongs to the Special Issue Wind Turbine 2015)

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Graphical abstract

18 pages, 4329 KiB

Open AccessArticle

Optimal Siting and Sizing of Distributed Generators in Distribution Systems Considering Cost of Operation Risk

by Qingwu Gong

, Jiazhi Lei^* and Jun Ye

School of Electrical Engineering, Wuhan University, Wuhan 430072, China

Energies 2016, 9(1), 61; https://doi.org/10.3390/en9010061 - 20 Jan 2016

Cited by 23 | Viewed by 6660

Abstract

With the penetration of distributed generators (DGs), operation planning studies are essential in maintaining and operating a reliable and secure power system. Appropriate siting and sizing of DGs could lead to many positive effects forthe distribution system concerned, such as the reduced total [...] Read more.

With the penetration of distributed generators (DGs), operation planning studies are essential in maintaining and operating a reliable and secure power system. Appropriate siting and sizing of DGs could lead to many positive effects forthe distribution system concerned, such as the reduced total costs associated with DGs, reduced network losses, and improved voltage profiles and enhanced power-supply reliability. In this paper, expected load interruption cost is used as the assessment of operation risk in distribution systems, which is assessed by the point estimate method (PEM). In light with the costs of system operation planning, a novel mathematical model of chance constrained programming (CCP) framework for optimal siting and sizing of DGs in distribution systems is proposed considering the uncertainties of DGs. And then, a hybrid genetic algorithm (HGA), which combines the GA with traditional optimization methods, is employed to solve the proposed CCP model. Finally,the feasibility and effectiveness of the proposed CCP model are verified by the modified IEEE 30-bus system, and the test results have demonstrated that this proposed CCP model is more reasonable to determine the siting and sizing of DGs compared with traditional CCP model. Full article

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

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Review

Jump to: Editorial, Research, Other

30 pages, 12045 KiB

Open AccessReview

Building Integrated Photovoltaics: A Concise Description of the Current State of the Art and Possible Research Pathways

by Bjørn Petter Jelle^1,2

¹ SINTEF Building and Infrastructure, Department of Materials and Structures, Trondheim NO-7465, Norway

² Norwegian University of Science and Technology (NTNU), Department of Civil and Transport Engineering, Trondheim NO-7491, Norway

Energies 2016, 9(1), 21; https://doi.org/10.3390/en9010021 - 31 Dec 2015

Cited by 111 | Viewed by 15930

Abstract

Building integrated photovoltaics (BIPV) offer an aesthetical, economical and technical solution to integrate solar cells harvesting solar radiation to produce electricity within the climate envelopes of buildings. Photovoltaic (PV) cells may be mounted above or onto the existing or traditional roofing or wall [...] Read more.

Building integrated photovoltaics (BIPV) offer an aesthetical, economical and technical solution to integrate solar cells harvesting solar radiation to produce electricity within the climate envelopes of buildings. Photovoltaic (PV) cells may be mounted above or onto the existing or traditional roofing or wall systems. However, BIPV systems replace the outer building envelope skin, i.e., the climate screen, hence serving simultanously as both a climate screen and a power source generating electricity. Thus, BIPV may provide savings in materials and labor, in addition to reducing the electricity costs. Hence, for the BIPV products, in addition to specific requirements put on the solar cell technology, it is of major importance to have satisfactory or strict requirements of rain tightness and durability, where building physical issues like e.g., heat and moisture transport in the building envelope also have to be considered and accounted for. This work, from both a technological and scientific point of view, summarizes briefly the current state-of-the-art of BIPV, including both BIPV foil, tiles, modules and solar cell glazing products, and addresses possible research pathways for BIPV in the years to come. Full article

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

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16 pages, 5269 KiB

Open AccessReview

Review of the Thermo-Physical Properties and Performance Characteristics of a Refrigeration System Using Refrigerant-Based Nanofluids

by Mahesh Suresh Patil¹

, Sung Chul Kim², Jae-Hyeong Seo³ and Moo-Yeon Lee^1,*

¹ Department of Mechanical Engineering, Dong-A University, Hadan 840, Saha-gu, Busan 604-714, Korea

² School of Mechanical Engineering, Yeungnam University, 280 Daehak-Ro, Gyeongsan, Gyeongbuk 712-749, Korea

³ R & D Division, NTF Tech Co., Hadan 840, Saha-gu, Busan 604-714, Korea

Energies 2016, 9(1), 22; https://doi.org/10.3390/en9010022 - 31 Dec 2015

Cited by 47 | Viewed by 7767

Abstract

Nanofluids are considered a promising choice for several heat transfer applications. With the increasing awareness for energy saving and efficiency improvement in various thermal systems, including refrigeration systems, there is a growing interest in the refrigerant-based nanofluids owing to their superior thermo-physical properties. [...] Read more.

Nanofluids are considered a promising choice for several heat transfer applications. With the increasing awareness for energy saving and efficiency improvement in various thermal systems, including refrigeration systems, there is a growing interest in the refrigerant-based nanofluids owing to their superior thermo-physical properties. Nanorefrigerants are a class of nanofluid, which consist of suspended nanoparticles in a base refrigerant. In this paper, it is intended to include many articles on refrigeration systems that use nanorefrigerants, published in the period from 2005 to 2015. Although this is an extensive review, it could not include all the papers, and only some major research works were selected. It is believed that the dependency of thermal conductivity and other properties on temperature will make the thermal systems more efficient while operating at a high temperature. The literature reviews associated with the performance characteristics of nanorefrigerants in refrigeration systems for the last 10 years have been compiled and presented in this paper. Furthermore, recent studies related to thermo-physical properties of nanorefrigerants and nanolubricants have also been summarized and reviewed in this paper. Full article

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23 pages, 288 KiB

Open AccessReview

On the Heat Flux Vector and Thermal Conductivity of Slags: A Brief Review

by Mehrdad Massoudi^1,*, Jeongho Kim² and Ping Wang¹

¹ U.S. Department of Energy (DOE), National Energy Technology Laboratory (NETL), 626 Cochrans Mill Road, P.O. Box 10940, Pittsburgh, PA 15236, USA

² Department of Mechanical Engineering, Kyung Hee University, Yong-in, Kyunggi-do 446-701, Korea

Energies 2016, 9(1), 27; https://doi.org/10.3390/en9010027 - 6 Jan 2016

Cited by 6 | Viewed by 4928

Abstract

The viscosity and the thermal conductivity of slag are among two of the most important material properties that need to be studied. In this paper we review the existing theoretical and experimental correlations for the thermal conductivity of slag. However, since, in general, [...] Read more.

The viscosity and the thermal conductivity of slag are among two of the most important material properties that need to be studied. In this paper we review the existing theoretical and experimental correlations for the thermal conductivity of slag. However, since, in general, slag behaves as a non-linear fluid, it is the heat flux vector which must be studied. Both explicit and implicit approaches are discussed and suggestions about the form of the heat flux vector and the thermal conductivity and their dependence on shear rate, porosity, deformation, etc. are provided. The discussion of the constitutive modeling of the heat flux vector for slag is from a theoretical perspective. Full article

(This article belongs to the Special Issue Recent Advances in Coal Combustion and Gasification)

35 pages, 10893 KiB

Open AccessReview

Progress of Space Charge Research on Oil-Paper Insulation Using Pulsed Electroacoustic Techniques

by Chao Tang^1,2,*

, Bo Huang², Miao Hao², Zhiqiang Xu², Jian Hao³

and George Chen²

¹ College of Engineering and Technology, Southwest University, Beibei, Chongqing 400715, China

² School of Electronics and Computer Science, University of Southampton, Highfield Campus, Southampton SO17 1BJ, UK

³ State Grid Chongqing Electric Power Corperation Chongqing Electric Power Research Institute, Chongqing 401123, China

Energies 2016, 9(1), 53; https://doi.org/10.3390/en9010053 - 18 Jan 2016

Cited by 34 | Viewed by 8321

Abstract

This paper focuses on the space charge behavior in oil-paper insulation systems used in power transformers. It begins with the importance of understanding the space charge behavior in oil-paper insulation systems, followed by the introduction of the pulsed electrostatic technique (PEA). After that, [...] Read more.

This paper focuses on the space charge behavior in oil-paper insulation systems used in power transformers. It begins with the importance of understanding the space charge behavior in oil-paper insulation systems, followed by the introduction of the pulsed electrostatic technique (PEA). After that, the research progress on the space charge behavior of oil-paper insulation during the recent twenty years is critically reviewed. Some important aspects such as the environmental conditions and the acoustic wave recovery need to be addressed to acquire more accurate space charge measurement results. Some breakthroughs on the space charge behavior of oil-paper insulation materials by the research team at the University of Southampton are presented. Finally, future work on space charge measurement of oil-paper insulation materials is proposed. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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Other

Jump to: Editorial, Research, Review

1 pages, 140 KiB

Open AccessCorrection

Correction: Jiménez, F., et al. System for Road Vehicle Energy Optimization Using Real Time Road and Traffic Information. Energies 2014, 7, 3576-3598

by Felipe Jiménez^*

, Wilmar Cabrera-Montiel and Santiago Tapia-Fernández

University Institute for Automobile Research (INSIA), Technical University of Madrid (UPM), Madrid 28031, Spain

Energies 2016, 9(1), 60; https://doi.org/10.3390/en9010060 - 21 Jan 2016

Cited by 1 | Viewed by 3719

Abstract

In the original version of the article [1], insufficient acknowledgement was given for the original Dynamic Programming optimization tool. We apologize for this error. To correct this fact, Santiago Tapia-Fernández has been added as an author, and the acknowledgements and authors contributions have [...] Read more.

In the original version of the article [1], insufficient acknowledgement was given for the original Dynamic Programming optimization tool. We apologize for this error. To correct this fact, Santiago Tapia-Fernández has been added as an author, and the acknowledgements and authors contributions have been corrected. Full article

1 pages, 142 KiB

Open AccessCorrection

Correction: Ding, X.; Liu, G.; Du, M.; Guo, H.; Qiao, H. and Gerada, C. Development of an Axial Flux MEMS BLDC Micromotor with Increased Efficiency and Power Density. Energies 2015, 8, 6608–6626

by Xiaofeng Ding¹, Guanliang Liu^1,†, Min Du^1,†, Hong Guo¹, Hao Qian^1,* and Christopher Gerada²

¹ School of Automation Science and Electrical Engineering, Beihang University, Beijing 100191, China

² Department of Electrical and Electronic Engineering, the University of Nottingham, Nottingham NG7 2RD, UK

^† These authors contributed equally to this work.

Energies 2016, 9(1), 62; https://doi.org/10.3390/en9010062 - 21 Jan 2016

Viewed by 4141

Abstract

We wish to make the following change to the published paper [1]. The name of the corresponding author should be “Hao Qian” instead of “Hao Qiao”. [...] Full article

2 pages, 340 KiB

Open AccessErratum

Erratum: Ellegård, K. and Palm, J. Who Is Behaving? Consequences for Energy Policy of Concept Confusion. Energies 2015, 8, 7618–7637

by Energies Editorial Office

MDPI AG, Klybeckstrasse 64, CH-4057 Basel, Switzerland

Energies 2016, 9(1), 63; https://doi.org/10.3390/en9010063 - 21 Jan 2016

Viewed by 3818

Abstract

We wish to make the following correction to the published paper [1]. [...] Full article

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

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