Energies

263 KiB

Open AccessArticle

Effects of Biodiesel Blend on Marine Fuel Characteristics for Marine Vessels

by Cherng-Yuan Lin

Energies 2013, 6(9), 4945-4955; https://doi.org/10.3390/en6094945 - 24 Sep 2013

Cited by 25 | Viewed by 7049

Biodiesel produced from vegetable oils, animal fats and algae oil is a renewable, environmentally friendly and clean alternative fuel that reduces pollutants and greenhouse gas emissions in marine applications. This study investigates the influence of biodiesel blend on the characteristics of residual and [...] Read more.

Biodiesel produced from vegetable oils, animal fats and algae oil is a renewable, environmentally friendly and clean alternative fuel that reduces pollutants and greenhouse gas emissions in marine applications. This study investigates the influence of biodiesel blend on the characteristics of residual and distillate marine fuels. Adequate correlation equations are applied to calculate the fuel properties of the blended marine fuels with biodiesel. Residual marine fuel RMA has inferior fuel characteristics compared with distillate marine fuel DMA and biodiesel. The flash point of marine fuel RMA could be increased by 20% if blended with 20 vol% biodiesel. The sulfur content of residual marine fuel could meet the requirement of the 2008 MARPOL Annex VI Amendment by blending it with 23.0 vol% biodiesel. In addition, the kinematic viscosity of residual marine fuel could be reduced by 12.9% and the carbon residue by 23.6% if 20 vol% and 25 vol% biodiesel are used, respectively. Residual marine fuel blended with 20 vol% biodiesel decreases its lower heating value by 1.9%. Moreover, the fuel properties of residual marine fuel are found to improve more significantly with biodiesel blending than those of distillate marine fuel. Full article

(This article belongs to the Special Issue Biomass and Biofuels 2013)

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677 KiB

Open AccessArticle

Design and Implementation of a High Quality Power Supply Scheme for Distributed Generation in a Micro-Grid

by Mingchao Xia and Xiaoliang Li

Energies 2013, 6(9), 4924-4944; https://doi.org/10.3390/en6094924 - 23 Sep 2013

Cited by 18 | Viewed by 6938

Abstract

A low carbon, high efficiency and high quality power supply scheme for Distributed Generation (DG) in a micro-grid is presented. A three-phase, four-leg DG grid-interfacing converter based on the improved structure of a Unified Power Quality Conditioner (UPQC, including a series converter and [...] Read more.

A low carbon, high efficiency and high quality power supply scheme for Distributed Generation (DG) in a micro-grid is presented. A three-phase, four-leg DG grid-interfacing converter based on the improved structure of a Unified Power Quality Conditioner (UPQC, including a series converter and a parallel converter) is adopted, and improved indirect and direct control strategies are proposed. It can be observed that these strategies effectively compensate for voltage sags, voltage swells and voltage distortion, as well as voltage power quality problems resulting from the nonlinear and unbalanced loads in a micro-grid. While solving the coupling interference from series–parallel, the grid-interfacing converter can achieve proper load power sharing in a micro-grid. In particular, an improved minimum-energy compensation method is proposed that can overcome the conventional compensation algorithm defects, ensure the load voltage’s phase angle stability, improve the voltage compensating ability and range, reduce the capacity and cost of converters, and reduce the shock of micro-grid switching between grid-connected mode and islanded mode. Moreover, the advantages/disadvantages and application situation of the two improved control strategies are analyzed. Finally, the performance of the proposed control strategies has been verified through a MATLAB/Simulink simulation under various operating conditions. Full article

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

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1082 KiB

Open AccessArticle

Life-Cycle Energy Use and Greenhouse Gas Emissions Analysis for Bio-Liquid Jet Fuel from Open Pond-Based Micro-Algae under China Conditions

by Xunmin Ou, Xiaoyu Yan, Xu Zhang and Xiliang Zhang

Energies 2013, 6(9), 4897-4923; https://doi.org/10.3390/en6094897 - 23 Sep 2013

Cited by 26 | Viewed by 10067

Abstract

A life-cycle analysis (LCA) of greenhouse gas (GHG) emissions and energy use was performed to study bio-jet fuel (BJF) production from micro-algae grown in open ponds under Chinese conditions using the Tsinghua University LCA Model (TLCAM). Attention was paid to energy recovery through [...] Read more.

A life-cycle analysis (LCA) of greenhouse gas (GHG) emissions and energy use was performed to study bio-jet fuel (BJF) production from micro-algae grown in open ponds under Chinese conditions using the Tsinghua University LCA Model (TLCAM). Attention was paid to energy recovery through biogas production and cogeneration of heat and power (CHP) from the residual biomass after oil extraction, including fugitive methane (CH₄) emissions during the production of biogas and nitrous oxide (N₂O) emissions during the use of digestate (solid residue from anaerobic digestion) as agricultural fertilizer. Analyses were performed based on examination of process parameters, mass balance conditions, material requirement, energy consumptions and the realities of energy supply and transport in China (i.e., electricity generation and heat supply primarily based on coal, multiple transport modes). Our LCA result of the BJF pathway showed that, compared with the traditional petrochemical pathway, this new pathway will increase the overall fossil energy use and carbon emission by 39% and 70%, respectively, while decrease petroleum consumption by about 84%, based on the same units of energy service. Moreover, the energy conservation and emission reduction benefit of this new pathway may be accomplished by two sets of approaches: wider adoption of low-carbon process fuels and optimization of algae cultivation and harvest, and oil extraction processes. Full article

(This article belongs to the Special Issue Algae Fuel 2013)

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354 KiB

Open AccessArticle

Short-Term Wind Power Forecasting Using the Enhanced Particle Swarm Optimization Based Hybrid Method

by Wen-Yeau Chang

Energies 2013, 6(9), 4879-4896; https://doi.org/10.3390/en6094879 - 20 Sep 2013

Cited by 56 | Viewed by 6721

Abstract

High penetration of wind power in the electricity system provides many challenges to power system operators, mainly due to the unpredictability and variability of wind power generation. Although wind energy may not be dispatched, an accurate forecasting method of wind speed and power [...] Read more.

High penetration of wind power in the electricity system provides many challenges to power system operators, mainly due to the unpredictability and variability of wind power generation. Although wind energy may not be dispatched, an accurate forecasting method of wind speed and power generation can help power system operators reduce the risk of an unreliable electricity supply. This paper proposes an enhanced particle swarm optimization (EPSO) based hybrid forecasting method for short-term wind power forecasting. The hybrid forecasting method combines the persistence method, the back propagation neural network, and the radial basis function (RBF) neural network. The EPSO algorithm is employed to optimize the weight coefficients in the hybrid forecasting method. To demonstrate the effectiveness of the proposed method, the method is tested on the practical information of wind power generation of a wind energy conversion system (WECS) installed on the Taichung coast of Taiwan. Comparisons of forecasting performance are made with the individual forecasting methods. Good agreements between the realistic values and forecasting values are obtained; the test results show the proposed forecasting method is accurate and reliable. Full article

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892 KiB

Open AccessArticle

A Power Supply System with ZVS and Current-Doubler Features for Hybrid Renewable Energy Conversion

by Cheng-Tao Tsai, Chih-Lung Shen and Jye-Chau Su

Energies 2013, 6(9), 4859-4878; https://doi.org/10.3390/en6094859 - 20 Sep 2013

Cited by 13 | Viewed by 8361

Abstract

In this paper, a power supply system for hybrid renewable energy conversion is proposed, which can process PV (photovoltaic) power and wind-turbine energy simultaneously for step-down voltage and high current applications. It is a dual-input converter and mainly contains a PV energy source, [...] Read more.

In this paper, a power supply system for hybrid renewable energy conversion is proposed, which can process PV (photovoltaic) power and wind-turbine energy simultaneously for step-down voltage and high current applications. It is a dual-input converter and mainly contains a PV energy source, a wind turbine energy source, a zero-voltage-switching (ZVS) forward converter, and a current-doubler rectifier. The proposed power supply system has the following advantages: (1) PV-arrays and wind-energy sources can alternatively deliver power to the load during climate or season alteration; (2) maximum power point tracking (MPPT) can be accomplished for both different kinds of renewable-energy sources; (3) ZVS and synchronous rectification techniques for the active switches of the forward converter are embedded so as to reduce switching and conducting losses; and (4) electricity isolation is naturally obtained. To achieve an optimally dynamic response and to increase control flexibility, a digital signal processor (DSP) is investigated and presented to implement MPPT algorithm and power regulating scheme. Finally, a 240 W prototype power supply system with ZVS and current-doubler features to deal with PV power and wind energy is built and implemented. Experimental results are presented to verify the performance and the feasibility of the proposed power supply system. Full article

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459 KiB

Open AccessArticle

Adaptive Wide-Area Damping Control Scheme for Smart Grids with Consideration of Signal Time Delay

by Guowei Cai, Deyou Yang and Cheng Liu

Energies 2013, 6(9), 4841-4858; https://doi.org/10.3390/en6094841 - 13 Sep 2013

Cited by 15 | Viewed by 7429

Abstract

As an important part of the smart grid, a wide-area measurement system (WAMS) provides the key technical support for power system monitoring, protection and control. But 20 uncertainties in system parameters and signal transmission time delay could worsen the damping effect and deteriorate [...] Read more.

As an important part of the smart grid, a wide-area measurement system (WAMS) provides the key technical support for power system monitoring, protection and control. But 20 uncertainties in system parameters and signal transmission time delay could worsen the damping effect and deteriorate the system stability. In the presented study, the subspace system identification technique (SIT) is used to firstly derive a low-order linear model of a power system from the measurements. Then, a novel adaptive wide-area damping control scheme for online tuning of the wide-area damping controller (WADC) parameters using the residue method is proposed. In order to eliminate the effects of the time delay to the signal transmission, a simple and practical time delay compensation algorithm is proposed to compensate the time delay in each wide-area control signal. Detailed examples, inspired by the IEEE test system under various disturbance scenarios, have been used to verify the effectiveness of the proposed adaptive wide-area damping control scheme. Full article

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

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3811 KiB

Open AccessArticle

Electrostatic Self-Assembly of Fe₃O₄ Nanoparticles on Graphene Oxides for High Capacity Lithium-Ion Battery Anodes

by Taegyune Yoon, Jaegyeong Kim, Jinku Kim and Jung Kyoo Lee

Energies 2013, 6(9), 4830-4840; https://doi.org/10.3390/en6094830 - 12 Sep 2013

Cited by 66 | Viewed by 10226

Abstract

Magnetite, Fe₃O₄_, is a promising anode material for lithium ion batteries due to its high theoretical capacity (924 mA h g⁻¹), high density, low cost and low toxicity. However, its application as high capacity anodes is still [...] Read more.

Magnetite, Fe₃O₄_, is a promising anode material for lithium ion batteries due to its high theoretical capacity (924 mA h g⁻¹), high density, low cost and low toxicity. However, its application as high capacity anodes is still hampered by poor cycling performance. To stabilize the cycling performance of Fe₃O₄ nanoparticles, composites comprising Fe₃O₄ nanoparticles and graphene sheets (GS) were fabricated. The Fe₃O₄/GS composite disks of mm dimensions were prepared by electrostatic self-assembly between negatively charged graphene oxide (GO) sheets and positively charged Fe₃O₄-APTMS [Fe₃O₄ grafted with (3-aminopropyl)trimethoxysilane (APTMS)] in an acidic solution (pH = 2) followed by in situ chemical reduction. Thus prepared Fe₃O₄/GS composite showed an excellent rate capability as well as much enhanced cycling stability compared with Fe₃O₄ electrode. The superior electrochemical responses of Fe₃O₄/GS composite disks assure the advantages of: (1) electrostatic self-assembly between high storage-capacity materials with GO; and (2) incorporation of GS in the Fe₃O₄/GS composite for high capacity lithium-ion battery application. Full article

(This article belongs to the Special Issue Li-ion Batteries and Energy Storage Devices)

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1489 KiB

Open AccessArticle

Research on an Axial Magnetic-Field-Modulated Brushless Double Rotor Machine

by Ping Zheng, Zhiyi Song, Jingang Bai, Chengde Tong and Bin Yu

Energies 2013, 6(9), 4799-4829; https://doi.org/10.3390/en6094799 - 12 Sep 2013

Cited by 26 | Viewed by 7634

Abstract

Double rotor machine, an electronic continuously variable transmission, has great potential in application of hybrid electric vehicles (HEVs), wind power and marine propulsion. In this paper, an axial magnetic-field-modulated brushless double rotor machine (MFM-BDRM), which can realize the speed decoupling between the shaft [...] Read more.

Double rotor machine, an electronic continuously variable transmission, has great potential in application of hybrid electric vehicles (HEVs), wind power and marine propulsion. In this paper, an axial magnetic-field-modulated brushless double rotor machine (MFM-BDRM), which can realize the speed decoupling between the shaft of the modulating ring rotor and that of the permanent magnet rotor is proposed. Without brushes and slip rings, the axial MFM-BDRM offers significant advantages such as excellent reliability and high efficiency. Since the number of pole pairs of the stator is not equal to that of the permanent magnet rotor, which differs from the traditional permanent magnet synchronous machine, the operating principle of the MFM-BDRM is deduced. The relations of corresponding speed and toque transmission are analytically discussed. The cogging toque characteristics, especially the order of the cogging torque are mathematically formulated. Matching principle of the number of pole pairs of the stator, that of the permanent magnet rotor and the number of ferromagnetic pole pieces is inferred since it affects MFM-BDRM’s performance greatly, especially in the respect of the cogging torque and electromagnetic torque ripple. The above analyses are assessed with the three-dimensional (3D) finite-element method (FEM). Full article

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

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723 KiB

Open AccessArticle

General and Simple Decision Method for DG Penetration Level in View of Voltage Regulation at Distribution Substation Transformers

by Il-Keun Song, Won-Wook Jung, Chul-Min Chu, Seong-Soo Cho, Hyun-Koo Kang and Joon-Ho Choi

Energies 2013, 6(9), 4786-4798; https://doi.org/10.3390/en6094786 - 10 Sep 2013

Cited by 11 | Viewed by 7993

Abstract

A distribution system was designed and operated by considering unidirectional power flow from a utility source to end-use loads. The large penetrations of distributed generation (DG) into the existing distribution system causes a variety of technical problems, such as frequent tap changing problems [...] Read more.

A distribution system was designed and operated by considering unidirectional power flow from a utility source to end-use loads. The large penetrations of distributed generation (DG) into the existing distribution system causes a variety of technical problems, such as frequent tap changing problems of the on-load tap changer (OLTC) transformer, local voltage rise, protection coordination, exceeding short-circuit capacity, and harmonic distortion. In view of voltage regulation, the intermittent fluctuation of the DG output power results in frequent tap changing operations of the OLTC transformer. Thus, many utilities limit the penetration level of DG and are eager to find the reasonable penetration limits of DG in the distribution system. To overcome this technical problem, utilities have developed a new voltage regulation method in the distribution system with a large DG penetration level. In this paper, the impact of DG on the OLTC operations controlled by the line drop compensation (LDC) method is analyzed. In addition, a generalized determination methodology for the DG penetration limits in a distribution substation transformer is proposed. The proposed DG penetration limits could be adopted for a simplified interconnection process in DG interconnection guidelines. Full article

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

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659 KiB

Open AccessArticle

Saving Building Energy through Advanced Control Strategies

by Stephen Treado and Yan Chen

Energies 2013, 6(9), 4769-4785; https://doi.org/10.3390/en6094769 - 10 Sep 2013

Cited by 30 | Viewed by 7272

Abstract

This article presents an analysis of the relationship between building energy usage and building control system operation and performance. A method is presented for estimating the energy saving potential of improvements in building and control system operation, including the relative impact of recommssioning [...] Read more.

This article presents an analysis of the relationship between building energy usage and building control system operation and performance. A method is presented for estimating the energy saving potential of improvements in building and control system operation, including the relative impact of recommssioning and hardware and software upgrades, based on a subjective assessment of the level of energy efficient design and the energy usage of the building relative to similar buildings as indicated by the Energy Utilization Index for the building. The method introduces a Building Design Index and a Building Operating Index to evaluate building energy performance versus similar buildings, and uses these indices to estimate potential savings and effectiveness of control system improvements. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2013)

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566 KiB

Open AccessReview

Microbial Conversion of Waste Glycerol from Biodiesel Production into Value-Added Products

by Cheng Li, Keaton L. Lesnik and Hong Liu

Energies 2013, 6(9), 4739-4768; https://doi.org/10.3390/en6094739 - 10 Sep 2013

Cited by 82 | Viewed by 14906

Abstract

Biodiesel has gained a significant amount of attention over the past decade as an environmentally friendly fuel that is capable of being utilized by a conventional diesel engine. However, the biodiesel production process generates glycerol-containing waste streams which have become a disposal issue [...] Read more.

Biodiesel has gained a significant amount of attention over the past decade as an environmentally friendly fuel that is capable of being utilized by a conventional diesel engine. However, the biodiesel production process generates glycerol-containing waste streams which have become a disposal issue for biodiesel plants and generated a surplus of glycerol. A value-added opportunity is needed in order to compensate for disposal-associated costs. Microbial conversions from glycerol to valuable chemicals performed by various bacteria, yeast, fungi, and microalgae are discussed in this review paper, as well as the possibility of extending these conversions to microbial electrochemical technologies. Full article

(This article belongs to the Special Issue Biomass and Biofuels 2013)

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631 KiB

Open AccessArticle

Recursive Pyramid Algorithm-Based Discrete Wavelet Transform for Reactive Power Measurement in Smart Meters

by Najam Ul Hasan, Waleed Ejaz, Mahin K. Atiq and Hyung Seok Kim

Energies 2013, 6(9), 4721-4738; https://doi.org/10.3390/en6094721 - 9 Sep 2013

Cited by 3 | Viewed by 8043

Abstract

Measurement of the active, reactive, and apparent power is one of the most fundamental tasks of smart meters in energy systems. Recently, a number of studies have employed the discrete wavelet transform (DWT) for power measurement in smart meters. The most common way [...] Read more.

Measurement of the active, reactive, and apparent power is one of the most fundamental tasks of smart meters in energy systems. Recently, a number of studies have employed the discrete wavelet transform (DWT) for power measurement in smart meters. The most common way to implement DWT is the pyramid algorithm; however, this is not feasible for practical DWT computation because it requires either a log N cascaded filter or O (N) word size memory storage for an input signal of the N-point. Both solutions are too expensive for practical applications of smart meters. It is proposed that the recursive pyramid algorithm is more suitable for smart meter implementation because it requires only word size storage of L × Log (N-L), where L is the length of filter. We also investigated the effect of varying different system parameters, such as the sampling rate, dc offset, phase offset, linearity error in current and voltage sensors, analog to digital converter resolution, and number of harmonics in a non-sinusoidal system, on the reactive energy measurement using DWT. The error analysis is depicted in the form of the absolute difference between the measured and the true value of the reactive energy. Full article

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

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1795 KiB

Open AccessArticle

Experimentally Based Model to Size the Geometry of a New OWC Device, with Reference to the Mediterranean Sea Wave Environment

by Luca Martinelli, Paolo Pezzutto and Piero Ruol

Energies 2013, 6(9), 4696-4720; https://doi.org/10.3390/en6094696 - 9 Sep 2013

Cited by 34 | Viewed by 8003

Abstract

This note presents the Seabreath wave energy converter, basically a multi-chamber floating oscillating water column device, and the lumped model used to size its chambers, the ducts and the turbine. The model is based on extensive testing carried out in the wave flume [...] Read more.

This note presents the Seabreath wave energy converter, basically a multi-chamber floating oscillating water column device, and the lumped model used to size its chambers, the ducts and the turbine. The model is based on extensive testing carried out in the wave flume of the University of Padova using fixed and floating models with a dummy power take off and indirect measurement of the produced power. A map with the available energy in the Mediterranean Sea is also proposed, showing possible ideal application sites. The Seabreath is finally dimensioned for a quarter scale test application in the Adriatic Sea, with a 3 kW turbine, and a capacity factor of 40%. Full article

(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)

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657 KiB

Open AccessCommentary

Lessons Learned from the 787 Dreamliner Issue on Lithium-Ion Battery Reliability

by Nicholas Williard, Wei He, Christopher Hendricks and Michael Pecht

Energies 2013, 6(9), 4682-4695; https://doi.org/10.3390/en6094682 - 9 Sep 2013

Cited by 266 | Viewed by 24628

Abstract

On 16 January 2013, all Boeing 787 Dreamliners were indefinitely grounded due to lithium-ion battery failures that had occurred in two planes. Subsequent investigations into the battery failures released through the National Transportation Safety Board (NTSB) factual report, the March 15th Boeing press [...] Read more.

On 16 January 2013, all Boeing 787 Dreamliners were indefinitely grounded due to lithium-ion battery failures that had occurred in two planes. Subsequent investigations into the battery failures released through the National Transportation Safety Board (NTSB) factual report, the March 15th Boeing press conference in Japan, and the NTSB hearings in Washington D.C., never identified the root causes of the failures—a major concern for ensuring safety and meeting reliability expectations. This paper discusses the challenges to lithium-ion battery qualification, reliability assessment, and safety in light of the Boeing 787 battery failures. New assessment methods and control techniques that can improve battery reliability and safety in avionic systems are then presented. Full article

(This article belongs to the Special Issue Li-ion Batteries and Energy Storage Devices)

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2335 KiB

Open AccessArticle

Coordinated Control of a Doubly-Fed Induction Generator-Based Wind Farm and a Static Synchronous Compensator for Low Voltage Ride-through Grid Code Compliance during Asymmetrical Grid Faults

by Zhong Zheng, Geng Yang and Hua Geng

Energies 2013, 6(9), 4660-4681; https://doi.org/10.3390/en6094660 - 9 Sep 2013

Cited by 25 | Viewed by 7033

Abstract

This paper aims to explore a viable solution for a doubly-fed induction generator (DFIG)-based wind farm to meet the reactive support requirement of the low voltage ride-through (LVRT) grid code with safe grid-connected operation during asymmetrical grid faults. First, the control scheme for [...] Read more.

This paper aims to explore a viable solution for a doubly-fed induction generator (DFIG)-based wind farm to meet the reactive support requirement of the low voltage ride-through (LVRT) grid code with safe grid-connected operation during asymmetrical grid faults. First, the control scheme for the DFIG-based wind energy conversion system (WECS) is designed. Then, the controllability issue is analyzed by means of an optimal method, and the derived controllable regions indicate that the DFIG-based WECS can only remain controllable under mild asymmetrical fault situations. Afterwards, the static synchronous compensator (STATCOM) is introduced as extra equipment to ensure that the DFIG-based wind farm remains controllable under severe asymmetrical fault situations. For this purpose, a voltage compensation control scheme and a corresponding capacity matching method for the STATCOM are proposed. The simulation results verify that, with the proposed coordinated control between the DFIG-based wind farm and the STATCOM, the required positive-sequence reactive current can be supplied to support the power grid. The oscillations on the electromagnetic torque and direct current (DC)-link voltage of the DFIG-based WECS can also be eliminated. Therefore, the control scheme can be helpful to improve the reliability of both the wind farm and the power system during grid faults. Full article

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460 KiB

Open AccessArticle

Towards Energy Efficiency: Forecasting Indoor Temperature via Multivariate Analysis

by Francisco Zamora-Martínez, Pablo Romeu, Paloma Botella-Rocamora and Juan Pardo

Energies 2013, 6(9), 4639-4659; https://doi.org/10.3390/en6094639 - 9 Sep 2013

Cited by 36 | Viewed by 7699

Abstract

The small medium large system (SMLsystem) is a house built at the Universidad CEU Cardenal Herrera (CEU-UCH) for participation in the Solar Decathlon 2013 competition. Several technologies have been integrated to reduce power consumption. One of these is a forecasting system based on [...] Read more.

The small medium large system (SMLsystem) is a house built at the Universidad CEU Cardenal Herrera (CEU-UCH) for participation in the Solar Decathlon 2013 competition. Several technologies have been integrated to reduce power consumption. One of these is a forecasting system based on artificial neural networks (ANNs), which is able to predict indoor temperature in the near future using captured data by a complex monitoring system as the input. A study of the impact on forecasting performance of different covariate combinations is presented in this paper. Additionally, a comparison of ANNs with the standard statistical forecasting methods is shown. The research in this paper has been focused on forecasting the indoor temperature of a house, as it is directly related to HVAC—heating, ventilation and air conditioning—system consumption. HVAC systems at the SMLsystem house represent 53:89% of the overall power consumption. The energy used to maintain temperature was measured to be 30%–38:9% of the energy needed to lower it. Hence, these forecasting measures allow the house to adapt itself to future temperature conditions by using home automation in an energy-efficient manner. Experimental results show a high forecasting accuracy and therefore, they might be used to efficiently control an HVAC system. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2013)

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335 KiB

Open AccessReview

Effects of Environmental Factors and Nutrient Availability on the Biochemical Composition of Algae for Biofuels Production: A Review

by Ankita Juneja, Ruben Michael Ceballos and Ganti S. Murthy

Energies 2013, 6(9), 4607-4638; https://doi.org/10.3390/en6094607 - 3 Sep 2013

Cited by 641 | Viewed by 35092

Abstract

Due to significant lipid and carbohydrate production as well as other useful properties such as high production of useful biomolecular substrates (e.g., lipids) and the ability to grow using non-potable water sources, algae are being explored as a potential high-yield feedstock for biofuels [...] Read more.

Due to significant lipid and carbohydrate production as well as other useful properties such as high production of useful biomolecular substrates (e.g., lipids) and the ability to grow using non-potable water sources, algae are being explored as a potential high-yield feedstock for biofuels production. In both natural and engineered systems, algae can be exposed to a variety of environmental conditions that affect growth rate and cellular composition. With respect to the latter, the amount of carbon fixed in lipids and carbohydrates (e.g., starch) is highly influenced by environmental factors and nutrient availability. Understanding synergistic interactions between multiple environmental variables and nutritional factors is required to develop sustainable high productivity bioalgae systems, which are essential for commercial biofuel production. This article reviews the effects of environmental factors (i.e., temperature, light and pH) and nutrient availability (e.g., carbon, nitrogen, phosphorus, potassium, and trace metals) as well as cross-interactions on the biochemical composition of algae with a special focus on carbon fixation and partitioning of carbon from a biofuels perspective. Full article

(This article belongs to the Special Issue Algae Fuel 2013)

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1488 KiB

Open AccessArticle

Method for Cost-Benefit Analysis of Improved Indoor Climate Conditions and Reduced Energy Consumption in Office Buildings

by Rokas Valancius, Andrius Jurelionis and Viktoras Dorosevas

Energies 2013, 6(9), 4591-4606; https://doi.org/10.3390/en6094591 - 3 Sep 2013

Cited by 25 | Viewed by 6770

Abstract

Indoor climate affects health and productivity of the occupants in office buildings, yet in many buildings of this type indoor climate conditions are not well-controlled due to insufficient heating or cooling capacity, high swings of external or internal heat loads, improper control or [...] Read more.

Indoor climate affects health and productivity of the occupants in office buildings, yet in many buildings of this type indoor climate conditions are not well-controlled due to insufficient heating or cooling capacity, high swings of external or internal heat loads, improper control or operation of heating, ventilation and air conditioning (HVAC) equipment, etc. However, maintenance of good indoor environmental conditions in buildings requires increased investments and possible higher energy consumption. This paper focuses on the relation between investment costs for retrofitting HVAC equipment as well as decreased energy use and improved performance of occupants in office buildings. The cost-benefit analysis implementation algorithm is presented in this paper, including energy survey of the building, estimation of occupants dissatisfied by key indoor climate indicators using questionnaire survey and measurements. Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) analysis is used in the proposed method for data processing. A case study of an office building is presented in order to introduce an application example of the proposed method. Results of the study verify the applicability of the proposed algorithm and TOPSIS analysis as a practical tool for office building surveys in order to maximize productivity by means of cost efficient technical building retrofitting solutions. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2013)

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448 KiB

Open AccessArticle

Optimization of Experimental Model Parameter Identification for Energy Storage Systems

by Daniele Gallo, Carmine Landi, Mario Luiso and Rosario Morello

Energies 2013, 6(9), 4572-4590; https://doi.org/10.3390/en6094572 - 3 Sep 2013

Cited by 38 | Viewed by 7144

Abstract

The smart grid approach is envisioned to take advantage of all available modern technologies in transforming the current power system to provide benefits to all stakeholders in the fields of efficient energy utilisation and of wide integration of renewable sources. Energy storage systems [...] Read more.

The smart grid approach is envisioned to take advantage of all available modern technologies in transforming the current power system to provide benefits to all stakeholders in the fields of efficient energy utilisation and of wide integration of renewable sources. Energy storage systems could help to solve some issues that stem from renewable energy usage in terms of stabilizing the intermittent energy production, power quality and power peak mitigation. With the integration of energy storage systems into the smart grids, their accurate modeling becomes a necessity, in order to gain robust real-time control on the network, in terms of stability and energy supply forecasting. In this framework, this paper proposes a procedure to identify the values of the battery model parameters in order to best fit experimental data and integrate it, along with models of energy sources and electrical loads, in a complete framework which represents a real time smart grid management system. The proposed method is based on a hybrid optimisation technique, which makes combined use of a stochastic and a deterministic algorithm, with low computational burden and can therefore be repeated over time in order to account for parameter variations due to the battery’s age and usage. Full article

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2296 KiB

Open AccessArticle

BubbleZERO—Design, Construction and Operation of a Transportable Research Laboratory for Low Exergy Building System Evaluation in the Tropics

by Marcel Bruelisauer, Kian Wee Chen, Rupesh Iyengar, Hansjürg Leibundgut, Cheng Li, Mo Li, Matthias Mast, Forrest Meggers, Clayton Miller, Dino Rossi, Esmail M. Saber, Kwok Wai Tham and Arno Schlueter

Energies 2013, 6(9), 4551-4571; https://doi.org/10.3390/en6094551 - 2 Sep 2013

Cited by 21 | Viewed by 9012

Abstract

We present the design, construction and operation of a novel building systems laboratory, the BubbleZERO—Zero Emission Research Operation. Our objective was to design a space to evaluate the performance of Swiss-developed low exergy building systems in the tropical climate of Singapore using an [...] Read more.

We present the design, construction and operation of a novel building systems laboratory, the BubbleZERO—Zero Emission Research Operation. Our objective was to design a space to evaluate the performance of Swiss-developed low exergy building systems in the tropical climate of Singapore using an integrated design approach. The method we employed for evaluation in the tropics was to design and build a test bed out of the shipping containers that transported the prototype low exergy systems from Switzerland to Singapore. This approach resulted in a novel laboratory environment containing radiant cooling panels and decentralized air supply, along with a self-shading, inflated “bubble” skin, experimental low emissivity (LowE) glazing, LED lighting, wireless sensors and distributed control. The laboratory evaluates and demonstrates for the first time in Singapore an integrated high-temperature cooling system with separate demand-controlled ventilation adapted for the tropics. It is a functional lab testing system in real tropical conditions. As such, the results showing the ability to mitigate the risk of condensation by maintaining a dew point below 18 °C by the separate decentralized ventilation are significant and necessary for potential future implementation in buildings. In addition, the control system provides new proof of concept for distributed wireless sensors and control for reliable automation of the systems. These key results are presented along with the integrated design process and real-life tropical operation of the laboratory. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2013)

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405 KiB

Open AccessArticle

Catalytic Conversion of Bio-Oil to Oxygen-Containing Fuels by Acid-Catalyzed Reaction with Olefins and Alcohols over Silica Sulfuric Acid

by Zhijun Zhang, Shujuan Sui, Fengqiang Wang, Qingwen Wang and Charles U. Pittman, Jr.

Energies 2013, 6(9), 4531-4550; https://doi.org/10.3390/en6094531 - 2 Sep 2013

Cited by 20 | Viewed by 8572

Abstract

Crude bio-oil from pine chip fast pyrolysis was upgraded with olefins (1-octene, cyclohexene, 1,7-octadiene, and 2,4,4-trimethylpentene) plus 1-butanol (iso-butanol, t-butanol and ethanol) at 120 °C using a silica sulfuric acid (SSA) catalyst that possesses a good catalytic activity and stability. [...] Read more.

Crude bio-oil from pine chip fast pyrolysis was upgraded with olefins (1-octene, cyclohexene, 1,7-octadiene, and 2,4,4-trimethylpentene) plus 1-butanol (iso-butanol, t-butanol and ethanol) at 120 °C using a silica sulfuric acid (SSA) catalyst that possesses a good catalytic activity and stability. Gas chromatography-mass spectrometry (GC-MS), Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (¹H-NMR) analysis showed that upgrading sharply increased ester content and decreased the amounts of levoglucosan, phenols, polyhydric alcohols and carboxylic acids. Upgrading lowered acidity (pH value rose from 2.5 to >3.5), removed the unpleasant odor and increased hydrocarbon solubility. Water content dramatically decreased from 37.2% to about 7.0% and the heating value increased from 12.6 MJ·kg⁻¹ to about 31.9 MJ·kg⁻¹. This work has proved that bio-oil upgrading with a primary olefin plus 1-butanol is a feasible route where all the original heating value of the bio-oil plus the added olefin and alcohol are present in the resulting fuel. Full article

(This article belongs to the Special Issue Biomass and Biofuels 2013)

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13209 KiB

Open AccessArticle

Modeling the Liquid Water Transport in the Gas Diffusion Layer for Polymer Electrolyte Membrane Fuel Cells Using a Water Path Network

by Robert Alink and Dietmar Gerteisen

Energies 2013, 6(9), 4508-4530; https://doi.org/10.3390/en6094508 - 2 Sep 2013

Cited by 25 | Viewed by 7967

Abstract

In order to model the liquid water transport in the porous materials used in polymer electrolyte membrane (PEM) fuel cells, the pore network models are often applied. The presented model is a novel approach to further develop these models towards a percolation model [...] Read more.

In order to model the liquid water transport in the porous materials used in polymer electrolyte membrane (PEM) fuel cells, the pore network models are often applied. The presented model is a novel approach to further develop these models towards a percolation model that is based on the fiber structure rather than the pore structure. The developed algorithm determines the stable liquid water paths in the gas diffusion layer (GDL) structure and the transitions from the paths to the subsequent paths. The obtained water path network represents the basis for the calculation of the percolation process with low calculation efforts. A good agreement with experimental capillary pressure-saturation curves and synchrotron liquid water visualization data from other literature sources is found. The oxygen diffusivity for the GDL with liquid water saturation at breakthrough reveals that the porosity is not a crucial factor for the limiting current density. An algorithm for condensation is included into the model, which shows that condensing water is redirecting the water path in the GDL, leading to an improved oxygen diffusion by a decreased breakthrough pressure and changed saturation distribution at breakthrough. Full article

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

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1159 KiB

Open AccessArticle

Improved Short-Term Load Forecasting Based on Two-Stage Predictions with Artificial Neural Networks in a Microgrid Environment

by Luis Hernández, Carlos Baladrón, Javier M. Aguiar, Lorena Calavia, Belén Carro, Antonio Sánchez-Esguevillas, Javier Sanjuán, Álvaro González and Jaime Lloret

Energies 2013, 6(9), 4489-4507; https://doi.org/10.3390/en6094489 - 29 Aug 2013

Cited by 40 | Viewed by 7907

Abstract

Short-Term Load Forecasting plays a significant role in energy generation planning, and is specially gaining momentum in the emerging Smart Grids environment, which usually presents highly disaggregated scenarios where detailed real-time information is available thanks to Communications and Information Technologies, as it happens [...] Read more.

Short-Term Load Forecasting plays a significant role in energy generation planning, and is specially gaining momentum in the emerging Smart Grids environment, which usually presents highly disaggregated scenarios where detailed real-time information is available thanks to Communications and Information Technologies, as it happens for example in the case of microgrids. This paper presents a two stage prediction model based on an Artificial Neural Network in order to allow Short-Term Load Forecasting of the following day in microgrid environment, which first estimates peak and valley values of the demand curve of the day to be forecasted. Those, together with other variables, will make the second stage, forecast of the entire demand curve, more precise than a direct, single-stage forecast. The whole architecture of the model will be presented and the results compared with recent work on the same set of data, and on the same location, obtaining a Mean Absolute Percentage Error of 1.62% against the original 2.47% of the single stage model. Full article

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

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477 KiB

Open AccessArticle

To Re-Explore the Causality between Barriers to Renewable Energy Development: A Case Study of Wind Energy

by Shih-Chieh Huang, Shang-Lien Lo and Yen-Ching Lin

Energies 2013, 6(9), 4465-4488; https://doi.org/10.3390/en6094465 - 29 Aug 2013

Cited by 15 | Viewed by 5821

Abstract

The development of wind energy in developing countries has its limitations. This study adapted quantitative approaches to explore the causality relationships among these barriers. It was found that different areas of obstacles did affect one another; by barrier inference we learned that a [...] Read more.

The development of wind energy in developing countries has its limitations. This study adapted quantitative approaches to explore the causality relationships among these barriers. It was found that different areas of obstacles did affect one another; by barrier inference we learned that a lack of national policy caused other disorders, and that the occurrence of these disorders eventually resulted either directly or indirectly in high investment costs. Thus, the question of how to effectively reduce the investment cost of wind energy development is the most important issue to developing countries. Furthermore, the results of this study clarified that wind intermittency would not be the main reason hindering short and mid-term wind power development. However, from a long-term perspective, the impact of intermittency still cannot be treated lightly, as it was found that for each standard deviation unit improvement of the intermittency, the investment cost-effectiveness improvement increased by 0.185 σ, which was 1.78 times higher than the impact from national policies. Therefore, aside from strengthening the national policies in establishing a suitable institutional framework, we recommend that policy-makers should also emphasize the establishment of an economic assessment of available sites, a detailed wind resource assessment and improved forecasting of technical applications. Full article

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Open AccessArticle

A Liquid Inorganic Electrolyte Showing an Unusually High Lithium Ion Transference Number: A Concentrated Solution of LiAlCl₄ in Sulfur Dioxide

by Robert Hartl, Matthias Fleischmann, Ruth M. Gschwind, Martin Winter and Heiner Jakob Gores

Energies 2013, 6(9), 4448-4464; https://doi.org/10.3390/en6094448 - 29 Aug 2013

Cited by 14 | Viewed by 9251

Abstract

We report on studies of an inorganic electrolyte: LiAlCl₄ in liquid sulfur dioxide. Concentrated solutions show a very high conductivity when compared with typical electrolytes for lithium ion batteries that are based on organic solvents. Our investigations include conductivity measurements and measurements [...] Read more.

We report on studies of an inorganic electrolyte: LiAlCl₄ in liquid sulfur dioxide. Concentrated solutions show a very high conductivity when compared with typical electrolytes for lithium ion batteries that are based on organic solvents. Our investigations include conductivity measurements and measurements of transference numbers via nuclear magnetic resonance (NMR) and by a classical direct method, Hittorf’s method. For the use of Hittorf’s method, it is necessary to measure the concentration of the electrolyte in a selected cell compartment before and after electrochemical polarization very precisely. This task was finally performed by potentiometric titration after hydrolysis of the salt. The Haven ratio was determined to estimate the association behavior of this very concentrated electrolyte solution. The measured unusually high transference number of the lithium cation of the studied most concentrated solution, a molten solvate LiAlCl₄ × 1.6SO₂, makes this electrolyte a promising alternative for lithium ion cells with high power ability. Full article

(This article belongs to the Special Issue Li-ion Batteries and Energy Storage Devices)

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852 KiB

Open AccessArticle

Analysis of Peak-to-Peak Current Ripple Amplitude in Seven-Phase PWM Voltage Source Inverters

by Gabriele Grandi and Jelena Loncarski

Energies 2013, 6(9), 4429-4447; https://doi.org/10.3390/en6094429 - 27 Aug 2013

Cited by 14 | Viewed by 8105

Abstract

Multiphase systems are nowadays considered for various industrial applications. Numerous pulse width modulation (PWM) schemes for multiphase voltage source inverters with sinusoidal outputs have been developed, but no detailed analysis of the impact of these modulation schemes on the output peak-to-peak current ripple [...] Read more.

Multiphase systems are nowadays considered for various industrial applications. Numerous pulse width modulation (PWM) schemes for multiphase voltage source inverters with sinusoidal outputs have been developed, but no detailed analysis of the impact of these modulation schemes on the output peak-to-peak current ripple amplitude has been reported. Determination of current ripple in multiphase PWM voltage source inverters is important for both design and control purposes. This paper gives the complete analysis of the peak-to-peak current ripple distribution over a fundamental period for multiphase inverters, with particular reference to seven-phase VSIs. In particular, peak-to-peak current ripple amplitude is analytically determined as a function of the modulation index, and a simplified expression to get its maximum value is carried out. Although reference is made to the centered symmetrical PWM, being the most simple and effective solution to maximize the DC bus utilization, leading to a nearly-optimal modulation to minimize the RMS of the current ripple, the analysis can be readily extended to either discontinuous or asymmetrical modulations, both carrier-based and space vector PWM. A similar approach can be usefully applied to any phase number. The analytical developments for all different sub-cases are verified by numerical simulations. Full article

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471 KiB

Open AccessArticle

Assessment of Potential Capacity Increases at Combined Heat and Power Facilities Based on Available Corn Stover and Forest Logging Residues

by Selvarani Radhakrishnan, Joel O. Paz, Fei Yu, Sandra Eksioglu and Donald L. Grebner

Energies 2013, 6(9), 4418-4428; https://doi.org/10.3390/en6094418 - 26 Aug 2013

Cited by 4 | Viewed by 5158

Abstract

Combined Heat and Power (CHP) production using renewable energy sources is gaining importance because of its flexibility and high-energy efficiency. Biomass materials, such as corn stover and forestry residues, are potential sources for renewable energy for CHP production. In Mississippi, approximately 4.0 MT [...] Read more.

Combined Heat and Power (CHP) production using renewable energy sources is gaining importance because of its flexibility and high-energy efficiency. Biomass materials, such as corn stover and forestry residues, are potential sources for renewable energy for CHP production. In Mississippi, approximately 4.0 MT dry tons of woody biomass is available annually for energy production. In this study, we collected and analyzed 10 years of corn stover data (2001–2010) and three years of forest logging residue data (1995, 1999, and 2002) in each county in Mississippi to determine the potential of these feed stocks for sustainable CHP energy production. We identified six counties, namely Amite, Copiah, Clarke, Wayne, Wilkinson and Rankin, that have forest logging residue feedstocks to sustain a CHP facility with a range of capacity between 8.0 and 9.8 MW. Using corn stover alone, Yazoo and Washington counties can produce 13.4 MW and 13.5 MW of energy, respectively. Considering both feedstocks and based on a conservative amount of 30% available forest logging residue and 33% corn stover, we found that 20 counties have adequate supply for a CHP facility with a capacity of 8.3 MW to 19.6 MW. Full article

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312 KiB

Open AccessReview

Demand Response and Economic Dispatch of Power Systems Considering Large-Scale Plug-in Hybrid Electric Vehicles/Electric Vehicles (PHEVs/EVs): A Review

by Wei Gu, Haojun Yu, Wei Liu, Junpeng Zhu and Xiaohui Xu

Energies 2013, 6(9), 4394-4417; https://doi.org/10.3390/en6094394 - 26 Aug 2013

Cited by 19 | Viewed by 7929

Abstract

Increasing concerns about global environmental issues have led to the urgent development of green transportation. The enthusiasm of governments should encourage the prosperity of the plug-in hybrid electric vehicles/electric vehicles (PHEVs/EVs) industry in the near future. PHEVs/EVs are not only an alternative to [...] Read more.

Increasing concerns about global environmental issues have led to the urgent development of green transportation. The enthusiasm of governments should encourage the prosperity of the plug-in hybrid electric vehicles/electric vehicles (PHEVs/EVs) industry in the near future. PHEVs/EVs are not only an alternative to gasoline but are also burgeoning units for power systems. The impact of large-scale PHEVs/EVs on power systems is of profound significance. This paper discusses how to use PHEVs/EVs as a useful new tool for system operation and regulation from a review of recent studies and mainly considers two mainstream methods: demand response and economic dispatch. The potential of using PHEVs/EVs to coordinate renewable energy resources is also discussed in terms of accepting more renewable resources without violating the safety and the reliability of power systems or increasing the operation cost significantly. Full article

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381 KiB

Open AccessArticle

A New Agro/Forestry Residues Co-Firing Model in a Large Pulverized Coal Furnace: Technical and Economic Assessments

by Weigang Xu, Yanqing Niu, Houzhang Tan, Denghui Wang, Wenzhi Du and Shien Hui

Energies 2013, 6(9), 4377-4393; https://doi.org/10.3390/en6094377 - 23 Aug 2013

Cited by 19 | Viewed by 6914

Abstract

Based on the existing biomass co-firing technologies and the known innate drawbacks of dedicated biomass firing, including slagging, corrosion and the dependence on fuel, a new model of agro/forestry residue pellets/shreds and coal co-fired in a large Pulverized Coal (PC) furnace was proposed, [...] Read more.

Based on the existing biomass co-firing technologies and the known innate drawbacks of dedicated biomass firing, including slagging, corrosion and the dependence on fuel, a new model of agro/forestry residue pellets/shreds and coal co-fired in a large Pulverized Coal (PC) furnace was proposed, and the corresponding technical and economic assessments were performed by co-firing testing in a 300 MW PC furnace and discounted cash flow technique. The developed model is more dependent on injection co-firing and combined with co-milling co-firing. Co-firing not only reduces CO₂ emission, but also does not significantly affect the fly ash use in cement industry, construction industry and agriculture. Moreover, economic assessments show that in comparison with dedicated firing in grate furnace, agro/forestry residues and coal co-firing in a large PC furnace is highly economic. Otherwise, when the co-firing ratio was below 5 wt%, the boiler co-firing efficiency was 0.05%–0.31% higher than that of dedicated PC combustion, and boiler efficiencies were about 0.2% higher with agro/forestry residues co-firing in the bottom and top burner systems than that in a middle burner system. Full article

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

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2667 KiB

Open AccessArticle

Assessment of Seasonal Energy Efficiency Strategies of a Double Skin Façade in a Monsoon Climate Region

by Taehoon Hong, Jimin Kim, Juyoung Lee, Choongwan Koo and Hyo Seon Park

Energies 2013, 6(9), 4352-4376; https://doi.org/10.3390/en6094352 - 23 Aug 2013

Cited by 37 | Viewed by 10512

Abstract

As climate change and global warming have become two of the most significant environmental issues today, the double-skin façade (DSF) is getting considerable attention as an energy-efficient passive design. This study is aimed at assessing the seasonal energy efficiency strategies of a DSF [...] Read more.

As climate change and global warming have become two of the most significant environmental issues today, the double-skin façade (DSF) is getting considerable attention as an energy-efficient passive design. This study is aimed at assessing the seasonal energy efficiency strategies of a DSF targeting library facilities in the climate region with hot summers and cold winters. Toward this end, this study was conducted in four steps: (i) establishment of seasonal energy-efficient strategies; (ii) application of seasonal energy-efficient strategies; (iii) analysis of energy saving effect by season; and (iv) life cycle cost and life cycle CO₂ analyses for selecting an optimal DSF. Results show that a shaft box DSF energy model (EM_S) #2, which applied winter strategies, was optimal with an energy saving rate of 4.13%, while a multi-story DSF energy model (EM_M) #5, which applied summer strategies, was optimal with an energy saving rate of 12.67%. In terms of savings to investment ratio (SIR₄₀) and breakeven point (BEP₄₀), the multi-story DSF (3.20; 9 years) was superior. The results of this study can be used for (i) seasonal energy efficiency strategies of a DSF in East Asian monsoon climates, and (ii) as a guideline for the application of a DSF both in existing and new buildings. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2013)

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Energies, Volume 6, Issue 9 (September 2013) – 31 articles , Pages 4331-4955

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