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Energies, Volume 6, Issue 1 (January 2013), Pages 1-565

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Open AccessArticle Operation and Power Flow Control of Multi-Terminal DC Networks for Grid Integration of Offshore Wind Farms Using Genetic Algorithms
Energies 2013, 6(1), 1-26; doi:10.3390/en6010001
Received: 11 October 2012 / Revised: 24 November 2012 / Accepted: 14 December 2012 / Published: 24 December 2012
Cited by 16 | PDF Full-text (706 KB) | HTML Full-text | XML Full-text
Abstract
For achieving the European renewable electricity targets, a significant contribution is foreseen to come from offshore wind energy. Considering the large scale of the future planned offshore wind farms and the increasing distances to shore, grid integration through a transnational DC network [...] Read more.
For achieving the European renewable electricity targets, a significant contribution is foreseen to come from offshore wind energy. Considering the large scale of the future planned offshore wind farms and the increasing distances to shore, grid integration through a transnational DC network is desirable for several reasons. This article investigates a nine-node DC grid connecting three northern European countries — namely UK, The Netherlands and Germany. The power-flow control inside the multi-terminal DC grid based on voltage-source converters is achieved through a novel method, called distributed voltage control (DVC). In this method, an optimal power flow (OPF) is solved in order to minimize the transmission losses in the network. The main contribution of the paper is the utilization of a genetic algorithm (GA) to solve the OPF problem while maintaining an N-1 security constraint. After describing main DC network component models, several case studies illustrate the dynamic behavior of the proposed control method. Full article
(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)
Open AccessArticle An Efficiency-Optimized Isolated Bidirectional DC-DC Converter with Extended Power Range for Energy Storage Systems in Microgrids
Energies 2013, 6(1), 27-44; doi:10.3390/en6010027
Received: 19 October 2012 / Revised: 29 November 2012 / Accepted: 14 December 2012 / Published: 24 December 2012
Cited by 9 | PDF Full-text (1956 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a novel extended-single-phase shift (ESPS) control strategy of isolated bidirectional full-bridge DC-DC converters (IBDCs) which are a promising alternative as a power electronic interface in microgrids with an additional function of galvanic isolation. Based on the mathematical models of [...] Read more.
This paper proposes a novel extended-single-phase shift (ESPS) control strategy of isolated bidirectional full-bridge DC-DC converters (IBDCs) which are a promising alternative as a power electronic interface in microgrids with an additional function of galvanic isolation. Based on the mathematical models of ESPS control under steady-state conditions, detailed theoretical and experimental analyses of IBDC under ESPS control are presented. Compared with conventional single-phase-shift (CSPS) control, ESPS control can greatly improve the efficiency of IBDCs in microgrids through decreasing current stress and backflow power considerably over a wide input and output voltage range under light and medium loads. In addition, ESPS control only needs to adjust one single phase-shift angel to control transmission power, thus it retains implementation simplicity in comparison with dual-phase-shift (DPS) control for microgrid applications. Furthermore, an efficiency-optimized modulation scheme based on ESPS and CSPS control is developed in the whole power range of IBDC for power distribution in microgrids. A 10 kW IBDC prototype is constructed and the experimental results validate the effectiveness of the proposed control strategy, showing that the proposed strategy can enhance the overall efficiency up to 30%. Full article
(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)
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Open AccessArticle Combined Heat and Power from Municipal Solid Waste: Current Status and Issues in South Korea
Energies 2013, 6(1), 45-57; doi:10.3390/en6010045
Received: 26 October 2012 / Revised: 24 November 2012 / Accepted: 24 December 2012 / Published: 27 December 2012
Cited by 7 | PDF Full-text (211 KB) | HTML Full-text | XML Full-text
Abstract
Municipal solid waste (MSW) is an important energy resource for combined heat and power (CHP) production. This study summarized an overview of CHP by MSW to energy (WtE) plants in South Korea and discussed the issues related to energy efficiency improvement. Given [...] Read more.
Municipal solid waste (MSW) is an important energy resource for combined heat and power (CHP) production. This study summarized an overview of CHP by MSW to energy (WtE) plants in South Korea and discussed the issues related to energy efficiency improvement. Given the dominant housing culture of apartment living in South Korea, the primary energy output of WtE plants has been for district heating. In 2010, approximately half of the 51 large WtE plants were CHP, while the rest produced heat. Power generation in the WtE CHP plants was estimated to be only 3.65% of the thermal input, while heat production was 60.79%. The R1 efficiency when compared to that in Europe was similar for the CHP plants and higher for heat-only plants. Improving power generation efficiency is required for new power plants producing steam at pressures higher than the current level of 20–30 bar. Over ten of the existing plants needed to increase their energy efficiency by installing new equipment such as steam turbines for excess steam. Finally, transboundary centralization of WtE plants between neighboring local authorities is essential for heat utilization since many existing small-scale plants (<50 t/day capacity) do not recover heat. Full article
(This article belongs to the Special Issue Combined Heat and Power – Strategy and Practice)
Open AccessArticle Variable DC-Link Voltage Algorithm with a Wide Range of Maximum Power Point Tracking for a Two-String PV System
Energies 2013, 6(1), 58-78; doi:10.3390/en6010058
Received: 24 October 2012 / Revised: 21 November 2012 / Accepted: 25 December 2012 / Published: 2 January 2013
Cited by 15 | PDF Full-text (2148 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a variable DC-link reference voltage algorithm for wide range of maximum power point tracking (MPPT) for two-string photovoltaic (PV) systems. A multi-string system, which is a kind of PV system, is widely used due to its many merits (such [...] Read more.
This paper proposes a variable DC-link reference voltage algorithm for wide range of maximum power point tracking (MPPT) for two-string photovoltaic (PV) systems. A multi-string system, which is a kind of PV system, is widely used due to its many merits (such as the ability to use low rating devices, high MPPT efficiency, and so forth). PV systems can choose their input voltages on the basis of their PV cell connection structure. The PV cell connection structure can be restricted because the input voltage and current affect the PV system design. This reduces the MPPT range under some weather conditions. In the restricted PV connection structure, this algorithm enlarges the MPPT range and minimizes the increment of the total harmonic distortion (THD) by selecting the appropriate DC-link voltage reference which is changed by comparing the sorted input voltage. To verify the proposed algorithm, simulation and experiments are conducted to show the results of the performance for the proposed algorithm. Full article
(This article belongs to the Special Issue Solar Energy Systems and Materials)
Open AccessArticle Second-Order Harmonic Reduction Technique for Photovoltaic Power Conditioning Systems Using a Proportional-Resonant Controller
Energies 2013, 6(1), 79-96; doi:10.3390/en6010079
Received: 17 November 2012 / Revised: 6 December 2012 / Accepted: 17 December 2012 / Published: 2 January 2013
Cited by 9 | PDF Full-text (4694 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a second-order harmonic reduction technique using a proportional-resonant (PR) controller for a photovoltaic (PV) power conditioning system (PCS). In a grid-connected single-phase system, inverters create a second-order harmonic at twice the fundamental frequency. A ripple component unsettles the operating [...] Read more.
This paper proposes a second-order harmonic reduction technique using a proportional-resonant (PR) controller for a photovoltaic (PV) power conditioning system (PCS). In a grid-connected single-phase system, inverters create a second-order harmonic at twice the fundamental frequency. A ripple component unsettles the operating points of the PV array and deteriorates the operation of the maximum power point tracking (MPPT) technique. The second-order harmonic component in PV PCS is analyzed using an equivalent circuit of the DC/DC converter and the DC/AC inverter. A new feed-forward compensation technique using a PR controller for ripple reduction is proposed. The proposed algorithm is advantageous in that additional devices are not required and complex calculations are unnecessary. Therefore, this method is cost-effective and simple to implement. The proposed feed-forward compensation technique is verified by simulation and experimental results. Full article
(This article belongs to the Special Issue Solar Energy Systems and Materials)
Open AccessArticle Burning Behaviour of High-Pressure CH4-H2-Air Mixtures
Energies 2013, 6(1), 97-116; doi:10.3390/en6010097
Received: 8 November 2012 / Revised: 7 December 2012 / Accepted: 20 December 2012 / Published: 2 January 2013
Cited by 6 | PDF Full-text (8980 KB) | HTML Full-text | XML Full-text
Abstract
Experimental characterization of the burning behavior of gaseous mixtures has been carried out, analyzing spherical expanding flames. Tests were performed in the Device for Hydrogen-Air Reaction Mode Analysis (DHARMA) laboratory of Istituto Motori—CNR. Based on a high-pressure, constant-volume bomb, the activity is [...] Read more.
Experimental characterization of the burning behavior of gaseous mixtures has been carried out, analyzing spherical expanding flames. Tests were performed in the Device for Hydrogen-Air Reaction Mode Analysis (DHARMA) laboratory of Istituto Motori—CNR. Based on a high-pressure, constant-volume bomb, the activity is aimed at populating a systematic database on the burning properties of CH4, H2 and other species of interest, in conditions typical of internal combustion (i.c.) engines and gas turbines. High-speed shadowgraph is used to record the flame growth, allowing to infer the laminar burning parameters and the flame stability properties. Mixtures of CH4, H2 and air have been analyzed at initial temperature 293÷305 K, initial pressure 3÷18 bar and equivalence ratio  = 1.0. The amount of H2 in the mixture was 0%, 20% and 30% (vol.). The effect of the initial pressure and of the Hydrogen content on the laminar burning velocity and the Markstein length has been evaluated: the relative weight and mutual interaction has been assessed of the two controlling parameters. Analysis has been carried out of the flame instability, expressed in terms of the critical radius for the onset of cellularity, as a function of the operating conditions. Full article
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Open AccessArticle Analytic Modeling of Vehicle Fuel Consumption
Energies 2013, 6(1), 117-127; doi:10.3390/en6010117
Received: 25 September 2012 / Revised: 19 December 2012 / Accepted: 24 December 2012 / Published: 4 January 2013
Cited by 7 | PDF Full-text (411 KB) | HTML Full-text | XML Full-text
Abstract
An analytical method of evaluating vehicle fuel consumption under standard operating conditions is presented. In the proposed model, vehicle fuel consumption is separated into two different operating modes: cruising at constant speed and acceleration. In each of these modes fuel consumption is [...] Read more.
An analytical method of evaluating vehicle fuel consumption under standard operating conditions is presented. In the proposed model, vehicle fuel consumption is separated into two different operating modes: cruising at constant speed and acceleration. In each of these modes fuel consumption is calculated based on the instantaneous engine efficiency, approximated using an analytical function rather than typically considered consumption map. The approximation is based on speed-power decoupling, employing two single dimension polynomials instead of a two-dimensional lookup table. The adequacy and accuracy of the model is verified using experimental calculations. Moreover, it is shown that the effect of various design parameters on vehicle fuel consumption can be studied utilizing the proposed model. Full article
Open AccessArticle Analytical Modeling of Partially Shaded Photovoltaic Systems
Energies 2013, 6(1), 128-144; doi:10.3390/en6010128
Received: 7 November 2012 / Revised: 14 December 2012 / Accepted: 19 December 2012 / Published: 4 January 2013
Cited by 40 | PDF Full-text (1969 KB) | HTML Full-text | XML Full-text
Abstract
As of today, the considerable influence of select environmental variables, especially irradiance intensity, must still be accounted for whenever discussing the performance of a solar system. Therefore, an extensive, dependable modeling method is required in investigating the most suitable Maximum Power Point [...] Read more.
As of today, the considerable influence of select environmental variables, especially irradiance intensity, must still be accounted for whenever discussing the performance of a solar system. Therefore, an extensive, dependable modeling method is required in investigating the most suitable Maximum Power Point Tracking (MPPT) method under different conditions. Following these requirements, MATLAB-programmed modeling and simulation of photovoltaic systems is presented here, by focusing on the effects of partial shading on the output of the photovoltaic (PV) systems. End results prove the reliability of the proposed model in replicating the aforementioned output characteristics in the prescribed setting. The proposed model is chosen because it can, conveniently, simulate the behavior of different ranges of PV systems from a single PV module through the multidimensional PV structure. Full article
(This article belongs to the Special Issue Solar Energy Systems and Materials)
Open AccessArticle Parameterization Studies of Solar Chimneys in the Tropics
Energies 2013, 6(1), 145-163; doi:10.3390/en6010145
Received: 30 October 2012 / Revised: 17 December 2012 / Accepted: 21 December 2012 / Published: 7 January 2013
Cited by 6 | PDF Full-text (613 KB) | HTML Full-text | XML Full-text
Abstract
The paper examines the effect of the solar chimney’s stack height, depth, width and inlet position on the interior performance (air temperature and speed at 1.20 m height above the ground) as well as proposes an optimal tropical solar chimney design. Simulations [...] Read more.
The paper examines the effect of the solar chimney’s stack height, depth, width and inlet position on the interior performance (air temperature and speed at 1.20 m height above the ground) as well as proposes an optimal tropical solar chimney design. Simulations show that the output air temperature remains constant while the solar chimney’s width is the most significant factor influencing output air speed. The solar chimney’s inlet position has limited influence on the output air speed although regions near the solar chimney’s inlet show an increase in air speed. Furthermore, a regression model is developed based on the solar chimney’s stack height, depth and width to predict the interior air speed. To optimize solar chimney in the tropics, the recommendation is to first maximize its width as the interior’s width, while allowing its stack height to be the building’s height. Lastly, the solar chimney’s depth is determined from the regression model by allocating the required interior air speed. Full article
(This article belongs to the Special Issue Energy Efficient Buildings and Green Buildings)
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Open AccessArticle A Comparison of Producer Gas, Biochar, and Activated Carbon from Two Distributed Scale Thermochemical Conversion Systems Used to Process Forest Biomass
Energies 2013, 6(1), 164-183; doi:10.3390/en6010164
Received: 18 September 2012 / Revised: 20 December 2012 / Accepted: 2 January 2013 / Published: 8 January 2013
Cited by 15 | PDF Full-text (853 KB) | XML Full-text
Abstract
Thermochemical biomass conversion systems have the potential to produce heat, power, fuels and other products from forest biomass at distributed scales that meet the needs of some forest industry facilities. However, many of these systems have not been deployed in this sector [...] Read more.
Thermochemical biomass conversion systems have the potential to produce heat, power, fuels and other products from forest biomass at distributed scales that meet the needs of some forest industry facilities. However, many of these systems have not been deployed in this sector and the products they produce from forest biomass have not been adequately described or characterized with regards to chemical properties, possible uses, and markets. This paper characterizes the producer gas, biochar, and activated carbon of a 700 kg h−1 prototype gasification system and a 225 kg h−1 pyrolysis system used to process coniferous sawmill and forest residues. Producer gas from sawmill residues processed with the gasifier had higher energy content than gas from forest residues, with averages of 12.4 MJ m−3 and 9.8 MJ m−3, respectively. Gases from the pyrolysis system averaged 1.3 MJ m−3 for mill residues and 2.5 MJ m−3 for forest residues. Biochars produced have similar particle size distributions and bulk density, but vary in pH and carbon content. Biochars from both systems were successfully activated using steam activation, with resulting BET surface area in the range of commercial activated carbon. Results are discussed in the context of co-locating these systems with forest industry operations. Full article
(This article belongs to the Special Issue Wood to Energy)
Open AccessArticle Experimental Study of a Triple Concentric Tube Heat Exchanger Integrated into a Wood-Based Air-Heating System for Energy-Efficient Dwellings
Energies 2013, 6(1), 184-203; doi:10.3390/en6010184
Received: 30 October 2012 / Revised: 18 December 2012 / Accepted: 21 December 2012 / Published: 8 January 2013
Cited by 2 | PDF Full-text (1025 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, experimental tests conducted on a new wood-based air-heating system for energy-efficient dwellings are presented. The main objective is to evaluate the resulting outlet temperatures and the amount of heat recovered by the ventilation air in order to assess feasibility [...] Read more.
In this paper, experimental tests conducted on a new wood-based air-heating system for energy-efficient dwellings are presented. The main objective is to evaluate the resulting outlet temperatures and the amount of heat recovered by the ventilation air in order to assess feasibility and performance of coupling a mechanical ventilation heat-recovery unit and a triple concentric tube heat exchanger integrated into the chimney of a room-sealed wood-pellet stove to heat an entire house. After introducing the context of this work, the three main components of the combined system developed here, the coupling configuration adopted, as well as the protocol used and the sensors implemented on an experimental setup carried out in a laboratory are detailed in turn. Then, the heat transfer rates obtained from measurements for the various fluids as well as the effectiveness of the heat exchangers are presented and discussed. Finally, the resulting outlet temperatures of the three fluids exchanging in the triple concentric tube heat exchanger studied here are compared to those provided by analytical solutions obtained with a mathematical model. It is shown that heat transfer rates are predicted with a relative difference that is lower than 5% compared to experimental values and that such a system enables to cover all or most of heat losses in an energy efficient building. Full article
(This article belongs to the Special Issue Energy Efficient Buildings and Green Buildings)
Open AccessArticle Numerical Simulation on Head-On Binary Collision of Gel Propellant Droplets
Energies 2013, 6(1), 204-219; doi:10.3390/en6010204
Received: 15 November 2012 / Revised: 25 December 2012 / Accepted: 26 December 2012 / Published: 8 January 2013
Cited by 3 | PDF Full-text (980 KB) | HTML Full-text | XML Full-text
Abstract
Binary collision of droplets is a fundamental form of droplet interaction in the spraying flow field. In order to reveal the central collision mechanism of two gel droplets with equal diameters, an axi-symmetric form of the Navier-Stokes equations are firstly solved and [...] Read more.
Binary collision of droplets is a fundamental form of droplet interaction in the spraying flow field. In order to reveal the central collision mechanism of two gel droplets with equal diameters, an axi-symmetric form of the Navier-Stokes equations are firstly solved and the method of VOF (volume of fluid) is utilized to track the evolution of the gas-liquid free interface. Then, the numerical computation model is validated with Qian’s experimental results on Newtonian liquids. Phenomena of rebound, coalescence and reflexive separation of droplets after collision are investigated, and structures of the complicated flow fields during the collision process are also analyzed in detail. Results show that the maximum shear rate will appear at the point where the flow is redirected and accelerated. Rebound of droplets is determined by the Weber number and viscosity of the fluid together. It can be concluded that the gel droplets are easier to rebound in comparison with the base fluid droplets. The results also show that the alternant appearance along with the deformation of droplets in the radial and axial direction is the main characteristic of the droplet coalescence process, and the deformation amplitude attenuates gradually. Moreover, the reflexive separation process of droplets can be divided into three distinctive stages including the radial expansion, the recovery of the spherical shape, and the axial extension and reflexive separation. The variation trend of the kinetic energy is opposite to that of the surface energy. The maximum deformation of droplets appears in the radial expansion stage; in the case of a low Weber number, the minimum central thickness of a droplet appears later than its maximum deformation, however, this result is on the contrary in the case of a high Weber number. Full article
Open AccessArticle Evaluation of the Water Scarcity Energy Cost for Users
Energies 2013, 6(1), 220-234; doi:10.3390/en6010220
Received: 26 November 2012 / Revised: 24 December 2012 / Accepted: 25 December 2012 / Published: 9 January 2013
Cited by 4 | PDF Full-text (1139 KB) | HTML Full-text | XML Full-text
Abstract
In systems experiencing water scarcity and consequent intermittent supply, users often adopt private tanks that collect water during service periods and supply users when the service is not available. The tank may be fed by gravity or by private pumping stations depending [...] Read more.
In systems experiencing water scarcity and consequent intermittent supply, users often adopt private tanks that collect water during service periods and supply users when the service is not available. The tank may be fed by gravity or by private pumping stations depending on the network pressure level. Once water resources are collected, the tank can supply users by gravity if it is located on the rooftop or by additional pumping if underground. Private tanks thus increase the energy cost of the water supply service for users by introducing several small pumping structures inside the network. The present paper aims to evaluate this users’ energy cost for different private tank configurations. A real case study was analysed, and the results showed that intermittent distribution causes inequalities not only in users’ access to water resource but also costs that users have to bear to have access to water. Full article
(This article belongs to the Special Issue Energy Efficient Buildings and Green Buildings)
Open AccessArticle Heating Energy and Peak-Power Demand in a Standard and Low Energy Building
Energies 2013, 6(1), 235-250; doi:10.3390/en6010235
Received: 7 November 2012 / Revised: 29 December 2012 / Accepted: 31 December 2012 / Published: 9 January 2013
Cited by 2 | PDF Full-text (986 KB) | HTML Full-text | XML Full-text
Abstract
Building energy efficiency legislation has traditionally focused on space heating energy consumption. This has led to a decrease in energy consumption, especially in space heating. However, in the future when more renewable energy is used both on site and in energy systems, [...] Read more.
Building energy efficiency legislation has traditionally focused on space heating energy consumption. This has led to a decrease in energy consumption, especially in space heating. However, in the future when more renewable energy is used both on site and in energy systems, the peak energy demand becomes more important with respect to CO2 emissions and energy security. In this study it was found out the difference between space heating energy consumption was 55%–62% when a low energy and standard building were compared. However, the difference in peak energy demands was only 28%–34%, showing the importance of paying attention to the peak demands as well. Full article
(This article belongs to the Special Issue Energy Efficient Buildings and Green Buildings)
Open AccessArticle Long Term Performance Study of a Direct Methanol Fuel Cell Fed with Alcohol Blends
Energies 2013, 6(1), 282-293; doi:10.3390/en6010282
Received: 7 November 2012 / Revised: 17 December 2012 / Accepted: 5 January 2013 / Published: 11 January 2013
Cited by 6 | PDF Full-text (1062 KB) | HTML Full-text | XML Full-text
Abstract
The use of alcohol blends in direct alcohol fuel cells may be a more environmentally friendly and less toxic alternative to the use of methanol alone in direct methanol fuel cells. This paper assesses the behaviour of a direct methanol fuel cell [...] Read more.
The use of alcohol blends in direct alcohol fuel cells may be a more environmentally friendly and less toxic alternative to the use of methanol alone in direct methanol fuel cells. This paper assesses the behaviour of a direct methanol fuel cell fed with aqueous methanol, aqueous ethanol and aqueous methanol/ethanol blends in a long term experimental study followed by modelling of polarization curves. Fuel cell performance is seen to decrease as the ethanol content rises, and subsequent operation with aqueous methanol only partly reverts this loss of performance. It seems that the difference in the oxidation rate of these alcohols may not be the only factor affecting fuel cell performance. Full article
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Open AccessArticle Optimal Allocation of Wind Turbines by Considering Transmission Security Constraints and Power System Stability
Energies 2013, 6(1), 294-311; doi:10.3390/en6010294
Received: 10 September 2012 / Revised: 27 December 2012 / Accepted: 27 December 2012 / Published: 14 January 2013
Cited by 5 | PDF Full-text (320 KB) | HTML Full-text | XML Full-text
Abstract
A novel optimization methodology consisting of finding the near optimal location of wind turbines (WTs) on a planned transmission network in a secure and cost-effective way is presented on this paper. While minimizing the investment costs of WTs, the algorithm allocates the [...] Read more.
A novel optimization methodology consisting of finding the near optimal location of wind turbines (WTs) on a planned transmission network in a secure and cost-effective way is presented on this paper. While minimizing the investment costs of WTs, the algorithm allocates the turbines so that a desired wind power energy-penetration level is reached. The optimization considers both transmission security and power system stability constraints. The results of the optimization provide regulators with a support instrument to give proper signals to WT investors, in order to achieve secure and cost effective wind power network integration. The proposal is especially aimed at countries in the initial stage of wind power development, where the WT network integration process can still be influenced by policy-makers. The proposed methodology is validated with a real power system. Obtained results are compared with those generated from a business-as-usual (BAU) scenario, in which the WT network allocation is made according to existing WT projects. The proposed WT network allocation scheme not only reduces the total investment costs associated with a determined wind power energy target, but also improves power system stability. Full article
Open AccessArticle Simulation Research on an Electric Vehicle Chassis System Based on a Collaborative Control System
Energies 2013, 6(1), 312-328; doi:10.3390/en6010312
Received: 16 October 2012 / Revised: 24 December 2012 / Accepted: 7 January 2013 / Published: 14 January 2013
Cited by 8 | PDF Full-text (488 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a collaborative control system for an electric vehicle chassis based on a centralized and hierarchical control architecture. The centralized controller was designed for the suspension and steering system, which is used for improving ride comfort and handling stability; the [...] Read more.
This paper presents a collaborative control system for an electric vehicle chassis based on a centralized and hierarchical control architecture. The centralized controller was designed for the suspension and steering system, which is used for improving ride comfort and handling stability; the hierarchical controller was designed for the braking system, which is used for distributing the proportion of hydraulic braking and regenerative braking to improve braking performance. These two sub-controllers function at the same level of the vehicle chassis control system. In order to reduce the potential conflict between the two sub-controllers and realize a coordination optimization of electric vehicle performance, a collaborative controller was built, which serves as the upper controller to carry out an overall coordination analysis according to vehicle signals and revises the decisions of sub-controllers. A simulation experiment was carried out with the MATLAB/Simulink software. The simulation results show that the proposed collaborative control system can achieve an optimized vehicle handling stability and braking safety. Full article
Open AccessArticle Ventilation Heat Recovery from Wood-Burning Domestic Flues. A Theoretical Analysis Based on a Triple Concentric Tube Heat Exchanger
Energies 2013, 6(1), 351-373; doi:10.3390/en6010351
Received: 9 November 2012 / Revised: 24 December 2012 / Accepted: 5 January 2013 / Published: 15 January 2013
Cited by 2 | PDF Full-text (396 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a new air-heating system concept for energy-efficient dwellings. It is a system designed to heat a low-energy building by coupling a heat-recovery ventilation system with a three-fluid heat exchanger located on the chimney of a wood-pellet stove. The proposed [...] Read more.
This paper presents a new air-heating system concept for energy-efficient dwellings. It is a system designed to heat a low-energy building by coupling a heat-recovery ventilation system with a three-fluid heat exchanger located on the chimney of a wood-pellet stove. The proposed work focuses on the heat transfer that occurs between flue gases, the ventilation air and the combustion air within a triple concentric tube heat exchanger with no insulation at its outer surface. The main objective is to predict outlet temperature for the specific geometry of the heat exchanger studied here. Thus, the governing differential equations are derived for a counter-co-current flow arrangement of the three fluids. Then analytical solutions for the steady-state temperature distribution are obtained as well as the amount of heat transferred to the outside. An expression for the effectiveness of the heat exchanger is also proposed. Based on these results, calculations are performed on a case study to predict the fluid temperature distribution along the heat exchanger. Finally, a parametric study is carried out on this case study to assess the influence of the relevant parameters on the effectiveness of the heat exchanger. In addition, computation of heat losses to the outside justifies whether insulation is needed. Full article
(This article belongs to the Special Issue Energy Efficient Buildings and Green Buildings)
Open AccessArticle A Comparison of Optimal Operation of a Residential Fuel Cell Co-Generation System Using Clustered Demand Patterns Based on Kullback-Leibler Divergence
Energies 2013, 6(1), 374-399; doi:10.3390/en6010374
Received: 9 November 2012 / Revised: 3 December 2012 / Accepted: 21 December 2012 / Published: 16 January 2013
Cited by 4 | PDF Full-text (3248 KB) | HTML Full-text | XML Full-text
Abstract
When evaluating residential energy systems like co-generation systems, hot water and electricity demand profiles are critical. In this paper, the authors aim to extract basic time-series demand patterns from two kinds of measured demand (electricity and domestic hot water), and also aim [...] Read more.
When evaluating residential energy systems like co-generation systems, hot water and electricity demand profiles are critical. In this paper, the authors aim to extract basic time-series demand patterns from two kinds of measured demand (electricity and domestic hot water), and also aim to reveal effective demand patterns for primary energy saving. Time-series demand data are categorized with a hierarchical clustering method using a statistical pseudo-distance, which is represented by the generalized Kullback-Leibler divergence of two Gaussian mixture distributions. The classified demand patterns are built using hierarchical clustering and then a comparison is made between the optimal operation of a polymer electrolyte membrane fuel cell co-generation system and the operation of a reference system (a conventional combination of a condensing gas boiler and electricity purchased from the grid) using the appropriately built demand profiles. Our results show that basic demand patterns are extracted by the proposed method, and the heat-to-power ratio of demand, the amount of daily demand, and demand patterns affect the primary energy saving of the co-generation system. Full article
Open AccessArticle Li-Ion Pouch Cells for Vehicle Applications — Studies of Water Transmission and Packing Materials
Energies 2013, 6(1), 400-410; doi:10.3390/en6010400
Received: 12 November 2012 / Revised: 21 December 2012 / Accepted: 11 January 2013 / Published: 16 January 2013
Cited by 1 | PDF Full-text (964 KB) | HTML Full-text | XML Full-text
Abstract
This study includes analysis of encapsulation materials from lithium-ion pouch cells and water vapour transmission rate (WVTR) measurements. WVTR measurements are performed on both fresh and environmentally stressed lithium-ion pouch cells. Capacity measurements are performed on both the fresh and the environmentally [...] Read more.
This study includes analysis of encapsulation materials from lithium-ion pouch cells and water vapour transmission rate (WVTR) measurements. WVTR measurements are performed on both fresh and environmentally stressed lithium-ion pouch cells. Capacity measurements are performed on both the fresh and the environmentally stressed battery cells to identify possible influences on electrochemical performance. Preparation of the battery cells prior to WVTR measurements includes opening of battery cells and extraction of electrode material, followed by resealing the encapsulations and adhesively mounting of gas couplings. A model describing the water diffusion through the thermal welds of the encapsulation are set up based on material analysis of the encapsulation material. Two WVTR equipments with different type of detectors are evaluated in this study. The results from the WVTR measurements show how important it is to perform this type of studies in dry environment and apply a rigorous precondition sequence before testing. Results from modelling confirm that the WVTR method has potential to be used for measurements of water diffusion into lithium-ion pouch cells. Consequently, WVTR measurements should be possible to use as a complement or alternative method to for example Karl Fisher titration. Full article
Open AccessArticle PAT Design Strategy for Energy Recovery in Water Distribution Networks by Electrical Regulation
Energies 2013, 6(1), 411-424; doi:10.3390/en6010411
Received: 23 November 2012 / Revised: 8 January 2013 / Accepted: 10 January 2013 / Published: 17 January 2013
Cited by 23 | PDF Full-text (944 KB) | HTML Full-text | XML Full-text
Abstract
In the management of water distribution networks, large energy savings can be yielded by exploiting the head drop due to the network pressure control strategy, i.e., for leak reductions. Hydropower in small streams is already exploited, but technical solutions combining efficiency and [...] Read more.
In the management of water distribution networks, large energy savings can be yielded by exploiting the head drop due to the network pressure control strategy, i.e., for leak reductions. Hydropower in small streams is already exploited, but technical solutions combining efficiency and economic convenience are still required. In water distribution networks, an additional design problem comes out from the necessity of ensuring a required head drop under variable operating conditions, i.e., head and discharge variations. Both a hydraulic regulation (HR)—via a series-parallel hydraulic circuit- and an electrical regulation (ER)—via inverter- are feasible solutions. A design procedure for the selection of a production device in a series-parallel hydraulic circuit has been recently proposed. The procedure, named VOS (Variable Operating Strategy), is based on the overall plant efficiency criteria and is applied to a water distribution network where a PAT (pump as a turbine) is used in order to produce energy. In the present paper the VOS design procedure has been extended to the electrical regulation and a comparison between HR and ER efficiency and flexibility within a water distribution network is shown: HR was found more flexible than ER and more efficient. Finally a preliminary economic study has been carried out in order to show the viability of both systems, and a shorter payback period of the electromechanical equipment was found for HR mode. Full article
Open AccessArticle Decisions on Energy Demand Response Option Contracts in Smart Grids Based on Activity-Based Costing and Stochastic Programming
Energies 2013, 6(1), 425-443; doi:10.3390/en6010425
Received: 20 November 2012 / Revised: 21 December 2012 / Accepted: 8 January 2013 / Published: 17 January 2013
Cited by 7 | PDF Full-text (668 KB) | HTML Full-text | XML Full-text
Abstract
Smart grids enable a two-way energy demand response capability through which a utility company offers its industrial customers various call options for energy load curtailment. If a customer has the capability to accurately determine whether to accept an offer or not, then [...] Read more.
Smart grids enable a two-way energy demand response capability through which a utility company offers its industrial customers various call options for energy load curtailment. If a customer has the capability to accurately determine whether to accept an offer or not, then in the case of accepting an offer, the customer can earn both an option premium to participate, and a strike price for load curtailments if requested. However, today most manufacturing companies lack the capability to make the correct contract decisions for given offers. This paper proposes a novel decision model based on activity-based costing (ABC) and stochastic programming, developed to accurately evaluate the impact of load curtailments and determine as to whether or not to accept an energy load curtailment offer. The proposed model specifically targets state-transition flexible and Quality-of-Service (QoS) flexible energy use activities to reduce the peak energy demand rate. An illustrative example with the proposed decision model under a call-option based energy demand response scenario is presented. As shown from the example results, the proposed decision model can be used with emerging smart grid opportunities to provide a competitive advantage to the manufacturing industry. Full article
(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)
Open AccessArticle State of Charge Estimation Using the Extended Kalman Filter for Battery Management Systems Based on the ARX Battery Model
Energies 2013, 6(1), 444-470; doi:10.3390/en6010444
Received: 6 November 2012 / Revised: 11 December 2012 / Accepted: 24 December 2012 / Published: 17 January 2013
Cited by 35 | PDF Full-text (935 KB) | HTML Full-text | XML Full-text
Abstract
State of charge (SOC) is a critical factor to guarantee that a battery system is operating in a safe and reliable manner. Many uncertainties and noises, such as fluctuating current, sensor measurement accuracy and bias, temperature effects, calibration errors or even sensor [...] Read more.
State of charge (SOC) is a critical factor to guarantee that a battery system is operating in a safe and reliable manner. Many uncertainties and noises, such as fluctuating current, sensor measurement accuracy and bias, temperature effects, calibration errors or even sensor failure, etc. pose a challenge to the accurate estimation of SOC in real applications. This paper adds two contributions to the existing literature. First, the auto regressive exogenous (ARX) model is proposed here to simulate the battery nonlinear dynamics. Due to its discrete form and ease of implemention, this straightforward approach could be more suitable for real applications. Second, its order selection principle and parameter identification method is illustrated in detail in this paper. The hybrid pulse power characterization (HPPC) cycles are implemented on the 60AH LiFePO4 battery module for the model identification and validation. Based on the proposed ARX model, SOC estimation is pursued using the extended Kalman filter. Evaluation of the adaptability of the battery models and robustness of the SOC estimation algorithm are also verified. The results indicate that the SOC estimation method using the Kalman filter based on the ARX model shows great performance. It increases the model output voltage accuracy, thereby having the potential to be used in real applications, such as EVs and HEVs. Full article
(This article belongs to the Special Issue Vehicle to Grid)
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Open AccessArticle Encouraging Environmentally Friendlier Cars via Fiscal Measures: General Methodology and Application to Belgium
Energies 2013, 6(1), 471-491; doi:10.3390/en6010471
Received: 27 November 2012 / Revised: 10 January 2013 / Accepted: 14 January 2013 / Published: 17 January 2013
Cited by 2 | PDF Full-text (531 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a Belgian tax reform plan is elaborated to respond to the EU proposal that requires member states to restructure passenger car taxation systems, preferentially based on the CO2 emissions of the car. A tax orientation on CO2 [...] Read more.
In this paper, a Belgian tax reform plan is elaborated to respond to the EU proposal that requires member states to restructure passenger car taxation systems, preferentially based on the CO2 emissions of the car. A tax orientation on CO2 emissions alone might however favour diesel vehicles, characterised by a higher fuel efficiency, whereas they release more polluting emissions (PM and NOx) than comparable gasoline vehicles. This paper introduces a methodology, the Ecoscore, as a potential tax assessment basis. The Ecoscore is based on a well-to-wheel framework and enables a comparison of the environmental burden caused by vehicles with different drive trains and using different fuels. A new proposal for a fixed vehicle taxation system, based on the Ecoscore, is launched. In addition, its impact on the life cycle cost of conventional as well as alternative fuelled cars is measured in order to examine its steering effect towards a cleaner vehicle choice. The overall result is that current tax distortions can be corrected by restructuring the vehicle registration tax and annual circulation tax, based on the Ecoscore. To stimulate behavioural changes, such a fiscal policy should however be paired with additional policies that act on the other important aspects that determine the car purchase decision. Full article
Open AccessArticle Gas Path Health Monitoring for a Turbofan Engine Based on a Nonlinear Filtering Approach
Energies 2013, 6(1), 492-513; doi:10.3390/en6010492
Received: 21 September 2012 / Revised: 4 December 2012 / Accepted: 27 December 2012 / Published: 17 January 2013
Cited by 8 | PDF Full-text (723 KB) | HTML Full-text | XML Full-text
Abstract
Different approaches for gas path performance estimation of dynamic systems are commonly used, the most common being the variants of the Kalman filter. The extended Kalman filter (EKF) method is a popular approach for nonlinear systems which combines the traditional Kalman filtering [...] Read more.
Different approaches for gas path performance estimation of dynamic systems are commonly used, the most common being the variants of the Kalman filter. The extended Kalman filter (EKF) method is a popular approach for nonlinear systems which combines the traditional Kalman filtering and linearization techniques to effectively deal with weakly nonlinear and non-Gaussian problems. Its mathematical formulation is based on the assumption that the probability density function (PDF) of the state vector can be approximated to be Gaussian. Recent investigations have focused on the particle filter (PF) based on Monte Carlo sampling algorithms for tackling strong nonlinear and non-Gaussian models. Considering the aircraft engine is a complicated machine, operating under a harsh environment, and polluted by complex noises, the PF might be an available way to monitor gas path health for aircraft engines. Up to this point in time a number of Kalman filtering approaches have been used for aircraft turbofan engine gas path health estimation, but the particle filters have not been used for this purpose and a systematic comparison has not been published. This paper presents gas path health monitoring based on the PF and the constrained extend Kalman particle filter (cEKPF), and then compares the estimation accuracy and computational effort of these filters to the EKF for aircraft engine performance estimation under rapid faults and general deterioration. Finally, the effects of the constraint mechanism and particle number on the cEKPF are discussed. We show in this paper that the cEKPF outperforms the EKF, PF and EKPF, and conclude that the cEKPF is the best choice for turbofan engine health monitoring. Full article
Open AccessArticle Enhanced Operation of Electricity Distribution Grids Through Smart Metering PLC Network Monitoring, Analysis and Grid Conditioning
Energies 2013, 6(1), 539-556; doi:10.3390/en6010539
Received: 2 October 2012 / Revised: 28 November 2012 / Accepted: 10 January 2013 / Published: 21 January 2013
Cited by 16 | PDF Full-text (1457 KB) | HTML Full-text | XML Full-text
Abstract
Low Voltage (LV) electricity distribution grid operations can be improved through a combination of new smart metering systems’ capabilities based on real time Power Line Communications (PLC) and LV grid topology mapping. This paper presents two novel contributions. The first one is [...] Read more.
Low Voltage (LV) electricity distribution grid operations can be improved through a combination of new smart metering systems’ capabilities based on real time Power Line Communications (PLC) and LV grid topology mapping. This paper presents two novel contributions. The first one is a new methodology developed for smart metering PLC network monitoring and analysis. It can be used to obtain relevant information from the grid, thus adding value to existing smart metering deployments and facilitating utility operational activities. A second contribution describes grid conditioning used to obtain LV feeder and phase identification of all connected smart electric meters. Real time availability of such information may help utilities with grid planning, fault location and a more accurate point of supply management. Full article
(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)
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Open AccessArticle Regulatory Compliance and Environmental Benefit Analysis of Combined Heat and Power (CHP) Systems in Taiwan
Energies 2013, 6(1), 557-565; doi:10.3390/en6010557
Received: 2 October 2012 / Revised: 8 January 2013 / Accepted: 10 January 2013 / Published: 22 January 2013
Cited by 2 | PDF Full-text (183 KB) | HTML Full-text | XML Full-text
Abstract
The energy conservation achieved by utilizing waste heat in the energy and industrial sectors has became more and more important after the energy crisis in the 1970s because it plays a vital role in the potential energy-efficiency improvement. In this regard, cogeneration [...] Read more.
The energy conservation achieved by utilizing waste heat in the energy and industrial sectors has became more and more important after the energy crisis in the 1970s because it plays a vital role in the potential energy-efficiency improvement. In this regard, cogeneration (combined heat and power, CHP) systems are thus becoming attractive due to the energy, economic, and environmental policies for pursuing stable electricity supply, sustainable development and environmental pollution mitigation in Taiwan. The objective of this paper is to present an updated analysis of CHP systems in Taiwan during the period from 1990 to 2010. The description in the paper is thus based on an analysis of electricity supply/consumption and its sources from CHP systems during the past two decades, and centered on two important regulations in compliance with CHP systems (i.e., Energy Management Law and Environmental Impact Assessment Act). Based on the total net power generation from CHP systems (i.e., 35,626 GWh) in 2011, it was found that the carbon dioxide reduction benefits were estimated to be around 20,000 Gg. Full article
(This article belongs to the Special Issue Combined Heat and Power – Strategy and Practice)

Review

Jump to: Research

Open AccessReview Smart Grid Technologies in Europe: An Overview
Energies 2013, 6(1), 251-281; doi:10.3390/en6010251
Received: 29 September 2012 / Revised: 5 December 2012 / Accepted: 18 December 2012 / Published: 9 January 2013
Cited by 25 | PDF Full-text (2226 KB) | HTML Full-text | XML Full-text
Abstract
The old electricity network infrastructure has proven to be inadequate, with respect to modern challenges such as alternative energy sources, electricity demand and energy saving policies. Moreover, Information and Communication Technologies (ICT) seem to have reached an adequate level of reliability and [...] Read more.
The old electricity network infrastructure has proven to be inadequate, with respect to modern challenges such as alternative energy sources, electricity demand and energy saving policies. Moreover, Information and Communication Technologies (ICT) seem to have reached an adequate level of reliability and flexibility in order to support a new concept of electricity network — the smart grid. In this work, we will analyse the state-of-the-art of smart grids, in their technical, management, security, and optimization aspects. We will also provide a brief overview of the regulatory aspects involved in the development of a smart grid, mainly from the viewpoint of the European Union. Full article
(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)
Open AccessReview Sustainability of the Biorefinery Industry for Fuel Production
Energies 2013, 6(1), 329-350; doi:10.3390/en6010329
Received: 12 November 2012 / Revised: 17 December 2012 / Accepted: 6 January 2013 / Published: 14 January 2013
Cited by 9 | PDF Full-text (475 KB) | HTML Full-text | XML Full-text
Abstract
Biofuels have been extensively explored and applied in the Brazilian market. In Brazil, ethanol and biodiesel are produced on an industrial scale. Ethanol is commercialized and used in engines in both the hydrated form (96% °GL) and the anhydrous form, mixed with [...] Read more.
Biofuels have been extensively explored and applied in the Brazilian market. In Brazil, ethanol and biodiesel are produced on an industrial scale. Ethanol is commercialized and used in engines in both the hydrated form (96% °GL) and the anhydrous form, mixed with gasoline at a proportion of up to 25% by volume. In turn, biodiesel is blended with diesel in a proportion of 5% by volume. Thus, the goal of the use of biofuels is to contribute to the mitigation of greenhouse gases and other pollutants emitted into the atmosphere during burning. This article describes some recent developments in the characterization of the environmental and economic impacts of the production of these biofuels from different biomass sources. On this regard, this review presents results of life-cycle assessments (LCAs), life-cycle cost assessments (LCCAs) and Structural Path Analysis (SPA), this last one depicting a sectorial perspective rather than LCA process level data approaches. The results showed that the inclusion of biofuels in transportation activities can lead to the mitigation of the environmental impacts of certain activities, such as emissions of greenhouse gases. However, greater attention must be paid to the improvement of agricultural management to decrease fuel, fertilizer and herbicide consumption. Full article
Open AccessReview Catalytic Fast Pyrolysis: A Review
Energies 2013, 6(1), 514-538; doi:10.3390/en6010514
Received: 9 November 2012 / Revised: 7 December 2012 / Accepted: 21 December 2012 / Published: 21 January 2013
Cited by 71 | PDF Full-text (541 KB) | HTML Full-text | XML Full-text
Abstract
Catalytic pyrolysis is a promising thermochemical conversion route for lignocellulosic biomass that produces chemicals and fuels compatible with current, petrochemical infrastructure. Catalytic modifications to pyrolysis bio-oils are geared towards the elimination and substitution of oxygen and oxygen-containing functionalities in addition to increasing [...] Read more.
Catalytic pyrolysis is a promising thermochemical conversion route for lignocellulosic biomass that produces chemicals and fuels compatible with current, petrochemical infrastructure. Catalytic modifications to pyrolysis bio-oils are geared towards the elimination and substitution of oxygen and oxygen-containing functionalities in addition to increasing the hydrogen to carbon ratio of the final products. Recent progress has focused on both hydrodeoxygenation and hydrogenation of bio-oil using a variety of metal catalysts and the production of aromatics from bio-oil using cracking zeolites. Research is currently focused on developing multi-functional catalysts used in situ that benefit from the advantages of both hydrodeoxygenation and zeolite cracking. Development of robust, highly selective catalysts will help achieve the goal of producing drop-in fuels and petrochemical commodities from wood and other lignocellulosic biomass streams. The current paper will examine these developments by means of a review of existing literature. Full article

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