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Energies, Volume 7, Issue 7 (July 2014) , Pages 4054-4726

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Open AccessArticle
Research on Cellular Instabilities of Lean Premixed Syngas Flames under Various Hydrogen Fractions Using a Constant Volume Vessel
Energies 2014, 7(7), 4710-4726; https://doi.org/10.3390/en7074710
Received: 2 April 2014 / Revised: 10 July 2014 / Accepted: 15 July 2014 / Published: 22 July 2014
Cited by 6 | Viewed by 2106 | PDF Full-text (1346 KB) | HTML Full-text | XML Full-text
Abstract
An experimental study of the intrinsic instabilities of H2/CO lean (φ = 0.4 to φ = 1.0) premixed flames at different hydrogen fractions ranging from 0% to 100% at elevated pressure and room temperature was performed in a constant volume vessel [...] Read more.
An experimental study of the intrinsic instabilities of H2/CO lean (φ = 0.4 to φ = 1.0) premixed flames at different hydrogen fractions ranging from 0% to 100% at elevated pressure and room temperature was performed in a constant volume vessel using a Schlieren system. The unstretched laminar burning velocities were compared with data from the previous literature and simulated results. The results indicate that excellent agreements are obtained. The cellular instabilities of syngas-air flames were discussed and critical flame radii were measured. When hydrogen fractions are above 50%, the flame tends to be more stable as the equivalence ratio increases; however, the instability increases for flames of lower hydrogen fractions. For the premixed syngas flame with hydrogen fractions greater than 50%, the decline in cellular instabilities induced by the increase in equivalence ratio can be attributed to a reduction of diffusive-thermal instabilities rather than increased hydrodynamic instabilities. For premixed syngas flames with hydrogen fractions lower than 50%, as the equivalence ratio increases, the cellular instabilities become more evident because the enhanced hydrodynamic instabilities become the dominant effect. For premixed syngas flames, the enhancement of cellular instabilities induced by the increase in hydrogen fraction is the result of both increasing diffusive-thermal and hydrodynamic instabilities. Full article
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Open AccessArticle
Modeling and Simulation of Enzymatic Biofuel Cells with Three-Dimensional Microelectrodes
Energies 2014, 7(7), 4694-4709; https://doi.org/10.3390/en7074694
Received: 19 March 2014 / Revised: 2 July 2014 / Accepted: 4 July 2014 / Published: 22 July 2014
Cited by 12 | Viewed by 2491 | PDF Full-text (3279 KB) | HTML Full-text | XML Full-text
Abstract
The enzymatic biofuel cells (EBFCs) are considered as an attractive candidate for powering future implantable medical devices. In this study, a computational model of EBFCs based on three-dimensional (3-D) interdigitated microelectrode arrays was conducted. The main focus of this research is to investigate [...] Read more.
The enzymatic biofuel cells (EBFCs) are considered as an attractive candidate for powering future implantable medical devices. In this study, a computational model of EBFCs based on three-dimensional (3-D) interdigitated microelectrode arrays was conducted. The main focus of this research is to investigate the effect of different designs and spatial distributions of the microelectrode arrays on mass transport of fuels, enzymatic reaction rate, open circuit output potential and current density. To optimize the performance of the EBFCs, numerical simulations have been performed for cylindrical electrodes with various electrode heights and well widths. Optimized cell performance was obtained when the well width is half of the height of the 3-D electrode. In addition, semi-elliptical shaped electrode is preferred based on the results from current density and resistive heating simulation. Full article
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Open AccessArticle
Current State of Technology of Fuel Cell Power Systems for Autonomous Underwater Vehicles
Energies 2014, 7(7), 4676-4693; https://doi.org/10.3390/en7074676
Received: 3 June 2014 / Revised: 8 July 2014 / Accepted: 16 July 2014 / Published: 22 July 2014
Cited by 25 | Viewed by 2952 | PDF Full-text (210 KB) | HTML Full-text | XML Full-text
Abstract
Autonomous Underwater Vehicles (AUVs) are vehicles that are primarily used to accomplish oceanographic research data collection and auxiliary offshore tasks. At the present time, they are usually powered by lithium-ion secondary batteries, which have insufficient specific energies. In order for this technology to [...] Read more.
Autonomous Underwater Vehicles (AUVs) are vehicles that are primarily used to accomplish oceanographic research data collection and auxiliary offshore tasks. At the present time, they are usually powered by lithium-ion secondary batteries, which have insufficient specific energies. In order for this technology to achieve a mature state, increased endurance is required. Fuel cell power systems have been identified as an effective means to achieve this endurance but no implementation in a commercial device has yet been realized. This paper summarizes the current state of development of the technology in this field of research. First, the most adequate type of fuel cell for this application is discussed. The prototypes and design concepts of AUVs powered by fuel cells which have been developed in the last few years are described. Possible commercial and experimental fuel cell stack options are analyzed, examining solutions adopted in the analogous aerial vehicle applications, as well as the underwater ones, to see if integration in an AUV is feasible. Current solutions in oxygen and hydrogen storage systems are overviewed and energy density is objectively compared between battery power systems and fuel cell power systems for AUVs. A couple of system configuration solutions are described including the necessary lithium-ion battery hybrid system. Finally, some closing remarks on the future of this technology are given. Full article
Open AccessArticle
SDP Policy Iteration-Based Energy Management Strategy Using Traffic Information for Commuter Hybrid Electric Vehicles
Energies 2014, 7(7), 4648-4675; https://doi.org/10.3390/en7074648
Received: 17 April 2014 / Revised: 26 May 2014 / Accepted: 18 June 2014 / Published: 22 July 2014
Cited by 13 | Viewed by 2824 | PDF Full-text (2387 KB) | HTML Full-text | XML Full-text
Abstract
This paper demonstrates an energy management method using traffic information for commuter hybrid electric vehicles. A control strategy based on stochastic dynamic programming (SDP) is developed, which minimizes on average the equivalent fuel consumption, while satisfying the battery charge-sustaining constraints and the overall [...] Read more.
This paper demonstrates an energy management method using traffic information for commuter hybrid electric vehicles. A control strategy based on stochastic dynamic programming (SDP) is developed, which minimizes on average the equivalent fuel consumption, while satisfying the battery charge-sustaining constraints and the overall vehicle power demand for drivability. First, according to the sample information of the traffic speed profiles, the regular route is divided into several segments and the statistic characteristics in the different segments are constructed from gathered data on the averaged vehicle speeds. And then, the energy management problem is formulated as a stochastic nonlinear and constrained optimal control problem and a modified policy iteration algorithm is utilized to generate a time-invariant state-dependent power split strategy. Finally, simulation results over some driving cycles are presented to demonstrate the effectiveness of the proposed energy management strategy. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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Open AccessArticle
Finite Action-Set Learning Automata for Economic Dispatch Considering Electric Vehicles and Renewable Energy Sources
Energies 2014, 7(7), 4629-4647; https://doi.org/10.3390/en7074629
Received: 19 May 2014 / Revised: 10 July 2014 / Accepted: 11 July 2014 / Published: 22 July 2014
Cited by 3 | Viewed by 3198 | PDF Full-text (466 KB) | HTML Full-text | XML Full-text
Abstract
The coming interaction between a growing electrified vehicle fleet and the desired growth in renewable energy provides new insights into the economic dispatch (ED) problem. This paper presents an economic dispatch model that considers electric vehicle charging, battery exchange stations, and wind farms. [...] Read more.
The coming interaction between a growing electrified vehicle fleet and the desired growth in renewable energy provides new insights into the economic dispatch (ED) problem. This paper presents an economic dispatch model that considers electric vehicle charging, battery exchange stations, and wind farms. This ED model is a high-dimensional, non-linear, and stochastic problem and its solution requires powerful methods. A new finite action-set learning automata (FALA)-based approach that has the ability to adapt to a stochastic environment is proposed. The feasibility of the proposed approach is demonstrated in a modified IEEE 30 bus system. It is compared with continuous action-set learning automata and particle swarm optimization-based approaches in terms of convergence characteristics, computational efficiency, and solution quality. Simulation results show that the proposed FALA-based approach was indeed capable of more efficiently obtaining the approximately optimal solution. In addition, by using an optimal dispatch schedule for the interaction between electric vehicle stations and power systems, it is possible to reduce the gap between demand and power generation at different times of the day. Full article
(This article belongs to the Special Issue Energy Transitions and Economic Change)
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Open AccessArticle
A Neural Network Combined Inverse Controller for a Two-Rear-Wheel Independently Driven Electric Vehicle
Energies 2014, 7(7), 4614-4628; https://doi.org/10.3390/en7074614
Received: 14 April 2014 / Revised: 12 June 2014 / Accepted: 8 July 2014 / Published: 22 July 2014
Cited by 7 | Viewed by 2792 | PDF Full-text (705 KB) | HTML Full-text | XML Full-text
Abstract
Vehicle active safety control is attracting ever increasing attention in the attempt to improve the stability and the maneuverability of electric vehicles. In this paper, a neural network combined inverse (NNCI) controller is proposed, incorporating the merits of left-inversion and right-inversion. As the [...] Read more.
Vehicle active safety control is attracting ever increasing attention in the attempt to improve the stability and the maneuverability of electric vehicles. In this paper, a neural network combined inverse (NNCI) controller is proposed, incorporating the merits of left-inversion and right-inversion. As the left-inversion soft-sensor can estimate the sideslip angle, while the right-inversion is utilized to decouple control. Then, the proposed NNCI controller not only linearizes and decouples the original nonlinear system, but also directly obtains immeasurable state feedback in constructing the right-inversion. Hence, the proposed controller is very practical in engineering applications. The proposed system is co-simulated based on the vehicle simulation package CarSim in connection with Matlab/Simulink. The results verify the effectiveness of the proposed control strategy. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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Open AccessArticle
Electrical Performance and Carbon Deposition Differences between the Bi-Layer Interconnector and Conventional Straight Interconnector Solid Oxide Fuel Cell
Energies 2014, 7(7), 4601-4613; https://doi.org/10.3390/en7074601
Received: 20 May 2014 / Revised: 7 July 2014 / Accepted: 16 July 2014 / Published: 22 July 2014
Cited by 4 | Viewed by 2694 | PDF Full-text (1020 KB) | HTML Full-text | XML Full-text
Abstract
Carbon deposition considered in a solid oxide fuel cell (SOFC) model may be influenced by the operating voltage, inlet water/methane ratio, working temperature and pressure, inlet molar fraction of fuel and so on. The effects of these parameters in a planar SOFC implementing [...] Read more.
Carbon deposition considered in a solid oxide fuel cell (SOFC) model may be influenced by the operating voltage, inlet water/methane ratio, working temperature and pressure, inlet molar fraction of fuel and so on. The effects of these parameters in a planar SOFC implementing a novel bi-layer interconnector are not well understood. This paper is focused on the numerical study of carbon deposition and electrical performance of a bi-layer interconnector planar SOFC. The results illustrate that the electrical performance of the bi-layer interconnector SOFC is 11% higher than that of the conventional straight interconnector SOFC with initial state. After 120 days of operation, the electrical performance of the bi-layer interconnector SOFC has a slight decrease and more carbon deposit because of the increased electrochemical reaction rate. However, these differences minimize if higher operating voltages are involved. Full article
(This article belongs to the Special Issue Reacting Transport Phenomena in Solid Oxide Fuel Cells)
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Open AccessDiscussion
Understanding of Sulfurized Polyacrylonitrile for Superior Performance Lithium/Sulfur Battery
Energies 2014, 7(7), 4588-4600; https://doi.org/10.3390/en7074588
Received: 20 May 2014 / Revised: 17 June 2014 / Accepted: 10 July 2014 / Published: 18 July 2014
Cited by 67 | Viewed by 4205 | PDF Full-text (998 KB) | HTML Full-text | XML Full-text
Abstract
Sulfurized polyacrylonitrile (SPAN) is one of the most important sulfurized carbon materials that can potentially be coupled with the carbonaceous anode to fabricate a safe and low cost “all carbon” lithium-ion battery. However, its chemical structure and electrochemical properties have been poorly understood. [...] Read more.
Sulfurized polyacrylonitrile (SPAN) is one of the most important sulfurized carbon materials that can potentially be coupled with the carbonaceous anode to fabricate a safe and low cost “all carbon” lithium-ion battery. However, its chemical structure and electrochemical properties have been poorly understood. In this discussion, we analyze the previously published data in combination with our own results to propose a more reasonable chemical structure that consists of short –Sx– chains covalently bonded onto cyclized, partially dehydrogenated, and ribbon-like polyacrylonitrile backbones. The proposed structure fits all previous structural characterizations and explains many unique electrochemical phenomena that were observed from the Li/SPAN cells but have not been understood clearly. Full article
(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)
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Open AccessArticle
Saturation Detection-Based Blocking Scheme for Transformer Differential Protection
Energies 2014, 7(7), 4571-4587; https://doi.org/10.3390/en7074571
Received: 26 February 2014 / Revised: 27 June 2014 / Accepted: 10 July 2014 / Published: 18 July 2014
Cited by 2 | Viewed by 2774 | PDF Full-text (794 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes a current differential relay for transformer protection that operates in conjunction with a core saturation detection-based blocking algorithm. The differential current for the magnetic inrush or over-excitation has a point of inflection at the start and end of each saturation [...] Read more.
This paper describes a current differential relay for transformer protection that operates in conjunction with a core saturation detection-based blocking algorithm. The differential current for the magnetic inrush or over-excitation has a point of inflection at the start and end of each saturation period of the transformer core. At these instants, discontinuities arise in the first-difference function of the differential current. The second- and third-difference functions convert the points of inflection into pulses, the magnitudes of which are large enough to detect core saturation. The blocking signal is activated if the third-difference of the differential current is larger than the threshold and is maintained for one cycle. In addition, a method to discriminate between transformer saturation and current transformer (CT) saturation is included. The performance of the proposed blocking scheme was compared with that of a conventional harmonic blocking method. The test results indicate that the proposed scheme successfully discriminates internal faults even with CT saturation from the magnetic inrush, over-excitation, and external faults with CT saturation, and can significantly reduce the operating time delay of the relay. Full article
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Open AccessArticle
Real World Operation of a Complex Plug-in Hybrid Electric Vehicle: Analysis of Its CO2 Emissions and Operating Costs
Energies 2014, 7(7), 4554-4570; https://doi.org/10.3390/en7074554
Received: 16 April 2014 / Revised: 7 July 2014 / Accepted: 7 July 2014 / Published: 16 July 2014
Cited by 3 | Viewed by 3200 | PDF Full-text (1888 KB) | HTML Full-text | XML Full-text
Abstract
Plug-in hybrid electric vehicles (pHEVs) could represent the stepping stone to move towards a more sustainable mobility and combine the benefits of electric powertrains with the high range capability of conventional vehicles. Nevertheless, despite the huge potential in terms of CO2 emissions [...] Read more.
Plug-in hybrid electric vehicles (pHEVs) could represent the stepping stone to move towards a more sustainable mobility and combine the benefits of electric powertrains with the high range capability of conventional vehicles. Nevertheless, despite the huge potential in terms of CO2 emissions reduction, the performance of such vehicles has to be deeply investigated in real world driving conditions considering also the CO2 production related to battery recharge which, on the contrary, is currently only partially considered by the European regulation to foster the diffusion of pHEVs. Therefore, this paper aims to assess, through numerical simulation, the real performance of a test case pHEV, the energy management system (EMS) of which is targeted to the minimization of its overall CO2 emissions. The paper highlights, at the same time, the relevance of the CO2 production related to the battery recharge from the power grid. Different technologies mixes used to produce the electricity required for the battery recharge are also taken into account in order to assess the influence of this parameter on the vehicle CO2 emissions. Finally, since the operating cost still represents the main driver in orienting the customer’s choice, an alternative approach for the EMS, targeted to the minimization of this variable, is also analyzed. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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Open AccessArticle
On the Design and Response of Domestic Ground-Source Heat Pumps in the UK
Energies 2014, 7(7), 4532-4553; https://doi.org/10.3390/en7074532
Received: 30 April 2014 / Revised: 7 July 2014 / Accepted: 9 July 2014 / Published: 15 July 2014
Cited by 6 | Viewed by 2622 | PDF Full-text (1013 KB) | HTML Full-text | XML Full-text
Abstract
The design and response of ground source heat pumps coupled to vertical closed loop arrays in UK domestic applications are investigated in this article. Two typical UK house types are selected as the vehicle for the study and a detailed dynamic thermal modelling [...] Read more.
The design and response of ground source heat pumps coupled to vertical closed loop arrays in UK domestic applications are investigated in this article. Two typical UK house types are selected as the vehicle for the study and a detailed dynamic thermal modelling method is used to arrive at time-series heating demands for the two houses. A new empirical heat pump model is derived using experimental data taking into account the deteriorating performance of the heat pump during periods of light load. The heat pump model is incorporated into an existing numerical ground model and completed with a classical effectiveness type heat exchange model of the closed loop array. The model is used to analyse array sizing and performance over an extended time period, as well as sensitivity of the design to soil conductivity and borehole heat exchanger resistance and sensitivity to over-sizing and part-load behavior of the heat pump. Results show that the UK’s standard for ground source design (the Microgeneration Certification Scheme) may lead to under-estimated array sizes and that heating system over-sizing and deleterious part-load heat pump performance can add up to 20% to the electrical consumption of these systems. Full article
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Open AccessArticle
Experimental and Numerical Study of Jet Controlled Compression Ignition on Combustion Phasing Control in Diesel Premixed Compression Ignition Systems
Energies 2014, 7(7), 4519-4531; https://doi.org/10.3390/en7074519
Received: 8 April 2014 / Revised: 27 May 2014 / Accepted: 8 July 2014 / Published: 15 July 2014
Cited by 4 | Viewed by 2474 | PDF Full-text (583 KB) | HTML Full-text | XML Full-text
Abstract
In order to directly control the premixed combustion phasing, a Jet Controlled Compression Ignition (JCCI) for diesel premixed compression ignition systems is investigated. Experiments were conducted on a single cylinder natural aspirated diesel engine without EGR at 3000 rpm. Numerical models were validated [...] Read more.
In order to directly control the premixed combustion phasing, a Jet Controlled Compression Ignition (JCCI) for diesel premixed compression ignition systems is investigated. Experiments were conducted on a single cylinder natural aspirated diesel engine without EGR at 3000 rpm. Numerical models were validated by load sweep experiments at fixed spark timing. Detailed combustion characteristics were analyzed based on the BMEP of 2.18 bar. The simulation results showed that the high temperature jets of reacting active radical species issued from the ignition chamber played an important role on the onset of combustion in the JCCI system. The combustion of diesel pre-mixtures was initiated rapidly by the combustion products issued from the ignition chamber. Moreover, the flame propagation was not obvious, similar to that in Pre-mixed Charge Compression Ignition (PCCI). Consequently, spark timing sweep experiments were conducted. The results showed a good linear relationship between spark timing in the ignition chamber and CA10 and CA50, which indicated the ability for direct combustion phasing control in diesel PCCI. The NOx and soot emissions gradually changed with the decrease of spark advance angle. The maximum reduction of NOx and soot were both over 90%, and HC and CO emissions were increased. Full article
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Open AccessArticle
Gain Scheduling Control of an Islanded Microgrid Voltage
Energies 2014, 7(7), 4498-4518; https://doi.org/10.3390/en7074498
Received: 19 May 2014 / Revised: 20 June 2014 / Accepted: 4 July 2014 / Published: 14 July 2014
Cited by 6 | Viewed by 2197 | PDF Full-text (925 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this research study has been to design a gain scheduling (GS) digital controller in order to control the voltage of an islanded microgrid in the presence of fast varying loads (FVLs), and to compare it to a robust controller. The [...] Read more.
The aim of this research study has been to design a gain scheduling (GS) digital controller in order to control the voltage of an islanded microgrid in the presence of fast varying loads (FVLs), and to compare it to a robust controller. The inverter which feeds the microgrid is connected to it through an inductance-capacitor-inductance (LCL) filter. The oscillatory and nonlinear behaviour of the plant is analyzed in the whole operating zone. Afterwards, the design of the controllers which contain two loops in cascade are described. The first loop concerns the current control, while the second is linked to the voltage regulation. Two controllers, one defined as Robust and another one as GS controller, are designed for the two loops, emphasizing in their robustness and their ability to damp the oscillatory plant behaviour. To finish, some simulations are carried out to study and compare the two kinds of controllers in different operating points. The results show that both controllers damp the oscillatory behaviour of the plant in closed loop (CL), and that the GS controller ensures a better rejection of current disturbances from FVLs. Full article
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Open AccessArticle
Thermoeconomic Analysis of Hybrid Power Plant Concepts for Geothermal Combined Heat and Power Generation
Energies 2014, 7(7), 4482-4497; https://doi.org/10.3390/en7074482
Received: 11 April 2014 / Revised: 20 May 2014 / Accepted: 1 July 2014 / Published: 14 July 2014
Cited by 12 | Viewed by 3389 | PDF Full-text (317 KB) | HTML Full-text | XML Full-text
Abstract
We present a thermo-economic analysis for a low-temperature Organic Rankine Cycle (ORC) in a combined heat and power generation (CHP) case. For the hybrid power plant, thermal energy input is provided by a geothermal resource coupled with the exhaust gases of a biogas [...] Read more.
We present a thermo-economic analysis for a low-temperature Organic Rankine Cycle (ORC) in a combined heat and power generation (CHP) case. For the hybrid power plant, thermal energy input is provided by a geothermal resource coupled with the exhaust gases of a biogas engine. A comparison to alternative geothermal CHP concepts is performed by considering variable parameters like ORC working fluid, supply temperature of the heating network or geothermal water temperature. Second law efficiency as well as economic parameters show that hybrid power plants are more efficient compared to conventional CHP concepts or separate use of the energy sources. Full article
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Open AccessReview
Effect of Lignocellulose Related Compounds on Microalgae Growth and Product Biosynthesis: A Review
Energies 2014, 7(7), 4446-4481; https://doi.org/10.3390/en7074446
Received: 4 May 2014 / Revised: 30 June 2014 / Accepted: 1 July 2014 / Published: 11 July 2014
Cited by 16 | Viewed by 4675 | PDF Full-text (936 KB) | HTML Full-text | XML Full-text
Abstract
Microalgae contain valuable compounds that can be harnessed for industrial applications. Lignocellulose biomass is a plant material containing in abundance organic substances such as carbohydrates, phenolics, organic acids and other secondary compounds. As growth of microalgae on organic substances was confirmed during heterotrophic [...] Read more.
Microalgae contain valuable compounds that can be harnessed for industrial applications. Lignocellulose biomass is a plant material containing in abundance organic substances such as carbohydrates, phenolics, organic acids and other secondary compounds. As growth of microalgae on organic substances was confirmed during heterotrophic and mixotrophic cultivation, lignocellulose derived compounds can become a feedstock to cultivate microalgae and produce target compounds. In this review, different treatment methods to hydrolyse lignocellulose into organic substrates are presented first. Secondly, the effect of lignocellulosic hydrolysates, organic substances typically present in lignocellulosic hydrolysates, as well as minor co-products, on growth and accumulation of target compounds in microalgae cultures is described. Finally, the possibilities of using lignocellulose hydrolysates as a common feedstock for microalgae cultures are evaluated. Full article
(This article belongs to the Special Issue Algae Based Technologies)
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Open AccessArticle
Promoting Second Generation Biofuels: Does the First Generation Pave the Road?
Energies 2014, 7(7), 4430-4445; https://doi.org/10.3390/en7074430
Received: 6 May 2014 / Revised: 3 July 2014 / Accepted: 7 July 2014 / Published: 11 July 2014
Cited by 15 | Viewed by 3311 | PDF Full-text (589 KB) | HTML Full-text | XML Full-text
Abstract
The U.S., Brazil and a number of European and other countries worldwide have introduced various support schemes for bioethanol and biodiesel. The advantage of these biofuels is that they are relatively easily integrated with the current fossil fuel-based transport sector, at least up [...] Read more.
The U.S., Brazil and a number of European and other countries worldwide have introduced various support schemes for bioethanol and biodiesel. The advantage of these biofuels is that they are relatively easily integrated with the current fossil fuel-based transport sector, at least up to a certain point. However, recent studies point to various negative effects of expanding the production of first generation (1G) biofuels further. 1G biofuels’ problems can be overcome by a transition to second generation (2G) biofuels. So far, 2G biofuels are much more costly to produce. We therefore ask: to what extent is targeted support to 2G biofuels likely to bring costs down? Additionally, are current support schemes for biofuels well designed in order to promote the development of 2G biofuels? We find that the prospects for cost reduction look better for 2G bioethanol than for 2G biodiesel. Bioethanol made from cellulose is far from a ripe technology, with several cost-reducing opportunities yet to be developed. Hence, targeted support to cellulosic ethanol might induce a switch from 1G to 2G biofuels. However, we find little evidence that production and use of 1G bioethanol will bridge the conversion to 2G bioethanol. Hence, to the extent that private investment in the development of 2G bioethanol is too low, current support schemes for 1G biofuels may block 2G bioethanol instead of promoting it. Full article
(This article belongs to the Special Issue Energy Transitions and Economic Change)
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Open AccessArticle
Microalgae Harvest through Fungal Pelletization—Co-Culture of Chlorella vulgaris and Aspergillus niger
Energies 2014, 7(7), 4417-4429; https://doi.org/10.3390/en7074417
Received: 6 June 2014 / Revised: 3 July 2014 / Accepted: 4 July 2014 / Published: 10 July 2014
Cited by 16 | Viewed by 2989 | PDF Full-text (625 KB) | HTML Full-text | XML Full-text
Abstract
Microalgae harvesting is a labor- and energy-intensive process and new approaches to harvesting microalgae need to be developed in order to decrease the costs. In this study; co-cultivatation of filamentous fungus (Aspergillus niger) and microalgae (Chlorella vulgaris) to form [...] Read more.
Microalgae harvesting is a labor- and energy-intensive process and new approaches to harvesting microalgae need to be developed in order to decrease the costs. In this study; co-cultivatation of filamentous fungus (Aspergillus niger) and microalgae (Chlorella vulgaris) to form cell pellets was evaluated under different conditions, including organic carbon source (glucose; glycerol; and sodium acetate) concentration; initial concentration of fungal spores and microalgal cells and light. Results showed that 2 g/L of glucose with a 1:300 ratio of fungi to microalgae provided the best culturing conditions for the process to reach >90% of cell harvest efficiency. The results also showed that an organic carbon source was required to sustain the growth of fungi and form the cell pellets. The microalgae/fungi co-cultures at mixotrophic conditions obtained much higher total biomass than pure cultures of each individual strains; indicating the symbiotic relationship between two strains. This can benefit the microbial biofuel production in terms of cell harvest and biomass production. Full article
(This article belongs to the Special Issue Algae Based Technologies)
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Open AccessArticle
Deep Geothermal Energy Production in Germany
Energies 2014, 7(7), 4397-4416; https://doi.org/10.3390/en7074397
Received: 5 May 2014 / Revised: 17 June 2014 / Accepted: 23 June 2014 / Published: 9 July 2014
Cited by 34 | Viewed by 6942 | PDF Full-text (2082 KB) | HTML Full-text | XML Full-text
Abstract
Germany uses its low enthalpy hydrothermal resources predominantly for balneological applications, space and district heating, but also for power production. The German Federal government supports the development of geothermal energy in terms of project funding, market incentives and credit offers, as well as [...] Read more.
Germany uses its low enthalpy hydrothermal resources predominantly for balneological applications, space and district heating, but also for power production. The German Federal government supports the development of geothermal energy in terms of project funding, market incentives and credit offers, as well as a feed-in tariff for geothermal electricity. Although new projects for district heating take on average six years, geothermal energy utilisation is growing rapidly, especially in southern Germany. From 2003 to 2013, the annual production of geothermal district heating stations increased from 60 GWh to 530 GWh. In the same time, the annual power production increased from 0 GWh to 36 GWh. Currently, almost 200 geothermal facilities are in operation or under construction in Germany. A feasibility study including detailed geological site assessment is still essential when planning a new geothermal facility. As part of this assessment, a lot of geological data, hydraulic data, and subsurface temperatures can be retrieved from the geothermal information system GeotIS, which can be accessed online [1]. Full article
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Open AccessArticle
Modeling of Proton-Conducting Solid Oxide Fuel Cells Fueled with Syngas
Energies 2014, 7(7), 4381-4396; https://doi.org/10.3390/en7074381
Received: 25 April 2014 / Revised: 27 June 2014 / Accepted: 3 July 2014 / Published: 9 July 2014
Cited by 8 | Viewed by 2631 | PDF Full-text (1319 KB) | HTML Full-text | XML Full-text
Abstract
Solid oxide fuel cells (SOFCs) with proton conducting electrolyte (H-SOFCs) are promising power sources for stationary applications. Compared with other types of fuel cells, one distinct feature of SOFC is their fuel flexibility. In this study, a 2D model is developed to investigate [...] Read more.
Solid oxide fuel cells (SOFCs) with proton conducting electrolyte (H-SOFCs) are promising power sources for stationary applications. Compared with other types of fuel cells, one distinct feature of SOFC is their fuel flexibility. In this study, a 2D model is developed to investigate the transport and reaction in an H-SOFC fueled with syngas, which can be produced from conventional natural gas or renewable biomass. The model fully considers the fluid flow, mass transfer, heat transfer and reactions in the H-SOFC. Parametric studies are conducted to examine the physical and chemical processes in H-SOFC with a focus on how the operating parameters affect the H-SOFC performance. It is found that the presence of CO dilutes the concentration of H2, thus decreasing the H-SOFC performance. With typical syngas fuel, adding H2O cannot enhance the performance of the H-SOFC, although water gas shift reaction can facilitate H2 production. Full article
(This article belongs to the Special Issue Reacting Transport Phenomena in Solid Oxide Fuel Cells)
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Open AccessArticle
Influence of Chemical Blends on Palm Oil Methyl Esters’ Cold Flow Properties and Fuel Characteristics
Energies 2014, 7(7), 4364-4380; https://doi.org/10.3390/en7074364
Received: 25 February 2014 / Revised: 28 June 2014 / Accepted: 2 July 2014 / Published: 8 July 2014
Cited by 24 | Viewed by 3129 | PDF Full-text (716 KB) | HTML Full-text | XML Full-text
Abstract
Alternative fuels, like biodiesel, are being utilized as a renewable energy source and an effective substitute for the continuously depleting supply of mineral diesel as they have similar combustion characteristics. However, the use of pure biodiesel as a fuel for diesel engines is [...] Read more.
Alternative fuels, like biodiesel, are being utilized as a renewable energy source and an effective substitute for the continuously depleting supply of mineral diesel as they have similar combustion characteristics. However, the use of pure biodiesel as a fuel for diesel engines is currently limited due to problems relating to fuel properties and its relatively poor cold flow characteristics. Therefore, the most acceptable option for improving the properties of biodiesel is the use of a fuel additive. In the present study, the properties of palm oil methyl esters with increasing additive content were investigated after addition of ethanol, butanol and diethyl ether. The results revealed varying improvement in acid value, density, viscosity, pour point and cloud point, accompanied by a slight decrease in energy content with an increasing additive ratio. The viscosity reductions at 5% additive were 12%, 7%, 16.5% for ethanol, butanol and diethyl ether, respectively, and the maximum reduction in pour point was 5 °C at 5% diethyl ether blend. Engine test results revealed a noticeable improvement in engine brake power and specific fuel consumption compared to palm oil biodiesel and the best performance was obtained with diethyl ether. All the biodiesel-additive blend samples meet the requirements of ASTM D6751 biodiesel fuel standards for the measured properties. Full article
(This article belongs to the Special Issue Renewable Energy for Agriculture)
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Open AccessArticle
Analysis of Operation Parameters in a Dual Fluidized Bed Biomass Gasifier Integrated with a Biomass Rotary Dryer: Development and Application of a System Model
Energies 2014, 7(7), 4342-4363; https://doi.org/10.3390/en7074342
Received: 7 May 2014 / Revised: 22 June 2014 / Accepted: 2 July 2014 / Published: 7 July 2014
Cited by 3 | Viewed by 3136 | PDF Full-text (912 KB) | HTML Full-text | XML Full-text
Abstract
An integrated system model was developed in UniSim Design for a dual fluidized bed (DFB) biomass gasifier and a rotary biomass dryer using a combination of user-defined and built-in unit operations. A quasi-equilibrium model was used for modelling biomass steam gasification in the [...] Read more.
An integrated system model was developed in UniSim Design for a dual fluidized bed (DFB) biomass gasifier and a rotary biomass dryer using a combination of user-defined and built-in unit operations. A quasi-equilibrium model was used for modelling biomass steam gasification in the DFB gasifier. The biomass drying was simulated with consideration of mass and energy balances, heat transfer, and dryer’s configuration. After validation using experimental data, the developed system model was applied to investigate: (1) the effects of gasification temperature and steam to biomass (S/B) ratio on the gasification performance; (2) the effect of air supplied to the fast fluidized bed (FFB) reactor and feed biomass moisture content on the integrated system performance, energy and exergy efficiencies. It was found that gasification temperature and S/B ratio have positive effects on the gasification yields; a H2/CO ratio of 1.9 can be achieved at the gasification temperature of 850 °C with a S/B ratio of 1.2. Consumption of excessive fuel in the system at higher biomass feed moisture content can be compensated by the heat recovery such as steam generation while it has adverse impact on exergy efficiency of the system. Full article
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Open AccessReview
A Critical Review of Wireless Power Transfer via Strongly Coupled Magnetic Resonances
Energies 2014, 7(7), 4316-4341; https://doi.org/10.3390/en7074316
Received: 21 March 2014 / Revised: 9 May 2014 / Accepted: 30 June 2014 / Published: 7 July 2014
Cited by 72 | Viewed by 7009 | PDF Full-text (1246 KB) | HTML Full-text | XML Full-text
Abstract
Strongly coupled magnetic resonance (SCMR), proposed by researchers at MIT in 2007, attracted the world’s attention by virtue of its mid-range, non-radiative and high-efficiency power transfer. In this paper, current developments and research progress in the SCMR area are presented. Advantages of SCMR [...] Read more.
Strongly coupled magnetic resonance (SCMR), proposed by researchers at MIT in 2007, attracted the world’s attention by virtue of its mid-range, non-radiative and high-efficiency power transfer. In this paper, current developments and research progress in the SCMR area are presented. Advantages of SCMR are analyzed by comparing it with the other wireless power transfer (WPT) technologies, and different analytic principles of SCMR are elaborated in depth and further compared. The hot research spots, including system architectures, frequency splitting phenomena, impedance matching and optimization designs are classified and elaborated. Finally, current research directions and development trends of SCMR are discussed. Full article
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Open AccessArticle
Energy Management and Control of Electric Vehicles, Using Hybrid Power Source in Regenerative Braking Operation
Energies 2014, 7(7), 4300-4315; https://doi.org/10.3390/en7074300
Received: 27 April 2014 / Revised: 27 June 2014 / Accepted: 1 July 2014 / Published: 4 July 2014
Cited by 11 | Viewed by 6029 | PDF Full-text (680 KB) | HTML Full-text | XML Full-text
Abstract
Today’s battery powered electric vehicles still face many issues: (1) Ways of improving the regenerative braking energy; (2) how to maximally extend the driving-range of electric vehicles (EVs) and prolong the service life of batteries; (3) how to satisfy the energy requirements of [...] Read more.
Today’s battery powered electric vehicles still face many issues: (1) Ways of improving the regenerative braking energy; (2) how to maximally extend the driving-range of electric vehicles (EVs) and prolong the service life of batteries; (3) how to satisfy the energy requirements of the EVs both in steady and dynamic state. The electrochemical double-layer capacitors, also called ultra-capacitors (UCs), have the merits of high energy density and instantaneous power output capability, and are usually combined with power battery packs to form a hybrid power supply system (HPSS). The power circuit topology of the HPSS has been illustrated in this paper. In the proposed HPSS, all the UCs are in series, which may cause an imbalanced voltage distribution of each unit, moreover, the energy allocation between the batteries and UCs should also be considered. An energy-management scheme to solve this problem has been presented. Moreover, due to the parameter variations caused by temperature changes and produced errors, the modelling procedure of the HPSS becomes very difficult, so an H current controller is presented. The proposed hybrid power source circuit is implemented on a laboratory hardware setup using a digital signal processor (DSP). Simulation and experimental results have been put forward to demonstrate the feasibility and validity of the approach. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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Open AccessArticle
Unit Commitment Considering Interruptible Load for Power System Operation with Wind Power
Energies 2014, 7(7), 4281-4299; https://doi.org/10.3390/en7074281
Received: 7 May 2014 / Revised: 20 June 2014 / Accepted: 26 June 2014 / Published: 3 July 2014
Cited by 11 | Viewed by 3199 | PDF Full-text (774 KB) | HTML Full-text | XML Full-text
Abstract
A high wind-power penetration level causes increased uncertainty in power system operation because of the variability and limited predictability of wind generation. This paper proposes a novel type of unit commitment (UC) considering spinning reserve and interruptible load (IL) as operating reserve facilities [...] Read more.
A high wind-power penetration level causes increased uncertainty in power system operation because of the variability and limited predictability of wind generation. This paper proposes a novel type of unit commitment (UC) considering spinning reserve and interruptible load (IL) as operating reserve facilities to increase system flexibility for reliable, economical operation. Two uncertainty sources, load and wind generation, were modeled via autoregressive moving averages (ARMA). The formulation of interruptible load was considered in the implementation of unit commitments. Lagrangian relaxation-dynamic programming (LR-DP) was used to solve the unit commitment problem efficiently. The expected energy not supplied (EENS) was regarded as a probabilistic reliability criterion. The effectiveness of the proposed unit commitment was evaluated using an IEEE 118-bus system. The simulation results clearly demonstrated that with demand-side participation, the operating cost was significantly reduced when handling the increased uncertainty due to wind power integration within the required reliability criteria. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
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Open AccessArticle
Research on Energy Saving Potential for Dedicated Ventilation Systems Based on Heat Recovery Technology
Energies 2014, 7(7), 4261-4280; https://doi.org/10.3390/en7074261
Received: 30 April 2014 / Revised: 6 June 2014 / Accepted: 19 June 2014 / Published: 2 July 2014
Cited by 7 | Viewed by 2760 | PDF Full-text (277 KB) | HTML Full-text | XML Full-text
Abstract
Research results have identified the use of heat pipe heat exchangers (HPHXs) for heat recovery as a way to reduce the pre-cooling and re-heating energy. This paper suggests decoupling dehumidification from cooling to reduce energy consumption. The feasible usage and the energy saving [...] Read more.
Research results have identified the use of heat pipe heat exchangers (HPHXs) for heat recovery as a way to reduce the pre-cooling and re-heating energy. This paper suggests decoupling dehumidification from cooling to reduce energy consumption. The feasible usage and the energy saving potential of heat pipe heat exchanger at the air handler dedicated in accomplishing this objective is investigated. In this paper a dedicated ventilation system combined with a HPHX to reduce energy consumption is tested and investigated under varying conditions by laboratory experiments. The energy saving potential and heat pipe (HP) effectiveness are tested and calculated under various outdoor conditions. The simulation and experimental results demonstrate that for all cases examined, the average HP effectiveness and energy savings have the same trend at various outdoor temperatures and Relative Humidity (RH) values. It has been found that the heat pipe can be applied to save over 60% energy for the air-conditioning operating hours. The reduction in overall energy is from 1.8% to 2.8% for the whole system. Therefore, the results confirm that the proposed set-up is useful for buildings to achieve intended energy saving objectives in subtropical climates where air-conditioning demand is highly variable. Full article
(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)
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Open AccessArticle
Estimating Limits for the Geothermal Energy Potential of Abandoned Underground Coal Mines: A Simple Methodology
Energies 2014, 7(7), 4241-4260; https://doi.org/10.3390/en7074241
Received: 30 April 2014 / Revised: 7 June 2014 / Accepted: 17 June 2014 / Published: 2 July 2014
Cited by 9 | Viewed by 3077 | PDF Full-text (514 KB) | HTML Full-text | XML Full-text
Abstract
Flooded mine workings have good potential as low-enthalpy geothermal resources, which could be used for heating and cooling purposes, thus making use of the mines long after mining activity itself ceases. It would be useful to estimate the scale of the geothermal potential [...] Read more.
Flooded mine workings have good potential as low-enthalpy geothermal resources, which could be used for heating and cooling purposes, thus making use of the mines long after mining activity itself ceases. It would be useful to estimate the scale of the geothermal potential represented by abandoned and flooded underground mines in Europe. From a few practical considerations, a procedure has been developed for assessing the geothermal energy potential of abandoned underground coal mines, as well as for quantifying the reduction in CO2 emissions associated with using the mines instead of conventional heating/cooling technologies. On this basis the authors have been able to estimate that the geothermal energy available from underground coal mines in Europe is on the order of several thousand megawatts thermal. Although this is a gross value, it can be considered a minimum, which in itself vindicates all efforts to investigate harnessing it. Full article
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Open AccessArticle
Thermal-Economic Modularization of Small, Organic Rankine Cycle Power Plants for Mid-Enthalpy Geothermal Fields
Energies 2014, 7(7), 4221-4240; https://doi.org/10.3390/en7074221
Received: 23 April 2014 / Revised: 18 June 2014 / Accepted: 22 June 2014 / Published: 2 July 2014
Cited by 14 | Viewed by 4410 | PDF Full-text (1648 KB) | HTML Full-text | XML Full-text
Abstract
The costs of the surface infrastructure in mid-enthalpy geothermal power systems, especially in remote areas, could be reduced by using small, modular Organic Rankine Cycle (ORC) power plants. Thermal-economic criteria have been devised to standardize ORC plant dimensions for such applications. We designed [...] Read more.
The costs of the surface infrastructure in mid-enthalpy geothermal power systems, especially in remote areas, could be reduced by using small, modular Organic Rankine Cycle (ORC) power plants. Thermal-economic criteria have been devised to standardize ORC plant dimensions for such applications. We designed a modular ORC to utilize various wellhead temperatures (120–170 °C), mass flow rates and ambient temperatures (−10–40 °C). A control strategy was developed using steady-state optimization, in order to maximize net power production at off-design conditions. Optimum component sizes were determined using specific investment cost (SIC) minimization and mean cashflow (MCF) maximization for three different climate scenarios. Minimizing SIC did not yield significant benefits, but MCF proved to be a much better optimization function. Full article
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Open AccessArticle
The Fuel Economy of Hybrid Buses: The Role of Ancillaries in Real Urban Driving
Energies 2014, 7(7), 4202-4220; https://doi.org/10.3390/en7074202
Received: 28 April 2014 / Revised: 24 June 2014 / Accepted: 26 June 2014 / Published: 1 July 2014
Cited by 15 | Viewed by 4740 | PDF Full-text (695 KB) | HTML Full-text | XML Full-text
Abstract
In the present context of the global economic crisis and environmental emergency, transport science is asked to find innovative solutions to turn traditional vehicles into fuel-saving and eco-friendly devices. In the last few years, hybrid vehicles have been shown to have potential benefits [...] Read more.
In the present context of the global economic crisis and environmental emergency, transport science is asked to find innovative solutions to turn traditional vehicles into fuel-saving and eco-friendly devices. In the last few years, hybrid vehicles have been shown to have potential benefits in this sense. In this paper, the fuel economy of series hybrid-electric and hybrid-mechanical buses is simulated in two real driving situations: cold and hot weather driving in the city of Taranto, in Southern Italy. The numerical analysis is carried out by an inverse dynamic approach, where the bus speed is given as a velocity pattern measured in the field tests performed on one of the city bus routes. The city of Taranto drive schedule is simulated in a typical tempered climate condition and with a hot temperature, when the air conditioning system must be switched on for passenger comfort. The fuel consumptions of hybrid-electric and hybrid-mechanical buses are compared to each other and with a traditional bus powered by a diesel engine. It is shown that the series hybrid-electric vehicle outperforms both the traditional and the mechanical hybrid vehicles in the cold weather driving simulation, reducing the fuel consumption by about 35% with respect to the traditional diesel bus. However, it is also shown that the performance of the hybrid-electric bus gets dramatically worse when the air-cooling system is continuously turned on. In this situation, the fuel consumption of the three different technologies for city buses under investigation is comparable. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
Open AccessCorrection
Correction: Ferreira, J.A.; Lennartsson, P.R.; Taherzadeh, M.J. Production of Ethanol and Biomass from Thin Stillage Using Food-Grade Zygomycetes and Ascomycetes Filamentous Fungi. Energies 2014, 7, 3872–3885
Energies 2014, 7(7), 4199-4201; https://doi.org/10.3390/en7074199
Received: 26 June 2014 / Revised: 27 June 2014 / Accepted: 27 June 2014 / Published: 1 July 2014
Cited by 1 | Viewed by 2123 | PDF Full-text (291 KB) | HTML Full-text | XML Full-text
Abstract
We have found two inadvertent errors in our paper [1], and thus would like to make the following corrections to this paper. [...] Full article
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Open AccessArticle
Refined Diebold-Mariano Test Methods for the Evaluation of Wind Power Forecasting Models
Energies 2014, 7(7), 4185-4198; https://doi.org/10.3390/en7074185
Received: 26 April 2014 / Revised: 17 June 2014 / Accepted: 23 June 2014 / Published: 1 July 2014
Cited by 3 | Viewed by 2795 | PDF Full-text (443 KB) | HTML Full-text | XML Full-text
Abstract
The scientific evaluation methodology for the forecast accuracy of wind power forecasting models is an important issue in the domain of wind power forecasting. However, traditional forecast evaluation criteria, such as Mean Squared Error (MSE) and Mean Absolute Error (MAE), have limitations in [...] Read more.
The scientific evaluation methodology for the forecast accuracy of wind power forecasting models is an important issue in the domain of wind power forecasting. However, traditional forecast evaluation criteria, such as Mean Squared Error (MSE) and Mean Absolute Error (MAE), have limitations in application to some degree. In this paper, a modern evaluation criterion, the Diebold-Mariano (DM) test, is introduced. The DM test can discriminate the significant differences of forecasting accuracy between different models based on the scheme of quantitative analysis. Furthermore, the augmented DM test with rolling windows approach is proposed to give a more strict forecasting evaluation. By extending the loss function to an asymmetric structure, the asymmetric DM test is proposed. Case study indicates that the evaluation criteria based on DM test can relieve the influence of random sample disturbance. Moreover, the proposed augmented DM test can provide more evidence when the cost of changing models is expensive, and the proposed asymmetric DM test can add in the asymmetric factor, and provide practical evaluation of wind power forecasting models. It is concluded that the two refined DM tests can provide reference to the comprehensive evaluation for wind power forecasting models. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
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