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Energies, Volume 12, Issue 13 (July-1 2019) – 185 articles

Cover Story (view full-size image): Operation and maintenance (O&M) costs of ocean energy devices have a significant influence on the Levelised Cost of Energy (LCOE). Due to the level of maturity of the sector, there are several uncertainties relating to the O&M figures that can only be reduced through real sea operation. This paper studies three cases to show the potential advantages of having real sea experience. One case considers an industry simplified approach in the absence of O&M experience. The other two cases consider O&M models calibrated with real sea data, based on the OPERA and EnFAIT projects. View this paper.
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19 pages, 2783 KiB  
Article
A Two-Phase Method to Assess the Sustainability of Water Companies
by Fátima Pérez, Laura Delgado-Antequera and Trinidad Gómez
Energies 2019, 12(13), 2638; https://doi.org/10.3390/en12132638 - 9 Jul 2019
Cited by 13 | Viewed by 3417
Abstract
Composite indicators are becoming more relevant for evaluating the performance of water companies from a holistic perspective. Some of them are related with economic aspects, and others focus on social and environmental features. Consequently, a multidimensional evaluation is necessary for handling the great [...] Read more.
Composite indicators are becoming more relevant for evaluating the performance of water companies from a holistic perspective. Some of them are related with economic aspects, and others focus on social and environmental features. Consequently, a multidimensional evaluation is necessary for handling the great amount of information provided by multiple single indicators of a different nature. This paper presents a two-phase approach to evaluate the sustainability of water companies. First, a partial composite indicator for each dimension (social, environmental, economic) is obtained using multi-criteria decision making (MCDM). Then, a global indicator is obtained, in terms of the values reached in the previous stage for every partial indicator, by means an optimization problem rooted in data envelopment analysis (DEA). Our proposal offers the possibility of analyzing the performance of each water company under each dimension that characterizes the concept of sustainability, as well as a joint assessment including all the dimensions, facilitating the decision-making process. We apply it to evaluate the sustainability of 163 Portuguese water companies. The results show the strengths and weaknesses of each unit and serve as a guideline to decision-makers on the aspects for improving the performance of water utilities. Full article
(This article belongs to the Special Issue Environmental and Energy Efficiency Evaluation Based on Data Envelopment Analysis (DEA))
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19 pages, 5792 KiB  
Article
An Integrated Design Approach for LCL-Type Inverter to Improve Its Adaptation in Weak Grid
by Chen Zheng, Yajuan Liu, Shuming Liu, Qionglin Li, Shuangyin Dai, Yuzheng Tang, Bo Zhang and Mingxuan Mao
Energies 2019, 12(13), 2637; https://doi.org/10.3390/en12132637 - 9 Jul 2019
Cited by 7 | Viewed by 3217
Abstract
To improve the robustness of grid-connected inverter against grid impedance in a weak grid an integrated design method of LCL-filter parameters and controller parameters is proposed. In the method the inherent relation of LCL-filter parameters and controller parameters is taken into consideration to [...] Read more.
To improve the robustness of grid-connected inverter against grid impedance in a weak grid an integrated design method of LCL-filter parameters and controller parameters is proposed. In the method the inherent relation of LCL-filter parameters and controller parameters is taken into consideration to realize their optimized match. A parameter normalization scheme is also developed to facilitate the system stability and robustness analysis. Based on the method all normalization parameters can be designed succinctly according to the required stability and robustness. Additionally, the LCL parameter and controller parameter can be achieved immediately by restoring normalization parameters. The proposed design method can guarantee the inverter stability and robustness simultaneously without needing any compensation network, additional hardware, or the complicated iterative computations which cannot be avoided for the conventional inverter design method. Simulation and experiment results have validated the superiority of the proposed inverter design method. Full article
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15 pages, 14363 KiB  
Article
Thermal Response of Mortar Panels with Different Forms of Macro-Encapsulated Phase Change Materials: A Finite Element Study
by Sih Ying Kong, Xu Yang, Suvash Chandra Paul, Leong Sing Wong and Branko Šavija
Energies 2019, 12(13), 2636; https://doi.org/10.3390/en12132636 - 9 Jul 2019
Cited by 12 | Viewed by 3402
Abstract
This paper presents a numerical investigation of thermal response of mortar panels, incorporating macro-encapsulated paraffin in different forms. Two types of macro capsules were fabricated and tested in this study using an instrumented hot plate device. The experimental results show that macro encapsulated [...] Read more.
This paper presents a numerical investigation of thermal response of mortar panels, incorporating macro-encapsulated paraffin in different forms. Two types of macro capsules were fabricated and tested in this study using an instrumented hot plate device. The experimental results show that macro encapsulated paraffin reduced the temperature and increased time lag in the mortar panels due to the latent heat capacity of paraffin. Finite element models adopting the effective heat capacity method to model phase change effects were able to capture the overall thermal response of panels incorporated with paraffin well. Then, a parametric study was conducted using the validated finite element (FE) modelling technique to investigate the effects of different forms of macro capsules, the quantity of paraffin and the position of macro capsules. It was found that the tube and sphere macro capsules showed similar thermal responses, while the plate shaped capsules may cause a non-uniform temperature distribution in mortar panels. The quantity and position of paraffin have significant effects on the thermal response of the mortal panels. A higher paraffin content results in a significantly longer temperature lag and a lower temperature during the phase transition of paraffin. Furthermore, placing the paraffin away from the heating face can cause a longer temperature lag on the other face, which is desirable for building façade applications. Full article
(This article belongs to the Section G: Energy and Buildings)
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18 pages, 871 KiB  
Article
The Consequences of Air Density Variations over Northeastern Scotland for Offshore Wind Energy Potential
by Alain Ulazia, Ander Nafarrate, Gabriel Ibarra-Berastegi, Jon Sáenz and Sheila Carreno-Madinabeitia
Energies 2019, 12(13), 2635; https://doi.org/10.3390/en12132635 - 9 Jul 2019
Cited by 28 | Viewed by 4614
Abstract
Hywind-Scotland is a wind farm in Scotland that for many reasons is at the leading edge of technology and is located at a paradigmatic study area for offshore wind energy assessment. The objective of this paper is to compute the Capacity Factor ( [...] Read more.
Hywind-Scotland is a wind farm in Scotland that for many reasons is at the leading edge of technology and is located at a paradigmatic study area for offshore wind energy assessment. The objective of this paper is to compute the Capacity Factor ( C F ) changes and instantaneous power generation changes due to seasonal and hourly fluctuations in air density. For that reason, the novel ERA5 reanalysis is used as a source of temperature, pressure, and wind speed data. Seasonal results for winter show that C F values increase by 3% due to low temperatures and denser air, with economical profit consequences of tens of thousands (US$). Hourly results show variations of 7% in air density and of 26% in power generation via FAST simulations, emphasizing the need to include air density in short-term wind energy studying. Full article
(This article belongs to the Section A3: Wind, Wave and Tidal Energy)
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18 pages, 4024 KiB  
Article
Beneficial Reuse of Industrial CO2 Emissions Using a Microalgae Photobioreactor: Waste Heat Utilization Assessment
by Daniel T. Mohler, Michael H. Wilson, Zhen Fan, John G. Groppo and Mark Crocker
Energies 2019, 12(13), 2634; https://doi.org/10.3390/en12132634 - 9 Jul 2019
Cited by 13 | Viewed by 5410
Abstract
Microalgae are a potential means of recycling CO2 from industrial point sources. With this in mind, a novel photobioreactor (PBR) was designed and deployed at a coal-fired power plant. To ascertain the feasibility of using waste heat from the power plant to [...] Read more.
Microalgae are a potential means of recycling CO2 from industrial point sources. With this in mind, a novel photobioreactor (PBR) was designed and deployed at a coal-fired power plant. To ascertain the feasibility of using waste heat from the power plant to heat algae cultures during cold periods, two heat transfer models were constructed to quantify PBR cooling times. The first, which was based on tabulated data, material properties and the physical orientation of the PBR tubes, yielded a range of heat transfer coefficients of 19–64 W m−2 K−1 for the PBR at wind speeds of 1–10 m s−1. The second model was based on data collected from the PBR and gave an overall heat transfer coefficient of 24.8 W m−2 K−1. Energy penalties associated with waste heat utilization were found to incur an 18%–103% increase in energy consumption, resulting in a 22%–70% reduction in CO2 capture for the scenarios considered. A techno-economic analysis showed that the cost of heat integration equipment increased capital expenditures (CAPEX) by a factor of nine and increased biomass production costs by a factor of three. Although the scenario is thermodynamically feasible, the increase in CAPEX incurs an increase in biomass production cost that is economically untenable. Full article
(This article belongs to the Section B: Energy and Environment)
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18 pages, 7227 KiB  
Article
The Impact of Air Pressure Conditions on the Performance of Single Room Ventilation Units in Multi-Story Buildings
by Alo Mikola, Raimo Simson and Jarek Kurnitski
Energies 2019, 12(13), 2633; https://doi.org/10.3390/en12132633 - 9 Jul 2019
Cited by 22 | Viewed by 6972
Abstract
Single room ventilation units with heat recovery is one of the ventilation solutions that have been used in renovated residential buildings in Estonia. In multi-story buildings, especially in a cold climate, the performance of units is affected by the stack effect and wind-induced [...] Read more.
Single room ventilation units with heat recovery is one of the ventilation solutions that have been used in renovated residential buildings in Estonia. In multi-story buildings, especially in a cold climate, the performance of units is affected by the stack effect and wind-induced pressure differences between the indoor and the outdoor air. Renovation of the building envelope improves air tightness and the impact of the pressure conditions is amplified. The aim of this study was to predict the air pressure conditions in typical renovated multi-story apartment buildings and to analyze the performance of room-based ventilation units. The field measurements of air pressure differences in a renovated 5-story apartment building during the winter season were conducted and the results were used to simulate whole-year pressure conditions with IDA-ICE software. Performance of two types of single room ventilation units were measured in the laboratory and their suitability as ventilation renovation solutions was assessed with simulations. The results show that one unit stopped its operation as a heat recovery ventilator. In order to ensure satisfactory indoor climate and heat recovery using wall mounted units the pressure difference values were determined and proposed for correct design. Full article
(This article belongs to the Special Issue Energy Performance and Indoor Climate Analysis in Buildings)
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19 pages, 917 KiB  
Article
Households’ Preferences for a New ‘Climate-Friendly’ Heating System: Does Contribution to Reducing Greenhouse Gases Matter?
by Stefania Troiano, Daniel Vecchiato, Francesco Marangon, Tiziano Tempesta and Federico Nassivera
Energies 2019, 12(13), 2632; https://doi.org/10.3390/en12132632 - 9 Jul 2019
Cited by 17 | Viewed by 4633
Abstract
This study investigates the preferences of Italian home-owners when choosing a new domestic heating system. The focus is on understanding the influence on consumer choice of a potential label certifying the effect of the heating system on the greenhouse effect. To this end, [...] Read more.
This study investigates the preferences of Italian home-owners when choosing a new domestic heating system. The focus is on understanding the influence on consumer choice of a potential label certifying the effect of the heating system on the greenhouse effect. To this end, we designed a survey including a discrete choice experiment and administered it to residents in north-eastern Italy. Our findings reveal that, on average, respondents pay particular attention to the green effect of their purchase. The carbon dioxide reduction label was considered second in terms of importance after cost. Further analysis found that our sample presents three clusters of customers, with intra-cluster homogeneous preferences. The cluster analysis showed that while the initial system costs are considered to varying degrees by the whole sample, the carbon dioxide reduction label was considered important by 79% of respondents (members of clusters 1 and 2). To achieve greater results in reducing the greenhouse effect of the domestic heating sector, a combination of policies should be used simultaneously to achieve greater effectiveness. Our simulations support the hypothesis that policymakers should achieve greater results in terms of reducing the domestic greenhouse gas emissions by applying a combined policy that leverages the importance citizens accord to the different characteristics of a heating system. From our results, the application of a ‘low carbon dioxide ( C O 2 ) emissions’ label will amplify the effect of a subsidy that reduces the initial system costs. Full article
(This article belongs to the Special Issue Economics of Sustainable and Renewable Energy Systems)
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18 pages, 931 KiB  
Article
Sensor-Based Early Activity Recognition Inside Buildings to Support Energy and Comfort Management Systems
by Francesca Marcello, Virginia Pilloni and Daniele Giusto
Energies 2019, 12(13), 2631; https://doi.org/10.3390/en12132631 - 9 Jul 2019
Cited by 8 | Viewed by 3656
Abstract
Building Energy and Comfort Management (BECM) systems have the potential to considerably reduce costs related to energy consumption and improve the efficiency of resource exploitation, by implementing strategies for resource management and control and policies for Demand-Side Management (DSM). One of the main [...] Read more.
Building Energy and Comfort Management (BECM) systems have the potential to considerably reduce costs related to energy consumption and improve the efficiency of resource exploitation, by implementing strategies for resource management and control and policies for Demand-Side Management (DSM). One of the main requirements for such systems is to be able to adapt their management decisions to the users’ specific habits and preferences, even when they change over time. This feature is fundamental to prevent users’ disaffection and the gradual abandonment of the system. In this paper, a sensor-based system for analysis of user habits and early detection and prediction of user activities is presented. To improve the resulting accuracy, the system incorporates statistics related to other relevant external conditions that have been observed to be correlated (e.g., time of the day). Performance evaluation on a real use case proves that the proposed system enables early recognition of activities after only 10 sensor events with an accuracy of 81 % . Furthermore, the correlation between activities can be used to predict the next activity with an accuracy of about 60 % . Full article
(This article belongs to the Special Issue Advanced Approaches, Business Models, and Novel Techniques for Management and Control of Smart Grids)
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22 pages, 1042 KiB  
Article
Energy-Effective Cooperative and Reliable Delivery Routing Protocols for Underwater Wireless Sensor Networks
by Ubaid Ullah, Anwar Khan, Mahdi Zareei, Ihsan Ali, Hasan Ali Khattak and Ikram Ud Din
Energies 2019, 12(13), 2630; https://doi.org/10.3390/en12132630 - 9 Jul 2019
Cited by 36 | Viewed by 4413
Abstract
Underwater deployed sensors nodes are energy-constrained. Therefore, energy efficiency becomes crucial in underwater wireless sensor networks (U-WSNs). The adverse channel corrupts the packets and challenges their reliability. To handle these challenges, two routing schemes are introduced in this paper. They are effective energy [...] Read more.
Underwater deployed sensors nodes are energy-constrained. Therefore, energy efficiency becomes crucial in underwater wireless sensor networks (U-WSNs). The adverse channel corrupts the packets and challenges their reliability. To handle these challenges, two routing schemes are introduced in this paper. They are effective energy and reliable delivery (EERD) and cooperative effective energy and reliable delivery (CoEERD). In EERD, the packets follow single-path routing and the best forwarder node is selected using a weight function such that packets are transferred via the reliable paths with low energy usage. Packet transfer via a single route in EERD has, however, compromised reliability as the undersea links bear harshness and unpredictability. Therefore, the CoEERD scheme adds cooperative routing to EERD, in which a relay node is introduced between a source–destination pair. The destination requests the relay when the packets it gets from the source are corrupted beyond a threshold value. Selection of weight function is unique and considers many factors to ensure low energy usage with reliability while considering nodes for data transfer. This also helps in selecting a single relay node rather than many relays in the conventional cooperative routing model. Based on simulation results, the EERD and CoEERD protocols have improved performance in energy usage, reliable packet transfer and delay. Full article
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17 pages, 4882 KiB  
Article
Water Mixtures as Working Fluids in Organic Rankine Cycles
by Costante Invernizzi, Marco Binotti, Paola Bombarda, Gioele Di Marcoberardino, Paolo Iora and Giampaolo Manzolini
Energies 2019, 12(13), 2629; https://doi.org/10.3390/en12132629 - 8 Jul 2019
Cited by 11 | Viewed by 4972
Abstract
This work explores the possibility to adopt in organic Rankine cycle (ORC) plants mixtures of water (acting as solvent) plus an organic compound (acting as solute) as the working fluid. Initially an evaluation of the thermodynamic properties of the mixtures is performed, in [...] Read more.
This work explores the possibility to adopt in organic Rankine cycle (ORC) plants mixtures of water (acting as solvent) plus an organic compound (acting as solute) as the working fluid. Initially an evaluation of the thermodynamic properties of the mixtures is performed, in order to assess their properties, and to point out the molar fractions which entail a near-azeotropic behaviour. Four species from three different classes of chemical compounds are investigated: 2,2,2-trifluoroethanol and n-butanol for alcohols, where the first is fluorinated, acetonitrile for nitrile class and 2-methylpyrazine as a heterocyclic aromatic compound. Simultaneously, the thermal stability of the pure substances considered as the possible solute for the mixtures is experimentally investigated in order to estimate the temperature applicability range. The ORC plant performance, from a low-enthalpy geothermal heat source (hot water stream from 100 to 200 °C), adopting the selected mixtures as the working fluid is finally evaluated, and the analysis includes a preliminary discussion on the turbine design; results are compared with respect to the reference case of a hypothetical plant adopting water as the working fluid. Full article
(This article belongs to the Special Issue Selected Papers from Heat Power Cycles Conference 2018)
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17 pages, 4942 KiB  
Article
Development of a Modified Plug-Flow Anaerobic Digester for Biogas Production from Animal Manures
by Daniel Gómez, Juan Luis Ramos-Suárez, Belén Fernández, Eduard Muñoz, Laura Tey, Maycoll Romero-Güiza and Felipe Hansen
Energies 2019, 12(13), 2628; https://doi.org/10.3390/en12132628 - 8 Jul 2019
Cited by 19 | Viewed by 8728
Abstract
Traditional plug-flow anaerobic reactors (PFRs) are characterized by lacking a mixing system and operating at high total solid concentrations, which limits their applicability for several kinds of manures. This paper studies the performance of a novel modified PFR for the treatment of pig [...] Read more.
Traditional plug-flow anaerobic reactors (PFRs) are characterized by lacking a mixing system and operating at high total solid concentrations, which limits their applicability for several kinds of manures. This paper studies the performance of a novel modified PFR for the treatment of pig manure, characterized by having an internal sludge mixing system by biogas recirculation in the range of 0.270–0.336 m3 m−3 h−1. The influence on the methane yield of four operating parameters (recirculation rate, hydraulic retention time, organic loading rate, and total solids) was evaluated by running four modified PFRs at the pilot scale in mesophilic conditions. While the previous biodegradability of organic matter by biochemical methane potential tests were between 31% and 47% with a methane yield between 125 and 184 LCH4 kgVS−1, the PFRs showed a suitable performance with organic matter degradation between 25% and 51% and a methane yield of up to 374 LCH4 kgVS−1. Operational problems such as solid stratification, foaming, or scum generation were avoided. Full article
(This article belongs to the Special Issue Biogas for Rural Areas)
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13 pages, 2333 KiB  
Article
The Influence of Freezing Temperature Storage on the Mechanical Durability of Commercial Pellets from Biomass
by Arkadiusz Dyjakon and Tomasz Noszczyk
Energies 2019, 12(13), 2627; https://doi.org/10.3390/en12132627 - 8 Jul 2019
Cited by 29 | Viewed by 3972
Abstract
The interest in pellets utilization for households heating has been growing significantly in the last several years. However, the pellets need to meet certain quality requirements, including the mechanical durability (DU) index. In the winter seasons, the pellets are very often [...] Read more.
The interest in pellets utilization for households heating has been growing significantly in the last several years. However, the pellets need to meet certain quality requirements, including the mechanical durability (DU) index. In the winter seasons, the pellets are very often stored in unheated in-door systems or are transported by trucks over long distances. As a result, the pellets are exposed to external weather factors, including very low temperatures (even freezing ones), which can have a negative impact on the quality parameters of the fuel. There are several parameters affecting mechanical durability, but little is known about the influence of a very low temperature on the pellet properties. The aim of this research was to analyze the influence of freezing temperature storage on the mechanical durability of commercial pellets made of different biomass. The research was carried out in accordance with the international standard for solid biofuels PN-EN ISO 17831-1:2016-02. The samples were investigated under three different conditions: after normal storage conditions (20 °C), after frozen storage conditions (−28 °C) and after the defrosting of the pellets. The results revealed that the freezing process and subsequent defrosting of the pellets only causes a small drop in their mechanical durability in comparison to the normal storage conditions. The highest mechanical durability was established for digestate pellet and pine sawdust pellet, at 99.0 ± 0.1% and 98.7 ± 0.1% respectively (p < 0.05). The greatest change of mechanical durability was observed after the defrosting process of pellets, which in the initial stage and at the normal storage temperature were characterized by low mechanical durability. The pellets made of sunflower husk (DU = 87.4%) and coal/straw blend (DU = 96.2%) were distinguished by the highest change in their mechanical durability (ΔDU = 1.7%, p < 0.05). Based on the obtained results, it was concluded that the storage of pellets at freezing temperature does not significantly affect their mechanical durability. However, if the mechanical durability decreases, this result is related to pellets with low initial mechanical durability. Full article
(This article belongs to the Section L: Energy Sources)
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11 pages, 4404 KiB  
Article
A Frequency Locking Method for ICPT System Based on LCC/S Compensation Topology
by Yansong Li, Minhao Wang, Weiwei Zhang, Mengmeng Zhao and Jun Liu
Energies 2019, 12(13), 2626; https://doi.org/10.3390/en12132626 - 8 Jul 2019
Cited by 5 | Viewed by 2685
Abstract
Aiming to maximize the transmission efficiency of inductively coupled power transmission (ICPT) system with the designed output power, a frequency locking method for an ICPT system based on LCC/S compensation topology is proposed in this paper. Firstly, the relationship between compensation component L [...] Read more.
Aiming to maximize the transmission efficiency of inductively coupled power transmission (ICPT) system with the designed output power, a frequency locking method for an ICPT system based on LCC/S compensation topology is proposed in this paper. Firstly, the relationship between compensation component Lf1 and output power was deduced by the lossless model, and the initial value of Lf1 was obtained. Then, considering the system loss, the designed output power and frequency were input into the frequency locking program, and Lf1 and other compensation parameters were dynamically tracked. At the same time, the transmission efficiency of the system was calculated, and the frequency that achieved maximum efficiency was automatically locked when the system met the requirements of the designed output power. Finally, based on the method, the output characteristics of the system were verified by experiments. Full article
(This article belongs to the Special Issue Intelligent Wireless Power Transfer System and Its Application)
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13 pages, 4588 KiB  
Article
Input Disturbance Suppression for Unidirectional Matrix Converter with a Stability-Enhancing Modulation Scheme
by Jiaxing Lei, Chaofan Wei and Shuang Feng
Energies 2019, 12(13), 2625; https://doi.org/10.3390/en12132625 - 8 Jul 2019
Cited by 1 | Viewed by 2527
Abstract
This paper proposes an input voltage disturbance suppression control strategy for the unidirectional matrix converter (UMC) with a new modulation scheme enhancing the stability. In the new scheme, the modulation index is directly, rather than reversely, proportional to the instantaneous amplitude of input [...] Read more.
This paper proposes an input voltage disturbance suppression control strategy for the unidirectional matrix converter (UMC) with a new modulation scheme enhancing the stability. In the new scheme, the modulation index is directly, rather than reversely, proportional to the instantaneous amplitude of input filter capacitor voltages. Contrary to traditional schemes, the stability of the UMC with this new scheme is even better with the increase of the transferred active power, which is particularly suitable for applications with sinusoidal and balanced input conditions. As to the disturbed input conditions, the new scheme could introduce low-frequency harmonics into output currents. To address this issue, a feedback control strategy of output current amplitude is further proposed to eliminate the additional harmonics. Stability analysis of a UMC with the proposed modulation scheme and feedback control strategy is presented. Experimental results have verified the validity of the proposed control solution. Full article
(This article belongs to the Section F: Electrical Engineering)
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27 pages, 36810 KiB  
Article
New Assessment Scales for Evaluating the Degree of Risk of Wind Turbine Blade Damage Caused by Terrain-Induced Turbulence
by Takanori Uchida and Yasushi Kawashima
Energies 2019, 12(13), 2624; https://doi.org/10.3390/en12132624 - 8 Jul 2019
Cited by 13 | Viewed by 5357
Abstract
The present study scrutinized the impacts of terrain-induced turbulence on wind turbine blades, examining measurement data regarding wind conditions and the strains of wind turbine blades. Furthermore, we performed a high-resolution large-eddy simulation (LES) and identified the three-dimensional airflow structures of terrain-induced turbulence. [...] Read more.
The present study scrutinized the impacts of terrain-induced turbulence on wind turbine blades, examining measurement data regarding wind conditions and the strains of wind turbine blades. Furthermore, we performed a high-resolution large-eddy simulation (LES) and identified the three-dimensional airflow structures of terrain-induced turbulence. Based on the LES results, we defined the Uchida-Kawashima Scale_1 (the U-K scale_1), which is a turbulence evaluation index, and clarified the existence of the terrain-induced turbulence quantitatively. The threshold value of the U-K scale_1 was determined as 0.2, and this index was confirmed to not be dependent on the inflow profile, the influence of the horizontal grid resolution, and the influence of the computed azimuth. In addition, we defined the Uchida-Kawashima Scale_2 (the U-K scale_2), which is a fatigue damage evaluation index based on the measurement data and the design value obtained by DNV GL’s Bladed. DNV GL (Det Norske Veritas Germanischer Lloyed) is a third party certification body in Norway, and Bladed has been the industry standard aero-elastic wind turbine modeling software. Using the U-K scale_2, the following results were revealed: the U-K scale_2 was 0.86 < 1.0 (within the designed value) in the case of northerly wind, and the U-K scale_2 was 1.60 > 1.0 (exceeding the designed value) in the case of easterly wind. As a result, it was revealed that the blades of the target wind turbine were directly and strongly affected by terrain-induced turbulence when easterly winds occurred. Full article
(This article belongs to the Special Issue Modeling of Wind Turbines and Wind Farms)
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12 pages, 3148 KiB  
Article
Concentrated Photovoltaic/Thermal Hybrid System Coupled with a Thermoelectric Generator
by Abdelrahman Lashin, Mohammad Al Turkestani and Mohamed Sabry
Energies 2019, 12(13), 2623; https://doi.org/10.3390/en12132623 - 8 Jul 2019
Cited by 18 | Viewed by 5181
Abstract
Concentrator photovoltaic (CPV) systems have displayed an important cost reduction and in the next few years could offer a competitive cost advantage compared to that of flat plate PV systems. Such CPV systems require some cooling methods to overcome high operating temperatures, which [...] Read more.
Concentrator photovoltaic (CPV) systems have displayed an important cost reduction and in the next few years could offer a competitive cost advantage compared to that of flat plate PV systems. Such CPV systems require some cooling methods to overcome high operating temperatures, which reduces their efficiency significantly. On the other hand, thermoelectric generators (TEG) are devices that convert thermal energy directly to electrical energy, provided that there is a temperature difference between its two faces. A hybrid concentrator photovoltaic/thermal (CPV/T) system is proposed in this work. Such a system uses TEG in a two-fold manner: to passively cool down the CPV cell in order to maintain its power conversion efficiency in such high temperature conditions, and to use the accumulated thermal energy to generate electrical energy, which is added to the system’s total power output. Two types of solar cells were investigated, namely, Ga0.35In0.65P/Ga0.83In0.17As with efficiency an of 28% at 250X, and a Laser Grooved Buried Contact (LGBC) silicon concentrator PV cell with an efficiency of 18.3% at 40X. These cells are assumed to be coupled with two TEGs of the same type but with a different number of junctions. Experimental results showed that coupling TEG modules to a CPV system could be a useful method for enhancing the overall output power, provided that PV cells are chosen with a low efficiency temperature coefficient and high PV performance. Also, TEG modules have to be chosen with a high figure of merit. Moreover, the operating optical concentration ratio, as well as the covered area of the TEG, have to be optimized in order to maximize the total system output. Full article
(This article belongs to the Section A2: Solar Energy and Photovoltaic Systems)
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15 pages, 3010 KiB  
Article
Characteristic Analysis of the Peak Braking Force and the Critical Speed of Eddy Current Braking in a High-Speed Maglev
by Chuntao Chen, Jie Xu, Xibo Yuan and Xinzhen Wu
Energies 2019, 12(13), 2622; https://doi.org/10.3390/en12132622 - 8 Jul 2019
Cited by 12 | Viewed by 3366
Abstract
In the eddy current braking system of high-speed maglev, the peak braking force and the critical speed are key factors determining the performance of eddy current braking force. In this paper, the analytical formula of eddy current braking force is derived by a [...] Read more.
In the eddy current braking system of high-speed maglev, the peak braking force and the critical speed are key factors determining the performance of eddy current braking force. In this paper, the analytical formula of eddy current braking force is derived by a subdomain method considering the skin effect of the induction plate, and, subsequently, the characteristics of peak braking force and critical speed are analyzed. The analytical model is set up in a 2D Cartesian coordinate system. The Poisson equations in each subdomain are listed by treating the vector magnetic potential as a variable. By combining the boundary conditions between two adjacent subdomains, the expressions of eddy current density and magnetic density in the induction plate are obtained. Then, the analytical formula of the eddy current braking force is obtained by the Ampere force formula. The results of finite-element analysis confirm the validity of the analytical calculation. The methods of improving the performance of eddy current braking force under high speed are proposed by parametric analysis of peak braking force and critical speed, which provides guidance for the design of the eddy current braking system in high-speed maglev. Full article
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15 pages, 1934 KiB  
Article
A Multi-Objective Optimization Problem for Optimal Site Selection of Wind Turbines for Reduce Losses and Improve Voltage Profile of Distribution Grids
by Amirreza Naderipour, Zulkurnain Abdul-Malek, Saber Arabi Nowdeh, Foad H. Gandoman and Mohammad Jafar Hadidian Moghaddam
Energies 2019, 12(13), 2621; https://doi.org/10.3390/en12132621 - 8 Jul 2019
Cited by 22 | Viewed by 3171
Abstract
In this paper, the optimal site and size selection of wind turbines (WTs) is presented considering the maximum allowable capacity constraint with the objective of loss reduction and voltage profile improvement of distribution grids based on particle swarm optimization (PSO as a multi-objective [...] Read more.
In this paper, the optimal site and size selection of wind turbines (WTs) is presented considering the maximum allowable capacity constraint with the objective of loss reduction and voltage profile improvement of distribution grids based on particle swarm optimization (PSO as a multi-objective problem using weighted coefficients method. The optimal site, size, and power factor of the WTs are determined using PSO. The proposed method is implemented on 84- and 32-bus standard grids. In this study, PSO algorithm is applied to determine the size, site, and power factor of WTs considering their maximum size constraint (with constraint, variant size) and also not considering their maximum size constraint (without constraint, constant size). The simulation results showed that the PSO is effective to find the site, size, and power factor of WTs optimally in the single and multi-objective problem. The results of this method showed that the power loss is reduced more and voltage profile improved more considering WTs maximum allowable size versus not considering this constraint. Additionally, the multi-objective results showed that there is a compromise between the objectives in the multi-objective WTs site selection and the multi-objective problem solution is a more realistic and accurate approach in comparison with the single-objective problem solution. Full article
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20 pages, 13748 KiB  
Article
Numerical Investigation of Flow through a Valve during Charge Intake in a DISI -Engine Using Large Eddy Simulation
by Kaushal Nishad, Florian Ries, Yongxiang Li and Amsini Sadiki
Energies 2019, 12(13), 2620; https://doi.org/10.3390/en12132620 - 8 Jul 2019
Cited by 16 | Viewed by 4670
Abstract
Apart from electric vehicles, most internal combustion (IC) engines are powered while burning petroleum-based fossil or alternative fuels after mixing with inducted air. Thereby the operations of mixing and combustion evolve in a turbulent flow environment created during the intake phase and then [...] Read more.
Apart from electric vehicles, most internal combustion (IC) engines are powered while burning petroleum-based fossil or alternative fuels after mixing with inducted air. Thereby the operations of mixing and combustion evolve in a turbulent flow environment created during the intake phase and then intensified by the piston motion and influenced by the shape of combustion chamber. In particular, the swirl and turbulence levels existing immediately before and during combustion affect the evolution of these processes and determine engine performance, noise and pollutant emissions. Both the turbulence characteristics and the bulk flow pattern in the cylinder are strongly affected by the inlet port and valve design. In the present paper, large eddy simulation (LES) is appraised and applied to studying the turbulent fluid flow around the intake valve of a single cylinder IC-engine as represented by the so called magnetic resonance velocimetry (MRV) flow bench configuration with a relatively large Reynolds number of 45,000. To avoid an intense mesh refinement near the wall, various subgrid scale models for LES; namely the Smagorinsky, wall adapting local eddy (WALE) model, SIGMA, and dynamic one equation models, are employed in combination with an appropriate wall function. For comparison purposes, the standard RANS (Reynolds-averaged Navier–Stokes) k- ε model is also used. In terms of a global mean error index for the velocity results obtained from all the models, at first it turns out that all the subgrid models show similar predictive capability except the Smagorinsky model, while the standard k- ε model experiences a higher normalized mean absolute error (nMAE) of velocity once compared with MRV data. Secondly, based on the cost-accuracy criteria, the WALE model is used with a fine mesh of ≈39 millions control volumes, the averaged velocity results showed excellent agreement between LES and MRV measurements, revealing the high prediction capability of the suggested LES tool for valve flows. Thirdly, the turbulent flow across the valve curtain clearly featured a back flow resulting in a high speed intake jet in the middle. Comprehensive LES data are generated to carry out statistical analysis in terms of (1) evolution of the turbulent morphology across the valve passage relying on the flow anisotropy map, (2) integral turbulent scales along the intake-charge stream, (3) turbulent flow properties such as turbulent kinetic energy, turbulent velocity and its intensity within the most critical zone in intake-port and along the port length, it further transpires that the most turbulence are generated across the valve passage and these are responsible for the in-cylinder turbulence. Full article
(This article belongs to the Special Issue Large-Eddy Simulations of Turbulent Flows)
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17 pages, 1507 KiB  
Article
A Minimum Side-Lobe Optimization Window Function and Its Application in Harmonic Detection of an Electricity Gird
by Zhenhua Li, Tinghe Hu and Ahmed Abu-Siada
Energies 2019, 12(13), 2619; https://doi.org/10.3390/en12132619 - 8 Jul 2019
Cited by 12 | Viewed by 4054
Abstract
Several window functions are currently applied to improve the performance of the discrete Fourier transform (DFT) harmonic detection method. These window functions exhibit poor accuracy in measuring the harmonic contents of a signal with high-order and weak-amplitude components when the power frequency fluctuates [...] Read more.
Several window functions are currently applied to improve the performance of the discrete Fourier transform (DFT) harmonic detection method. These window functions exhibit poor accuracy in measuring the harmonic contents of a signal with high-order and weak-amplitude components when the power frequency fluctuates within a small range. In this paper, a minimum side-lobe optimization window function that is aimed at overcoming the abovementioned issue is proposed. Moreover, an improved DFT harmonic detection algorithm based on the six-term minimum side-lobe optimization window and four-spectrum-line interpolation method is proposed. In this context, the minimum side-lobe optimization window is obtained by optimizing the conventional cosine window function according to the optimization rules, and the characteristics of the new proposed window are provided to analyze its performance. Then, the proposed optimization window function is employed to improve the DFT harmonic detection algorithm based on the six-term minimum side-lobe optimization window and four-spectrum-line interpolation method. The proposed technique is used to detect harmonics of an electricity gird in which the six-term minimum side-lobe optimization window is utilized to eliminate the influence of spectrum leakage caused by nonsynchronous sampling of signal processing. The four-spectrum-line interpolation method is employed to eliminate or mitigate the fence effect caused by the inherent measurement error of the DFT method. Simulation experiments in two complex conditions and an experiment test are carried out to validate the improved performance of the proposed window. Results reveal that the six-term minimum side-lode optimization window has the smallest peak side lobe when compared with existing windows, which can effectively reduce the interaction influence of spectrum leakage, improve the measurement accuracy of the DFT harmonic detection method, and meet the standard requirement of harmonic measurement in complex situations. Full article
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18 pages, 2282 KiB  
Article
A Composite Strategy for Harmonic Compensation in Standalone Inverter Based on Linear Active Disturbance Rejection Control
by Hui Li, Yue Qu, Junwei Lu and Shuang Li
Energies 2019, 12(13), 2618; https://doi.org/10.3390/en12132618 - 8 Jul 2019
Cited by 12 | Viewed by 3711
Abstract
This paper proposes a harmonic compensation control with disturbance rejection function for a standalone inverter. Due to the LC type three-phase three-leg inverter is connected to nonlinear loads, low-order harmonic components appears in the inverter output current. These harmonic current generate harmonic voltage [...] Read more.
This paper proposes a harmonic compensation control with disturbance rejection function for a standalone inverter. Due to the LC type three-phase three-leg inverter is connected to nonlinear loads, low-order harmonic components appears in the inverter output current. These harmonic current generate harmonic voltage drops when flowing through the filter inductor and the feeder impedance, which causes the output voltage of the inverter distorted. In order to compensate harmonics and produce sinusoidal voltage without additional compensation devices, virtual harmonic impedance method can be added to the fundamental voltage control. Due to the compensation effect of virtual harmonic impedance are very sensitive to the fluctuation of filter inductance. Therefore, inductance variation, as a disturbance in physical system, should be considered. In this paper, linear active disturbance rejection control (LADRC) is proposed in the fundamental voltage control loop to reduce the sensitivity of virtual harmonic impedance and decouple the model. Compared with traditional dual-loop PI control, the proposed strategy has faster dynamic response in control performance and fewer acquisition modules in engineering applications. The whole design process of virtual harmonic impedance and stability analyses of this strategy are provided. The simulation and experiment results show the good performance of the proposed strategy. Full article
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17 pages, 3081 KiB  
Article
A Carbide Slag-Based, Ca12Al14O33-Stabilized Sorbent Prepared by the Hydrothermal Template Method Enabling Efficient CO2 Capture
by Xiaotong Ma, Yingjie Li, Yi Qian and Zeyan Wang
Energies 2019, 12(13), 2617; https://doi.org/10.3390/en12132617 - 8 Jul 2019
Cited by 16 | Viewed by 3967
Abstract
Calcium looping is a promising technology to capture CO2 from the process of coal-fired power generation and gasification of coal/biomass for hydrogen production. The decay of CO2 capture activities of calcium-based sorbents is one of the main problems holding back the [...] Read more.
Calcium looping is a promising technology to capture CO2 from the process of coal-fired power generation and gasification of coal/biomass for hydrogen production. The decay of CO2 capture activities of calcium-based sorbents is one of the main problems holding back the development of the technology. Taking carbide slag as a main raw material and Ca12Al14O33 as a support, highly active CO2 sorbents were prepared using the hydrothermal template method in this work. The effects of support ratio, cycle number, and reaction conditions were evaluated. The results show that Ca12Al14O33 generated effectively improves the cyclic stability of CO2 capture by synthetic sorbents. When the Al2O3 addition is 5%, or the Ca12Al14O33 content is 10%, the synthetic sorbent possesses the highest cyclic CO2 capture performance. Under harsh calcination conditions, the CO2 capture capacity of the synthetic sorbent after 30 cycles is 0.29 g/g, which is 80% higher than that of carbide slag. The superiority of the synthetic sorbent on the CO2 capture kinetics mainly reflects at the diffusion-controlled stage. The cumulative pore volume of the synthetic sorbent within the range of 10–100 nm is 2.4 times as high as that of calcined carbide slag. The structure of the synthetic sorbent reduces the CO2 diffusion resistance, and thus leads to better CO2 capture performance and reaction rate. Full article
(This article belongs to the Special Issue Carbon Capture, Storage and Utilization)
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39 pages, 9022 KiB  
Review
Conceptual Framework of Antecedents to Trends on Permanent Magnet Synchronous Generators for Wind Energy Conversion Systems
by K. Padmanathan, N. Kamalakannan, P. Sanjeevikumar, F. Blaabjerg, J. B. Holm-Nielsen, G. Uma, R. Arul, R. Rajesh, A. Srinivasan and J. Baskaran
Energies 2019, 12(13), 2616; https://doi.org/10.3390/en12132616 - 8 Jul 2019
Cited by 10 | Viewed by 8985
Abstract
Wind Energy Conversion System (WECS) plays an inevitable role across the world. WECS consist of many components and equipment’s such as turbines, hub assembly, yaw mechanism, electrical machines; power electronics based power conditioning units, protection devices, rotor, blades, main shaft, gear-box, mainframe, transmission [...] Read more.
Wind Energy Conversion System (WECS) plays an inevitable role across the world. WECS consist of many components and equipment’s such as turbines, hub assembly, yaw mechanism, electrical machines; power electronics based power conditioning units, protection devices, rotor, blades, main shaft, gear-box, mainframe, transmission systems and etc. These machinery and devices technologies have been developed on gradually and steadily. The electrical machine used to convert mechanical rotational energy into electrical energy is the core of any WECS. Many electrical machines (generator) has been used in WECS, among the generators the Permanent Magnet Synchronous Generators (PMSGs) have gained special focus, been connected with wind farms to become the most desirable due to its enhanced efficiency in power conversion from wind energy turbine. This article provides a review of literatures and highlights the updates, progresses, and revolutionary trends observed in WECS-based PMSGs. The study also compares the geared and direct-driven conversion systems. Further, the classifications of electrical machines that are utilized in WECS are also discussed. The literature review covers the analysis of design aspects by taking various topologies of PMSGs into consideration. In the final sections, the PMSGs are reviewed and compared for further investigations. This review article predominantly emphasizes the conceptual framework that shed insights on the research challenges present in conducting the proposed works such as analysis, suitability, design, and control of PMSGs for WECS. Full article
(This article belongs to the Special Issue Power Electronic Converter Configuration and Control for DC Microgrid Systems)
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17 pages, 3260 KiB  
Article
Experimental Tests and Modeling on a Combined Heat and Power Biomass Plant
by Guido Marseglia, Carlo Maria Medaglia, Alessandro Petrozzi, Andrea Nicolini, Franco Cotana and Federico Sormani
Energies 2019, 12(13), 2615; https://doi.org/10.3390/en12132615 - 8 Jul 2019
Cited by 21 | Viewed by 4984
Abstract
Renewable energy sources can help the countries to achieve some of the Sustainable Development Goals (SDGs) provided from the recent 2030 Agenda, allowing for clean, secure, reliable and affordable energy. Biomass technology is a relevant renewable energy to contribute to reach a clean [...] Read more.
Renewable energy sources can help the countries to achieve some of the Sustainable Development Goals (SDGs) provided from the recent 2030 Agenda, allowing for clean, secure, reliable and affordable energy. Biomass technology is a relevant renewable energy to contribute to reach a clean and affordable energy production system with important emissions reduction of greenhouse gases (GHG). An innovative technological application of biomass energy consisting of a burner coupled with an external fired gas turbine (EFGT) has been developed for the production of electricity. This paper shows the results of the plant modelling by Aspen Plus environment and preliminary experimental tests; the validation of the proposed model allows for the main parameters to be defined that regulate the energy production plant supplied by woodchips. Full article
(This article belongs to the Special Issue Sustainable Energy Development Strategies: Energy Efficiency and Renewables)
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12 pages, 1554 KiB  
Article
Assessment of the Effect of Nitrogen Concentration on Fermentation and Selection of a Highly Competitive Saccharomyces cerevisiae Strain for Efficient Ethanol Production
by Patricia Portero Barahona, Jesús Martín-Gil, Pablo Martín-Ramos, Ana Briones Pérez and Enrique Javier Carvajal Barriga
Energies 2019, 12(13), 2614; https://doi.org/10.3390/en12132614 - 7 Jul 2019
Cited by 3 | Viewed by 3936
Abstract
The optimum nitrogen concentration for media supplementation and strain dominance are aspects of key importance to the industrial production of ethanol with a view to reducing costs and increasing yields. In this work, these two factors were investigated for four ethanologenic Saccharomyces cerevisiae [...] Read more.
The optimum nitrogen concentration for media supplementation and strain dominance are aspects of key importance to the industrial production of ethanol with a view to reducing costs and increasing yields. In this work, these two factors were investigated for four ethanologenic Saccharomyces cerevisiae strains (CLQCA-INT-001, CLQCA-INT-005, CLQCA-10-099, and UCLM 325), selected from the screening of 150 isolates, mostly from Ecuadorian yeast biodiversity. The effect of nitrogen concentration was assessed in terms of cellular growth, glucose consumption and ethanol production, and the yeast strains’ dominance was evaluated in continuous co-fermentation with cellular recycling by mitochondrial DNA analyses. Among the four selected yeast strains under study, CLQCA-INT-005 presented the highest glucose consumption at a nitrogen supplement concentration as low as 0.4 g·L−1, attaining an ethanol yield of up to 96.72% in 24 h. The same yeast strain was found to be highly competitive, showing a dominance of 80% after four cycles of fermentation in co-culture. Thus, CLQCA-INT-005 may be deemed as a very promising candidate to be used both at pilot-plant scale and at industrial scale cellulosic ethanol production. Full article
(This article belongs to the Special Issue Biotechnological Processes for Biofuel Production)
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15 pages, 2767 KiB  
Article
Numerical Investigation of Flow and Heat Transfer in a Rotor-Stator Cavity with Centripetal Carbon Dioxide Through-Flow
by Bo Hu, Xuesong Li, Xiaodong Ren and Jiaxing Lu
Energies 2019, 12(13), 2613; https://doi.org/10.3390/en12132613 - 7 Jul 2019
Cited by 2 | Viewed by 3126
Abstract
A centrifugal carbon dioxide compressor is a kind of general machine with extensive applications. The geometry of the side chambers of the compressors can be determined by studying the rotor-stator cavity with centripetal through-flow. In this paper, numerical simulations were conducted to predict [...] Read more.
A centrifugal carbon dioxide compressor is a kind of general machine with extensive applications. The geometry of the side chambers of the compressors can be determined by studying the rotor-stator cavity with centripetal through-flow. In this paper, numerical simulations were conducted to predict the characteristics of flow and heat transfer. Three different speeds of rotation and two axial gap widths were considered. The correlations of the core swirl ratios were determined by fitting the results for two axial gap widths. The amounts of the moment coefficients of the disk were predicted. In order to better analyze the temperature field, the radial distributions of the local heat transfer coefficient were numerically investigated. According to the simulation results, the average Nusselt number was found to be dominated by the turbulent flow parameter. It also seemed to be proportional to the moment coefficient at a fixed circumferential Reynolds number. Full article
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13 pages, 2132 KiB  
Article
Gasification of Waste Cooking Oil to Syngas by Thermal Arc Plasma
by Andrius Tamošiūnas, Dovilė Gimžauskaitė, Mindaugas Aikas, Rolandas Uscila, Marius Praspaliauskas and Justas Eimontas
Energies 2019, 12(13), 2612; https://doi.org/10.3390/en12132612 - 7 Jul 2019
Cited by 21 | Viewed by 5064
Abstract
The depletion and usage of fossil fuels causes environmental issues and alternative fuels and technologies are urgently required. Therefore, thermal arc water vapor plasma for a fast and robust waste/biomass treatment is an alternative to the syngas method. Waste cooking oil (WCO) can [...] Read more.
The depletion and usage of fossil fuels causes environmental issues and alternative fuels and technologies are urgently required. Therefore, thermal arc water vapor plasma for a fast and robust waste/biomass treatment is an alternative to the syngas method. Waste cooking oil (WCO) can be used as an alternative potential feedstock for syngas production. The goal of this experimental study was to conduct experiments gasifying waste cooking oil to syngas. The WCO was characterized in order to examine its properties and composition in the conversion process. The WCO gasification system was quantified in terms of the produced gas concentration, the H2/CO ratio, the lower heating value (LHV), the carbon conversion efficiency (CCE), the energy conversion efficiency (ECE), the specific energy requirements (SER), and the tar content in the syngas. The best gasification process efficiency was obtained at the gasifying agent-to-feedstock (S/WCO) ratio of 2.33. At this ratio, the highest concentration of hydrogen and carbon monoxide, the H2/CO ratio, the LHV, the CCE, the ECE, the SER, and the tar content were 47.9%, 22.42%, 2.14, 12.7 MJ/Nm3, 41.3% 85.42%, 196.2 kJ/mol (or 1.8 kWh/kg), and 0.18 g/Nm3, respectively. As a general conclusion, it can be stated that the thermal arc-plasma method used in this study can be effectively used for waste cooking oil gasification to high quality syngas with a rather low content of tars. Full article
(This article belongs to the Special Issue Plasma Processes for Renewable Energy Technologies)
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14 pages, 4850 KiB  
Article
Design and Implementation of a Low-Power Low-Cost Digital Current-Sink Electronic Load ‡
by Wei Jiang, Jieyun Wang, Qianlong Wang, Song Xu, Seiji Hashimoto and Zhong Liu
Energies 2019, 12(13), 2611; https://doi.org/10.3390/en12132611 - 7 Jul 2019
Cited by 2 | Viewed by 3415
Abstract
Electronic load (e-load) is essential equipment for power converter performance test, where a designated load profile is executed. Electronic load is usually implemented with the analog controller for fast tracking of the load profile reference. In this paper, a low-power low-cost electronic load [...] Read more.
Electronic load (e-load) is essential equipment for power converter performance test, where a designated load profile is executed. Electronic load is usually implemented with the analog controller for fast tracking of the load profile reference. In this paper, a low-power low-cost electronic load is proposed. MOSFETs (metal-oxide-semiconductor field-effect transistors) are used as the power consumption devices, which are regulated to the active region as controlled current-sink. In order to achieve fast transient response using the low-cost digital signal controller (DSC) PWM peripherals, the interleaving PWM method is proposed to achieve active current ripple mitigation. To obtain the system open-loop gain for current-sink operation, an offline digital system identification method, followed by model reduction, is proposed by applying Pseudo-Random Binary Sequence (PRBS) excitation. Pole-zero cancelation method is used in the control system design and later implemented in a DSC. The prototype is built and tested, in which meaningful testing scenarios under constant current-sink mode, pulse current sink mode, and double line-frequency current mode are verified. The experimental results indicate that the proposed e-load can sink pre-programmed current profile with well-attenuated ripple for static and dynamic load testing, and is applicable to fully digitalized power testing equipment. Full article
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15 pages, 2281 KiB  
Article
Real-Time Monitoring of Micro-Electricity Generation Through the Voltage Across a Storage Capacitor Charged by a Simple Microbial Fuel Cell Reactor with Fast Fourier Transform
by Jung-Chieh Su, Szu-Ching Tang, Po-Jui Su and Jung-Jeng Su
Energies 2019, 12(13), 2610; https://doi.org/10.3390/en12132610 - 7 Jul 2019
Cited by 5 | Viewed by 3921
Abstract
The pattern of micro-electricity production of simple two-chamber microbial fuel cells (MFC) was monitored in this study. Piggery wastewater and anaerobic sludge served as fuel and inocula for the MFC, respectively. The output power, including voltage and current generation, of triplicate MFCs was [...] Read more.
The pattern of micro-electricity production of simple two-chamber microbial fuel cells (MFC) was monitored in this study. Piggery wastewater and anaerobic sludge served as fuel and inocula for the MFC, respectively. The output power, including voltage and current generation, of triplicate MFCs was measured using an on-line monitoring system. The maximum voltage obtained among the triplicates was 0.663 V. We also found that removal efficiency of chemical oxygen demand (COD) and biochemical oxygen demand (BOD) in the piggery wastewater was 94.99 and 98.63%, respectively. Moreover, analytical results of Fast Fourier Transform (FFT) demonstrated that the output current comprised alternating current (AC) and direct current (DC) components, ranging from mA to μA. Full article
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18 pages, 47391 KiB  
Article
CFD Simulation of Defogging Effectivity in Automotive Headlamp
by Michal Guzej and Martin Zachar
Energies 2019, 12(13), 2609; https://doi.org/10.3390/en12132609 - 7 Jul 2019
Cited by 5 | Viewed by 6400
Abstract
In the past decade, the condensation of internal air humidity in automotive headlamps has become more prevalent than ever due to the increased usage of a new light source—LEDs. LEDs emit far less heat than previously-used halogen lamps, which makes them far more [...] Read more.
In the past decade, the condensation of internal air humidity in automotive headlamps has become more prevalent than ever due to the increased usage of a new light source—LEDs. LEDs emit far less heat than previously-used halogen lamps, which makes them far more susceptible to fogging. This fogging occurs when the internal parts of the headlamp fall to a temperature below the dew point. The front glass is most vulnerable to condensation due to its direct exposure to ambient conditions. Headlamp fogging leads to a decrease in performance and the possibility of malfunctions, which has an impact not only on the functional aspect of the product’s use but also on traffic safety. There are currently several technical solutions available which can determine the effectivity of ventilation systems applied for headlamp defogging. Another approach to this problem may be to use a numerical simulation. This paper proposes a CFD (computational fluid dynamics) simulation with a slightly simplified 3D model of an actual headlamp, which allows simulation of all the phenomena closely connected with fluid flow and phase change. The results were validated by real experiments on a special fogging–defogging test rig. This paper compares three different simulations and their compliance with real experiments. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)
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