1,720,961 research outputs found
Efficiency comparison of DC and AC coupling solutions for large-scale PV+BESS power plants
Full text linkIn large-scale photovoltaic (PV) power plants, the integration of a battery energy storage system (BESS) permits a more flexible operation, allowing the plant to support grid stability. In hybrid PV+BESS plants, the storage system can be integrated by using different power conversion system (PCS) layouts and different charge–discharge strategies. In the AC-coupling layout, the BESS is connected to the ac-side of the system through an additional inverter. In the DC-coupling layout, the BESS is connected to the dc-side, with or without a dedicated dc–dc converter, and no additional inverter is needed. Referring to a 288 MWp PV plant with a 275 MWh BESS, this paper compares the PCS efficiency between AC-and DC-coupling solutions. The power injected into the grid is obtained considering providing primary power-frequency regulation services. A charging and dis-charging strategy of the BESS is proposed to ensure cyclic battery energy shifting. The power flows in the different components of the system that are obtained under realistic operating conditions, and total energy losses and annual average efficiency are calculated accordingly. Finally, results show a higher efficiency of DC-coupling compared to the AC-coupling layout
Electric vehicle aggregate power flow prediction and smart charging system for distributed renewable energy self-consumption optimization
Full text linkIn the context of electric vehicle (EV) development and positive energy districts with the growing penetration of non-programmable sources, this paper provides a method to predict and manage the aggregate power flows of charging stations to optimize the self-consumption and load profiles. The prediction method analyzes each charging event belonging to the EV population, and it considers the main factors that influence a charging process, namely the EV’s characteristics, charging ratings, and driver behavior. EV’s characteristics and charging ratings are obtained from the EV model’s and charging stations’ specifications, respectively. The statistical analysis of driver behavior is performed to calculate the daily consumptions and the charging energy request. Then, a model to estimate the parking time of each vehicle is extrapolated from the real collected data of the arrival and departure times in parking lots. A case study was carried out to evaluate the proposed method. This consisted of an industrial area with renewable sources and electrical loads. The obtained results show how EV charging can negatively impact system power flows, causing load peaks and high energy demand. Therefore, a charging management system (CMS) able to operate in the smart charging mode was introduced. Finally, it was demonstrated that the proposed method provides better EV integration and improved performance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Impact of Environmental Variables on Tilt Selection for Energy Yield Maximization in Bifacial Photovoltaic Modules: Modeling Review and Parametric Analysis
Full text linkAmong the different photovoltaic technologies, bifacial photovoltaic modules outperform monofacial ones by being able to harvest the rear incident irradiance. In fact, they achieve higher power output under identical operating conditions. Consequently, the transition from monofacial to bifacial photovoltaic modules is progressing in residential and utility contexts. However, it remains to be fully clarified which installation conditions allow bifacial modules to perform best under different operating conditions. After discussing the different modeling techniques presented in the literature, this paper isolates and evaluates the influence of ground reflectivity, module height, and cloudy weather conditions on the annual incident irradiance and, consequently, the optimal tilt angle of a bifacial photovoltaic module. To focus on the bifacial aspect, each factor is analyzed from the perspectives of the front surface, the back surface, and both. Therefore, different patterns are isolated. The results show that ground reflectivity is key in determining the optimal tilt angle, as it affects the back incident irradiance by up to 431% when compared to a low reflectivity scenario. In contrast, module height and weather conditions do not affect the optimal tilt angle, although they do affect the incident irradiance by up to 5% and 24%, respectively
Comparative Assessment of Energy Production of Bifacial and Monofacial Photovoltaic Modules in Floating Installations
No full textAmong the various technologies related to photovoltaic production, so-called bifacial modules have been finding increasing success in recent years. Compared with the classic single-sided version, these modules offer the possibility of harvesting also the irradiance incident on the back surface while retaining the same construction characteristics. For these reasons, bifacial modules are gaining popularity as a replacement for their monofacial counterparts. In evaluations about the convenience of such substitution, special attention should be paid to the important role played by the surface area below the module, which has an impact on the albedo coefficient, and to the fact that bifacial modules have a lower temperature coefficient. This paper focuses on the specific installation mode of floating plants for which the water surface near the modules has an impact as much in the albedo coefficient as in the operating temperature compared to on-land installations. The work therefore aims to evaluate the effectiveness of replacing monofacial modules with bifacial modules in a floating installation through the development and use of dedicated modeling. The results obtained on the floating installation are compared with an on-land installation
Flexible and Modular Model for Smart Trolleybus Grids
Full text linkThe reduction of climate-changing emissions is vital, especially in urban areas. To reach this goal, the decarbonization of the public transport sector is crucial. Dynamic conductive power transfer through catenary systems is potentially a carbon-neutral solution. This paper focuses on trolleybus grids, already established in several metropolises, which are re-emerging as a smart city-oriented electrified transport system. A better integration of trolleybus grids with renewable sources, energy storage, and the existing electric network of the urban area is necessary to increase the efficiency of the system and optimize energy flows, favouring the transition towards smarter and greener cities. Moreover, trolleybus systems may act as a DC backbone for charging stations powering private electric vehicles, thus contributing to a closer interconnection between public and private mobility. A modular model of the electric traction grid in Matlab-Simulink is explored to simulate the actual complexity of novel trolleybus network topologies. By means of graphical and numerical results illustrating the behaviour of the main electrical line parameters, the model flexibility towards the inclusion of smart city-oriented technologies, such as stationary battery energy storage systems and electric vehicle chargers, is verified in this work. The trolleybus electrical infrastructure of the city of Bologna was chosen as a case study
Modular DC/DC Boost Converter for Efficient and Ripple-Free Conversion in Fuel Cell-Based Powertrains
Full text linkThe need to reduce emissions in the transport sector is making fuel-cell electric vehicles an option of increasing interest. However, several problems are still associated with this type of vehicles, including high costs and reliability. This paper discusses the issues related to the effects of the current ripple on PEM-type fuel cells and how a simple converter control strategy can be adopted to mitigate it. The study considers an interleaved boost converter in relation to its modular architecture and its present wide use in the automotive sector. The effect of different powertrain design parameters on the converter and its control technique is studied. Finally, a numerical analysis of the converter's efficiency is carried out to assess the possibility of achieving ripple-free operation even when phase shedding is adopted to increase the converter efficiency at partial loads
Smart Charging for Electric Car-Sharing Fleets Based on Charging Duration Forecasting and Planning
Full text linkElectric car-sharing (ECS) is an increasingly popular service in many European cities. The management of an ECS fleet is more complex than its thermal engine counterpart due to the longer ”refueling“ time and the limited autonomy of the vehicles. To ensure adequate autonomy, the ECS provider needs high-capacity charging hubs located in urban areas where available peak power is often limited by the system power rating. Lastly, electric vehicle (EV) charging is typically entrusted to operators who retrieve discharged EVs in the city and connect them to the charging hub. The timing of the whole charging process may strongly differ among the vehicles due to their different states of charge on arrival at the hub. This makes it difficult to plan the charging events and leads to non-optimal exploitation of charging points. This paper provides a smart charging (SC) method that aims to support the ECS operators’ activity by optimizing the charging points’ utilization. The proposed SC promotes charging duration management by differently allocating powers among vehicles as a function of their state of charge and the desired end-of-charge time. The proposed method has been evaluated by considering a real case study. The results showed the ability to decrease charging points downtime by 71.5% on average with better exploitation of the available contracted power and an increase of 18.8% in the average number of EVs processed per day
Current Pulse Generation Methods for Li-ion Battery Chargers
Full text linkLithium-Ion batteries are playing an essential role in electric vehicles and renewable sources development. In order to reduce the charging time, high power chargers are necessary. However, lithium-ion chemistry limits the maximum current and charging speed. The diffusion rate of lithium ions into the electrodes determines the rate of charging. The slow lithium diffusion, especially experienced after high current rates, inevitably results in concentration polarization. The increase of the concentration polarization, in addition to the growth of the charging time, may lead to a faster battery deterioration. To deal with this obstacle, the Pulse Charging (PC) protocol has been proposed. There is no common opinion about the benefits given by the PC to the battery charging process in comparison with the conventional constant-current, constant-voltage (CCCV) protocol. Nevertheless, the purpose of this work is to provide an overview of possible methods that can be used to generate current pulses, without focusing on its advantages. Different techniques with the corresponding control algorithms have been implemented and analyzed through simulations in MATLAB/Simulink environment
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