1,720,987 research outputs found
Life cycle estimation of battery energy storage systems for primary frequency regulation
No full textAn increasing share of renewable energy sources in power systems requires ad-hoc tools to guarantee the closeness of the system's frequency to its rated value. At present, the use of new technologies, such as battery energy storage systems, is widely debated for its participation in the service of frequency containment. Since battery installation costs are still high, the estimation of their lifetime appears crucial in both the planning and operations of power systems' regulation service. As the frequency response of batteries is strongly dependent on the stochastic nature of the various contingencies which can occur on power systems, the estimation of the battery lifetime is a very complex issue. In the present paper, the stochastic process which better represents the power system frequency is analyzed first; then the battery lifetime is properly estimated on the basis of realistic dynamic modeling including the state of the charge control strategy. The dynamic evolution of the state of charge is then used in combination with the celebrated rain-flow procedure with the aim of evaluating the number of charging/discharging cycles whose knowledge allows estimating the battery damage. Numerical simulations are carried out in the last part of the paper, highlighting the resulting lifetime probabilistic expectation and the impact of the state of the charge control strategy on the battery lifetime. The main findings of the present work are the proposed autoregressive model, which allows creating accurate pseudo-samples of frequency patterns and the analysis of the incidence of the control law on the battery lifetime. The numerical applications clearly show the prominent importance of this last aspect since it has an opposing impact on the economic issue by influencing the battery lifetime and technical effects by modifying the availability of the frequency regulation service. © 2018 energies. All rights reserved
Comparison of different scenarios of users distribution among charging infrastructure in an urban area
No full textFast charging stations are becoming more common in cities. However, the most suitable positioning and size remain problems to be solved. The work focuses on the analysis of demand and the supply of fast recharging points in an urban area, using fuzzy models to simulate users behavior. The proposed model simulates real-world traffic situation, to obtain a 'what-if' analysis of different scenarios, in which the parameters of the model were changed in turn to observe the implications on the results. Different decision models are proposed to simulate the charge policy for users distribution among the available charging point. Various charging behaviors are also compared. The results reported show that the variables involved in the charging infrastructure design strongly influence the output scenarios. The model can be a valuable tool to support decision making in an urban area
Tools for Life Cycle Estimation of Energy Storage System for Primary Frequency Reserve
No full textBattery energy storage systems are widely recognized as viable means for providing frequency regulation in electrical systems characterized by the massive deployment of renewable resources. In this case, the estimation of the battery lifetime is very complex since its response depends strongly on the stochastic nature of various contingencies. By starting from the characterization of the power system frequency in terms of the stochastic process, in this paper, tools needed for the battery lifetime estimation are detailed. On the basis of a realistic dynamic model, the state of charge profile requested to a battery providing primary frequency regulation is derived, with the aim of characterizing statistically its degradation. In this way, it is expected to obtain an efficient battery lifetime estimation compared to the heuristic methods. Numerical simulations are carried out in the last part of the paper, illustrating a simulation tool for the estimation of the battery working cycle. © 2018 IEEE
Accelerated life tests of complete lithium-ion battery systems for battery life statistics assessment
No full textThe paper investigates the performances of automotive lithium-ion battery systems, which are considered as one of the most promising candidates for the use on electric and hybrid vehicles. Indeed, lithium batteries show technical properties and features particularly suitable for these applications in which high energy and power densities are required. In order to investigate lithium-ion battery major technical limitations, a set of experimental testing activities has been carried on battery packs and systems, whose behaviours are expected to be significantly different from the test results on single cells. One of the most crucial challenge is the problem of the battery lifetime. Many approaches have been proposed in the relevant literature, but a lot of difficulties persist, being related to the incidence of many factors which do not allow to derive a quite general model able to describe in an exhaustive way battery performances under different operating conditions. In the paper, a method is proposed which takes into account the randomness of the battery parameters, such as design maximum specific power and operating environment, in real operating condition, with reference to lithium ion batteries designed for a small electric bus (public transport service). Based on available experimental data, the lifetime probability distribution of these batteries has been estimated by means of a Weibull model. © 2016 IEEE
Accelerated life tests of complete lithium-ion battery systems
No full textA battery design method for lithium-ion batteries is discussed in the paper. The method takes into account the dependence of battery lifetime on different parameters, such as temperature, design maximum specific power, S.O.C., and relates it to the operating environment and economical aspect. The methods relies on a large set of experimental measurements, in particular accelerated life tests. The method allows to determine the optimal size, in terms of Life Cycle Cost, for a lithium ion battery designed for a small electric bus (public transport service)
Experimental Analysis of NMC Lithium Cells Aging for Second Life Applications
No full textNowadays the electric power system is facing new challenges related to the integration of renewable sources, more and more frequently combined with energy storage systems. The use of these technologies is very promising, although it requires sophisticated control architectures in order to successfully balance the intermittence and unpredictability of renewables, and provide the power grid with new services. The presence of a storage state estimator is absolutely required to correctly identify the storage performance and present conditions, in terms of stored energy, aging or possible failures; this is crucial to assess the real exploitability of the battery, both during its first or second life application. This paper focuses in particular on aging mechanisms, describing and comparing three possible models and their deployment procedures. Flexibility of implementation, accuracy in aging determination, and ease of use of each technique have been deeply analysed and compared. İ 2018 IEEE
Influence of Battery Aging on the Operation of a Charging Infrastructure
No full textThe increasingly widespread use of electric vehicles requires proper planning of the charging infrastructure. In addition to the correct identification of the optimal positions, this concerns the accurate sizing of the charging station with respect to energy needs and the management of power flows. In particular, if we consider the presence of a renewable energy source and a storage system, we can identify strategies to maximize the use of renewable energy, minimizing the purchase costs from the grid. This study uses real charging data for some public stations, which include “normal” chargers (3 kW and 7 kW) and “quick” ones (43 kW and 55 kW), for the optimal sizing of a photovoltaic system with stationary storage. Battery degradation due to use is included in the evaluation of the overall running costs of the station. In this study, two different cost models for battery degradation and their influence on energy flow management are compared, along with their impact on battery life
Evolution from BCS superconductivity to Bose-Einstein condensation: Current correlation function in the broken-syemmetry phase
No full textWe consider the current correlation function for a three-dimensional system of fermions embedded in a
homogeneous background and mutually interacting via an attractive short-range potential, below the ~superconducting!
critical temperature. Diagrammatic contributions in the broken-symmetry phase are identified,
which yield for the ~wave-vector and frequency-dependent! current correlation function the fermionic BCS
approximation in the weak-coupling limit and the bosonic Bogoliubov approximation in the strong-coupling
limit ~whereby composite bosons form as bound-fermion pairs!. The temperature dependence of the superfluid
density ~from the BCS exponential behavior at weak coupling to a power-law behavior at strong coupling! and
the form of the Pippard-like kernel at zero temperature are explicitly obtained from weak to strong coupling.
Quite generally, it is shown that the Pippard-like kernel is the sum of a local ~London-like! term and of a
nonlocal component, the local term being dominant in the strong-coupling limit and the nonlocal component in
the BCS ~weak-coupling! limit. It is also shown that the range of the nonlocal component is determined by the
coherence length measuring the spatial correlations of the amplitude of the order parameter, namely, the
correlations among different Cooper pairs ~or composite bosons!, rather than between the fermionic partners of
a given pair. In addition, a prescription is provided for mapping the fermionic onto the bosonic diagrammatic
theories in the broken-symmetry phase, thus complementing what has been already done in the normal phase
Comparing Charging Management Strategies for a Charging Station in a Parking Area in North Italy
Full text linkVia the analysis of a set of parking and journey information for vehicles traveling to the parking site at the University of Brescia (Italy), we evaluated the possibility of managing the electric recharging of these vehicles, which are hypothesized to be electric. The paper investigates charging optimization techniques that can limit the charge power peaks and distribute the energy demand throughout the day. A cost assessment for an auxiliary system consisting of a photovoltaic energy source (PV) and battery stationary storage (BSS) is also carried out. Optimal power management at the station with PV and BSS is introduced, and the performance of two feedback controllers based on the optimized results is compared with that of a real-time management algorithm in the presence of randomness in charging requests and insolation. The results show that the BSS degradation cost plays a primary role in determining the strategy to adopt to minimize the operating expenditure of a charging station
A demand-side approach to the optimal deployment of electric vehicle charging stations in metropolitan areas
No full textDespite all the acknowledged advantages in terms of environmental impact reduction, energy efficiency and noise reduction, the electric mobility market is below expectations. In fact, electric vehicles have limitations that pose several important challenges for achieving a sustainable mobility system: among them, the availability of an adequate charging infrastructure is recognized as a fundamental requirement and appropriate approaches to optimize public and private investments in this field are to be delineated. In this paper we consider actual data on conventional private vehicle usage in the urban area of Rome to carry out a strategy for the optimal allocation of charging infrastructures into portions (subareas) of the urban area, based on an analysis of a driver sample under the assumption of a complete switch to an equivalent fleet of electric vehicles. Moreover, the energy requirement for each one of the subareas is estimated in terms of the electric energy used by the equivalent fleet of electric vehicles to reach their destination. The model can be easily generalized to other problems regarding facility allocation based on user demand. © 2016 Elsevier Lt
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