Critères de choix d'un système de stockage électrochimique hybride d'énergie photovoltaïque

International audienceThe design of battery systems is an important issue in many cases conditioned by several constraints and modeling challenges. This work proposes a design method for electrochemical hybrid energy storage system associated with photovoltaic modules. Based on this method, an optimization procedure is used to discuss the interest of creating a hybrid system combining two different types of batteries. The batteries are modeled as a constant voltage source in series with an internal resistance and the finite capacity of the batteries is considered independent from their use. The model uses the battery capacity, maximum charge rate, internal resistance and cost given at the beginning of the battery life.Une procédure d'optimisation et de dimensionnement d'un système de stockage électrochimique d'énergie associé à des panneaux solaires est décrite et discutée. Elle permet d'étudier l'intérêt ou non de réaliser un système hybride associant deux types de batteries différents. Cet outil utilise un modèle simplifié de batteries : elles sont considérées comme une source de tension constante en série avec une résistance interne avec une capacité finie indépendante du type d'utilisation. Le modèle prend ainsi en compte des caractéristiques de batteries à l'état neuf : capacité, régime maximal de charge, résistance interne et coût

A very easy kinetics determination for feedback curves with a microdisk SECM tip and rather rapid substrate reaction

International audienceA new description of the steady-state feedback currents in SECM (scanning electrochemical microscopy) experiments using a microdisk with rather irreversible rapid kinetics reaction at the substrate is discussed. In this case, the feedback approach curve can be very accurately deduced from a simple translation of the pure positive feedback curve along the tip-substrate distance axis. The shifting between both curves gives directly the inverse value of the kinetics parameter. The accuracy of this kinetics determination is discussed in comparison with previously published results. This method allows dimensionless kinetics parameters comprised between 2 and 100 with dimensionless distance values comprised between 0.2 and 1 to be easily and accurately determined. Another sound advantage of this method is that the results are valid for any kind of microdisk, which was not the case for the previously used analytical approximations

A unified new analytical approximation for positive feedback currents with a microdisk SECM tip

International audienceAnalytical approximations for steady-state positive feedback currents in scanning electrochemical microscopy (SECM) experiments using a microdisk are discussed. The use of a conformal map transformation leads to the use of new mathematical functions. A general analytical expression for all values of tipsubstrate distances and all types of microdisk (with various insulator thicknesses) are thus obtained with only four adjustable parameters

Optimisation des stratégies de gestion des batteries au plomb utilisées dans les systèmes photovoltaïques

Les batteries à usage photovoltaïque subissent des conditions opératoires pénalisantes liées à la non maîtrise de l'énergie disponible. Les effets peuvent en être minimisées par une stratégie de gestion optimisée. Cette étude concerne la recharge à courant pulsé des batteries au plomb, les plus utilisées dans ces systèmes. Les effets de cette recharge sont mis en évidence sur des cellules de laboratoire et sur des batteries commerciales. L'influence des paramètres fréquence, rapport cyclique et taux de charge sur les profils de tension est étudiée de manière précise. Dans une seconde approche, un modèle simplifié de la batterie au plomb a été développé et validé après analyse de sa sensibilité aux paramètres ajustables. Il décrit les phénomènes de transport dans l'électrolyte de manière globale par un temps caractéristique fonction de l'état de charge, et rend bien compte des réponses en tension de la batterie après introduction des termes de non idéalité dans les tensions interfaciales.Batteries used in photovoltaic systems are subjected to penalizing operating conditions due to the intermittency of the solar resource. Their effects may be reduced by the optimisation of energy management strategies. This study deals with the pulse charge of lead acid batteries, the most used ones for this application. The effects of this charge mode are shown both on experimental cells and commercial batteries. The influence of the parameters, frequency, dut Y cycle and charge factor, on the voltage profiles is precisely studied. ln a second approach, a simplified model of the lead-acid battery is developed and experimentally validated after the analysis of its sensitivity to the adjustable parameters. It shows that transport phenomena in the electrolyte may be well described by a global characteristic time depending only on the state of charge. It accounts for the voltage response of the battery after adding the terms describing the non ideal behavior of the interfacial voltages.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Détermination du rôle de la dispersion des caractéristiques entre blocs dans un système d'alimentation sans interruption (ASI) comprenant plusieurs accumulateurs à recombinaison de gaz raccordés en série, sur la durée de vie du système

GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Studying permeable films with scanning electrochemical microscopy (SECM): Quantitative determination of permeability parameter

International audienceA new analysis of scanning electrochemical microscopy (SECM) data is proposed in the case of a substrate covered by a film (porous material or electrolyte film,…) with diffusion-limited reactions. In a lot of experimental situations, the approach curve (measure of the current as function of the tip-substrate distance) is alike the one for a bare substrate with an irreversible kinetics reaction. In all these cases, this work demonstrates a very simple relationship between the apparent irreversible kinetics parameter extracted from the approach curve and film characteristics, giving the ratio between the permeability and the thickness of the film. The validity domain of the new data analysis is carefully determined. It is then applied to experimental data on Nafion films taken from literature

New analytical approximations for negative feedback currents with a microdisk SECM tip

International audienceAnalytical approximations for steady-state negative feedback currents in scanning electrochemical microscopy (SECM) experiments using a microdisk are discussed. Previously published results are precisely discussed and lead to an analytical approximation valid (with an error below ±0.01 on normalized current) for all values of tipsubstrate distances and microdisk with an insulator thickness characterized by Rg values between 57 and 1000. More interesting from an experimental point of view, the use of new mathematical expressions allows the proposition of an analytical expression valid for all values of tipsubstrate distances and microdisk with Rg values between 1.3 and 62

Développement et optimisation de techniques analytiques à l'aide de simulations numériques, pour le microscope électrochimique

Ce travail est une contribution au développement de la microscopie électrochimique (SECM) comme outil d'analyse quantitatif. Il s'appuie sur des simulations numériques par éléments finis, pour différentes situations expérimentales, décrites dans la littérature. L'examen détaillé des résultats numériques obtenus, permettent de proposer à la communauté scientifique des outils quantitatifs d'analyse des données expérimentales qui ne font plus appel à la simulation numérique. Les travaux présentés portent tant sur des situations très classiques comme celles d'un substrat où survient une réaction irréversible d'ordre 1, que sur des activités beaucoup moins courantes comme la transformation localisée de surface. D'autres substrats rencontrés en SECM sont par ailleurs étudiés: caractérisation d'une cinétique enzymatique, de film poreux déposé sur substrat, ou de source réactive sur substrat isolant.In this work, various SECM configurations are studied thanks to finite elements numerical simulations. Rigorous analysis of numerical results, associated with careful attention to SECM community preoccupations lead to simple and reliable method, that can be used without numerical simulations. The research presented here focuses bothon common situations such as first order irreversible kinetics on substrate and on less common ones such as localised surface transformations. Other SECM situations are also studied : enzymatic kinetics, porous film on a surface, surface source spot. A method to assess the geometrical parameters of microdisk tip through approach curves is also suggested.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

A unified new analytical approximation for negative feedback currents with a microdisk SECM tip

International audienceAnalytical approximations for steady-state negative feedback currents in scanning electrochemical microscopy (SECM) experiments using a microdisk are discussed. A precise study of the limit behavior for small tipsubstrate distances and all microdisks leads to an analytical expression without any fit. From this analytical limit a new mathematical function is proposed which is the first expression that accurately fit any negative feedback approach curve with only three adjustable parameters (for a given Rg value, characterizing the insulator thickness of the microdisk electrode, between 1.001 and 1000). Finally a unified new analytical approximation of all negative feedback approach curves with tipsubstrate distances and Rg as variables is demonstrated. Except for very large Rg values (over 200), which is not an experimental interesting configuration, the error is below ±0.01 on normalized current

New analytical approximation of feedback approach curves with a microdisk SECM tip and irreversible kinetic reaction at the substrate

International audienceAvailable approximate expressions used in the kinetic data treatment of (scanning electrochemical microscopy) SECM experiments in the case of steady-state feedback currents with irreversible reaction at the substrate and a microdisk tip are discussed. The necessity of new expressions is thus pointed out. A new expression of the current is then produced and discussed. It covers all usual experimental configurations (microdisks with Rg below 20, Rg characterizing the surrounding insulator thickness) and dimensionless tip-substrate distances larger than 0.1, with an accuracy of ±0.025 for any kinetics