Developing vanadium redox flow technology on a 9-kW 26-kWh industrial scale test facility: Design review and early experiments

Redox Flow Batteries (RFBs) have a strong potential for future stationary storage, in view of the rapid expansion of renewable energy sources and smart grids. Their development and future success largely depend on the research on new materials, namely electrolytic solutions, membranes and electrodes, which is typically conduced on small single cells. A vast literature on these topics already exists. However, also the technological development plays a fundamental role in view of the successful application of RFBs in large plants. Despite that, very little research is reported in literature on the technology of large RFB systems. This paper presents the design, construction and early operation of a vanadium redox flow battery test facility of industrial size, dubbed IS-VRFB, where such technologies are developed and tested. In early experiments a peak power of 8.9 kW has been achieved with a stack specific power of 77Wkg−1. The maximum tested current density of 635 mA cm−2 has been reached with a cell voltage of 0.5 V, indicating that higher values can be obtained. The test facility is ready to be complemented with advanced diagnostic devices, including multichannel electrochemical impedance spectroscopy for studying aging and discrepancies in the cell behaviors

Historic building and green energy. Strategies to make supply from renewable sources compatible with conservation

The challenges of today are largely summarized in the United Nations 2030 Agenda. Buildings are also part of the 17 sustainability goals in several re- spects, one of them being the role of reducing greenhouse gas emissions, reduc- ing waste, assessing the life cycle of materials, limiting heat loss and introducing renewable energy sources. In particular, the contribution deals with how to ensure the supply of energy from renewable sources for cultural assets and buildings that are part of historic centers. In these cases, it can be very difficult to achieve both the objective of protecting the monument or landscape as well as that of installing or connecting the building or urban or rural settlement to renewable energy sources. Through some European and Italian examples in particular, where about 8 million buildings were constructed before 1945, about 25% of the total, virtu- ous ways will be presented that make it possible to achieve both objectives sim- ultaneously. The regulations that favor this dual objective will also be high- lighted, such as the one of the Veneto Region on so-called energy communities and the national one that allows the deferral of energy production from one place of cultural interest to another that has none, without serious costs for the final beneficiary and safeguarding the cultural asset

Maximizing Vanadium Redox Flow Battery Efficiency: Strategies of Flow Rate Control

Vanadium redox flow batteries (VRFBs) are one of the most promising technologies for large-scale energy storage due to their flexible energy and power capacity configurations. The energy losses evaluation assumes a very important rule on the VRFB characterization in order increase the efficiency of the battery. Very few papers describe the relations between hydraulic, electrical and chemical contributions to the system energy losses, especially in a large size VRFB system. In the first part a fluid dynamics characterization of a 9kW / 27 kWh VRFB test facility has been conducted. In particular, we will consider the internal resistance as the sum of an ohmic and a transport resistance. Secondly, an overall loss assessment based on both numerical and experimental results has been carried out. Finally, some improvements in the battery management strategy and in stack engineering are proposed, that results from this work and can help the future designer to develop more efficient VRFB stack with a compact design

Enhancing the efficiency of kW-class vanadium redox flow batteries by flow factor modulation: An experimental method

he paper presents a control method of the electrolyte flow factor in kW-class Vanadium Redox Flow Batteries that minimizes transport losses without affecting the battery's electrical performance. This method uses experimental data acquired on a 9 kW/27 kWh test facility at varying operating conditions. The effects of overpotentials on the polarization curves are then modeled as non-linear electrical resistances that vary with the stack current, state of charge and electrolyte flow rates. Our analysis of these variables shows that the optimal performance is found if the flow factor is modulated during operation according to stack current and the battery state, so as to minimize the overall flow-dependent losses. The optimal profiles have been identified as functions of the battery's operating conditions. Based on these results, a dynamic control for the electrolyte flow rates has been implemented at a software level (i.e. without modifying the hardware of the test facility), which is capable of maximizing the round-trip efficiency and exceeds the performance achieved with a constant flow factor strategy, as proposed in previous literature. The implementation of the optimal flow rate control requires a preliminary test campaign to collect performance data, which are then used in the control protocol to manage the battery's operation. This scheme is easily implementable at a software level in other industrial redox flow batteries

Dissimilarity Bandits

We study a novel sequential decision-making setting, namely the dissimilarity bandits. At each round, the learner pulls an arm that provides a stochastic d-dimensional observation vector. The learner aims to identify the pair of arms with the maximum dissimilarity, where such an index is computed over pairs of expected observation vectors. We propose Successive Elimination for Dissimilarity (SED), a fixed-confidence best-pair identification algorithm based on sequential elimination. SED discards individual arms when there is statistical evidence that they cannot belong to a pair of most dissimilar arms and, thus, effectively exploits the structure of the setting by reusing the estimates of the expected observation vectors. We provide results on the sample complexity of SED, depending on {HP}, a novel index characterizing the complexity of identifying the pair of the most dissimilar arms. Then, we provide a sample complexity lower bound, highlighting the challenges of the identification problem for dissimilarity bandits, which is almost matched by our SED. Finally, we compare our approach over synthetically generated data and a realistic environmental monitoring domain against classical and combinatorial best-arm identification algorithms for the cases d=1 and d>1

Teoria crítica e luta por reconhecimento: Axel Honneth em pauta

The critical-theoretical model of Axel Honneth presents the conflict as the force that drives social development. Starting from this premise, this paper seeks to explain the genesis of social conflicts from Honneth´s point of view, demonstrating the centrality of patterns of inner subjective recognition - the love, duty and solidarity - in the formal conception of eticity - or formal conception of good life - which leads to social theory of normative content erected by Honneth. Therefore, we seek clues to the author’s assessment of the contribution to Critical Theory - especially emphasizing his called frankfurtian heritage, which has Jünger Habermas as the main interlocutor - as well as a reflection about the conception of emancipation that underlies his theory.O modelo teórico-crítico de Axel Honneth apresenta o conflito como a força que impulsiona o desenvolvimento social. Partindo de tal premissa, o presente trabalho busca explicitar a gênese dos conflitos sociais do ponto de vista honnethiano, demonstrando a centralidade dos padrões de reconhecimento intersubjetivo, sendo eles o amor, o direito e a solidariedade, na concepção formal de eticidade – ou concepção formal de vida boa – na qual desemboca a teoria social de teor normativo erigida por Honneth. Com isso, buscamos elementos que permitam a avaliação da contribuição do autor à Teoria Crítica - enfatizando sobretudo sua chamada herança frankfurtiana, que tem Jünger Habermas como principal interlocutor - assim como uma reflexão acerca da concepção de emancipação que subjaz sua teoria

Stochastic Rising Bandits

This paper is in the field of stochastic Multi-Armed Bandits (MABs), i.e., those sequential selection techniques able to learn online using only the feedback given by the chosen option (a.k.a. arm). We study a particular case of the rested and restless bandits in which the arms’ expected payoff is monotonically non-decreasing. This characteristic allows designing specifically crafted algorithms that exploit the regularity of the payoffs to provide tight regret bounds. We design an algorithm for the rested case (R-ed-UCB) and one for the restless case (R-less-UCB), providing a regret bound depending on the properties of the instance and, under certain circumstances, of $\widetilde{\mathcal{O}}(T^{\frac{2}{3}})$. We empirically compare our algorithms with state-of-the-art methods for non-stationary MABs over several synthetically generated tasks and an online model selection problem for a real-world dataset. Finally, using synthetic and real-world data, we illustrate the effectiveness of the proposed approaches compared with state-of-the-art algorithms for the non-stationary bandits

Análise de cafeína em café por voltametria cíclica e com eléctrodos compósitos de grafite, óxidos de metal e resina epoxílica

Mestrado com dupla diplomação com a Universidade Tecnológica Federal do ParanáEste trabalho incidiu na análise de cafeína por voltametria cíclica com o objetivo estudar o desempenho de eléctrodos de trabalho compósitos de grafite, óxidos de metal e resina epoxílica. Especificamente, pretende-se averiguar se o sistema voltamétrico permite a análise de cafeína em amostras de café. Usaram-se 13 amostras de café adquiridas numa superfície comercial, na forma de grão e de várias origens: Angola, Brasil, Camarões, Colombia, Costa do Marfim, Costa Rica, Guatemala, Índia, Portugal, São Tomé e Príncipe, Timor Leste, Uganda e Vietnam. Este estudo preliminar envolveu a construção de 13 elétrodos de trabalho com composições diferentes e a seleção de seis com maior sensibilidade à cafeína: C, C+PbO 7,5%, C+Cu2O 7,5%, C+PbO2 15%, C+PbO2 7,5% e C+Al2O3 15%. A composição da solução que melhor incrementava o sinal de cafeína foi de H2SO4 0,1 mol/L e um pH de 1,25. A voltametria cíclica foi realizada no intervalo de potencial entre -2 e +2 V, com velocidade de varrimento de 0,4 V/s e num intervalo de leitura da corrente de 10 mA/V. Os eléctrodos de trabalho usados analisaram a solução redox de ferrocianeto/ferricianeto como um processo quase-reversível, mostrando bom desempenho eletroquímico. Na análise da cafeína, os voltamogramas cíclicos mostram a presença de 2 picos anódicos (aproximadamente a +0,82 e +1,7 V) e 1 pico catódico (aproximadamente a -0,82 V) com variação na intensidade de corrente associada à variação da concentração de cafeína na solução, como se verificou nos estudos de calibração. Extratos de café foram analisados por HPLC, tendo-se obtidos níveis de cafeína entre 0,38 e 1,90 mg/g de café. O café com maior concentração de cafeína foi o de origem Costa do Marfim e embora o café de Costa Rica apresente o nível mínimo de cafeína, também as mostras de Brasil, Colômbia, Guatemala e Timor apresentaram níveis baixos. Na análise eletroquímica, verificou-se que a informação voltamétrica tinha influência da matriz do extrato. No estudo da relação entre a informação quantitativa da cafeína e voltamogramas cíclicos parciais, usando regressão PLS, verificouse que os eléctrodos de trabalho selecionados permitem obter informação sobre a cafeína nos extratos de cafeína. Em trabalho futuro, será necessário otimizar o procedimento de análise voltamétrica principalmente na análise dos extratos de café, onde a concentração de cafeína deve ser incrementada, e ter uma maior caracterização química do extrato de para se perceber a sua influência nos voltamogramas cíclicos e, por isso, na quantificação.This work focused on the analysis of caffeine by cyclic voltammetry with the objective of studying the performance of graphite, metal oxides and epoxy resin composite working electrodes. Specifically, it was intended to investigate if the voltammetric system allows the analysis of caffeine in coffee samples. Thirteen coffee samples purchased on a commercial surface, in the form of grain and from various origins, were used: Angola, Brazil, Cameroon, Colombia, Ivory Coast, Costa Rica, Guatemala, India, Portugal, São Tome and Principe, Uganda and Vietnam. This preliminary study involved the construction of 13 working electrodes with different compositions and the selection of six with higher sensitivity to caffeine: C, C + PbO 7.5%, C + Cu2O 7.5%, C + PbO2 15%, C + PbO2 7.5% and C + Al2O3 15%. The composition of the solution that best enhanced the caffeine signal was with 0.1 mol/L of H2SO4 and a pH of 1.25. Cyclic voltammetry was performed in the potential range between -2 and +2 V, with a scanning rate of 0.4 V/s and a current reading range of 10 mA/V. The working electrodes analyzed the ferrocyanide / ferricyanide redox solution as a quasireversible process, showing good electrochemical performance. In the caffeine analysis, the cyclic voltammograms show the presence of 2 anode peaks (approximately at +0.82 and +1.7 V) and 1 cathode peak (approximately at -0.82 V) with variation in current intensity associated with concentration of caffeine in the solution, as found in the calibration studies. Coffee extracts were analyzed by HPLC and caffeine levels were obtained between 0.38 and 1.90 mg/g coffee. The coffee with the highest concentration of caffeine was originated in Ivory Coast, and although coffee in Costa Rica has the minimum level of caffeine, the samples from Brazil, Colombia, Guatemala and Timor also had low levels. In the electrochemical analysis, it was verified that the voltammetric information had influence of the matrix of the extract. In the study of the relationship between quantitative caffeine information and partial cyclic voltammograms using PLS regression, it was found that the selected working electrodes allow to obtain information about caffeine in caffeine extracts. In future work, it will be necessary to optimize the voltammetric analysis procedure mainly in the analysis of the coffee extracts, where the concentration of caffeine must be increased, and to have a greater chemical characterization of the coffee’s extract to see its influence on the cyclic voltamograms. Keywords: Caffeine; coffee; composite electrodes; cyclic voltammetry; HPLC