As society strives to transition for sustainable energy generation is it a major challenge to optimize and develop the renewable energy generation that currently exists, both in terms of individual components and their interactions in the entire energy system. The generation from renewable sources is often irregular and not always when the demand arises. By being able to store the excess energy generated and then deliver it when the demand occur results in a more sustainable energy system. Flow batteries are a possible technology for energy storage. An important component of flow batteries are vanadium and to find methods for extracting vanadium in an economical way is an important step in the development of this technology. The idea behind the thesis was therefore to investigate different extraction methods for vanadium where the most promising methods, from an economic and energy perspective, are examined in more detail. The vanadium should then be used to electrolyte in flow batteries. It has also been examined how the cost is affected by moving a planned facility for extraction from the ashes to a developing country with lower personnel costs. In the thesis was also included to explore similar projects on a larger scale conducted in Sweden, how the view of vanadium is from an EU perspective and how flow batteries can be a part of an energy system. The methods considered most promising is extraction from mineral mining and extraction from ashes. A planned production plant has been dimensioned for both processes of production and energy demand is calculated. The study showed that both processes are expected to produce vanadium below current purchase price, which would then contribute to a cheaper production cost of flow batteries. It turned out that the production of vanadium from ash extraction would be significantly reduced by moving the business to a developing country. The operation stage in the mining operation which accounts for the highest energy demand is the size reduction of the ore. In the extraction process of vanadium from ash, it is primarily the fusion furnace and the fly ash filter required which has the highest energy demand. The similar extraction projects investigated was, from ashes, the so-called SOTEX process in Stenungsund and the mineral mining process had the Ranstad project as reference. The EU approach to vanadium is currently that the metal is not classified as a critical raw material but if economic instability would occur in any of the major manufacturing countries it would be considered as a more critical raw material. Flow batteries functioning as energy storage in a PV hybrid system was investigated and it was concluded that flow batteries are technically well suited for energy storage in this type of system. / Då samhället strävar efter att övergå till en hållbar energiproduktion är det en stor utmaning att effektivisera och utveckla den förnyelsebara energiproduktion som idag finns, både när det gäller enskilda komponenter och deras samspel i hela energisystem. Produktion från förnyelsebara energikällor sker ofta ojämnt och inte alltid när behovet uppstår. Genom att kunna lagra den överskottsenergi som produceras och sedan leverera den då behovet uppstår medför det till ett mer hållbart energisystem. Flödesbatterier är en möjlig teknik för lagring av energi. En viktig komponent i flödesbatterierna är vanadin och att hitta metoder för att utvinna vanadin på ett ekonomiskt sätt är ett viktigt steg i utvecklingen av denna teknik. Idén bakom examensarbetet var därför att kartlägga olika utvinningsmetoder för vanadin där de mest lovande metoderna, från ett ekonomiskt och energi perspektiv, undersöks mer utförligt. Vanadinet i sin tur ska sedan användas till elektrolyt i flödesbatterier. Det har även undersökts hur kostnaden påverkas av att flytta en tänkt anläggning för utvinning ur aska till ett utvecklingsland med lägre personalkostnader. I examensarbetet ingick även att undersöka liknande projekt i större skala som bedrivits i Sverige, hur synen på vanadin är ur ett EU perspektiv samt hur flödesbatterier kan vara en del av ett energisystem. De metoder som ansetts mest lovande är utvinning från mineralbrytning samt utvinning ur aska. En tänkt produktionsanläggning har dimensionerats för båda processer där produktionskostnad och energiförbrukning beräknats. Studien visade att båda processerna förväntas kunna producera vanadin under dagens inköpspris vilket då skulle bidra till en billigare produktionskostnad för flödesbatterier. Det visade sig att produktionen av vanadin ur askutvinning skulle minskas avsevärt genom att flytta verksamheten till ett utvecklingsland. Det moment i gruvdriften som står för största energiförbrukningen är storleksreduceringen av den malm som bryts. Vid processen för utvinning av vanadin ur aska är det främst den smältningsugn samt det filter för flygaska som krävs. De liknande projekt som verkat inom utvinning ur aska var den s.k. SOTEX processen i Stenungsund och för mineralbrytning har Ranstad projektet undersökts. EU:s syn på vanadin är i nuläget att metallen inte klassas som en kritisk råvara men om ekonomisk instabilitet skulle uppstå i något av de större tillverkande länderna skulle råvaran klassas som mer kritisk. Flödesbatteri fungerande som energilagring i ett förnyelsebart energisystem undersöktes där slutsatsen var att flödesbatterier tekniskt sett är mycket väl lämpade som energilagring i denna typ av system.

Les batteries redox à circulation d'électrolyte constituent une solution prometteuse pour le stockage de masse de l'électricité. Parmi elles, la technologie au plomb soluble dans l'acide méthanesulfonique est intéressante pour son architecture de cellule simplifiée et son faible coût potentiel. Ses performances sont toutefois limitées par l'électrode positive de PbO2 qui implique un faible rendement énergétique et une courte durée de vie des cellules. Le premier objectif de cette thèse est de mieux comprendre les mécanismes électrochimiques en jeu à l'électrode positive. La cinétique de la réaction parasite de production d'oxygène est étudiée. Des mécanismes de dissolution du PbO2 sont proposés et des additifs sont testés pour améliorer sa cyclabilité. Les réponses complexes du potentiel de l'électrode en cyclage galvanostatique sont également interprétées. Le second objectif est de proposer un réacteur innovant comprenant une électrode positive de grande surface spécifique. La structure « nid d'abeilles » est en particulier étudiée. Un réacteur utilisant cette structure est proposé, ses caractéristiques principales sont simulées avec un modèle électrochimique ad hoc, et des prototypes sont fabriquées et testés en cyclage. / Redox-flow batteries are considered as a promising solution for massive electrical storage. In particular, the soluble lead-methanesulfonic acid technology is interesting due to the simple design of the cells and the potentially low associated costs. However some hurdles remain for its development, namely a low energy efficiency as well as a very limited lifetime, both of which being associated with the positive PbO2-electrode. The first goal of this Ph.D. thesis is to provide a better understanding of the electrochemical mechanisms taking place at the positive electrode. The kinetic behaviour of the parasitic oxygen evolution during charging is assessed. Some mechanisms involved in the dissolution of PbO2 are proposed and additives are tested for improving its cyclability. The complex potential responses of the electrode during galvanostatic cycling are also interpreted. The second purpose is to suggest a new reactor comprising a high specific surface area positive electrode. The honeycomb structure is especially studied. A reactor that includes a honeycomb-shaped positive electrode is proposed: its main characteristics are simulated using an electrochemical model and prototypes are fabricated and experimentally tested in cycling.

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The domestic sector will play an important role in the decarbonisation and decentralisation of the energy sector in the future. Installation numbers of building-integrated small-scale energy systems such as photovoltaics (PV), wind turbines and micro-combined heat and power (CHP) have significantly increased. However, the power output of PV and wind turbines is inherently linked to weather conditions; thus, the injected power into the public grid can be highly intermittent. With the increasing share of renewable energy at all voltage levels challenges arise in terms of power stability and quality. To overcome the volatility of such energy sources, storage technologies can be applied to temporarily decouple power generation from power consumption. Two emerging storage technologies which can be applied at residential level are hydrogen systems and vanadium-redox-flow-batteries (VRFB). In addition, the building-integrated energy sources and storage system can be combined to form a hybrid renewable energy system (HRES) to manage the energy flow more efficiently. The main focus of this thesis is to investigate the dynamic performance of two emerging energy storage technologies, a hydrogen loop composed of alkaline electrolyser, gas storage and proton exchange membrane (PEM) fuel cell, and a VRFB. In addition, the application of building-integrated HRES at customer level to increase the self-consumption of the onsite generated electricity and to lower the grid interaction of the building has been analysed. The first part deals with the development of a research test-bed known as the Hybrid Renewable Energy Park (HREP). The HREP is a residential-scale distributed energy system that comprises photovoltaic, wind turbine, CHP, lead acid batteries, PEM fuel cell, alkaline electrolyser and VRFB. In addition, it is equipped with programmable electronic loads to emulate different energy consumption patterns and a charging point for electric vehicles. Because of its modular structure different combinations of energy systems can be investigated and it can be easily extended. A unified communication channel based on the local operating network (LON) has been established to coordinate and control the HREP. Information from the energy systems is gathered with a temporal resolution of one second. Integration issues encountered during the integration process have been addressed. The second part presents an experimental methodology to assess the steady state and dynamic performance of the electrolyser, the fuel cell and the VRFB. Operational constrains such as minimum input/output power or start-up times were extracted from the experiments. The response of the energy systems to single and multiple dynamic events was analysed, too. The results show that there are temporal limits for each energy system, which affect its response to a sudden load change or the ability to follow a load profile. Obstacles arise in terms of temporal delays mainly caused by the distributed communication system and should be considered when operating or simulating a HRES at system level. The third part shows how improved system models of each component can be developed using the findings from the experiments. System models presented in the literature have the shortcoming that operational aspects are not adequately addressed. For example, it is commonly assumed that energy systems at system level can respond to load variations almost instantaneously. Thus, component models were developed in an integrated manner to combine theoretical and operational aspects. A generic model layout was defined containing several subsystems, which enables an easy implementation into an overall simulation model in MATLAB®/Simulink®. Experimental methods were explained to extract the new parameters of the semi-empirical models and discrete operational aspects were modelled using Stateflow®, a graphical tool to formulate statechart diagrams. All system models were validated using measured data from the experimental analysis. The results show a low mean-absolute-percentage-error (<3%). Furthermore, an advanced energy management strategy has been developed to coordinate and to control the energy systems by combining three mechanisms; statechart diagrams, double exponential smoothing and frequency decoupling. The last part deals with the evaluation, operation and control of HRES in the light of the improved system models and the energy management strategy. Various simulated case studies were defined to assess a building-integrated HRES on an annual basis. Results show that the overall performance of the hydrogen loop can be improved by limiting the operational window and by reducing the dynamic operation. The capability to capture the waste heat from the electrolyser to supply hot water to the residence as a means of increasing the overall system efficiency was also determined. Finally, the energy management strategy was demonstrated by real-time experiments with the HREP and the dynamic performance of the combined operation has been evaluated. The presented results of the detailed experimental study to characterise the hydrogen loop and the VRFB as well as the developed system models revealed valuable information about their dynamic operation at system level. These findings have relevance to the future application and for simulation studies of building-integrated HRES. There are still integration aspects which need to be addressed in the future to overcome the proprietary problem of the control systems. The innovations in the HREP provide an advanced platform for future investigations such as electric-vehicles as decentralised mobile storage and the development of more advanced control approaches.

Carbon nanotubes (CNTs) have been assessed for their use in electrochemical energy storage applications, namely Hydrogen Storage and Vanadium Redox Flow Batteries. Furthermore;fundamental electrochemical studies have been conducted on aligned arrays of carbon nanotubes, and for the first time electrochemistry on pure, defect free, single layer graphene is reported. CNTs have been assessed for their potential as an electrochemical hydrogen storage material,finding a maximum recorded capacity for a single walled nanotube sample (SWNT) that was comparable to literature gas phase adsorption values. In-situ Raman spectroelectrochemistry was used to probe structural changes of the SWNTs with applied potential: no chemical functionalisation of the tubes or intercalation of protons was observed. It was concluded, therefore, that CNTs present no unique electrochemical hydrogen storage ability, other than their role as an adsorbent for gaseous hydrogen, which was evolved electrochemically. CNTs were also assessed as a possible electrode material for the VO(2+)/VO2(+) reaction, used in the positive half cell of commercial vanadium redox flow batteries and widely reported to exhibit quasi-reversible kinetics on carbon electrodes. Initial investigations revealed apparently reversible kinetics using a SWNT, the first time such a response has been observed on Carbon, and in contradiction to published work using CNTs for this application. Analysis via a range of electrochemical techniques highlighted the difficulty in using cyclic voltammetry to assess reversibility, particularly for CNT modified electrodes. The system was subsequently found to be quasi-reversible, with the deceptively small peak separation inferred to arise from the pores of the CNT electrode, therefore thin layer cell behaviour was observed. The porous contribution was confirmed using an electrode exhibiting poor kinetics (very small, indistinct Faradaic peaks), increasing the electrode porosity (using an aligned array of CNT) had a remarkable effect, with large Faradaic peaks (low separation ˜ 0.02-0.04 V) observed for a sample that was chemically identical. This work highlights the fundamental error in a portion of CNT literature, where kinetic enhancement is quantified by voltammetric peak separation, which can be erroneous unless the inherent porosity of the electrodes is considered. In contrast to the complexity of CNTs, graphene represents an ideal electrode material, allowing for direct determination of the electrochemical response of the graphene basal plane, eliminating the contribution of edge sites. An initial investigation towards this goal is presented.

With its long cycle life and scalable design, the vanadium redox flow battery (VRB) is a promising technology for grid energy storage. However, high materials costs have impeded its commercialization. An essential but costly component of the VRB is the ion-exchange membrane. The ideal VRB membrane provides a highly conductive path for protons, prevents crossover of reactive species, and is tolerant of the acidic and oxidizing chemical environment of the cell. In order to study membrane performance and optimize cell design, mathematical models of the separator membrane have been developed. Where previous VRB membrane models considered minimal details of membrane transport, generally focusing on conductivity or self-discharge at zero current, the model presented here considers coupled interactions between each of the major species by way of rigorous material balances and concentrated solution theory. The model describes uptake and transport of sulfuric acid, water, and vanadium ions in Nafion membranes, focusing on operation at high current density. Governing equations for membrane transport are solved in finite difference form using the Newton-Raphson method. Model capabilities were explored, leading to predictions of Ohmic losses, vanadium crossover, and electro-osmotic drag. Experimental methods were presented for validating the model and for further improving estimates of uptake parameters and transport coefficients. / text

A comparison between a traditional fixed high voltage direct current energy transmission system and a mobile transmission system utilizing vanadium redox flow batteries has been conducted in this degree work.  The purpose of this comparison was to evaluate if a mobile energy transmission system could be competitive in terms of energy efficiency and cost-effectiveness for use in offshore wind power applications. A literary study was made to fully grasp the various technologies and to create empirical ground of which cost estimation methods and energy calculations could be derived. A specific scenario was designed to compare the two transmission systems with the same conditions. To perform the comparison, a model was designed and simulated in MATLAB. The results from the model showed that the flow battery system fell behind in energy efficiency with a total energy loss of 33.3 % compared to the 11.7 % of the traditional system, future efficiency estimations landed it at a more competitive 17.5 %. The techno-economic results proved that a mobile flow battery system would be up to nine times more expensive in comparison to a traditional transmission system, with the best-case scenario resulting in it being roughly two times more expensive. The main cause of this was found out to be the expensive energy subsystem, specifically the electrolyte, used in the flow battery system. Several environmental risks arise when using a flow battery system with this electrolyte as well which could harm marine life severely. In conclusion; with further development and cost reductions, a case could be made for the advantages of a truly mobile energy transmission system. Specifically, in terms of the pure flexibility and mobility of the system, allowing it to circumvent certain complications. The mobility of the system gives the possibility of selling energy where the spot prices are at their highest, providing a higher revenue potential compared to a traditional fixed system. As for now though, it is simply too expensive to be a viable solution.