Vanadium redox battery pdf

The application timeframe of the MA technique is a very important issue and must be carefully chosen. In [6] the authors explore timeframes of 2. This study [10] shows that a shorter timeframe results in a higher number of controlled ramps successfully. Taking into account this conclusion and the technical limits of the microgrid used for the experimental validation of the present study, it was chosen to use a period of 20s for the MA. Further details are presented in the next section.

Nowadays, PV for self-consumption is the most studied and applied strategy to operate a PV system with or without a battery depending on the load consumption. Also, this study [12] used the Germany specific grid feed-in limitations to relieve the grid from the VER.

In this work, Section 2 will present the methodology, including previous solar PV data analysis 2. In Section 3, the simulation and the implementation details are presented, focusing on the simulation of the studied EMSs, and on the implementation for validation in the real microgrid, consisting of a PV system and a VRFB, its programming and control. Section 4 presents the results regarding the simulations, the KPIs and the battery SoC, followed by its discussion.

The conclusions for this work are presented in Section 5. Methodology 2. The data was compiled in samples of one minute, and the ramp rates were calculated for the entire year of The RR results summary is shown in Table 1.

It should be noted that, in order to increase the degree of confidence of these results, this analysis requires a substantially longer data period, ideally several years. The existence of systems with monitoring of long-term PV production data with high frequency e. Similar to the analysis of solar radiation meteorological data, and due to the direct relationship between this solar radiation data and the occurrence of power ramps, the results in the previous table are only representative for the location and specifications tilt, azimuth, etc.

These EMS are explored in this work. The self-consumption maximization SCM — strategy 1 is a very simple strategy which is applied to maximize the usage of the PV generation throughout the day, made available by a PV system.

The user installation can benefit from a battery to increase this PV generation utilization. This strategy is usually the most applied overall, in the industry and in residential solutions, due to its simple application and improved match with the consumption demands.

As previously explained, the continuous increase of PV system installations worldwide will have impacts on the grid management, due to its intermittency and variability characteristics, probably requiring for ramp-rate limitations. Applying these ramp limitations either for up or down ramps , will strengthen the SC maximization strategy.

In this case, the self-consumption is carried out by the PV system with the help of the battery, although when the ramp is violated, the battery unit is used primarily to control the ramp. In this strategy, the ramp is calculated as a percentage per minute over the nominal PV power.

When there is no violation of the ramp limit, the PV self- consumption maximization strategy is used. In this strategy, a SoC control is not carried out. This decision was made in order to evaluate the extent of the impact of not having a SoC control. One of the most important factors in the ability to use a ramp rate algorithm with a battery is the battery SoC when needed. In this sense, ramp control is a concurrent objective with the maximization of self-consumption for the use of the battery.

In the average load curve characteristic of a domestic or services installation, a peak consumption at the end of the day often occurs after sunset or at night. Supplying this night-time consumption, in order to maximize photovoltaic self-consumption, has the consequence that the battery SoC can reach the next morning close to its minimum limit.

These available power technical restrictions prevent the full control of power ramps. In the last strategy, a SoC control is implemented, with a battery charging-discharging command target conditioned to the weather forecast for the next 12h for the site. The meteorological forecast categories that best could indicate the probability of the occurrence of ramps were selected. More details about this method are presented in section 2. This microgrid is equipped with a PV system with 3.

The VRFB is physically constituted by two tanks of electrolyte, two pumps which allow the electrolyte flowing, and a stack: the energy conversion unit. The stack is a dynamic system, and its performance depends on multiple effects: electrochemical, fluid dynamics, electric and thermal. This VRFB was the object of study in previous works, and the most recent include the battery full electrical modelling, developed and validated on a real scale, considering its general operating conditions.

This model is fully detailed in the research conducted in [15]. The presented VRFB model [15] was implemented in the control algorithm and energy management strategies. IPMA is a Portuguese public body, which is responsible for, among other many tasks, forecast the states of the weather and sea for all necessary needs. The forecast data associated with the geographical sites, and seismic events location, in the JSON format, are made available in their API application programming interface [16].

In this API it can be found online daily meteorological data forecast up to 5 consecutive days by region, and daily meteorological data forecast up to 3 consecutive days with aggregated information per day. Each Portuguese region has a global code id, which identifies it.

Every twelve hours the forecast information is updated in the website, for each region. IPMA forecasts roughly 41 regions, both onshore and offshore. In this work we choose to give relevance to the id weather type, for which a number is attributed, corresponding to a weather description, which can be observed in Table 2.

With the help of this information, the battery SoC is prepared for the next day, as needed. The preparation is made through battery charging during the night hours in general there is very low energy consumption from domestic users during those hours , and for that reason, this control type is optimal for the Portuguese bi- hourly and tri-hourly household tariffs, with lower electricity price during the night [19].

The command will be a charging only command, since it is expected that the battery at the end of the day, to be near its lowest SoC limit , given the load curve profiles used. Time frame The moving averaging timeframe is an aspect that should be sensibly weighted. The study developed in [20] researches carefully the PV time averages impacts on the small and medium- sized PV installations.

The authors conclude that a timeframe of minute averages describes these ramps poorly. Because of this concern, an adequate time frame to apply in this work evaluation was considered. The obtained values are presented in Table 3. Table 3 - Controlled ramps for the studied week, over different timeframes of PV average values; impact on the controlled ramps.

The 2s corresponds to the raw data extracted from the PV installation in study. Remaining timeframes are the PV averaging correspondent to each of that timeframe. The results obtained support the study previously referred, for the domestic PV installations. The main conclusion is that as the average timeframe increases, the less ramps are detected and controlled. Alternatively, if the average timeframe is too small, the impact will be short. In any way, a careful sensitivity analysis of this parameter must be carried out.

The simple moving average, being simple to implement and with low computational effort, can let trough unexpected artefacts such as peaks in the results. In accordance, the timeframe of 20 seconds was chosen. This PV averaging timeframe can be observed in Figure 6, from the h to the h to be appropriately visible of the 1st of January of The MA was the method used in this study as the power smoothing technique, for the reasons previously referred.

Appl Surf Sci — J Colloid Interface Sci — Colloid Surf A — Int J Hydrog Energy — Kim J, Jeon J, Kwak S Sulfonated poly ether ether ketone composite membranes containing microporous layered silicate AMH-3 for improved membrane performance in vanadium redox flow batteries. Mohammadi T, Kazacos MS Evaluation of the chemical stability of some membranes in vanadium solution. Download references. You can also search for this author in PubMed Google Scholar. Correspondence to Jicui Dai.

Reprints and Permissions. Teng, X. J Mater Sci 53, — Download citation. Received : 08 October Accepted : 06 December Published : 14 December Issue Date : April Anyone you share the following link with will be able to read this content:.

Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative. Skip to main content. Search SpringerLink Search. Abstract How to solve the crossover of vanadium ions through ion exchange membrane is a key issue in vanadium redox flow battery VRB , especially for ultra-thin membranes used for VRB to obtain a lower cell resistance. Scheme 1. Yost, Journal of the American Chemical Society 7 The second obstacle is the solubility of V V compounds such as V 2 O 5.

The present inventors have found that the rate of dissolution of V 2 O 5 is very low at room temperature. For example, with sonification, 0. The solubility limit of V 2 O 5 in 1. After 12 days, complete dissolution was observed for 1 g V 2 O 5 per ml, while 2 g per ml required 30 days for complete dissolution. This problem of slow dissolution of V 2 O 5 in acids, is often dealt with by first dissolving in NaOH solution and then acidifying the solution see G.

Bengtsson, Acta Chem. However from a redox cell point of view the use of NaOH is undesirable due to the additional cost. An object of this invention is to provide an all-vanadium redox battery, an uncharged all-vanadium redox battery and all-vanadium redox battery systems which ameliorate the diffusion, stability and solubility problems of the prior art.

Another object is to provide processes for charging, recharging and producing electricity from, an all-vanadium redox battery in which the diffusion, stability and solubility problems of the prior art are ameliorated. The inventors have discovered that tetravalent and pentavalent vanadium ions are stable in electrolytes such as aqueous H 2 SO 4 , trivalent vanadium ions exhibit stability in de-aerated H 2 SO 4 and divalent vanadium ions are stable in sealed and de-aerated H 2 SO 4.

The inventors have also discovered that at least 2M pentavalent vanadium ions can be prepared in solution in an electrolyte such as an 2M H 2 SO 4. In a second embodiment this invention provides an uncharged all-vanadium redox battery having a positive compartment containing a catholyte having tetravalent vanadium ions in electrical contact with a positive electrode and a negative compartment containing an anolyte having tetravalent vanadium ions in electrical contact with a negative electrode; and an ionically conducting separator disposed between the positive and negative compartments and in contact with the catholyte and anolyte to provide ionic communication therebetween.

In a third embodiment this invention provides a process for charging an all-vanadium redox battery having a positive compartment containing an anolyte having tetravalent vanadium ions in electrical contact with a negative electrode and a positive compartment containing a catholyte having tetravalent vanadium ions in electrical contact with a positive electrode; and an ionically conducting separator disposed between the positive and negative compartments and in contact with the catholyte and anolyte to provide ionic communication therebetween which process comprises providing electrical energy from an external circuit to the positive and negative electrodes to derive divalent vanadium ions in the anolyte and pentavalent vanadium ions in the catholyte.

The invention includes charged or partially charged all-vanadium redox battery produced by the above charging process. The invention further includes an all-vanadium redox battery produced by the above re-charging process. An all-vanadium redox battery system may be assembled from the all-vanadium redox battery of the first or second embodiments by including an anolyte reservoir for further anolyte having anolyte supply and return lines between the anolyte reservoir and the negative compartment, a catholyte reservoir for further catholyte having catholyte supply and return lines between the catholyte reservoir and the positive compartment; and pumping means associated with the anolyte lines and with the catholyte lines for pumping the anolyte between the negative compartment and the anolyte reservoir and for pumping the catholyte between the positive compartment and the catholyte reservoir.

Aqueous H 2 SO 4 having a concentration in the range 0. It is even more preferred that H 2 SO 4 concentration 0.

The reduction is typically carried out in 2M H 2 SO 4 which has been de-aerated and is in a sealed compartment. The pentavalent vanadium ions are reduced to tetravalent vanadium ions in the positive compartment during discharging of a redox battery of the invention. More preferably said anolyte and said catholyte are prepared by preparing a 0.

Preparing the catholyte by dissolving VOSO 4 in an aqueous solution of H 2 SO 4 and oxidising the resultant tetravalent vanadium ions to pentavalent vanadium ions is particularly advantageous since at least 2M pentavalent vanadium ions can be prepared in solution in 2M H 2 SO 4 compared with an upper limit of about 0.

The increased concentration of pentavalent vanadium ions means that the redox battery has a corresponding increased capacity for a given catholyte volume. Another advantage of preparing the anolyte and catholyte in this manner is divalent vanadium ions are stable in sealed de-aerated H 2 SO 4 whilst trivalent vanadium ions resulting from the oxidation of the divalent ions are also stable in de-aerated H 2 SO 4.

In addition, tetravalent and pentavalent vanadium ions have been found to be stable in H 2 SO 4. Platinised titanium and carbon cloth GF are preferred materials for the positive electrode and graphite is a preferred material for the negative electrode. The ionically conducting separator can be a sulphonated polyethylene membrane or polystyrene sulphonic acid membrane or other like membrane. A polystyrene sulphonic acid membrane is preferred.

A non-aqueous electrolyte such as room temperature molten salt aluminium chloride-butyl pyridinum chloride can also be used. An advantage of the all-vanadium redox battery of this invention is that if some cross-mixing of the anolyte and catholyte occurs the regeneration of the solution can be simply effected by charging the battery.

In mixed metal redox systems used in prior redox batteries cross-contaminated anolyte and catholyte are replaced or regenerated by removing and externally treating the solutions. Preferably the anolyte includes trivalent vanadium ions: divalent vanadium ions in the concentration range from a trace More preferably the anolyte includes trivalent vanadium ions:divalent vanadium ions in the concentration range from a trace Even more preferably the anolyte comprises trivalent vanadium ions:divalent vanadium ions in the concentration range from a trace It is preferred that the electrolyte includes sulphate anions associated with said divalent vanadium ions, said trivalent vanadium ions, said tetravalent vanadium ions and said pentavalent vanadium ions.

The anolyte can also include of a salt of the formula VO X y. The preferred concentration of the salt is from 0. Preferably the negative compartment is sealed air-tight and the anolyte is de-aerated. It is also preferred that the positive compartment is sealed air-tight and the catholyte is de-aerated.

This invention will now be described by way of example with reference to the drawings in which:. Japan and graphite plate electrodes. Curves a' and b' --as above, except that positive graphite electrode replaced with DSA electrode Iridium oxide on Titanium-Diamong Shamrock. Curves correspond to the second charge and discharge cycles. Referring to FIG. Negative compartment 12 contains an anolyte in electrical contact with negative electrode 13 and positive compartment 14 contains a catholyte in electrical contact with positive electrode Battery 11 includes ionically conducting separator 16 disposed between positive and negative compartments 12, 14 and in contact with the catholyte and anolyte to provide ionic communication therebetween.

The anolyte and catholyte are prepared by dissolving VOSO 4 in aqueous H 2 SO 4 to form a solution of tetravalent vanadium ions and this solution is loaded into anolyte reservoir 17 and negative compartment 12 and catholyte reservoir 18 and positive compartment The anolyte is then pumped through negative compartment 12 and anolyte reservoir 17 via anolyte supply and return lines 19, 20 by pump 21 and simultaneously the catholyte is pumped through positive compartment 14 and catholyte reservoir 18 via catholyte supply and return lines 22, 23 by catholyte pump Battery 11 is then charged by providing electrical energy from power source 25 to positive and negative electrodes 13, 15 by closing switch 26 and opening switch 27 to derive divalent vanadium ions in the anolyte and pentavalent vanadium ions in the catholyte.

Electricity is produced from battery 11 by opening switch 26 closing switch 27 and withdrawing electrical energy via load 28 which is in electronic communication with negative and positive electrodes 13, Battery 11 is re-charged by opening switch 27, closing switch 26 and providing electrical energy from power source 25 to derive divalent vanadium ions in the anolyte and quinvalent vanadium ions in the catholyte.

Any cross-contamination between the anolyte and catholyte is rectified during the recharging process. One advantage of the all-vanadium redox battery system is that the divalent, trivalent, tetravalent and pentavalent vandium ions are relatively stable in de-aerated and sealed aqueous sulphuric acid. The charging, recharging and electricity production processes of battery system 50 are carried out in a similar way to those described for battery system 10 except that the processes in negative and positive compartments 12, 14 are performed as batch processes rather than the re-circulation procedure of battery system A series of charge-discharge experiments were conducted using the battery of FIG.

Several materials were tested as positive electrodes. These were:. Sulphonated polyethylene anion-selective type membranes and polystyrene sulphonic acid cation-selective type membranes were also tested. The electrolyte composition ranged from 0. During initial charging, the following redox reactions take place:. For full charging of the negative electrolyte during the first charge, twice the number of coulombs are required as for the positive electrolyte.

To avoid over-charging of the positive half-cell and oxygen generation, therefore, when the positive half-cell electrolyte was fully charged, it was replaced by a new portion of uncharged solution and charging continued. During charging, nitrogen was bubbled through the negative half cell solution to remove dissolved oxygen and to stop diffusion of air into the compartment.

Removal of oxygen prevented reoxidation of reduced electrolyte. In practice this will not be needed if the cell is airtight.

More oxygen and hydrogen evolution could be observed on the electrodes when the cell was almost fully charged. The stability of the open circuit cell voltage after full charging was tested and the potential remained constant at 1. Current efficiency during discharge varied for different electrode materials and membranes.

Reproducibility of results obtained with different electrolyte concentrations was good. No accelerated decomposition at high temperatures, nor crystallisation at low temperatures was observed.

The results are summarised below: titanium sheet proved unsuitable because of its anodic passivation with formation of a high electrically resistant surface layer. Platinised titanium mesh did not exhibit this problem and performed well both as anode and cathode. No chemical attack was observed. Although the graphite rods and plates showed acceptable reaction rates for the vanadium species, these materials were not resistant in the oxidising solution during the charging cycle.

After several charge-discharge cycles the surface of the graphite appeared "etched" and a fine dispersion of carbon particles was observed in the positive electrolyte. The negative electrode remained unchanged after several experiments. Similar mechanical disintegration was observed with the carbon fibre.

The anode was oxidised especially in the area of the highest current density. The fifth electrode material tested was the carbon cloth, GF The material was fastened to the graphite plate and tested as an anode. No noticeable attack was observed on the surface of the cloth but disintegration of the underlying graphite was evident.

Of the materials tested, the dimensionally stable anode IrO 2 on Ti appears to be particularly suitable for the positive electrode of the vanadium cell. Two types of ion selective membranes were tested for suitability as ionically conducting separators.

These were sulphonated polyethylene and polystyrene sulphonic acid. The sulphonated polyethylene anion--selective type membrane performed well. After several experiments, however, it changed its colour and consistency. It became more rigid and harder, and its electrical resistivity increased. The polystyrene sulphonic acid cation--selective type membrane had better electrical properties.

Its resistivity was lower and there was no noticeable change after hours of testing. A laboratory-scale redox battery as shown in FIG. The cell consists of two separate compartments, an anodic and cathodic compartment separated by an ion-selective membrane. The capacity of each compartment was approximately ml. Both half-cells have water-jackets for temperature control. Graphite plates were used as electrodes and the membrane was sulphonated polyethylene anion-selective material.