Mena 1:00 Team R15 Disclaimer: This paper partially fulfills a writing requirement for first-year (freshmen) engineering students at the University of Pittsburgh Swanson School of Engineering. This paper is a student paper, not a professional paper. This paper is not intended for publication or public circulation. This paper is based on publicly available information, and while this paper might contain the names of actual companies, products, and people, it cannot and does not contain all relevant information/data or analyses related to companies, products, and people named. All conclusions drawn by the authors are the opinions of the authors, first-year (freshmen) students completing this paper to fulfill a university writing requirement. If this paper or the information therein is used for any purpose other than the authors' partial fulfillment of a writing requirement for first-year (freshmen) engineering students at the University of Pittsburgh Swanson School of Engineering, the users are doing so at their own--not at the students', at the Swanson School's, or at the University of Pittsburgh's--risk. VANADIUM REDOX FLOW BATTERIES FOR GREEN ENERGY GRID STORAGE Patrick Connor [email protected], Brady Pilsbury [email protected], Sean Rinkel [email protected] Abstract— Vanadium redox flow batteries have the potential have been researching and developing methods to efficiently to bridge the gap between periods of heightened green store the energy produced by renewable energy sources so energy production and heightened energy demand, which is that they can be more widely adopted as a practical one of the biggest obstacles preventing the wider adoption of alternative to fossil fuel burning power plants. Among these green energy sources. alternative sources of energy are solar and wind energy. A flow battery works by pumping a liquid solution of These two forms of energy have increased in popularity over metallic salts through a core, which consists of a membrane the past few decades, but the intermittent nature of their separating an anode and a cathode. Reduction and oxidation energy makes them unreliable and poses challenges to grid reactions take place at the electrodes, creating a difference operators [1]. By developing batteries for grid energy in electrochemical potential between the solutions on either storage, engineers hope they can create a green energy grid side of the membrane. This process effectively stores energy. that offers grid operators more control over how the energy Vanadium redox batteries are especially well suited for produced by renewable sources is distributed. grid energy storage because of their durability and stability. Currently, grid operators have limited control over how This is a consequence of both the anolyte and catholyte the energy from solar and wind sources is distributed to the solutions consisting of different oxidation states of user. Solar panels tend to produce the most energy around vanadium, which prevents crossover between the species midday when they are exposed to the most direct sunlight from resulting in irreparable damage. Their long-life cycle [1]. In places like California that have developed a and low maintenance costs often makes vanadium redox significant amount of solar infrastructure, the solar panels batteries a financially viable alternative to other battery sometimes risk producing more energy than the grid is technologies. equipped to handle [1]. To avoid overloading the grid, grid UniEnergy Technologies (UET) constructed a operators often curtail the production of solar energy during vanadium redox battery system in Pullman Washington. The its peak period of production [1]. Operators typically curtail system is relatively small in terms of storage but the energy output of solar plants by physically disconnecting demonstrated the potential that vanadium redox flow some solar panels from the grid [1]. As a consequence, batteries have if scaled for larger grid storage. Researchers significant amounts of the energy produced by solar panels and officials involved with the project are optimistic that at certain times of day effectively go to waste. Some vanadium redox flow batteries will allow for the wider calculations suggest curtailment rates may at times exceed adoption of renewable energy sources and help to create a 30% for certain solar energy plants, meaning that 30% of more sustainable future. solar energy produced at peak hours of solar energy production could be going to waste [1]. Key Words—Vanadium Redox Flow Battery, Energy Large batteries that store the energy produced by the Storage, Grid, Green Energy, Sustainability, Evaluation solar panels could prevent that energy from being wasted. The stored energy could be released back to the grid at a THE NEED FOR GREEN ENERGY later time, creating a more flexible energy grid that can STORAGE better accommodate the fluctuating levels of output from solar energy sources [1]. Wind energy sources also face the In order to promote a sustainable future and avoid the issue of curtailment, often reaching peak energy production damaging effects of climate change, scientists and engineers during the night when winds are stronger but demand for 1 University of Pittsburgh, Swanson School of Engineering First-Year Conference Paper 29.03.2019 Mena 1:00 Team R15 energy is relatively low [1]. Wind energy could similarly referred to as the anolyte solution [3]. The other storage tank 2+ + benefit from increased grid energy storage. is filled with an electrolyte solution of VO and VO2 ions, Another major shortcoming of solar and wind energy referred to as the catholyte solution [3]. The vanadium atoms sources is that their energy production is dependent on in each species of the electrolyte solutions are at different weather and time conditions outside of human control. A oxidation states, which is how the oxidation reduction grid that relies entirely on solar energy would provide no reactions that effectively store and release the battery’s power at night if none of the energy produced by the solar energy are able to take place [3]. These reactions are panels is stored. In the more distant future, large scale grid described further in the following subsections. energy storage could be a solution to this issue, supplying Pumps move the electrolyte solutions from their energy to the grid when solar or wind sources are not storage tanks to the central electrochemical cell [2]. A producing energy. semipermeable membrane splits the cell in half [2]. This A sustainable energy grid must be able to meet the membrane prevents crossover between the anolyte and demands of end users, pose little risk to the environment or catholyte solutions [2]. Crossover between anolyte and human health, and be economic viable for energy catholyte species can cause corrosive damage and companies. This paper seeks to demonstrate that vanadium irreversible chemical reactions in certain types of redox flow redox flow batteries, a particular type of battery that is well batteries [3]. This does not occur in vanadium redox flow suited for large scale energy storage, can help make energy batteries, and if crossover does occur the proper vanadium grids more sustainable in all of these criteria when deployed species can be regenerated on either side of the cell through and utilized appropriately. Vanadium redox flow batteries electrochemical manipulation, which is one of the particular essentially function by creating a difference in benefits of vanadium redox flow batteries [3]. Positively electrochemical potential between two solutions containing charged hydrogen atoms are able to cross the membrane [3]. different oxidation states of vanadium ions. This paper will The flow of protons between the two sides of the cell begin by describing how a vanadium redox flow battery chamber is necessary to maintain current flow between works and will proceed by evaluating some of the particular electrodes [3]. Figure 1, from a paper published in the benefits of the technology over other types of batteries. This Journal of The Electrochemical Society, shows a visual paper will then discuss how the technology should be representation of the structure of a redox flow battery. promoted in the real world to promote sustainability and will describe a real life example of how a vanadium redox flow battery was able to do so in Pullman, Washington. While research is ongoing and some more developments may be needed before they can be more widely adopted, vanadium redox flow batteries are a promising way to create the grid energy storage needed to make renewable energy sources more practical. STRUCTURE AND FUNCTION OF VANADIUM REDOX FLOW BATTERY In order to evaluate the vanadium redox flow battery, it is necessary to have some understanding of how the technology works. This section will seek to explain the FIGURE 1 [4] electrochemistry behind vanadium redox flow batteries that Redox flow battery diagram allows them to effectively store energy produced by solar panels and wind turbines. First, the parts of the vanadium The above figure shows the major components of a redox flow battery will be identified and then used in context generic redox flow battery. The electrolyte solutions are to explain the processes involved with charging and stored in separate tanks and pumped to the electrochemical discharging. cell in the center. The ion-selective membrane prevents the electrolyte species from crossing over. Reactions at the Structure porous carbon electrodes create a difference in electrical potential between the electrodes so that they induce a current Vanadium redox flow batteries consists of several parts when connected to a circuit. This current is what sends that operate together to create an effective energy storage electricity to the energy grid [4]. device. Two electrolyte solutions are stored in separate There is one electrode on either side of the semi- storage tanks [2]. One tank is filled with an electrolyte permeable membrane [2]. The electrodes are where the solution containing vanadium II and vanadium III ions, 2 University of Pittsburgh, Swanson School of Engineering First-Year Conference Paper 29.03.2019 Mena 1:00 Team R15 reduction-oxidation reactions occur.