A Look Inside Large-Scale Electrochemical Storage Systems Simulation

Why Are Redox Flow Batteries Important?

Renewable electricity produced by solar and wind energy is taking an ever-increasing share of the total electricity generated. However, the fluctuating nature of these renewable energy sources makes grid management challenging without a reliable energy storage system. Electricity production from solar and wind generators is often curtailed when the supply exceeds the demand during the day[i]. Large-scale electrochemical storage systems are expected to play a critical role in managing grid demand fluctuations.

Among the various types of electrochemical storage systems, such as lithium-ion and lead-acid batteries, one that’s well suited for grid energy storage are vanadium redox flow batteries (VRFB). VRFBs are considered due to their fast response rate, long charging/discharging cycle lives, and non-flammable aqueous electrolytes [ii].

Modeling and Simulation of Redox Flow Batteries

Simulation platforms such as GT-SUITE can be used to model different aspects of VRFBs both at the cell level and systems level using components from different physical domains covering fuel cells, battery modeling, fluid flow, thermal management, control, and chemistry applications. Simulations can be used to perform a variety of virtual experiments to assess the performance of VRFBs with different design and operating parameters such as size of tanks and stack, electrolyte flow rate, vanadium concentration, and temperature. In this blog, we will show the effect of a few of these variables on battery performance.

Figure 1 shows the main components and operating principles of VRFBs. The anolyte tank stores the solution consisting of V²⁺ and V³⁺ ions, and the catholyte tank stores the solution consisting of VO²⁺ (V⁴⁺) and VO₂⁺ (V⁵⁺) ions. Pumps are used to circulate the electrolyte solution through the electrochemical cell consisting of carbon-based positive and negative electrodes separated by a proton exchange membrane.

Figure 1: Schematic view of Vanadium Redox Flow Battery

With GT-SUITE, we have built a model of VRFBs as shown in Figure 2. This model accurately calculates the cell voltage by considering different physical and chemical processes such as: 

• Varying concentrations of different vanadium ions within the electrodes and tanks 
• Activation losses using the Butler-Volmer equation with proper dependence on vanadium ion concentrations and cell temperature 
• Ohmic losses in the electrolyte (using Bruggeman correction), Nafion membrane (empirical relationship with water content and temperature as parameters), and current collectors 

Figure 2: Overview of model set-up in GT-SUITE

Results of Simulating Redox Flow Batteries 

We used this model to study how different operating parameters affect battery performance. Figure 3 shows the net voltage and open cell voltage (OCV) during the charging and discharging cycle for two different temperatures. The battery performs better at 313K than 283K primarily due to lower activation losses (i.e., faster reactions at electrodes) at higher temperatures.  

Figure 3: Effect of temperature on the battery voltage during charging and discharging

Figure 4 shows the voltage for two different volumetric flow rates. A higher flow rate leads to slightly better battery performance because vanadium ion concentrations in the electrodes are rapidly replenished by the flow from tanks. 

Figure 4: Effect of volumetric flow rate on the battery voltage during charging and discharging

Finally, total vanadium concentration is varied between 1200 mol/m3 and 1600 mol/m3 by keeping all other parameters the same. As shown in figure 5, higher vanadium concentration allows the battery to be charged and discharged for longer durations (i.e., higher capacity).  

Figure 5: Effect of Vanadium concentration on the battery voltage during charging and discharging

Learn How to Simulate a Variety of Electrochemical Devices  

Explore the domain libraries and capabilities GT-SUITE has to offer to model a variety of electrochemical devices such as fuel cells, electrolyzers, and batteries. 

Contact us to learn more. 

Citations

[i] California’s curtailments of solar electricity generation continue to increase. (n.d.). Retrieved October 28, 2022, from https://www.eia.gov/todayinenergy/detail.php?id=49276

[ii] Kebede, A. A., Kalogiannis, T., Van Mierlo, J., & Berecibar, M. (2022). A comprehensive review of stationary energy storage devices for large scale renewable energy sources grid integration. Renewable and Sustainable Energy Reviews, 159, 112213. https://doi.org/10.1016/j.rser.2022.112213