# Hybrid Wind-Redox Flow Battery System for Decarbonizing Off-Grid Mining Operations
## 1 Introduction
[14] claim that each ESS technology has unique strengths and limitations, influencing its applicability and suitability for specific applications. The choice of an ESS is influenced by factors such as energy density, cost, scalability, and the intended use case, whether for short-term grid balancing or long-term energy storage. It is crucial to consider the climatic conditions of a region before implementing any energy storage system [15]. Table 1 focuses on ESSs currently proficient in providing critical storage capacities of at least 20 MW. Redox flow battery technology has gained significant attention as a viable solution for large-scale energy storage due to its high efficiency, long cycle life, and independent scalability of power and capacity [16; 17; 18; 19; 20; 21]. These batteries are considered one of the most promising technologies for integrating renewable energy into electricity grids [22; 23; 24], offering low-cost and long-duration storage capabilities [25]. The large-scale deployment of variable renewable energy resources is heavily influenced by the availability of cost-effective, long-duration storage solutions [26]. Despite their advantages, flow batteriesaccounted for only 5% of the 16 GWh installed energy storage capacity worldwide in 2021, highlighting the need for further technological advancements and economic optimizations to expand their adoption. A flow battery is a reversible and rechargeable electrochemical system that stores energy in chemical form and converts it back into electrical energy when needed. The fundamental operating principle of these batteries involves the circulation of an electrolytic solution (electrolyte) from one or more storage reservoirs into electrochemical cells facilitated by pumps [16; 27]. These cells, consisting of two half-cells (positive and negative), serve as the site for redox reactions, enabling the storage and release of energy. Flow batteries can be configured in series and/or parallel to achieve the desired voltage and current characteristics. They are often considered a hybrid technology between fuel cells and conventional batteries, where hydrogen (H\({}_{2}\)) and oxygen (O\({}_{2}\)) gases in fuel cells are replaced by electrolytes capable of storing electrical charges [28]. The schematic representation of a flow battery system is illustrated in Figure 1. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline
**Storage System Type** & **Max Power Rating [MW]** & **Discharge Time** & **Max Cycles or Lifetime [Wh/L]** & **Energy Density [Wh/L]** & **Efficiency** \\ \hline Pumped hydro & \(\sim\)3000+ & 4 h–16 h & 30–60 years & 0.2–2 & 70–85\% \\ \hline Compressed air & \(\sim\)1000 & 2 h–30 h & 20–40 years & 2–6 & 40–70\% \\ \hline Molten salt & 100–150 & Several hours & -30 years & 70–210 & 80–90\% \\ \hline Li-ion battery & 1–100+ & 1 min–8 h & 1000–10,000 cycles & 200–400 & 85–95\% \\ \hline Lead–acid & 1–100 & 1 min–8 h & 6–40 years & 50–80 & 80–90\% \\ \hline Flow battery & 10–100+ & Several hours & 12,000–14,000 cycles & 20–70 & 60–85\% \\ \hline Hydrogen & \(\sim\)100+ & Minutes–weeks & 5–30 years & \(\sim\)600 (at 700 bar) & 25–45\% \\ \hline Flywheel & 1–20 & Seconds–minutes & 20,000–100,000+ cycles & 20–80 & 70–95\% \\ \hline \end{tabular}
\end{table} 
Table 1: Comparison and characteristics of energy storage systems [13]. Figure 1: Schematics and working principle of redox flow batteries [16]. Several studies have explored the application of flow batteries for energy storage in different renewable energy systems. [PERSON] et al. [25] investigated the performance of a vanadium redox flow battery (VRFB) within a microgrid integrating a biomass gasifier and a solid oxide fuel cell designed for electricity generation in rural environments (Figure 2). Their findings indicate that the electrolyte flow rate plays a crucial role in battery performance, with an efficiency of 84% achieved during peak shaving operations. [PERSON] et al.