Energy storage has long been one of the primary challenges facing the global shift towards renewable energy. Without an efficient means of storing energy, the power grid remains dependent on non-renewable sources. Battery technology has been a crucial component of the solution, but has often been limited by the low volumetric power densities of rechargeable batteries. This is where flow batteries come in.
Flow battery technology is an emerging technology in the field of energy storage. The fundamental principle behind flow batteries is the separation of the stored energy and the power capability into two separate metrics. This is accomplished by having the electrochemical cells partially separated, and the electrochemical reactions occurring in two separate electrolyte solutions that are “flowed” across a membrane when the battery is charged or discharged. Unlike rechargeable batteries, which store energy in solid electrodes, flow batteries use a liquid electrolyte, which can be reused. This solution of electroactive chemicals, or redox pairs, in liquid form, flows through a fuel cell-style stack of cells and generates electricity via electrochemical conversion when the battery is discharged.
At the heart of flow battery technology is the electrolyte solution, which is what separates flow batteries from other types of batteries. This solution can store hundreds of megawatt-hours of energy and can be charged and discharged an infinite amount of times, making them ideal for grid-scale energy storage and powering heavy machinery. With recent advancements, the costs of these systems are decreasing while the performance metrics make it a compelling option for specific energy storage applications.
Advantages of Flow Batteries
Flow batteries offer multiple advantages in the area of large-scale energy storage. Here are just a few examples:
- Flexible Power/ Energy Capacity: Flow batteries provide complete separation of the power and energy capacity of a battery, which means that they can be designed for a specific application with optimized power and energy capabilities to maximize economic and performance feasibility.
- Long Lifespan: The lifespan of flow batteries is an attractive feature, thanks to the smooth operation of liquid components with lower degradation. It is also because the redox pairs can be subtracted and added to the electrolyte with ease, avoiding the need for frequent battery replacement.
- Safe: Compared to other battery technologies, flow batteries are considered generally safe for deployment. Electrolyte leakage, high risk of thermal runaway, and flammable liquids are all safety risks. However, with flow batteries, the risks are largely reduced, as the fluids used are aqueous electrolyte solutions.
- Scalability: Flow batteries are easily scalable. Their modular designs allow for various sizing, and can be designed to fit specific energy storage applications, often with greater efficiency than other energy storage devices.
- Load Balancing: Flow batteries can be used for load balancing, a key feature for grid management. By storing power, they can release it to the grid when demand is high and generate power to store when demand is low, reducing the need for peaker plants.
With the advantages of flexibility, scalability, and safety, one can see why flow batteries are positioned with such promise for grid-scale storage. However, there are also significant challenges with flow batteries, which must be considered if they are to be accepted as a high-volume solution for energy storage applications.#Challenges Facing Flow Batteries
Despite many advantages, flow batteries face challenges to market penetration compared to competing lithium-ion technology. Here are some common concerns surrounding the technology:
- Upfront Costs: One of the most significant barriers to the adoption of flow battery technology is the high upfront costs. Vanadium-based batteries, in particular, require costly raw materials, while newer chemistries are also more expensive in their early stages.
- Limited Commercialization: Compared to the more popular lithium-ion batteries, flow batteries remain virtually unknown to the vast majority of the global market. There are relatively few companies focusing on the technology, and there also exist few available suppliers.
- Supply Chain Reliability: A challenge for vanadium-based batteries is the need for a stable supply to maintain production, as the supply chain for vanadium supply is often limited and limiting. The scaling up of the current facilities will also need to match the growing demand for flow batteries.
- Standards: The industry lacks guidance regarding the manufacture and application of flow batteries, making regulation difficult for grid integration and deployment.
- Electrolyte Cross-Contamination: During operation, electrolytes in flow batteries can become cross-contaminated, leading to the loss of battery efficiency and longevity.
With supply chain, scale-up, standardization, manufacturing and process efficiency, lacking commercial market presence, flow batteries face significant obstacles to be fully adopted as a solution for energy storage.
Technological Advances in Flow Batteries
Despite challenges facing the industry, significant advancements in the technology and applications of flow batteries are attracting prestigious researchers and investors into flow batteries.
Sponsors of Large projects such as the Pacific Northwest National Laboratories (PNNL) and Unienergy Technologies have turn their attention to flow battery technology. PNNL conducts research and testing, evaluates project suitability and performs techno-economic analyses to develop technologies to integrate renewables into electric grids, while Unienergy, specialises in designing and producing flow batteries and energy storage solutions for energy storage applications.
Recent developments in materials for batteries could eventually make flow battery technology even more cost-effective. The scalability of flow batteries is one of the aspects that makes them attractive for energy storage applications. Companies such as UniEnergy Technologies and ESS are designing and producing larger-format batteries designed specifically for grid-scale energy storage, leveraging economies of scale to achieve attractive levelized costs of energy. Many new designs focus on adding higher energy density, improving energy conversion efficiency and more compatibility with production processes used for traditional electrode-type cells.
Additionally, there is increasing interest in “hybrid” redox flow batteries, which combine the liquid energy-storage approach of traditional flow batteries with solid-electrode-based systems. Hybrid flow batteries could offer several benefits, such as higher power ratings, more stable power outputs, and a wider range of operating temperatures. The new path to adoption may lie in these hybrid design approaches, which can address some of flow battery technology’s critical challenges and receiving increased focus among researchers.
One recent promising example of hybrid flow batteries is a true hybrid flow battery developed at MIT using two separate liquid electrolytes. The design is intended to combine the benefits of conventional batteries’ high energy density with flow batteries’ excellent scalability and safety. Innovation such as this illustrates the rapid pace of progress, and hint at the potential of flow batteries for energy storage applications in the future.
In conclusion, Flow batteries are a promising technology for grid-scale energy storage applications. Their modular and scalable designs make them perfect for a large range of applications such as wind energy, photovoltaics, and behind-the-meter installations. Although there are limitations for adoption like upfront costs, supply chain issues, and limited standards, new advancements in hybrid flow battery technologies and materials chemistry are introducing environmental benefits and cost-effectiveness. As technology progresses, flow batteries look set to play an increasingly significant role in providing energy storage solutions, making strides to become integral to the transition to a cleaner energy future.