In this first part of a series of articles from IDTechEx, an overview of the flow batteries characteristics is provided, extrapolated from IDTechEx's recent report "Redox Flow Battery 2020-2030: Forecast, Challenges, Opportunities".
While Li-ion batteries are dominating the stationary energy storage sector, a growing number of companies are developing different technologies to be competitive in the near future and bring to the market a more competitive energy storage system. Among the Li-ion batteries competitors, the Redox Flow Battery (RFB) is one of the main competitors currently approaching the market.
Recently IDTechEx performed an in-depth analysis of redox flow batteries from a technical and market aspect, evaluating their potential to address the evolving stationary energy storage market.
While it is clear that Li-ion batteries will dominate the scene for the near future, this promising competitor has already shown its capability to gain its portion of the energy storage market, pushing the ES industry toward new horizons.
The extensive volumetric (Wh/L) and gravimetric (Wh/kg) energy density of Li-ion batteries make this technology well suited to address the EV market. Pushed by the cost decreasing from the EV market, this technology started to also be competitive in the stationary energy storage market, for front-of-meter (FTM), and behind-the-meter (BTM) applications. The capability to address the complete spectrum of the energy storage market is translated in a power range of few kWs for behind-the-meter use, to MWs power output for front-of-meter applications.
These properties make Li-ion batteries extremely competitive and difficult to be challenged, although other technologies are starting to appear in the market.
Figure 1: Schematic representation of the electricity grid, showing the separation of front-of-meter and behind-the-meter. Source: IDTechEx
Besides the great advantage of Li-ion batteries, the hazardous materials adopted make them prone to ignite, if not carefully handled. In addition, once ignited these systems are very difficult to extinguish. PSA Group, in collaboration with the firefighter department, designed a specific solution to flood the battery stack and easily extinguish the fire, in case of ignition.
Besides the risk of ignition, for stationary energy storage applications, Li-ion batteries offer a reduced cycle life (ca. 10,000 cycles) in comparison to other devices, such as RFBs which offer more than 20,000 cycles.
Therefore, the larger cycle life and the safer chemistry adopted in redox flow batteries, despite the lower energy density, make this technology well suited for stationary applications.
Differently from the Li-ion batteries, the redox flow batteries working principle is based on flowing two liquids, the electrolytes, across the electrode. In this way, the electroactive species contained in the electrolyte react on the electrode surface generating electricity. Therefore, the larger the amount of electrolyte, the bigger the amount of energy is stored in the battery. The power output of an RFB is instead defined by the size of the electrode stack, and the kinetic of the chemical reaction.
Therefore, a further advantage of redox flow batteries is provided by the decoupled energy, and power capacity, which allows simpler customization of this kind of system.
Figure 2: Exploded representation of a redox flow battery, showing the different constituents. Source: Engineering aspects of the design, construction and performance of modular redox flow batteries for energy storage - L.F. Arenas, C. Ponce de León, F.C. Walsh - Journal of Energy Storage (2017).
Moreover, RFBs present longer cycle-life (RFB >25,000 cycles; Li-ion < 10,000), which is then reflected in a much lower levelized cost of storage, in comparison to Li-ion batteries.
Although promising, the high technology capital cost is still the major limitation for this technology to enter the market.
In March 2020, IDTechEx performed an in-depth analysis, from a technical and market aspect of Redox Flow Batteries, to understand the current status of development of the redox flow batteries and their possibilities to address the market.
The results of this analysis, published in the report titled: "Redox Flow Battery 2020-2030: Forecast, Challenges, Opportunities", have shown a CAGR of 30% in the next 10 years, pushed by the large interest in energy storage systems, to support the electricity grid.
Figure 3: Front cover of IDTechEx's Redox Flow Battery Report. Source: IDTechEx
Redox flow batteries are expected to be the direct competitor of Li-ion batteries for stationary energy storage applications for front-of-meter and behind-the-meter applications.
In fact, from the analysis conducted by IDTechEx, a considerable amount of companies manufacturing RFBs are developing large scale systems for Front-of-Meter applications, while a solid, but smaller amount of companies are addressing the development of smaller-scale systems, addressing the Behind-the-Meter applications.
Among the different chemistries present on the market, the Vanadium Redox Flow Batteries (VRFB) is currently the most adopted type of chemistry, also due to its long historical development from the 1980s. Although this chemistry is currently the most investigated and adopted, other chemistries are also approaching the market, such as the all-iron RFB developed by ESS inc., the Zinc/Bromine flow batteries (ZBB), and the organic flow batteries.