Large-scale energy storage is increasingly being seen as a key technology to support the renewable energy transition and make our electricity grids more flexible and resilient. Lithium-ion batteries have dominated the stationary storage market so far, but flow batteries may emerge as a more viable long-term solution due to their unique advantages. Let’s take a deeper look at flow battery technology.
What is a Flow Battery?
A flow battery works by storing energy in chemical components dissolved in liquids contained within external tanks. During charging, chemical reactions occur between the liquids which are then separated into the tanks. During discharging, the liquids are pumped through a cell where a reversing reaction releases electrons that become an electric current.
Unlike conventional batteries that are limited by the size of internal components, flow batteries can be “powered up” by simply increasing the size of the external liquid storage tanks or adding additional ones. This allows them to easily scale up capacity simply by changing the volume of electrolyte solutions. The energy capacity is determined by the size of the storage tanks rather than by the size of the battery itself.
Types of Flow Batteries
There are several types of Flow Batteries currently under development but the main categories are vanadium and zinc-bromine flow batteries.
Vanadium redox flow batteries, the most mature technology, use vanadium in different oxidation states dissolved in aqueous solutions as the electrolytes. These batteries are highly efficient, have a long operational lifetime of over 15 years, and can discharge 100% of stored energy. However, the vanadium electrolyte material remains fairly expensive, limiting their widespread adoption.
Zinc-bromine flow batteries utilize zinc and bromine solutions as electrolytes. These have lower costs than vanadium batteries but also have a shorter lifetime of around 5-10 years. Hybrid chemistries that blend different materials are also being explored as researchers seek to optimize performance and costs.
Advantages Over Lithium-ion
The unique design of flow batteries gives them several advantages compared to conventional lithium-ion batteries that make them better suited for large-scale stationary storage applications:
– Near-infinite Scalability: As mentioned, their energy capacity can be increased simply by enlarging the storage tanks or adding more stacks. This allows them to easily scale up to the megawatt-hour level required by the grid.
– Increased Safety: Flow battery electrolytes are usually non-flammable and stored in tanks outside the battery enclosure, eliminating fire risks. This makes them inherently safer than lithium-ion batteries.
– Long Lifetime: Properly maintained flow batteries can last over 15 years compared to 5-10 years for lithium-ion, lowering long-term costs by reducing replacement needs.
– Resilience: Unlike solid-state lithium-ion batteries, flow battery stacks can be replaced individually without having to decommission the entire system.
Applications and Outlook
These compelling advantages mean flow batteries are ideal for multi-hour stationary storage applications like renewable energy integration, grid-scale backup power, and load-balancing services. Several projects demonstrating their value for the grid have already been commissioned around the world.
As the technology continues to advance, flow batteries are emerging as a strong competitor to lithium-ion for utility-scale energy storage needs. While upfront costs remain higher compared to lithium-ion currently, flow batteries have a lower overall lifetime cost profile that improves further with scale. With innovation reducing electrolyte costs and advances in areas like power density, flow batteries are well positioned to play a major role in building the energy storage infrastructure vital for our clean energy future.
Vanadium Flow Battery Projects
Let’s examine two notable vanadium flow battery projects that highlight their capabilities:
Japan’s Kashima Project
One of the largest vanadium flow battery installations to date is operating at a convention center in Kashima, Japan since 2018. With an output of 1 MW / 4 MWh, it provides backup power and supports the local grid. The project owner valued the long 25-year lifespan over conventional batteries that need frequent replacement.
Australia’s Dalrymple Battery
Commissioned in 2019, the Dalrymple battery energizes a telecom tower in rural South Australia with its 300 kW/1.2 MWh storage capacity. It overcomes the area’s intermittent solar and wind resources and has more than doubled the amount of affordable renewable energy that can be hosted locally.
Future Prospects
As these demonstrations affirm flow batteries’ potential for utility-scale stationary storage, more large-scale projects are planned worldwide. Government investments and policy support are also fueling R&D to decrease costs further. By the end of the decade, flow battery deployments are projected to start rivalling lithium-ion particularly in the multi-megawatt-hour sector critical for renewable energy and grid management.
With their inherent power density and lifespan advantages, flow batteries may ultimately displace lithium-ion as the technology of choice for long-duration stationary energy storage needs at the terawatt-hour levels expected by mid-century. Continued innovation is poised to make them a mainstream storage solution supporting clean energy economies around the globe.
