Vanadium batteries are a subtype of redox flow batteries, which are characterised by having separate power generation and energy storage components. They get their name because stored energy is supplied through a reduction-oxidation reaction (redox) between two electrolyte fluids across a membrane. Unlike lead-acid or lithium-ion batteries, which are subject to a charging cycle, redox flow batteries have external tanks where the electrolyte solutions can be replenished even when the system is supplying power.
Vanadium redox flow batteries (VRFB) were included in a 2017 study by the International Renewable Energy Agency (IRENA), comparing multiple energy storage technologies and their outlook for 2030. In general, vanadium batteries have a higher upfront cost than many other battery types, but they are also offer a longer service life and a lower cost per kilowatt-hour stored.
The more popular lithium-ion batteries have a rapid response and operating flexibility, and they are effective for managing short term power imbalances. However, the operating cost of lithium batteries rises dramatically for bulk energy storage, where vanadium batteries are better suited for the task.
According to the IRENA study, vanadium batteries have promising applications for both network operators and electricity consumers, as well as in isolated small-scale grids. Since their power generation and energy storage components are separate, vanadium batteries offer design flexibility: any storage capacity can be matched with any power output capacity. Lithium-ion and lead-acid batteries do not offer this flexibility, since both are produced in modules with a rated storage capacity and power output. Vanadium batteries also come with built-in cooling, since the flow of electrolytes helps dissipate heat.
In power network operation, vanadium batteries are effective as frequency restoration reserve: bringing grid frequency back to the nominal value after a disturbance. Vanadium batteries are also suitable for energy shifting and load leveling, capable of matching the performance of pumped-storage hydroelectricity (PSH). Other types of batteries tend to fall short when deployed for bulk storage, while vanadium batteries have been used successfully in applications with up to 20 hours of continuous discharge.
For energy users connected to the grid, VRFBs show promise as an energy reserve for periods lasting several hours. While lead-acid and lithium-ion batteries can also perform this role, they are better suited for events in the scale of minutes. A vanadium battery system can be extremely useful when the electricity tariff shows a large difference in kWh price between peak hours and off-peak hours. The bulk storage capacity of these batteries allows consumption to be shifted completely to off-peak hours with cheaper electricity.
VRFBs have also been identified as a useful addition for small-scale power grids in islands or remote villages. Interconnection with larger power grids is limited or nonexistent in these cases, and vanadium batteries can help balance local generation and consumption. These small-scale grids typically rely on dispatchable power sources like diesel generators, but the use of vanadium batteries allows a larger share of solar power and other renewable generation systems.
Vanadium batteries are also characterised by a very long service life, typically above 10,000 cycles. However, this could eventually reach the range of 100,000 to 200,000 cycles as the technology continues to evolve.
Although they are the best batteries for bulk energy storage, vanadium batteries lack the fast response of their lithium-ion counterparts. For example, utility scale vanadium batteries can restore frequency after a disturbance, but lithium-ion batteries can respond to the event as it occurs and prevent its effects altogether. Vanadium batteries can respond effectively during extended periods of high demand, but they may be unable to handle sudden demand peaks. Vanadium batteries are not slow; in fact they are among the fastest battery types, but not as fast as lithium-ion cells.
Another limitation of vanadium batteries is their limited use in small-scale applications. According to IRENA they work better in the range of 100 kW to 10 MW, but are not cost effective when scaled down for small-scale applications. Vanadium batteries also require a lot of space, making them impractical for electric vehicles and other mobile applications.
Vanadium batteries are also outclassed by lithium-ion batteries round-trip efficiency. On average they offer 85% efficiency, which is not bad, but lithium ion batteries are already above 95%.
As implied by their names, these batteries use vanadium ions in their electrolyte solutions. Vanadium is an expensive metal, which drives up the cost of a VRFB system compared with other battery types.
Vanadium batteries should be analysed as a long-term investment: their upfront cost is high, but it is spread throughout a very long service life. The following table compares the price range of vanadium batteries with the two most common options, lead-acid and lithium-ion, according to data gathered by IRENA. The service life range is also included to demonstrate how a higher upfront cost delivers more charging cycles
|Battery Type||Installed Cost Range||Service Life Range|
|Vanadium redox flow battery||$315 to $1050 per kWh||12,000 – 14,000|
|Lithium-ion (lithium iron phosphate)||$200 to $840 per kWh||1,000 – 10,000|
|Flooded lead-acid battery||$105 to $473 per kWh||250 – 2,500|
Ongoing price reductions are expected for all three types of batteries, and IRENA projects the following cost range for 2030: $108-$360/kWh for VRFB, $77-$326/kWh for lithium iron phosphate, and $53-$237/kWh for flooded lead-acid. Vanadium batteries will continue to have the highest upfront cost, but the operating cost per kWh per cycle will decrease in general.
Vanadium redox flow batteries provide an effective energy storage solution when you need to manage kilowatt-hours in bulk. They can contribute to power network stabilisation in the timeframe of hours, balancing periods of surplus generation with periods of high demand. However, lithium-ion batteries are better suited for handling short-term events that threaten to destabilise grid voltage and frequency.
An important feature of VRFBs is their ability to replenish charge and provide power simultaneously, which is very useful when both generation and consumption are unpredictable. This makes them a powerful addition for microgrid projects, as well as remote grids in islands or rural locations.