Gonzalo Sanz Segovia | 24/02/2026
As an alternative to lithium batteries, flow batteries, or redox flow batteries, are cleaner, safer, and much more durable, although they’re currently more expensive and less efficient, as they require greater space to store the same amount of energy.
Spain leads Europe in the production and consumption of renewable energies. This strong commitment to a more sustainable model also involves certain supply risks, due to sudden variations of voltage in energies like wind energy or photovoltaic energy, as was evident with the “big blackout” on April 28 of last year. Nevertheless, a promising solution is emerging on the horizon of renewable energy: flow batteries.
Flow batteries are rechargeable systems that store energy in liquid electrolytes contained in external tanks, unlike traditional batteries, which do so with solid electrodes. They are perfect for renewables, as they can store large amounts of energy, they’re durable (+10,000 charging cycles), and they’re safer because they’re not flammable. A key feature is that they separate the power from storage capacity, making these systems more flexible and scalable. This means that if more power is needed, demand peaks can be met by installing more tanks in series. And if more storage capacity is needed, all you need to do is enlarge the tanks, or add more of them.
What all flow batteries have in common is that the electrolytes are liquids, but across the different patents (the first version of which dates back to one created by NASA in the 1970s) there are several types depending on the materials used.
Types of flow batteries
Vanadium redox battery (VRB)
VRBs are the most widely used so far and employ a heavy metal, vanadium, in different oxidation statuses in liquid solutions to store energy and release energy.
They’re very efficient, have a long service life (20 years and more than 10,000 charging cycles), and are safe, but their initial cost is higher. They’re mainly used in large-scale energy storage applications and to integrate renewable energy sources, as they provide virtually unlimited capacity and offer stability, as well as power control and voltage control.
High costs, the scarcity of vanadium, and geopolitical reasons (China and Russia are the main producers of this metal) mean many of the new patents are being developed with other materials.
Zinc-bromine battery (ZBB)
ZBBs use a zinc and bromine electrolyte system and are more economical than vanadium batteries, but don’t offer the same durability – between 2,000 and 3,000 load cycles over about 10 years.
They experience something similar to sodium/bromo polysulfide batteries (PBB) and iron-chromium flow batteries, which avail of much more common materials as electrolytes, but with lower performance output. As such, they’re much less frequently deployed.
However, there are very promising alternatives still in the experimental phase: organic flow batteries, which use organic compounds like acetone and ammonia, instead of metals, to generate the electrolytes. The goal is for them to be much more economical and sustainable. This would represent a breakthrough, as these raw materials could easily be produced at low cost in any laboratory.
China, Japan, and Korea are leading the development of patents for flow batteries, although China is far ahead and already has enormous production plants in operation. Spain is taking its first steps in this area, and the Spanish National Research Council (CSIC) already has some patents and projects for vanadium flow batteries. A photovoltaic plant in Son Orlandis (Mallorca) uses vanadium redox flow technology, with a power base of 1.1 MW and a capacity of 5.5 MWh. This facility represents a safe and cost-effective long-term storage solution – it has an almost infinite life span and it’s clean too, since vanadium is recyclable, non-toxic, and reusable.
A seriously interesting alternative
Their durability makes flow batteries a very interesting alternative worthy of exploration. Public administrations and private companies recognize this and are advancing the development of a technology that can offer almost unlimited capacity, simply by using larger storage tanks; that can remain completely discharged for long periods without harmful effects; and that can be recharged simply by replacing the electrolyte if there’s no power source available. Furthermore, it’s a very safe technology, since the battery isn’t permanently damaged if the electrolytes accidentally mix together.
Despite all these advantages, the main handicap facing vanadium redox technology (and other metals) is its relatively low energy density (energy-volume and weight ratio), which limits its applications practically to the industrial field. It also presents some complexity in assembly and maintenance compared to standard storage batteries (lithium-ion and lead-acid).
In the energy market, just like on the stock market, it’s advisable to diversify and have a portfolio that’s as broad as possible, where different components complement each other and provide a balanced response to varying demand levels. In the case of flow batteries, it looks like they’ll find their place in the storage and stabilization of intermittent renewable energies, such as wind and photovoltaic, and most of the research efforts are headed in that direction.
