The use of renewable energy around the world has been rising fast and could continue to grow by as much as 50% over the next five years. Low cost solar power is predicted to really take off this decade with a 600 gigawatt jump in global capacity — that’s roughly half of the entire US energy capacity1.

But one thing that’s preventing renewables from taking over completely is the issue of storage. Because we can’t always rely on the weather, we need effective ways of saving up enough energy for when the sun isn’t shining or the wind isn’t blowing, and to provide added resilience in case of natural disasters. Batteries already exist that can help energy grids cope better during peak times, but if we want to replace fossil fuels entirely, we need to build batteries that can store enough energy to power entire cities for much longer periods. So, how might we achieve this, and where do we currently stand with the technology?

We’re all familiar with batteries — from the simple AA’s that make our TV remotes and flashlights work to the lithium-ion units that power our portable devices, they’re a convenient form of energy storage that we use every day and have perhaps taken for granted. They’ve become an essential part of modern life, and our dependence on this technology is only going to grow as we transition towards electric vehicles and continue to decarbonize our energy systems in favor of renewable alternatives. At the moment, pumped hydro is by far the most common way of storing large amounts of electricity, representing 99% of global storage capacity. But this won’t work as a universal solution because hydroelectric dams can only be built in specific locations2. Instead, we need storage infrastructure that can be placed anywhere and scaled according to demand, and that’s where advanced large-scale battery technology comes in.

Batteries can provide power almost instantly, which is why they’re seen as ideal replacements for peaker plants, which are power plants that exist primarily to operate only when there’s high demand. They mostly run on fossil fuels, like natural gas, and compared to modern battery technology they’re expensive to run and not nearly as fast to start up3. But this only scratches the surface of what modern batteries can do … and what we need them to do. Without batteries that can deliver grid-scale storage, we won’t be able to rely on renewables alone4. Fortunately, good progress is already being made.

As well as being built into our phones and laptops, lithium-ion (or li-ion) is the most popular form of battery for storing energy generated from solar and other renewables. Due to its applications being so critical and far-reaching — with everyone now owning a phone and electric vehicle investment soaring — R&D in this particular field has been going into overdrive and costs are beginning to come down. Tesla’s battery day is due any day now and it’s widely believed that they’ve broken the $100/kWh milestone5.

However, lithium ion is still far from cheap when implemented at mass scale, which is what we’ll need to fix our renewables problem. And that’s not the only drawback — producing the millions of cells that would be required for a grid-level storage system is an extreme task, and manufacturers are already struggling to cope with the demand for batteries from other sectors such as consumer electronics and automotive. But perhaps the most important point is that they can only be used for relatively short durations — not ideal when we would need our grid-scale batteries to discharge for ten hours or more at their rated power6. There have also been concerns about some of the materials used to make these batteries — namely lithium and cobalt — in some areas there major human rights issues with the mining and the more we consume them prices could go up as well, which will continue to exacerbate the human rights issues.

But these issues haven’t been putting too many people off — at least in the US. Over the past five years or so, the vast majority of energy storage systems deployed here use li-ion batteries, and the developments that we’re currently seeing in this space are likely to see this trend continue for a while. For example, lifespan has been another problem area for lithium-ion historically, but this appears to be changing. CATL, the Chinese company that makes electric car batteries for the likes of Tesla and Volkswagen claims to have created a power pack that could take a vehicle more than a million miles and last for 16 years7. In comparison, a typical warranty on an electric car only covers around 150,000 miles or eight years. This would surely give those who have criticized lithium-ion for degrading too quickly something to think about.

That issue of disposal is also now being addressed by companies such as Tesla, which recycles and repurposes its batteries8. Companies like American Manganese have recycling techniques that are able to recover nearly 100% of a spent battery into materials ready for manufacturing new batteries9, and there are other firms out there with similar capabilities.

But despite the advancements we’re now seeing that are shortening the list of negatives with lithium-ion, that problem of duration remains quite a significant one — and this is an area where redox flow batteries hold a distinct advantage.

So, what are they? In redox flow batteries, energy is stored in solutions comprised of liquid electrolytes. These are pumped into a chamber containing a series of electrochemical cells. Inside this chamber, known as the ‘stack’, ions are exchanged through a membrane and either charged or discharged depending on the direction they’re moving in, which generates electricity from the resulting chemical reactions. The electrolyte solutions are held within a pair of external fluid tanks — one that acts as the cathode where reduction (or the gaining of electrons) occurs and the other serves as the anode, where oxidation (or the loss of electrons) takes place. This is where the term ‘redox’ comes from1011.

Many experts see flow batteries as having several advantages over self-contained varieties such as lithium-ion. For instance, need more storage capacity? Just increase the size of the storage tanks and the quantity of the electrolyte. A much simpler and cost effective solution than having to increase the number of cells in a lithium ion battery pack, which can be more costly. They can also be used for longer durations at a time — typically around 10-12 hours a day — with minimal degradation, they have longer lifespans than most types of lithium-ion batteries as well as higher levels of safety due to a lack of combustible materials12. However, all of this does come at a price, as many of the ingredients used to make the electrolyte solutions are rare and expensive, and some of them are highly toxic.

Flow batteries come in different variations as well depending on what elements are used for the electrolyte solution, with the most common being vanadium. This is due to the material’s proven capability of delivering thousands of charge and discharge cycles13 with high reliability. These batteries also use vanadium as the dissolved active material of both electrolytes14, which eliminates the risk of cross-contamination that can happen in flow batteries that use two types of active species15. Hybrid varieties such as those that use a zinc-bromine combination are another popular option. This is where one of the active materials — in this case the metal zinc — is deposited as a solid layer on the electrode16.

They might not be cheap, but flow batteries are seen as promising for large-scale renewable storage because they can draw in energy when the source is abundant, like on a sunny day, and then release it as electricity when needed. Capacity can remain largely unchanged even after many hundreds of cycles and their core components can be recycled more easily than most other batteries too. The global market for flow batteries is also experiencing major growth. In 2018 it was valued at around $130 million but it is predicted to reach over $400 million by 202617, and some estimates are far higher.

The Asia-Pacific region — in particular China, Japan, India and Australia — is projected to dominate this new sector in the coming years. These countries, especially China and Australia, are ahead of the rest of the world on implementing new battery technologies for large-scale energy storage and generally modernizing their power infrastructure, with several working high-power flow battery installations already in place18. China’s Dalian Rongke Power is one the leading global players in flow batteries. It aims to build the world’s biggest vanadium battery, which should complete this year and provide enough energy to power thousands of homes — that’s 200MW/800MWh18. To compare, the world’s biggest lithium-ion battery, the Tesla-made Hornsdale Power Reserve in Australia, is only 100MW/129MWh, although storage and output is due to be expanded by 50%19.

Redox flow batteries were originally developed by NASA back in the ’70s for its space applications, but when a number of key patents for the technology expired in 2006, this allowed private companies all over the world to start innovating their own solutions20. One recent example comes from a team of scientists at the University of Southern California. They have designed a battery that utilises iron sulfate — a waste product of the mining industry that is cheap and plentiful. This is combined with anthraquinone disulfonic acid — an organic material that can already be found in some flow batteries and is known for its stability and solubility — to create the electrolyte solution. According to USC, if their batteries were produced at scale, they could generate electricity at half the cost of vanadium flow batteries21. Apparently, during testing, they also discovered that the battery was capable of charging and discharging hundreds of times with “virtually no loss of power.21

This is just one of many potential alternatives to vanadium-powered batteries currently being proposed. A new Canadian company, Zinc8, has created a zinc-air battery that it claims could transform the energy storage market. Their hybrid flow battery can allegedly store energy to last several days, it doesn’t suffer from degradation, it’s explosion-proof and is far less expensive than lithium-ion.

They work by taking electricity from the grid to break up chemical zincate into zinc, water and oxygen. This creates charged zinc particles capable of storing electricity for several weeks. When the time comes for it to be released, a combination of the charged zinc, oxygen and water unleashes the stored electricity while also producing zincate, which is used to start the whole process again22.

Another newcomer is Form Energy, which has developed a 1MW battery system that promises up to 150 hours of storage duration. Of course, how they managed to figure out the chemistry to achieve this remains a mystery. All that’s known is that it’s some kind of “aqueous-air” solution that makes use of what the company says are “some of the cheapest, safest, most abundant materials on the planet.” The company has teamed up with Great River Energy — a Minnesota-based utility company that has been looking to switch from coal power to an energy mix largely made up of renewables — to carry out a pilot project using Form Energy’s new innovation, which is due to complete by 202323.

The ability to store large amounts of energy and then release it over longer durations is becoming increasingly important as our dependency on renewables grows, but perfecting the technology that allows us to do this needs to be achieved quicker than what we’ve seen in the past. It’s taken around 40 years for lithium-ion to reach the stage where it is now24, but we don’t have that kind of time to wait for grid-scale storage to mature. However, this sector appears to be taking some significant strides forward, completing the crucial next phase should be achievable in a much shorter timeframe.

  1. The Guardian – Renewable energy to expand by 50% in next five years – report ↩︎
  2. Energy Post – umped Thermal Electricity Storage: grid-scale, cheap materials, known tech, compact, install anywhere ↩︎
  3. IEEE – It’s Big and Long-Lived, and It Won’t Catch Fire: The Vanadium Redox-⁠Flow Battery ↩︎
  4. ScienceDaily – New tools show a way forward for large-scale storage of renewable energy ↩︎
  5. Car & Driver – Report: Tesla’s Next Battery Will Make EVs Cost the Same as Gas Cars ↩︎
  6. Advanced Research Projects Agency (ARPA) – Why Long-duration energy storage matters ↩︎
  7. Bloomberg – A Million-Mile Battery From China Could Power Your Electric Car ↩︎
  8. Tesla – Tesla Environmental Impact Report – 2019 ↩︎
  9. American Manganese – Making Lithium-ion Last Forever ↩︎
  10. Engineering.com – Massive 800 MegaWatt-hour Battery to Be Deployed in China ↩︎
  11. New Atlas – Flow battery could make renewable energy storage economically viable ↩︎
  12. Energy Storage News – US Department of Defense-funded study finds vanadium flow batteries worthy of further scrutiny ↩︎
  13. Australian Energy Council – Batteries going with the flow ↩︎
  14. Korea Institute of Science and Technology – Vanadium Redox Flow Batteries: Electrochemical Engineering ↩︎
  15. VanadiumCorp – Vanadium redox flow batteries: A technology review ↩︎
  16. International Flow Battery Forum – What is a flow battery? ↩︎
  17. Allied Market Research – Redox Flow Battery Market Outlook – 2026 ↩︎
  18. Markets and Markets – Flow Battery Market by Type (Redox, and Hybrid), Material (Vanadium, Zinc–Bromine), Storage (Compact and Large scale), Application (Utilities, Commercial & Industrial, Military, EV Charging Station), and Geography – Global Forecast to 2023 ↩︎
  19. Al Jazeera – World’s biggest lithium-ion battery is about to grow even larger ↩︎
  20. eeNews/IDTechEx – Redox Flow Batteries get ready for the big time ↩︎
  21. University of Southern California – New flow battery could help unleash renewable energy ↩︎
  22. Recharge – New zinc-air battery is ‘cheaper, safer and far longer-lasting than lithium-ion’ ↩︎
  23. Energy Storage News – Form Energy’s mystery battery chemistry to be used in 150 hour duration pilot ↩︎
  24. Forbes – Energy’s Future – Battery and Storage Technologies ↩︎

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