Longer duration energy storage

By Don Smolensk, Contributing Editor | TLT Machinery June 2025

Alternatives to expensive lithium-ion batteries are currently in development.
A field with wind turbines and energy storage
Lithium-ion batteries have generally been the choice for grid storage of renewable energy for short periods. Examples are for solar panels on cloudy days or wind turbines during windless periods.1 However, they are relatively expensive for use for longer periods. There has been a lot of interest lately in alternatives to address this issue, such as flow batteries or metal-air batteries.2 One company has developed an iron-air battery, which uses a water-based electrolyte and iron Fe(OH2), and functions by a charging cycle that uses renewable energy to convert Fe(OH2) to iron. The discharge cycle reacts iron with oxygen to produce Fe(OH2) while releasing the stored energy. These batteries have the capability to store energy for up to 100 hours.3 Also, iron, being plentiful, circumvents the issues of mining the metals used in lithium-ion batteries. In addition to manufacturing batteries, this company has developed software which allows optimizing over real-world weather conditions, yielding reliable and cost-effective designs for power systems. The government and private industry have invested over $1 billion in these new technologies. 

There are also flow batteries (also known as Oxidation-Reduction [redox] batteries), which have been around for decades, that use liquids to store chemical energy. These are rechargeable batteries that incorporate two electrolytes in different tanks containing dissolved substances that react to either release or store electrons. Pumps circulate electrolytes through different electrodes. During charging, electrons are transferred from one electrolyte to the other. During discharging, the electrons are transferred back in the opposite direction. The size of the tanks can be adjusted for demand, so these batteries can be very flexible. Typically these batteries achieve efficiencies in the range of 50% to 80%. They are generally long lasting and easy to maintain, which makes them potentially less expensive than lithium-ion batteries. Most commonly, though, a relatively expensive vanadium electrolyte is employed. Another company has been researching organic substitutes for vanadium to reduce the cost. Zinc flow batteries are also showing promise. 

Lithium-ion batteries are a proven technology, often reaching 90% efficiency. The iron-air battery looks to be potentially significantly cheaper than the lithium-ion battery, with flow batteries likely somewhere in between. The timing of bringing longer duration batteries on line is extremely difficult to forecast. There are also several logistical issues to consider. Some in the industry believe there will be a strong market for zinc-iron batteries, but not for about five years. Grid use of batteries has risen significantly, especially since 2020. Some long duration battery developers are receiving funding from the Department of Energy, the Science Foundation and/or other governmental entities. Recent government priorities have significantly favored fossil fuels and have been hostile to renewable energy. This will likely detrimentally inhibit the growth of this renewable energy technology.

REFERENCES
1. Blois, M. (Feb. 21, 2025), “The search for long-duration energy storage,” Chemical and Engineering News. Available at https://cen.acs.org/energy/energy-storage-/search-long-duration-energy-storage/103/i5
2. https://about.bnef.com/blog/lithium-ions-grip-on-storage-faces-wave-of-novel-technologies/
3. https://formenergy.com
 
Don Smolenski is president of his own consultancy, Strategic Management of Oil, LLC, in St. Clair Shores, Mich. You can reach him at donald.smolenski@gmail.com.