ESS Iron Flow Batteries: Powering Clean, Safe Electrification

Iron flow batteries, also known as iron-air batteries or iron-redox flow batteries, are energy storage technology that stores electrical energy in chemical form. They are a specific subset of flow batteries that are gaining attention as a promising alternative to lithium-ion batteries, primarily due to their safety characteristics, scalability, and the use of abundant and non-toxic materials, such as iron and salt, in their construction. These features make them well-suited for applications requiring long-duration energy storage and a focus on environmental sustainability, particularly in clean energy and electrification efforts.

ESS Inc.—a provider of long-duration energy storage (LDES) solutions—is catalyzing a cleaner energy future by levering the features of iron flow batteries. Morgan Pitts, Director of Corporate Communications at ESS Inc., spoke to Battery Technology about his company’s energy solutions:

Can you explain the technological advantages that ESS’ non-lithium battery technology brings to the table in terms of supporting clean energy and electrification goals? 

Pitts: As more renewable energy sources are added to the grid, energy storage will be critical for providing a clean, reliable, and resilient power supply when the sun is not shining and the wind is not blowing. ESS’s Iron flow batteries store energy for up to 12 hours, vastly exceeding the roughly 4 hours of storage that lithium-ion and other traditional battery chemistries typically provide. In further contrast to lithium-ion, ESS’s safe and sustainable iron flow technology is capable of unlimited cycling without capacity fade over a 25-year design life, delivering significant cost savings and revenue opportunities over the system's lifetime. These characteristics enable ESS technology to complement renewable energy generation and meet the grid's needs 24/7. 

How does your iron flow battery technology address the safety concerns associated with lithium-ion batteries, particularly in environments prone to wildfires or other hazardous conditions? 

Pitts: Lithium-ion batteries can be susceptible to thermal runaway, which can cause fires. The technology also requires temperature and ventilation controls to maintain performance. Iron flow batteries pose no risk of thermal runaway and can maintain peak efficiency without AC or any other cooling systems required. 

As certified by ETL, our battery modules conform to Underwriters Laboratories’ (UL) 9540A, 1973, and 9540 standards, affirming their safety and environmental performance for outdoor and indoor installations. ESS technology can be safely placed in densely populated urban areas or remote locations and can operate under nearly any environmental condition.  

Could you provide insights into the environmental impact of ESS’ iron flow batteries compared to traditional lithium-ion solutions, including resource availability, production processes, and end-of-life considerations? 

Pitts: ESS’s iron flow batteries are manufactured with ethically sourced, non-toxic and earth-abundant materials – primarily iron, salt, and water. Most components and materials required for ESS systems can be sourced domestically, and iron flow batteries contain one-third of the embodied CO2 emissions of lithium-ion batteries. Thanks to their use of common components and earth-abundant materials, ESS products can be largely reused or recycled at the end of their life.  

How do ESS’s iron flow batteries address the need for scalability and grid integration in the context of growing renewable energy installations and the demand for more resilient power systems? 

Pitts: ESS systems provide resilient, sustainable energy storage well-suited for multiple use cases necessary to enable renewable energy adoption to continue to scale and ultimately replace fossil generation. These include incorporation into utility distribution and transmission infrastructure, remote solar & storage microgrids, providing solar load-shifting and peak shaving, and other ancillary grid services. With up to 12 hours of energy storage and unlimited cycling with zero capacity fade, ESS systems can capture multiple value streams, enabling customers to maximize revenue and deliver clean energy 24/7.  

ESS is scaling its manufacturing capacity to 2 GWh in the coming years to meet the growing demand for LDES. In fact, McKinsey & Co. estimates that 30-40 TWh of LDES will be required to decarbonize the US electrical grid by 2040. For example, LDES can address transmission line congestion in peak periods of the day by storing power when in excess and deploying it when needed.  

What strategies or innovations has ESS implemented to ensure that ESS’s iron flow batteries remain competitive in terms of efficiency, cycle life, and cost-effectiveness while contributing to the broader transition to sustainable energy sources? 

Pitts: ESS technology is sustainable and cost-effective, helping utilities and other commercial customers achieve decarbonization and energy resilience goals. The technology’s 25-year design life is consistent with the typical lifespan of utility-scale solar projects, and it’s easily scalable, enabling customers to meet their energy storage needs easily. On a total cost of ownership, ESS systems are significantly less costly to own than lithium-ion, thanks to earth-abundant materials and readily available components. 

Can you share examples of successful deployments of ESS technology in power systems and their contributions to clean energy integration and electrification goals? 

Pitts: ESS has entered into several agreements with major customers, including leading utilities such as the Sacramento Municipal Utility District (SMUD), which has ordered up to 2 GWh of ESS technology in coming years, with the first six Energy Warehouse units already delivered. Additional customers include Portland General Electric, Consumers Energy, Enel Green Power, Burbank Water and Power, and Turlock Irrigation District. ESS has also partnered with Amsterdam Schiphol Airport, the second largest airport in Europe, to leverage ESS’ technology to retire polluting diesel generators and support the airport’s 2030 carbon neutrality goal.   

Most recently, ESS signed an initial agreement with LEAG, a major German energy provider, to build a 50 MW / 500 MWh iron flow battery system to help it transition from coal to clean energy. This project is expected to displace 50,000 tons of coal mined and burned daily with clean, renewable energy and eliminate 20 million tons of CO2 annually. Once completed, this will be the largest flow battery site in Europe and one of the biggest in the world.