Iron Flow Battery

Energy Storage Systems (ESS)
10kW 80kWh Energy Storage System Based on All-Iron Hybrid Flow Battery
ARPA-E Award: 
Portland, OR
Project Term: 
10/01/2012 to 08/30/2017
Project Status: 
Technical Categories: 
Critical Need: 
Our national electric grid has limited ability to store excess energy, so electricity must constantly be generated to perfectly match demand. Though wind and solar power are promising clean alternatives to fossil fuels, their natural unpredictability and intermittency make them incapable of delivering the power on demand necessary to operate today's grid. The U.S. needs technologies that can cost effectively store renewable energy for future grid use at any location. Flexible, large-scale storage would create a stronger and more robust electric grid by enabling renewables to contribute to reliable power generation.
Project Innovation + Advantages: 
ESS is developing a cost-effective, reliable, and environmentally friendly all-iron hybrid flow battery. A flow battery is an easily rechargeable system that stores its electrolyte--the material that provides energy--as liquid in external tanks. Currently, flow batteries account for less than 1% of the grid-scale energy storage market because of their high system costs. The ESS flow battery technology is distinguished by its cost-effective electrolytes, based on earth-abundant iron, and its innovative battery hardware design that dramatically increases power density and enables a smaller and less costly battery. Creating a high-performing and low-cost storage system would enable broad adoption of distributed energy storage systems and help bring more renewable energy technologies--such as wind and solar--onto the grid.
Potential Impact: 
If successful, the ESS' advanced all-iron flow battery technology would ultimately achieve an energy storage cost of $125 per kilowatt hour, representing a substantial price reduction relative to today's most advanced energy storage technologies.
A more efficient and reliable grid would be more resilient to potential disruptions. Distributed energy storage would improve consumer and grid electricity reliability.
Electricity generation accounts for over 40% of U.S. carbon dioxide (CO2) emissions. Enabling large-scale contributions of wind and solar power for our electricity generation would result in a substantial decrease in CO2 emissions.
Increases in the availability of wind and solar power would reduce fossil fuel demand, resulting in reduced fuel prices and more stable electricity rates. Distributed energy storage would reduce consumer electricity costs and improve efficiency.
Innovation Update: 
(As of May 2016)
Since the project began in 2014, ESS has made promising advances in developing a high-power, low-cost iron flow battery for grid-level storage. ESS’s first market for its product is smaller scale (less than 100kW), customer-owned systems. The company’s first customers include the U.S. Army Corps of Engineers and Stone Edge Farms, a California winery. Additionally, ESS has approximately $1M in firm orders for delivery in the first half of 2016. In 2015, Pangaea Ventures invested $3.2M in Series A funding to help ESS scale-up manufacturing and meet its initial orders. 
ESS initially focused on improving the energy density of its battery system. While iron-based flow batteries are less expensive than batteries incorporating other chemistries, ESS needed to improve the conventionally low-power densities offered by iron-based batteries. The team adapted its existing high-power cell and stack design to use low-cost iron chloride electrolytes. The resulting cell demonstrated four times the power density of existing iron flow battery technologies. ESS also had to overcome the limited cycle life of iron flow batteries. The team developed an effective chemical rebalancing system that ensures its battery can cycle over extended periods (more than 2,500 cycles) with greater round trip efficiency (about 70%).
For a detailed assessment of the ESS team's project and impact, please click here.
ARPA-E Program Director: 
Dr. Grigorii Soloveichik
Project Contact: 
Dr. Julia Song
Release Date: