Iron Flow Battery technology and its role in Energy Storage

Energy storage is a hot topic of discussion in the utilities sector and alternative energy generation because it is crucial to support grid electrical supply, transmission, and distribution systems. For our utilities provider, regulators, and grid operators, that means a more resilient and reliable way to feed the grid during the peak power demand period, reducing the strain on more traditional sources of power generation like coal or gas-powered power plants. 

The result is higher efficiencies and reduced reliance on greenhouse gas-producing energy sources. Advances in batteries are making electric heaters effective solutions for decarbonization. There is a transition away from gases which traditionally were a primary option before the advent of energy storage solutions. 

Applications of energy storage solutions

The utilization of energy storage systems falls into six categories:

  • Helping renewable energy sources integrate with the commercial grid. Since renewable energy sources like wind, solar, and biomass can fluctuate in generating capacity, the sustainable energy storage solution provides a reliable supply to the grid.
  • They can improve the grid efficiency due to their higher energy density, increasing the capacity factor of existing resources, thus “balancing” the grid and reducing the trend to offset the need for energy produced from polluting power plants.
  • During the ramp-up period of coal, gas, or furnace oil-based power plants, the energy storage solutions provide efficient delivery of electricity.
  • They can reduce the operational costs of the entire grid infrastructure due to their modular and less maintenance-intensive architecture.
  • They can store energy when electricity prices are low and retrieve it when prices climb, thus reducing the cost to the end-users. 

iron flow battery storage solutions

Iron flow battery-based storage solutions have recently made a historical breakthrough to counter some of the disadvantages of lithium-ion battery solutions. They offer a safe, non-flammable, non-explosive, high power density, and cost-effective energy storage solution.

In essence, iron flow batteries are electrochemical cells where an electrolyte stored in externals storage tanks acts as an energy source. The flow pumps transfer the electrolytes to electrodes, extracting electrons and providing energy to the grid. In turn, the spent electrolyte is pumped back into storage tanks until the main power source, such as a solar power plant or windmill, is back-generating power. In that case, the spent electrolyte is pumped to the electrode, thus charging the electrolyte and pumping it to the external storage tank. 

The electrolyte of iron flow batteries consists of iron salts which are abundant earth minerals in ionized form which store the electrical energy in the form of chemical energy. 

Insight into iron flow battery Redox reaction

The redox chemical reaction in all iron flow batteries consists of FeCl2 and FeCl3 coupled at the anode (positive electrode) and FeCl2 and metallic iron made up at the cathode (negative electrode). During the electricity production or discharge phase, the FeCl3 at the anode is reduced to FeCl2, and at the cathode (negative electrode) the metallic iron dissolves into electrolyte as FeCl2. The process reverses in the charging phase. 

An ion exchange membrane separates the two chemical solutions (FeCl2+FeCl3 and FeCl+ Fe). The ions are exchanged through these membranes while the liquids circulate in their own respective compartments. It is important to note that in iron flow or redox flow batteries, both compartments are filled with soluble redox pairs.

Comparison of Iron flow battery with Li-Ion battery

Although Li-ion batteries are one of the most popular batteries for energy storage, they are plagued with the problems of high toxicity, no advantages of long-term energy storage, high flammability, and shelf life dependent on the charging-discharging cycles. 

The iron flow battery can store energy up to 12 hours in existing technology with prospects of stretching it to 15 hours. Li-ion batteries are limited to a maximum of 4 hours. They are not flammable, non-toxic and there is no risk of explosion compared to Li-ion batteries. 

The lithium hydrates are toxic and react violently when they encounter water. They also corrode in the air, while iron is non-toxic and only slightly reactive with water and air. Theoretically, the iron flow batteries have unlimited cycle life, and their store change does not degrade, even after multiple years of charging and discharging. 

In contrast, the Li-ion battery is limited to 7000 cycles to 10,000 cycles and 7-10 years of use, after which environmental disposal of these batteries becomes a real challenge. The operating temperatures of the iron flow batteries range from -10˚C to 50˚C with no requirement for ventilation of cooling systems. Ventilation plays a crucial role for Li-Ion batteries. Especially for commercial-scale systems and preferred temperature of operation is 24 ˚C to 26 ˚C after while their ability to hold or store the charge is negatively affected. 

Size and Scalability

One advantage of Li-ion batteries is that they are designed for mobile applications like laptops, cell phones, and other mobility solutions. They are small, compact, and mobile, whereas iron flow batteries have a much larger footprint. Thus, making iron flow batteries suitable for large-scale commercial and industrial storage. 

Li-ion batteries are not specifically developed for commercial scale and grid applications. However, they offer large-scale availability, much higher power density, same capital cost as the Iron flow batteries, and manufacturing efficiencies have accelerated their growth. This makes them a strong competition to the flow batteries until flow batteries catch up. 

Another important aspect is the scalability of iron flow battery systems. While the fixed equipment like power electronics, tank, power module, and support structure remains the same, they offer an easier way to enhance the storage duration is adding more electrolytes. 

Since the energy is stored in the electrolyte, the more electrolytes stored the more scalable the storage. The electrolyte is essentially based on iron, water, and salt, all earth-abundant elements. Thus, making the solution more environmentally friendly than the Li-ion battery. Based on rare earth metals, the Li-Ion takes 67% more greenhouse gas emissions than the iron flow battery and poses an environmental risk when it reaches its end of life disposal.