Iron-redox-flow batteries

Green electricity, available around the clock, that is our goal. With the GigawattFactory, we are exploring new horizonts.

The Project

One of the core problems of the energy transition is the storage of green electricity on a large scale. This is what needs to be solved. Together with ESS Tech Inc (ESS), a leading global manufacturer of long-term energy storage systems, we are focusing on iron redox flow technology. At the Boxberg site, we want to realise a corresponding 50 MW/500 MWh, which is to be commissioned in 2027 - our first energy center.

We look forward to partnering with LEAG to develop the model for utilities and communities worldwide transitioning from coal to clean, renewable energy. The deployment of renewables and long-duration energy storage will not only deliver reliable, clean energy to effectively replace the baseload power currently provided by coal, it will deliver economic opportunity and a cleaner environment for Germany.

Eric Dresselhuys

Advantages of iron redox flow batteries

Power on Demand

< 1 second response time, more than 20,000 life cycles, use up to 10 hours+ possible

Safe, clean and affordable

Safe and non-toxic, use at temperatures from -5 to 50 degrees Celsius, safeguarded technology risks


Easily procurable materials, recyclable, "Plug&Play" with a shelf life of 25 years

A key requirement for our transformation into Germany’s Green Powerhouse is the deployment of cost-effective Long-Duration Energy Storage. We are energized to demonstrate the value of iron flow battery technology at scale. The Energy Resilience Leadership Group and Breakthrough Energy have provided an ideal framework to drive rapid technology development and deployment to meet emissions goals as soon as possible.

Thorsten Kramer

The principle

Redox flow batteries - also called liquid batteries, flow batteries or wet cells - are based on a uniform principle, it is already contained in the name:

Redox stands for reduction/oxidation and symbolises the circuit as a storage principle. Here, the electrolytic fluid flows through the battery cells in two circuits. When electrical energy is stored, the electrolyte is reduced in the negative half-cell and oxidised in the positive half-cell. When discharging, this process is reversed again. 

Flow stands for the pumping system that guides the electrolytic fluid through the battery cell. The advantage is that the electrolytic liquid can be stored outside the actual battery in tanks with different oxidation levels.

The electricity is produced in a cell, similar to the fuel cell. The size of the cell determines the power (kW), the energy (kWh) depends on the tank size - the amount of liquid used.

What is special about the iron redox flow battery is that it is based on materials that are cheap, abundant and non-toxic: Iron, salt and water. The ESS iron redox flow battery uses the same electrolyte on both sides of the battery, positive and negative. It is iron chloride dissolved in water.

Strong partnerships

LEAG and ESS have joined the Energy Resilience Leadership Group (ERLG), a multi-stakeholder initiative led by Breakthrough Energy and Siemens Energy that brings together corporate CEOs, policy makers, financial institutions and start-ups at the technology frontier. The group was launched at the 2023 Munich Security Conference with the aim of improving Europe's energy resilience through the rapid deployment of new climate technologies. The ERLG forges partnerships between start-ups and companies to develop commercially viable projects within 24 months. The LEAG and ESS project is one of the projects that the ERLG network is helping to accelerate.