## Cummins invests $24M in flow battery leader VoltStorage ##### 01 August 2022 Cummins has invested$24 million in Germany-based VoltStorage, a developer of stationary flow batteries. The company says that it has the largest fleet of operating flow batteries in the world.

Cummins is committed to developing a range of solutions that will enable our customers’ success as we advance our Destination Zero strategy and decarbonize our diverse markets. By investing in VoltStorage, we are taking steps to advance solutions focused on the grid and energy storage.

—Jennifer Rumsey, President and COO, Cummins

Headquartered in Munich, VoltStorage was founded in 2016 by Jakob Bitner, Michael Peither and Felix Kiefl. VoltStorage develops and produces commercial storage systems based on the particularly ecological vanadium redox flow technology for commercial and agricultural enterprises. In addition, the international research and development team is working on the low-cost iron-salt battery, the properties of which make it particularly suitable for ensuring base load capability for wind and solar farms.

Vanadium redox flow battery cell. The cells of a vanadium redox flow battery each consist of two half cells. Each half cell contains a frame with specially designed channels to ensure evenly distributed electrolyte supply to the entire electroactive area. The electroactive area is located in the center of the half cell and is completely filled with graphite felt. The half cells are separated by an ion exchange membrane. Each battery cell is enclosed by two bipolar plates. Source: VoltStorage

With the development of the iron-salt technology, the company is setting new standards in the field of long-duration energy storage, offering wind and solar farms a highly cost-effective and resource-saving option for ensuring base load capability.

According to VoltStorage, Cummins’ investment will go toward developing larger-scale redox flow storage systems for commercial and agricultural enterprises and residential neighborhoods. In addition, product development of the iron-salt technology will be accelerated towards commercialization.

Iron-Salt technology is a highly temperature-resistant battery technology that can be used worldwide, even in climatically challenging regions. In addition, the storage system can be connected to existing infrastructures in a space-saving and decentralized manner, which additionally ensures the self-sufficient functionality of the storage solution and increases reliability.

The iron-salt redox flow battery unit is based on two battery half-cells through which liquid electrolyte is pumped in independent cycles. The half-cells are separated by a membrane and together form the full battery cell. The electrolyte is enriched with iron chloride.

During charging or discharging, ions and electrons are transferred between the two half-cells, storing, or releasing energy in the electrolyte. In the uncharged state, both cells have identical oxidation levels; charging leads to reducing the electrolyte in one half-cell and oxidizing electrolyte in the other. Within the negative half-cell, the iron in the electrolyte is deposited as metal on the electrode.

The battery capacity is dependent on the iron deposition: an increasing amount of iron deposition leads to a higher capacity. The reaction is fully reversible, and iron is re-dissolved in the electrolyte during discharging.

Their website just gives a vague:

'over 70% efficiency'

https://voltstorage.com/en/long-duration-battery/applications/

Are they talking about input, round trip efficiency, or what?

And what is the self discharge rate?

I have learnt to listen out for 'the dog that did not bark' when people are claiming this and that for new energy technologies.

I think the EnergyDome system looks better, at any rate they provide decent figures, and trial systems are being built right now:

https://energydome.com/co2-battery/

they give the RTE of over 75%, and it can be deployed just about anywhere.
Standard off the shelf components mean that the, very long, service life can be calculated.

Insulation means that it should have a very low rate of self discharge.

I really like this liquified CO2 solution.

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