The Redflow Zinc-Bromine Module (ZBM) is the smallest commercially available hybrid zinc-bromine flow battery in the world. The size of these 10kWh energy storage modules means they can be deployed in applications, such as telco tower sites, that were previously impossible to address with flow batteries, yet they can also scale to grid-level energy storage.
The Redflow ZBM is a convention-breaking energy storage machine. It can be thought of as a miniature, reversible, zinc electroplating machine made largely of recyclable plastic. The innovative Redflow battery design uses abundant and relatively cheap minerals in its electrolyte formulation. These attributes gives the product strong environmental credentials.
I recently spent some time at Redflow’s Brisbane headquarters taking a close look at the new Redflow Gen3 energy storage module. It is impressive to see just how far the Gen3 project has progressed in recent months and to appreciate the level of innovation it embodies.
Redflow has developed and optimised the design of its Gen3 battery in various stages during the past five years, incorporating knowledge and optimisations based on field deployment of the Gen2.5 product. The Gen3 battery utilises the advanced manufacturing capability developed by the company in its own dedicated factory and delivers a streamlined product designed for reliable and high volume production.
The Gen3 ZBM is slightly smaller, and yet delivers the same baseline performance specifications as the Gen2.5 module. Gen3 is designed to be an easy, drop-in replacement for the previous model in any customer application.
Redflow initiated Gen3 customer trials at the end of 2020 and also undertook further lab testing of key components and complete new Gen3 batteries. This has led to further design advances in Gen3 flow distribution, management of shunt currents and software optimisation. The current expectation is that Gen3 will be introduced into production around the end of 2021.
This is what a Redflow Gen3 ZBM looks like:
It is time to take a look under the hood… and the more you look, the more improvements become evident.
This is a photo of some Gen2.5 batteries, for comparison, sitting beside a Gen3 battery undergoing testing at Redflow:
There are many improvements in Gen3, all designed to reduce parts count and cost while also making the product easier to manufacture.
Single Stack vs Dual Stacks
The key Gen3 improvements are related to the “heart” the device, the electrode stack.
This unique battery stack design, materials set and manufacturing system are where the majority of the Intellectual Property, Patents and Know-How developed by Redflow over the past 10 years resides. The new Gen3 stack represents a major step forward for the company in all of these respects.
This new product implements a single 10kWh stack at the top of the Gen3, replacing a pair of 5kWh stacks on the Gen2.5 model. Having just one stack instead of two delivers an obvious long-term reliability benefit.
That single stack also lowers production cost and reduces complexity in physical, chemical, and electrical terms. Redflow has also revised the internal construction of the new stack, including the fluid flow paths and the stack surface itself, for simpler and faster manufacture.
This single stack design eliminates the need to wire the two stacks together in parallel with an adaptor plate on the front of the stack, reducing parts count and complexity.
Moving to one stack also removes the requirement to bind the two stacks tightly together with large metal plates and long bolts. The Gen2.5 requires these relatively costly structures to maintain a consistent electrolyte fluid seal and to manage consistent electrolyte flow across both stacks. In Gen3, none of that is needed
The single new stack is simply strapped on to the top of the battery tanks, making it easier to replace the stack in the future, if required.
Because the stack is also a major cost item in the ZBM bill of materials and is also a critical path item in manufacturing time, the single stack delivers obvious and profound implications in terms of increased peak factory production rate and decreased overall production cost.
New Electronics Module (MMS)
The Module Management System (MMS) – the electronics box on the front of the battery stack – contains power-handling and control electronics which are run by an on-board device management computer.
The Gen3 MMS has been totally redesigned, delivering both short and long-term benefits.
The Gen2.5 battery MMS contains several separate circuit boards, due to more than a decade of incremental development. Gen3 puts them all on a single, redesigned, higher performance board.
The Gen3 battery MMS also has battery terminals on the front of the unit, rather than ‘behind’ the MMS, which makes electrical interfacing a lot easier.
The Gen3 design eliminates the separate “Energy Extraction Device” (EED) sold with Gen2.5 batteries by building that functionality into the MMS as a software-controlled element.
The new MMS costs much less to make and is far more powerful in terms of CPU and I/O capability.
Advanced current flow management and software-driven bidirectional DC/DC conversion circuitry allows for the development of improved MMS firmware to deliver new software-driven current control and voltage control features, along with other planned improvements. These will be rolled out to customers through in-field software updates via the Redflow Battery Management System (BMS).
Other improvements in the new MMS Include the use of solid-state circuit-switching hardware based on Field-Effect Transistors (FETs) to connect, disconnect and mediate energy flow into each ZBM, versus the use of three physical ‘Contactors’ inside the Gen2.5 MMS. This eliminates some expensive moving parts from the MMS by replacing them with devices that are not only faster but that have an essentially unlimited cycle life in this application.
Redesigned electrolyte tanks, pumps, and cooling structure
The ZBM has two electrolyte tanks, each with its own pump. The Gen2.5 uses a nested, ‘tank within a tank” arrangement that, while elegant, is quite complex and expensive to make. Gen2.5 tanks are also constructed with many sharp corners and a complex side-wall design, making high volume manufacturing even more challenging.
The new Gen3 tanks are quite different. This is a picture of the new tanks with pumps without any other parts installed. You can see that there is a new plastic formulation and that they feature distinctly rounded corners:
This is all designed to optimise the tank for volume production. This design is easier to build and has an increased tolerance for variation between tanks during the manufacturing process. The new tanks are also arranged as a simple left-right pair – much simpler than the Gen2.5 nested tank structure, further improving ease of assembly.
The pumps have also changed. For historical reasons, the Gen2.5 pumps are actually 140 volt DC pumps that require a custom-designed voltage uplift circuit inside the MMS to drive them. The Gen3 pumps are 24 Volt DC pumps that can be more easily and efficiently driven from the MMS.
As part of the new Gen3 design, Redflow is also introducing a new cooling system using a new set of Filtering Polymeric Fibrous materials which will improve battery performance.
All up, the new tank cooling system and pump set represent a major improvement, designed, like the rest of Gen3, for repeatable high-volume manufacture at a lower production cost.
Purpose-built electrolyte ‘bund’
In many markets, energy storage devices that use fluid electrolyte in field deployments need to include a ‘bund’ – somewhere to catch and hold electrolyte fluid in the unlikely event of a fluid leak.
For the Gen3 battery Redflow has a new purpose-built bund. This is the plastic enclosure extending to about halfway up the battery on all sides, that is visible in the lab test photo above.
The intention is to ship Gen3 batteries with this bund included, saving installers the need to arrange and install a separate bund.
Gen3 Summary: Greater reliability, lower cost, faster production
The Gen3 module marks a major transition for Redflow.
Gen3 is designed for volume manufacture, with a design emphasis on fewer parts, greater ease of manufacture, and more compatibility with automated production techniques. By intent, this all leads to a lower production cost and greater long-term reliability.
These improvements benefit both Redflow and its customers as the company moves to ramp production volumes to meet the rapidly expanding global demand for scalable, sustainable and reliable energy storage.
Simon Hackett 
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