REDT - Flow Battery For Efficient Energy Storage


REDT has developed an energy storage solution, which is based on a vanadium-vanadium redox couple.

The REDT product has the following attributes:


  • Fully recyclable, compared to alternative technologies like Lead Acid and Lithium.
  • High cycle ability and charge acceptance.
  • Reliable performance with very low maintenance for lowest total cost of ownership.
  • System life: more than 10,000 charge/discharge cycles matching PV and wind generator life.
  • Electrolyte has indefinite life.
  • The company holds exclusive IP rights for the REDT technology.

The Technology

REDT has investigated various storage technologies and has focused on the Vanadium Redox Flow Battery ("VRFB") - now a mature technology which has been shown to have outstanding reliability and the lowest whole life cost of any competitive system. The company has designed, developed, built and tested prototype stack modules and is now scaling-up for cost-effective commercialisation of this technology.


The VRFB technology utilizes the flow of two electrolytes separated by an ion exchange membrane. A reversible electrochemical reaction allows electrical energy to be stored and subsequently returned. The system has these key attributes:


  • Energy is stored in the chemical composition of the electrolytes;
  • Electrolytes comprise Vanadium dissolved in sulphuric acid which allows diffusion of ions between the two liquids;
  • Flow is regulated by pumps and valves, which manage the two liquids; and,
  • Total energy storage is a function of the capacity of the tanks and the volume of electrolyte held.


The VRFB is an advanced energy storage system which has a major advantage over conventional batteries in the separation of power and energy.  Analogous to an engine and its fuel tank, the engine delivers power rated in kW and the fuel, Vanadium electrolyte, delivers energy rated in kW hours. As a consequence: 

  • The system is easily scalable - it is possible to extend the storage capacity from hours to days without the need to upgrade the power generation system, and there are no emissions at its point of use;
  • Unlike the other flow battery technologies, the VRFB system has unique intrinsic reliability - it uses Vanadium compounds on both sides of its ion selective membrane which eliminates cross contamination and allows for simple maintenance procedures;
  • The electrolyte does not have to be replaced: it lasts indefinitely;
  • The charge acceptance of the system is 1.2:1 (optimal) and 1:1 (nominal).  It is also capable of deep and partial cycles with no loss of system integrity;
  • The system does not self-discharge when in standby mode and can store energy for long periods when not in use.


REDT’s unique stack design and construction is protected by patent in most major industrialised countries; additional patents are envisaged for more recently developed improvements.  REDT also holds patents on a unique liquid refuelling system for electric locomotives, buses and trucks which may be further developed at a later date.

See appendix 1 for more technical details about the VRFB technology.

Key technical aspects of the REDT technology

Efficiency – The patented stack design features specially engineered sealing and porting which minimises losses, and results in round trip efficiencies in the 75% to 82% region.


Charge acceptance – A key feature of the REDT system is its ability to accept charge at the same rate that it can be discharged.  Renewable energy systems are dynamic and their generation rates change rapidly so any effective storage device must have the ability to cycle energy rapidly. The REDT system can accept many tens or even hundreds of shallow charge discharge cycles per day without any deleterious effect on system life.


Life of the stack - The stack design life is ten years and uses a demountable design which can be refurbished for around 25% of original cost. This cost is accounted for as part of O&M - the electrolyte has a virtually unlimited life and requires minimal servicing – a simple rebalancing operation, which can be remotely activated, is required at approximately two monthly intervals.  All operating characteristics can be remotely monitored.


Power density - REDT’s advanced stack design also has low ‘effective impedance’ which results in a relatively high power density.  This outstanding feature is the result of six years of development work, providing an overall lower cost per kW and improved turnaround efficiency.


Low cost production – Taken over its 20 year life, the REDT VRFB system has the lowest levelised cost per kWh of all competitive battery systems (see appendix 4 for detailed calculations).  Low total cost of ownership (TCO) benefits will be further enhanced by REDT’s optional, leveraged electrolyte rental program.


Environment and Safety - The VRFB does not have operational hazard issues. The system operates at ambient temperature and pressure unlike many competitive systems.  In addition, there are no disposal issues since the Vanadium does not degrade over time, is totally re-usable thus making this system environmentally friendly - unlike many other battery technologies. We have engaged with the EPA in relation to the technology and they see no permitting issues.


Scalability – REDT’s R&D team is now working on a utility scale stack design which is based on a ‘flow by’ operation as opposed to ‘flow through’. This will allow individual stacks to be scaled up to 20, 50 or 100kW. Stacks are arranged in series parallel strings to allow systems up to 10MW or larger. Multiple electrolyte tanks will also allow scaling of discharge duration up to 100MWh or larger.

The Product

The product consists of the two main system components: the stack and the electrolyte. The system is flexible, scalable and modular. Since the product can separate time and energy, customers can create a system which is uniquely configured to the required specifications e.g. by varying the number of hours (liquid electrolyte) or rating (number of stacks) required for different applications.

REDT - Flow Battery For Effecient Energy Storage REDT - Flow Battery For Effecient Energy Storage




The modularity of the product introduces flexibility and the ability to cater for a wide range of applications:




5kW x 2-20hrs Off-grid power supply
UPS (Uninterruptible Power Supply)
Off-grid telecom towers
Data centres, hospitals
10kW-100kW x 2-20hrs Renewable off-grid power supply Small to medium wind and solar
100kW to 10MW x 2-20hrs Utility scale energy storage Renewable energy generation
Grid support


The lead product developed by REDT is the 5kW x 6hrs system (called ENIFY). It is housed in a sub assembly frame as shown in the image below (shown without the additional external casing that would cover the entire system).


REDT 5kW x 6hrs system - ENIFY REDT 5kW x 6hrs system - ENIFY

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