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.