redT energy storage machines use proprietary vanadium redox flow technology to store energy in liquid without degrading.

The technology uses the flow of vanadium electrolyte across an ion exchange membrane.

When this exchange occurs, a reversible electrochemical reaction takes place, allowing electrical energy to be stored and subsequently returned. The technology relies on the ability of vanadium to exist in four different oxidation states (V2+, V3+, V4+ and V5+), each of which holds a different electrical charge.

redT’s storage machines use this ‘flow’ of the vanadium electrolyte, separated by an ion exchange membrane.

The setup of the electrolyte and the membrane stack can be compared to that of an engine and fuel tanks. The membrane stack (the engine) delivers power rated in kilowatts (kW), whilst the vanadium electrolyte (the fuel) delivers energy rated in kilowatt hours (kWh).

When a redox reaction occurs, the composition of the electrolyte changes. This creates a surplus of electrons at the negative terminal, relative to the positive terminal. When the system is discharged, electrons flow from the negative terminal to the positive terminal, generating an electrical current.

The redox reaction is reversed by applying an electrical current to the terminals. This returns the machine to its original state, charging the system.

Modular energy storage
In conventional batteries, power and energy are fixed together in a cell which limits the ability to size the system accurately to the application requirements.

By contrast, redT’s energy storage machines are not constrained by these limits as the electrolyte is stored in tanks, outside of the cell stack, thus separating the power and energy components. This creates much greater flexibility as more electrolyte or stacks can be added as required on a modular basis.

As such, we prefer to use the phrase “vanadium redox flow machine (VRFM)” rather than “vanadium redox flow battery (VRFB)”.

Our flow machines have a technology life of over 25 years.