Innovatory energy storage could boost renewables

Patented technology differs from conventional batteries in that it stores energy in a liquid

A battery technology that promises to vastly improve the industrial-scale storage of renewable energy is being tested in Scotland.

RedT is installing its 1.68MWh Vanadium Redox Flow Battery (VRFB) energy storage system on the Isle of Gigha, off the west coast of Scotland, to manage grid constraints associated with four community-owned wind turbines on the island. The Gigha system is the largest energy storage unit RedT has produced to date and is expected to enable as much as 30% more power to be used from these turbines.

The VRFB units are modular and can be stacked together to create larger energy storage systems.

The patented VRFB technology differs from conventional batteries in that it stores energy in a liquid, as opposed to a solid-state cell. The technology relies on the ability of vanadium to exist in four different oxidation states, each of which holds a different electrical charge.

On charge, vanadium electrolyte is pumped through the central stack containing an ion-exchange membrane, which separates the positive and negative half cells. A reversible reduction-oxidation (“redox”) reaction takes place where the vanadium ions in the positive half-cell give up an electron. This electron is transferred over to the vanadium ions in the negative half-cell, causing them to change. On discharge, the redox reaction is reversed. This creates a surplus of electrons at the negative terminal, relative to the positive terminal, causing an electric current to flow.

Richard Flynn, product manager at RedT, said: “Our technology does not degrade like conventional lithium or lead-acid batteries and has a lifetime of up to 25,000 cycles, which equates to over 20 years’ service.

“The technology also has a 100% usable depth of discharge so the energy storage machines can be heavily cycled on a daily basis without suffering degradation. And because the charged electrolyte is contained in two separate tanks there is no self-discharge over time, meaning that the system can be left idle for long periods without any loss of charge.”