Custom Power Solutions

Flow batteries allow storage of the active materials external to the battery and these reactants are circulated through the cell stack as required. The first such battery was Zinc/chlorine battery in which the chlorine was stored in a separate cylinder. It was first used in 1884 by Charles Renard to power his airship La France which contained its own on board chlorine generator.

The technology was revived in the mid 1970s.

	Flow Battery

Modern flow batteries are generally two electrolyte systems in which the two electrolytes are pumped through the cell. The great advantage that this system provides is the almost unlimited electrical storage capacity, the limitation being only the capacity of the electrolyte storage reservoirs. Opportunities for thermal management are also facilitated by using the electrolyte as the thermal working fluid as it is pumped through the cells. High power batteries are constructed using a multiple stack of cells in a bipolar arrangement.

The Zinc-Bromine battery is a modern example of a flow battery. It is based on the reaction between two commonly available chemicals, Zinc and Bromine. The battery consists of a Zinc negative electrode and a Bromine positive electrode separated by a microporous separator. An aqueous solution of Zinc Bromide is circulated through the two compartments of the cell from two separate reservoirs. The other electrolyte stream in contact with the positive electrode contains Bromine. The Bromine storage medium is immiscible with the aqueous solution containing Zinc Bromide.

The battery uses electrodes that cannot and do not take part in the reactions but merely serve as substrates for the reactions. There is therefore no loss of performance, as in most rechargeable batteries, from repeated cycling causing electrode material deterioration. When the Zinc-Bromine battery is completely discharged, all the metal Zinc plated on the negative electrodes is dissolved in the electrolyte and again produced the next time the battery is charged. In the fully discharged state the Zinc-Bromine battery can be left indefinitely.

Energy densities three times better than Lead Acid batteries are claimed.

The flow battery technologies provide very high power and very high capacity batteries for load levelling applications on the national electricity grid system.

The so called Redox Battery is an example of a two electrode flow system.

The Regenesys Sodium Polysulfide Bromine battery is another example.

These are very high cost systems and so far there are very few successful installations.