Friday, April 15, 2011

Redox Batteries at Less Than Half Price?


New Life
70% Extra Capacity
for Old Redox Batteries?

I have written a number of times about the need for electrical storage in wind-generated energy. One of the current ways of doing this is the Redox or Flow Battery. There are various incarnations of the flow battery; one of these is the “vanadium” ion flow battery.

The general use of vanadium redox batteries has however been limited by both high capital cost and by their inability to work well in varying temperatures, especially in high temperatures. At high temperatures they require very costly cooling systems that also have the disadvantage of using up quite a bit of the electrical power.

Recent findings might indicate that this 20+-year-old technology could get a new lease of life simply by using a modified electrolyte; the performance could be greatly improved.

Half  Price Redox Batteries?

A researcher team at the US D.O.E Pacific Northwest National Laboratory experimented with adding hydrochloric acid to the sulphuric acid typically used in vanadium batteries. They thus increasing the batteries' storage capacity by as much as 70% and at the same time, greatly expanded the temperature range in which they can efficiently operate.

The ability of a Redox battery to store electricity depends on how many ions it can pack into the electrolyte. Vanadium Redox batteries traditionally use sulphuric acid as the electrolyte. Sulphuric acid is limited in the number of ions it can absorb and another drawback is that the batteries have a very limited working range of temperatures, just 10 to 40 C.

On the lower end of that critical temperature range, the ion-infused sulphuric acid crystallizes, and over the top end, and the battery overheats, causing unwanted chemical reactions and the formation of solids which could permanently damage the battery. In order to maintain the optimum working temperature range, various temperature maintaining systems need to be used which result in up to 20% efficiency loss.

The research team experimented with various mixtures of both hydrochloric and sulphuric acids. They found an “ideal balance” when they mixed 6 parts hydrochloric acid with 2.5 parts sulphuric acid. Their tests indicated that the new electrolyte mixture could hold 70% more vanadium ions, giving the battery essentially 70% greater capacity.

The new electrolyte also gives the battery the ability to work in a very broad range of temperatures from -5 to +50 Celsius. This means more flexibility and by reducing the need for cooling etc., it significantly reduces both the capital and the running costs. The new electrolyte has the same general efficiency at room temperature as the old one. Giving 87% efficiency over 20 days.


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