This weeks New Scientist is running a story about a improved method of storing electricity (you need a subscription to read the whole article) from wind or other transient renewable energy source. It uses flow batteries which store up electricity as chemical energy in the same way as conventional batteries, except that the electrolyte is drawn out and stored up in tanks. Charge flows across a membrane between two solutions however the membranes in previous batteries had been known to leak.
This [research] focused on one of the big weaknesses of these devices. The
membranes separating the two electrolytes allowed molecules of electrolyte to
leak across. As a result, each solution became increasingly contaminated with
the other, reducing the battery's output.
The type of battery featured in the article - at Kings Island Australia - gets around this by making both solutions with vanadium in different oxidation states.
Best of all, it didn't matter too much if a few vanadium
ions on one side of the membrane leaked across to the other: this slightly
discharged the battery, but after a recharge the electrolyte on each side was
as good as new...
....One of the key advantages of flow batteries is
their scalability. To increase peak power output you add more battery cells, but
the amount of energy they will store - and therefore the time they will operate
on a full charge - can be expanded almost indefinitely by building bigger tanks
and filling them with chemicals. The result is that the batteries can be used in
a wide range of roles, from 1-kilowatt-hour units (like a large automotive
battery, say), to power-station scales of hundreds of megawatt-hours.
Research into these batteries is continuing.
Vanadium sulphate solutions cannot be made very concentrated
so the energy stored in a given volume of vanadium flow batteries is about half
that of lead-acid batteries. This rules them out for applications where
compactness and low weight are at premium - electric cars being a prime example.
So Skyllas-Kazacos and her team
want to replace vanadium sulphate with vanadium bromide, which is more than
twice as soluble. She expects that research to be completed by 2008.
Also in new Scientist(these don't require subscribtion):