[ijames]

Well, that diagram above shows two electrolyte tanks, one that starts out with a vanadium salt in the +2 oxidation state that gets oxidized to the +3 oxidation state as power is produced, and the other tank has a vanadium salt that starts in the +5 oxidation state and gets reduced to the +4 oxidation state. Actually, they don't have to be salts but it is most likely they are. So in the loosest sense, both tanks contain "salt water" because they contain water with a salt dissolved in it, but it isn't sea water and it isn't sodium chloride which is what everyone thinks of when you say salt water. I'm sure some chemist (don't you hate those guys, um, us :-)) said the tanks contained a salt solution and some advertising flak took that to mean sea water.

Think of this as a primary battery, non-rechargeable, like an alkaline cell. As power is produced the electrolytes are consumed, but instead of changing out the entire cell they just pump in fresh electrolyte. Since they will get cooling from the flow as well, they probably get a nice boost in current density before meltdown, too. However, to regenerate the electrolytes they have to take them out and go do some other processing, probably with different electrodes for better efficiency or maybe even adding a different reagent to do the oxidation and/or reduction that they can then remove and regenerate, so you can't just recharge in place.