Interesting idea,the fundamental electrochemistry is sound. I always tend to slide toward the door when somebody is getting the word out about their great process but then pulls the old "Can't tell you any details because of (pick one: the patent, the lawyers, the confidentiality agreement etc. etc.)." Nine times out of ten it's the prelude to a snake-oil pitch. I'll give this one the benefit of the doubt, though.

The biggest problem I see with this is the scale needed. Molten metals at 700C are going to take a lot of containment, including a bunch of engineers and technicians that know what they're doing. Small scale won't be practical. They mention an aluminum plant in the piece and that sounds about right for size. Capital cost of several hundred millions to single-digit billions. Solar's not going to feed this thing, it needs DC input and output and the line losses between the solar farms and the storage plant (for pure DC) or conversion losses (for AC transmission plus rectifiers) will destroy the profitability of the thing. Ditto for wind. We're talking many (as in hundreds of) square miles devoted to this thing for solar cells or wind turbines; it's that big.

Maybe there's a niche use. Bay-of-Fundy-size tidal might work. Something like that for a power source. You could use it for supplying peak loads, at peak load prices, which would help a lot with the economics. These are never going to be common but they'd be way cool for people like me who like aluminum refineries and smelters and stuff like that. Can't see how it does much to solve our energy problem but every bit helps.