[dest]

The energy density of the system is surprisingly high (in my modest perspective). It looks like 800kWh per ton of iron. Isn't it ~five times as much as the batteries we have in cars?

[ben_w]

I've seen claims up to 300 Wh/kg for batteries, but yes this is still more than that.

[AtlasBarfed]

Is that lithium iron or for sulfur chemistries?

And for good batteries their density doesn't really matter.

Sodium ion batteries will be fantastic grid storage simply because they're just going to be dirt cheap