It doesn’t freeze, for one (well, or, not in a way that impacts operation - it works with solid aluminum).
The concept is that you have a centralized “reprocessing” plant that does the high temperature work on surplus PV exported to the grid, and gets you aluminum pellets that you can use locally for heat and power. Waste is shipped back to be reprocessed.
In the winter, you run the pellets through a reaction that gets you heat (for building heat), hydrogen (for a fuel cell for power), and the waste that’s then processed again.
I don’t know enough about aluminum metallurgy to really evaluate what they’re doing, but it sounds like once you’ve gotten to aluminum, the process is circular, especially if you’re not using carbon based electrodes for the smelting.