Huh? How do you get the electricity back out of the aluminium?

Oh, OK, I get it.

Region A consumes a lot of electricity smelting aluminium. Region B has cheap electricity so a smelting company moves there and ships the aluminium to region A. Region A now has one smelting company's worth of extra electricity available.

Smelting aluminum from ore requires a lot of electricity, more so than any other common metal. It's sufficiently high that the dominant factor in the price of aluminum is the cost of electricity used to produce it (and not the cost of the ore or transporting ore and finished product), so smelting aluminum is a relatively easy way to export electricity.

They are just pointing out that the price of aluminum production is largely dominated by electricity costs. Effectively all excess electricity can be used my aluminum producers.

You don't. You use the aluminium instead of aluminium from a less clean source you'd usr otherwise.

Then I don't understand how "Aluminium is pretty much electricity in a form that can be put on a truck".

It is called a "figure of speech".

OK, so interpret my question as asking for an explanation of the figure of speech!

It's a little bit surprising to get such pushback on a genuine question when there are substances you could describe as "electricity you can put on the back of a truck" such as hydrogen canisters and various forms of battery!

OP here...

As others have said, I was mostly referring not to the ability to easily convert to and from aluminium, but instead the fact aluminium is easily transportable and such a useful material that there is rarely surplus (if aluminium were cheaper, it would take over lots of places where steel is used, and even some uses of concrete).

That in effect means that if there is excess electricity in a region, it can in many cases work out cheaper to build a decent road to the region and build aluminium smelters than to build power transmission lines out of the region.

I think the OP just used this figure of speech to illustrate the amount of energy that goes IN, not to say that you can get it easily out again.

But then there is this: https://en.wikipedia.org/wiki/Aluminium%E2%80%93air_battery so who knows.

Aluminium plant moves to location with cheap electricity.

The electricity becomes available at its former location.