Except that aluminum smelting requires near constant power levels or the smelting pots will freeze and need to be replaced. So it's not really relevant here.

The smelteries use hydropower, and the power wasn't just laying around, each smeltery requires building a massive dedicated hydropower plant.

Fun fact: this is why the US aerospace industry grew up in the pacific northwest.

At the beginning of the 20th century we went on a bit of a dam building spree up there (and all over, but heavily up there). Then when WWII broke out and we got a huge demand for airplanes (which require light aluminum), the industry congregated around where there was an excess of cheap hydro. Hence Boeing, Lockheed, and friends all being out of Seattle.

I was just on this https://www.youtube.com/watch?v=-Ss_wHCS1Aw