Why can't you do those things on solar? Actually, I'd think they're ideal matches. Aluminium smelters use so much electricity that even ones that are connected to non-renewable grids have contracts to ramp production up or down at a moment's notice, to absorb supply and demand swings in the rest of the grid. However much electricity you think they use, they use twenty times that. These are places wired with 100 kiloamp busbars.

The point is they're well used to variable electricity supply. Cloud comes past? No problem, the furnaces run slower for a moment. I think they need a certain base load to keep them hot as they can't restart them if the aluminium solidifies inside.

Aluminium smelting is an electrochemical process. Running electricity through the ore turns it into the metal and that's why they need so much. It's not just electric heating. They use direct current, so that's a good match for solar panels too. Two and a half volts per cell.

Fertilizer is something similar, as far as I know. They use electrochemical arc reactors to make nitrogen compounds from air. These can also scale up and down instantly.

AI training is pretty good too. If a cloud comes past you can pause the training run for a moment or underclock. The firmware for that might not be there yet, but the laws of physics quite like the idea.

Why do you think these particular things require natural gas?