Melting aluminium is an *ideal* use for unreliable power: the primary cells can run at variable rates or even in reverse to stabilize the grid, or some of the molten product can be staged for running optimized Al air batteries. Germany is already doing this,
From that link, other energy-intensive processes may be suitable, "including those used to manufacture cement, paper, and chemicals. Making chlorine, used to produce paper, plastic, fabric, paint, drugs, and antiseptics, also requires electrolysis."
Don't forget Ammonia, by fixating Nitrogen from the atmosphere.
About half the "green revolution"(*) was due to availability of Ammonia due to the Haber process, which means our ammonia production supports about half the food production on the planet.
Haber is energy intensive, requiring half a million Joules of energy per mole (17g) of ammonia produced, which comes out to about 5% of all energy used worldwide.
It's largely startable/stoppable, so would make another good choice for unreliable or unneeded (ie - solar panels in uninhabited areas) power.
(*) The other half due to pesticides.