You can't just do those things when the weather is good.

Not without huge tax breaks to incentivise load following, because intermittent production of large scale industrial processes is hard and not cheap.

They already do this without any gov intervention. The local steel recycling plant only operates when power is cheap. While they do need some advance notice to make sure they have enough people to run, they probably can get a good enough idea from a weather forecast (power here is mostly hydro with a dollop of wind and fossil).

Some processes are better fits than others. If you have 2-5x extra capacity that is sold cheap on sunny days, someone will figure out how to use it.

Do we have any numbers on what it means that they run only when the power is cheap?

Does that mean they can operate in 4hr windows? Or do they run have to run the furnace for a minimum period? A large quantity of steel takes a large amount of energy to melt.

Interesting question. Brief research says the cycle time is ~1 hour (or less):

http://www.steel.org/making-steel/how-its-made/processes/pro...

It could also be a plant for shredding scrap, where I guess it wouldn't be a time issue so much (and if it doesn't have the material inflows to run full time, timing cheap power would make sense).

Thanks for the link, looks pretty detailed. I work in steel fabrication, so it'll make interesting reading for me.