So, if we want to produce 1,888 millions tons of crude steel with solar panels, and assuming we can supply with Jichuan solar park 10 plants producing 300T of steel:
1,888/3 = 630 steel factory = 630 Jichuan Solar park = 56700km2. It's a bit larger than Croatia. For steel only. And it's assuming ideal production, only solar panel surface...So it could be Ireland actually.
As for the "nice in theory", my small demonstration is actually in this ball park, because the other dead-spot is that I account for electric production. It represent ~30PWh and worldwide consumption of energy is ~180 PWh (85% of those are from fossil).
So this 5% increase of renewable energy, of total electricity production, is actually swimming in those 15%.
The main obstacle for investment is political stability and alignment.
Most of the world's steel is produced from ore, which not only requires three times the energy of recycling scrap but also vast quantities of carbon from fossil fuels to incorporate into the alloy. I believe there's a relatively new electrolytic process for the ore but at far smaller scale and it requires even more power.
I'm not an expert in arc furnaces, but I would be a little worried about steel with is temperature bouncing around its melting point, as power becomes available or not. Both from energy wasted due to cooling while the process is paused, but also freeze cycles inside the furnace.
I also think steel is a fairly capital intensive production, which doesn't help either.
Also, another thing that's good about these types of energy intensive industrial operations is they can essentially act as a sort of battery - it's a large load on the grid but (I'm guessing, someone correct me if I'm wrong) could potentially be more flexible with respect to time shifting: if it's a bright sunny day, crank up the furnaces to full speed, but if it's cloudy, back off. That helps make solar installations more economical if there is a good chance something will be there to take up extra power.