Mid-day is off-peak for solar in many markets, and they curtail their output so that they don't oversupply. As there is more solar built, more and more will be curtailed.

Both nuclear and solar would need a hydrolysis system that was economical even if not run 24x7 in order to utilize their supply-demand mismatches. This is the biggest road block to hydrogen production with the GWh of "free" electricity that we could currently be generating in the spring in California, but currently just don't use.