Nuclear can absolutely produce power on demand

so slight correction here, they don't produce power on demand, unless we include energy storage, but that's the storage not the plant, nuclear plants are explicitly designed to be a base load service. Which is incredibly well suited to be paired with cheap renewables like solar.

Nuclear plants often have a capacity factor of close to 100%, and sometimes even over it. Though usually it's 80-90% for most plants. Gas plants are often 40% ish, hydro is even lower, 20-30% is really common for hydro, especially if it's stored. Though actual hydro plants can realistically run for most of the year, and will more than likely have a more considerable capacity factor, probably somewhere around 60% or higher.