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.