Again, you exaggerate the fluctuations in energy demand. This is a good primer on the hourly and seasonal fluctuations of electricity demand: https://www.eia.gov/todayinenergy/detail.php?id=42915

Even in the summer in Texas, where we experience the largest demand fluctuations, minimum demand is around 60% that of peak demand. And this is indeed a good use case for rooftop solar, especially since it can be used to power A/C in the same building on which its mounted - I never said we should have zero solar power, just that it's infeasible to use for the primary source of electricity. Rooftop solar is indeed a good way to mitigate A/C power draw. But outside of summer peak and minimum power draw is only about 20% difference, and again the peak power is at night.

I don't doubt that nuclear power is expensive. But at least is feasible to build. "Feasible but expensive" is much better than "not feasible regardless of cost". Intermittent sources are only feasible in a grid backed by fossil fuel and hydroelectric sources that can flexibly respond to solar and wind's variation. Once you enter the realm of a predominantly renewable grid, this changes drastically. Storage at a scale anywhere close to what's required to smooth the intermittency of renewables is not even feasible regardless of cost. No amount of money is going to provision the amount of storage required to smooth out the daily fluctuations of solar, let among the seasonal variations of both solar and wind. Overproduction and HVDC connections only take you so far unless you're going to cross the Atlantic (which is also of dubious feasibility). Even just a few hours of storage is well outside of reach. Don't be misled by a handful of battery stations in the MWh scale: actually trying to providing 2 TWh of storage would cause prices to skyrocket because production cannot remotely fulfill that level of demand. Not to mention it'd kill electric vehicle adoption.

This is why most proposals for a primarily renewable grid involve a novel storage system. Will hydrogen, or compressed air, or giant flywheels deliver the required scale? Maybe, in the same vein that maybe deep-drilled geothermal power will deliver cheap decarbonized energy. Those are unknown factors in that one cannot assume will work out. Would you consider it a reasonable plan to assume deep-drilled geothermal will solve decarbonization? After, Iceland has used geothermal for decades, and we have lots of experience drilling for oil? This is how we ought to regard things like hydrogen electricity storage or ammonia: they're in the realm of possibility not feasibility.

Again, it's not a question of cost it's a question of what's even possible without an engineering breakthrough. Maybe we'll figure out a way to build storage at grid scale. And maybe we'll figure out geographically independent geothermal power. But both of those are things not presently within our technical capabilities.

> ...and take the plant offline for weeks to refuel etc, then things look much worse.

Nuclear has historically had the highest capacity factor of all generation sources [2]. This hasn't been an issue with existing generation sources with even more downtime, so why would it be an issue with nuclear?

1. https://www.deegesolar.co.uk/do_solar_panels_work_in_the_win...!

2. https://www.eia.gov/tools/glossary/index.php?id=Capacity_fac....