They both provide non-dispatchable power. Renewables have a slight edge at moderate penetration with no storage because you can turn them off whenever you want without incurring massive costs and solar output is biased towards peak time.
Then there's hybrid PV-CSP which is available in about half of the world and is dispatchable. I guess you're probably right in that nuclear doesn't compete because hybrid CSP is vastly cheaper even in FOAK form and dispatchable power is superior.
No it isn't. Ramping is slow and can't be done beyond 20% very often or you destroy your fuel and control rods
Reducing output doesn't reduce costs, it increases them. This is the opposite of dispatchable.
If you can only pay for your reactor by coercing people into buying daytime electricity for 20c/kWh rather than buying a solar panel that will pay for itself in 3 years then it's not dispatchable.
You don't need to alter the thermal output of the reactor to modulate a nuclear plant's electrical output. You can more aggressively cool the reactor to reduce the energy delivered to the turbine. This isn't often done since it's essentially deliberately reducing the efficiency of the plant.
> Ramping is slow and can't be done beyond 20% very often or you destroy your fuel and control rods
It's not slow: the turbine water is can be cooled more aggressively immediately, and will start reducing output with one circuit of the generation turbine. Also, modulation only needs to vary 20-30% over the span of entire days not of tens of seconds. And no, dispatchable generation does not ramp in 10s of seconds. Natural gas plants - the most popular peaking generation plant - still takes an hour to activate. But this isn't an issue because electricity use doesn't fluctuate by 20% in the matter of tens of seconds.
Then there's hybrid PV-CSP which is available in about half of the world and is dispatchable. I guess you're probably right in that nuclear doesn't compete because hybrid CSP is vastly cheaper even in FOAK form and dispatchable power is superior.