With a few SMR projects built and operational at this point, and more plants under development, the Institute for Energy Economics and Financial Analysis (IEEFA) concludes in a report that SMRs are “still too expensive, too slow to build, and too risky to play a significant role in transitioning away from fossil fuels.”
That is why you overbuilt solar and wind and also add storage. Wind and solar can easily be shut down, so that is an option or the electiricty can be used for making heat and storing that, charge up EVs or something similar. So doubling the average needed solar + wind and having enough storage to balance out a day is enough. Also things like biomass and even more importantly conventional hydro storage are good options. Norway for example has 86TWh of hydro storage alone today.