Some things that are easy in theory are not as easy in practice.
In theory it's so easy to build lots of huge solar power plants. We all know that solar is dirt cheap, because we've all seen the Lazard report with the levelized costs of energy.
In practice, here's the list of solar power stations in California [1]. None is close to 1 GW. Only 3 are above half a gigawatt nameplate capacity. But their capacity factor is on average less than 30%.
Or to put it differently, 20% of the electricity generated in California comes from solar, and 9% from nuclear (i.e. from Diablo). If you want to replace nuclear with solar, you need to increase the current solar generation by 50%. That's doable, but it's not something you do overnight, it will very likely take a few years. Meanwhile, guess what you'd use to replace Diablo? Of course, it would be natural gas, which, by the way, accounts for 47% of the current generation.
We've heard the story of nuclear being replaced with renewable in my state, New York. Two reactors, with a combined capacity of 2.1 GW were shut down in 2020 and 2021. But instead of renewables, they were replaced with natural gas [2].
> As a result of the permanent shutdown of the plant, three new natural-gas fired power plants: Bayonne Energy Center, CPV Valley Energy Center, and Cricket Valley Energy Center were built, with a total capacity of 1.8 GW, replacing 90% of the 2.0 GW of carbon-free electricity previously generated by the plant.[6] As a consequence, New York is expected to struggle to meet its climate goals
[1]
https://en.wikipedia.org/wiki/List_of_power_stations_in_Cali...[2] https://en.wikipedia.org/wiki/Indian_Point_Energy_Center