It's not like you can ramp a coal-fired or nuclear power station up and down on a whim either though. It takes time and planning to modify the output if you don't have storage capacity. Power companies do a lot of predictive analysis to forecast demand and make sure they're running a little ahead. Here in the UK we even have a term called "TV pickup" where the electricity demand for the country increases significantly immediately after popular TV shows when we all go and put our kettles on for another cup of tea[1].
Power demand varies a lot, and in a reasonably predictable way, so you're fine so long as you have a mix of generation technologies. For most places that'll end up being solar, wind and nuclear, with extensive storage capacity.
At least nuclear you can relatively fast. In terms of KW/min change rate faster then most gas peaker plants. It is not done much outside of France though as the operating costs of a nuclear power plant are pretty much identical when operating at 5% or 100% output.
edit:
German nuclear power plants also used to do load matching.
https://www.oecd-nea.org/upload/docs/application/pdf/2021-12...
Source for the KW/min change rate of nuclear vs CCGT/coal
https://snetp.eu/wp-content/uploads/2020/05/SNETP-Factsheet-...
Those types of real time viewing figures are limited to live England matches in the euros/World Cup, and very unusual events like the PM’s covid broadcast back in 2020
I’m surprised the US doesn’t have the phenomenon during the super bowl. I guess the lack of kettles and the main attraction of the Super Bowl being the adverts dampens it down though.
You can with nuclear: thermally it is kept running, but the steam bypasses the generators and so there is no electrical production.
Even if California made it the final 3% to reach 100% renewable energy (by the headline metric), it will still depend on a significant amount of non-renewable energy for significant parts of every single day (or else it will have blackouts).