"Baseload" is load, not generation. It's not necessary -- for example the small northern grids that only have diesel generators operate fine even though they have no generators that don't have the capacity for quick cycling.
Baseload was a cost optimization. Back in the day it was cheaper to build coal & nuclear plants that took days to power on. Somebody figured out that if a grid was built of a mix of those cheaper plants and more expensive plants that could start up quicker, it would lower costs. The typical grid was baseload coal and gas peakers. But ~20 years ago gas peakers became cheaper than baseload coal and any need or desire for baseload generation went away.
China is building a lot of coal plants to complement their solar buildout. Notably these are not base load plants. Their new coal plants do not run 24/7, they only run at night.
Similarly, many new nuclear plant designs are not base load designs; they are designs that can be safely and quickly turned on and off.
P.S. the correct term for generation is "non-dispatchable", not "baseload"
> Their new coal plants do not run 24/7, they only run at night
That’s baseload! Baseload is load you can’t turn off: the minimum load that’s required in a 24 hour period. It can be fulfilled with non-dispatchable sources, but it need not be. In this case, China is building coal plants to address the baseload that doesn’t go away at night when the solar isn’t producing.
Note that China has started building battery banks at massive scale recently.
Is china building new coal plants or not?
Do you want to hazard a guess as to why?
The answer is because we still do not know how to supply expanding electricity demand with wind, solar and batteries. The side of the story that people on this website love to bring up is the fact that China happens to be the largest builder of solar and wind, which is true, but the increased electricity demand is being met via coal, for the most part.