It's backup power. The power plants will never pay for themselves, but they enable much wider solar deployment because you can use the plants the 1 day a year when the whole country is cloudy.
Not in China. China has lots of coal but has to import gas, so they build coal peakers instead of gas peakers. China builds their coal plants a little differently so they spin up faster, but mostly they just use plain old weather prediction. 4 hour weather prediction is highly accurate, so they know far enough in advance to know when to spin up the coal.
So, if you have plentiful natural gas, then, yes, certainly, that's what you'll do; it's far, far easier and cheaper. China does not have plentiful natural gas, and is indeed building coal peaker plants.
