I definitely suggest Practical Engineering's power grid series for a better explanation about how this stuff works, but grid balancing is certainly nontrivial.
Edit: You can actually see realtime transmission outage data via OASIS (http://oasis.caiso.com/mrioasis/logon.do), under the Transmission -> Transmission Outages tab. There are other tabs in OASIS that show related grid factors too.
They also don’t cite any credible sources for their claims that CA is headed to a power glut.
The authors do not seem to realize that transition to EVs will require to at least double the available electrical capacity.
If a power plant takes ten years from beginning to first megawatt, you need to be approving plants ten years before the one they’ll replace goes offline.