Something that I have yet to see mentioned in these articles - and don't get me wrong, I don't disagree with the conclusions that ERCOT fucked up and the competitive system isn't far enough forward-looking to incentivize grid improvements- is that this happened on the back half of a four day gas trading weekend. So not only was it a five or six sigma weather event, it was also really bad timing on the trading calendar. Had this happened on a non-holiday weekday, a lot of the power supply issues would have been avoided or minimized. (Some other poster way upthread alluded to this when he was talking about buying gas for his power plant)
For the most part, these resources are traded and managed "day ahead", meaning that gas is purchased and power sold and plants brought up or down the immediate day before. (There is something else called "real time" but that is more like fine tuning what is already up and running, you don't usually startup cold power plants in RT)
It's hard enough to schedule and manage supply for normal weekends, which cover Saturday, Sunday, and Monday. Saturday and Sunday have lower demand than Monday, but you have to trade the same amount of product for each day and then you manage it during the day after the schedule is set. Saturday and Sunday positions will sometimes get closed out at a loss with the expectation that Monday's profit will make up for it.
For Monday holidays, they add Tuesday to the weekend package, so now you are trading four days of equal volumes and price but you have a different load profile on each of those days.
Last Friday, when the cold was on its way here, it was already in Oklahoma and points north, and that caused gas prices to spike in those areas. Where gas is normally $2 or $3 per MMBTU it was $100 or more. And it was so cold up north that a lot of their wells were frozen off and unable to supply, so they were buying gas in South Texas and shipping it north, which made the price of South Texas gas - "Houston Ship Channel", "Waha", "NGPL STX" - spike as well, FOR THE WHOLE FOUR DAY WEEKEND. Instead of the usual $3, it was trading $200. 10-20x higher than it has ever traded.
Well, ERCOT underestimated the demand on Monday and a lot of Texas generators woke up on Friday and looked at the Ship Channel price for the four day package and said, "Fuck that. That's too expensive." and they shut their plants down for the 4 day weekend. Then when the shit hit the fan on Monday, those plants were all cold and there wasn't any gas to run them anyway because it had all been exported north AND the wells in Texas were frozen off too AND one of the STP nuclear units got shut down because the water intake was freezing.
And that's how you end up with no power supply when demand is going through the roof.
As I said at the beginning, had this happened on a normal weekday, a lot of those resources would have been online and available. The bad forecast for the back end of a four day weekend with record gas prices is a big part of why the power grid went down.
Also, as mentioned above, Houston generators got socked the hardest because there is a very large amount of gas generation here AND it is a gas trading hub AND it typically doesn't get as cold here so the plants are more susceptible.