During very cold weather, wind speeds fall dramatically, and ERCOT only expected 7% of generation capacity from wind. Cloudy weather limited solar generation.
It turns out only about half the natural gas capacity was available, reducing total capacity to 59,000 MW compared to 69,000 in demand. ERCOT raised power prices to the $9,000/megawatt-hour cap from the usual $25 to $50 range to discourage use.
ERCOT can call on large industrial electric customers to curtail use. Still, the reaction just wasn’t fast enough, so circuits either tripped or were shut down by ERCOT. Texas is unique in having almost no connection to power from other states in an emergency.
In winter, much of the natural gas supply goes directly into heating furnaces reducing supply for power plants. There is very little storage for natural gas. Instead, new production is supposed to keep the pipeline full, and high compression pressures increase capacity in the pipelines themselves. Cold temperatures froze wells and pipeline valves reducing volume, and pressure.
As recently as 2015, coal capacity was 40% higher, but coal plants have been shut down. After the 2011 weather event, a study recommended winterization infrastructure be added, but additions were only partially implemented.
Going forward, ERCOT needs to get serious about completing weatherization improvements instead of continuing to add more unreliable wind and solar power.