Some Texas power plants unexpectedly went offline last week. The grid operator says it still doesn’t know why

Last Monday, Texas’ main power grid operator asked Texans, mid-heat wave, to turn their thermostats to 78 degrees during the afternoon and evening for the week to reduce electricity demand on the grid after 12,000 megawatts of power generation unexpectedly went offline — enough to power 2.4 million homes on a hot summer day.

By the end of the week, that appeal from the Electric Reliability Council of Texas expired without a public announcement, and ERCOT officials still have not …