When power reserves dropped steeply Wednesday evening, pushing the Texas power grid into emergency mode, people had a lot of theories about what happened. Did a large power plant suddenly break down? Did the shorter fall days cut solar power just when we needed it? Was it something else entirely?
ERCOT, the Electric Reliability Council of Texas, which operates the state grid, initially remained quiet. But, by Thursday evening, one main cause had come to light. It had to do with a longtime challenge facing the state’s grid: bottlenecks on vital transmission lines that move energy across the state.
So-called “congestion” on transmission lines has long been a problem on the Texas grid. It happens when lines don’t have the capacity to move all the energy that is being produced in one place to the place where it is needed. This congestion puts the transmission at risk of being overloaded, and power along it needs to be cut.
This problem usually results in higher energy costs in some regions of the state than others, because some parts of the state have plentiful energy — often from inexpensive renewable sources — while other regions suffer from scarcity. One report estimated that congestion cost Texas ratepayers over $2 billion in 2021.
But, on Wednesday, congestion also helped bring Texas close to its first blackout since 2021.
What happened to the grid in South Texas?
During the power emergency, ERCOT worried that a transmission line that runs power from South Texas to the rest of the state could overload with electricity. That put the transmission line itself at risk of, essentially, frying. Rather than risk the line tripping off or breaking down, ERCOT cut the flow of power running over the system right when people needed it most.
Given the fact that the power was moving from wind-rich South Texas, it seems likely it was wind-generated electricity that was curtailed.
That complicates the grid operator's frequent suggestions that low wind output is responsible for this summer’s requests for energy conservation. There was, apparently, wind power being produced in the state on Wednesday. The grid simply didn’t have the capacity to move it.
“All the wind that was on in the south was struggling to get to Dallas to help meet demand,” former ERCOT head Brad Jones told Bloomberg. “So right in the middle of this, ERCOT had to reduce generation in the south to prevent that line from being overloaded.”
Jones says ERCOT needed to cut about 1,000 megawatts. That’s about enough energy to power 200,000 homes, a significant amount of power in an energy emergency.
In an email to KUT, ERCOT confirmed that “a transmission limitation in the south Texas region that restricted the flow of generation out of South Texas to the rest of the grid” factored into Wednesday’s emergency.
Congestion problems persist
It is also possible the same problem could cause another emergency Friday night.
On Thursday, current ERCOT CEO Pablo Vegas wrote a letter to the Department of Energy requesting permission to suspend emissions rules for some power plants, allowing them to operate during this time of high energy demand in Texas.
ERCOT says it needs to allow power plants to pollute more than usual in order to keep the lights on.
In the letter, Vegas outlined the reasons for recent grid instability, citing the transmission congestion that the grid operator has been aware of "for a few weeks." He writes that trouble on the transmission line “required a decrease in output from certain units” on Wednesday and said the same problem may occur Thursday and Friday night as well.
“Such an overload would require ERCOT to reduce output of resources impacting the loading on that element, exacerbating ERCOT’s scarcity concern,” Vegas wrote.
The Department of Energy approved the request.
