'Massive failure': Why are millions in Texas in the dark amid rolling blackouts, winter weather?

Extreme energy demand and overloaded frozen utility plants amid an unprecedented deep freeze in Texas are among the factors that led to nearly 4.5 millions customer without power in the Lone Star State on Tuesday, experts say.

Outages spread across Texas left millions in the dark and bitter cold amid single-degree temperatures and a winter storm that buried the state in snow and ice in recent days.

Power outages across Texas

"No matter which way you cut it, this is a massive failure for a grid and a state that holds up energy and electricity as a shining example," said Varun Rai, the director of the Energy Institute at the University of Texas at Austin.

During a Tuesday press conference, representatives from the Electric Reliability Council of Texas (ERCOT), said there are 45,000 megawatts offline. Of that, 15,000 megawatts are wind and 30,000 are gas and coal. Between two and three million customers were without power as of early Tuesday evening.

45,000 megawatts of power offline in Texas

ERCOT, which manages about 90% of the state's power for 26 million customers, has said it is instituting rolling outages across the system to prevent more outages as it worked to restore power for Texans.

Gov. Greg Abbott called the situation "unacceptable" and said he would be adding an emergency item to the state's legislative session on reforming ERCOT. The non-profit corporation is subject to oversight from the Public Utility Commission of Texas and the Texas Legislature.

"Far too many Texans are without power and heat for their homes as our state faces freezing temperatures and severe winter weather," Abbott said.

States with power outages

Why is Texas having power outages, rolling blackouts?

Daniel Cohan, an associate professor of civil and environmental engineering at Rice University, said that, at the most basic level, the outages have been caused because demand amid the bitter cold has outpaced supply of energy that is used to heat and power homes.

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A combination of mostly natural gas, some coal and a nuclear power plant failed to meet up with the demand that customers had, Cohan said.

Texas net electricity generation

According to ERCOT, supply fell short by about 34,000 megawatts (MW) of energy. For comparison, ERCOT said that when it restored 2,500 MW on Monday, that was enough power to serve 500,000 households.

Cohan said three different factors were likely at play, though it's too soon to say to what degree each played a role in causing the outages.

First, some power plants may not have been operational due to routine maintenance, Cohan said. Peak demand typically occurs in the summer, so it's not unexpected for a coal or natural gas plant to be offline in an effort to tune up for the warmer months.

Second, some power plants may have failed to operate in the cold, Cohan said. "Plants are optimized to run under our typical and our extreme summer conditions but they aren't as well prepared and engineered for extreme cold," he said.

According to Rai, if plants operate for too long in too extreme of conditions, it could be too costly to operate as well as cause damage to the equipment, which could further exacerbate the outages for longer periods of time.

Third, some natural gas plants may not have been able to get adequate supply of gas to be converted into electricity, Cohan said. Unlike a coal plant that has an ready stockpile, natural gas plants don't store as much on site, meaning any disruption at the supply source will lead to a disruption in turning on the lights.

Carey King, an assistant director and research scientist at the Energy Institute at the University of Texas at Austin, said it's possible that power outages at natural gas production sites lead to failures in the electric compressors that move the gas.

"This is far beyond what the power system operators expected, a far deeper freeze and a far worse performance form our natural gas power plants than anyone anticipated," Cohan added.

To help offset potential outages, ERCOT told customers on Sunday to conserve power by turning down thermostats, turning off and unplugging appliances and lights and avoiding large appliances.

Cohan said some large industrial and petrochemical plants not operating at full capacity this week likely helped the situation, too, by decreasing the overall demand.

Rai said conservation was necessary to lessen the problem, but the issue was not at the margin. "The reality is very, very large. 30-50% of capacity in parts of Texas went down," he said. "You're not out 5 to 10% of the power."

ERCOT also said it was implementing rolling blackouts on Monday to "to protect the electric grid from uncontrolled, cascading outages."

However, instead of the outages being spread across neighborhoods in shorter intervals, some areas have lost power for days while others have kept it the entire time, Cohan said.

Are frozen wind turbines to blame?

Some have pointed to freezing on wind turbines as a potential cause of the widespread outages, arguing the renewable energy source was not reliable, but Cohan said these arguments were "a red herring."

According to Rai, there are times of the year when wind is an extremely important energy sources for Texas, powering half of the state's electricity supply.

However, this week, operators knew and planned for much less wind capacity, in the range of 1,000 to 3,000 megawatts, Cohan said.

So called "firm resources" such as gas, coal, and nuclear, failed to supply around 30,000 megawatts, which contributed to the bulk of the problem, Cohan said.

Why was Texas not prepared for this?

In 2011, a similar deep freeze event caused widespread power outages in Texas, but the extent of the outages was not as great, Cohan said.

Grid operators did learn some lessons from that experience and made adjustments, but clearly underestimated that demand could rise even higher, Cohan said.

Still, Cohan said issues on the supply side better explain what happened. "I think there wasn't enough planning for how interdependent our natural gas and electricity systems were."

Every summer during peak demand, the grid's reliability comes into question, Rai said, so it shouldn't be a shock that there could be a weather event that caused so much disruption.

However, even though it occurred in the winter, there should be better planning, he said. While climate change typically is thought of as leading to warmer temperatures, it also causes more unpredictable and severe weather. Blaming the failures on this cold being a one-in-thirty-years weather event is not an excuse, knowing that those events could become more common, he said. "Why are we only thinking about 30 years as a society?"

"One solution is if you can have capacity that is designed for conditions like this," Rai added. King said incentivizing power plants to better weatherize should also be prioritized.

While having that energy capacity is costly, that there have been two power outage events in 10 years because of the cold shows that it is necessary and should be incentivized, he said.

Follow USA TODAY's Ryan Miller on Twitter @RyanW_Miller

Carlie Procell, Janet Loehrke, Barry Harrell, Javier Zarracina, and Shawn Sullivan contributed to this report.

This article originally appeared on USA TODAY: Texas weather, power outage: Rolling blackouts leave millions in dark