Power plant shutdowns
The Electric Reliability Council of Texas warns that more rotating power outages may be necessary during peak demand hours of 6-10 p.m. Wednesday and 6-8 a.m. Thursday.
Consumers are being asked to reduce energy consumption.
ERCOT said the extreme cold knocked out some 50 generating units that supply more than 5,000 megawatts of electrciity.
With the entire grid at risk of going dark, ERCOT ordered rolling blackouts early Thursday.
"They had lost some generation, combined that with the peaking demand at this time, they couldn't keep it in balance," explained Oncor CEO Bob Shapard. "They asked us to reduce load to match that."
Luminant, the biggest electric power generator in Texas, said the unusual cold froze pipes and knocked out gauges in plants that automatically tripped off.
Luminant said its plants were responsible for about half of the 7,000 megawatts suddenly lost.
Oncor — the poles and power lines company that delivers electricity — started blackouts lasting 15 to 45 minutes affecting 300,000 customers at a time.
Important government buildings, hospitals, and downtown Dallas and Fort Worth were exempt from the cutoff.
"People are trapped in elevators other issues with critical city services, so the downtown network is typically not taken off load," Shapard said.
That left businesses and homes to shoulder the blackouts.
"A typical homeowner might see their power out for 15 minutes, come back on, and two or three hours later we'll do it to them again as we just systematically roll through the system," Shapard said.
Lt. Gov. David Dewhurst said this is something that "should not happen." He said the demand placed on the Texas grid was nowhere near peak capacity on Wednesday, adding he was frustrated by the situation.
By 1:30 p.m. Wednesday, power providers brought back enough electricity to halt the rolling blackouts.
And ERCOT urged consumers to conserve all they can, to avoid the need for additional power cuts.
The Associated Press contributed to this report.