The Electric Reliability Council of Texas asked consumers to limit or reduce power usage from 3-7 p.m. Thursday.
ERCOT officials in Austin say usage Wednesday surpassed 67,000 megawatts for the first time since 2011. Demand for the day peaked at 67,590 megawatts.
One megawatt is enough electricity to power about 200 homes during the highest demand conditions and about 500 homes during a mild spring day.
Systems operations director Dan Woodfin says some power plants have had unplanned outages, including less wind generation available.
ERCOT in March said electric users should have sufficient supply for summer, estimating peak demand at 69,000 megawatts. ERCOT predicted nearly 77,000 megawatts of available generation resources.
Consumers can help ensure the system is able to continue serving current power needs by taking the following steps to reduce demand on the system during the 3-7 p.m. peak demand hours:
The Associated Press contributed to this report.