By Katharine Jackson

WASHINGTON Texas' electric grid operator asked residents and businesses to conserve energy on Sunday as its reserves were expected to decrease during a scorching heat wave that has caused demand to surge.

The Electric Reliability Council of Texas (ERCOT) issued an appeal for conservation from 4 p.m. to 9 p.m. local time (2100-0200 GMT) on its website, saying reserves could run low due to high demand and a lack of wind and solar power generation.

"We request Texas businesses and residents conserve electricity use, if safe to do so," ERCOT said in a statement posted on X, formerly known as Twitter.

ERCOT had issued another conservation appeal for the afternoon and evening on Saturday, which was lifted at around 10 p.m. that night.

An excessive heat warning remained in effect for Houston and Galveston, Texas, on Sunday as "dangerously hot conditions" with high temperatures that could reach 110 degrees Fahrenheit (43.3 Celsius), the National Weather Service said on Sunday.

The fragility of the Texas grid was highlighted in 2021, when a massive blackout killed dozens and left millions without power, water and heat for days as gas supply lines and power plants froze.

(Reporting by Katharine Jackson; Editing by Bill Berkrot)