HOUSTON (REUTERS) - The operator of Texas's power grid on Sunday (July 10) called on state residents for the second time this year to conserve energy, warning of potential rolling blackouts amid predictions for record-high temperatures on Monday.

The state faces a "potential reserve capacity shortage with no market solution available," the Electric Reliability Council of Texas (ERCOT) said in an operating notice on its website, adding that it was issuing an energy emergency alert that advised of the potential for rolling blackouts.

ERCOT, which oversees power to more than 26 million customers, had assured residents earlier this year that it has enough reserves to meet demand after millions of people suffered through a deep freeze in early-2021 that knocked out most of the grid for several days.

Temperatures across the state hit records on Sunday, with 40.6 degrees Celsius recorded at Houston's Bush Intercontinental Airport, surpassing the record of 38.3 deg C set in 1909, according to the US National Weather Service (NWS).

The NWS also warned of excessive or dangerous heat levels for central and east Texas on Monday, with temperatures exceeding 38 deg C.

ERCOT has asked residents to conserve electricity between 2pm and 8pm, saying demand on Monday could reach a record of nearly 79,700 megawatts (MW), not far from its expected 80,200 MW of available reserves.

The grid operator has called for more power from suppliers and has asked large industrial consumers to have their electricity turned off.

It last called for conservation in May, during an earlier heatwave that drove up prices to more than US$4,000 a megawatt hour after six generators tripped offline.

The state's day-ahead market has Monday's prices listed at more than US$2,000 a megawatt hour across the entire state in the afternoon, that is more than twice the peak market price on Sunday.

One megawatt can power around 1,000 US homes on a typical day, but only about 200 homes on a hot summer day in Texas.