Rotating power outages were put into force in Texas as the state’s electricity grid operator grappled with surging demand amid a bitter arctic chill. The Electric Reliability Council of Texas, the grid operator, ordered transmission companies to reduce demand on the system after reserves dropped below 1,000 megawatts, according to a Monday alert posted on its website.

About half of the state’s wind turbines were inoperable Sunday morning because of ice and cold, according to the Electric Reliability Council of Texas, the grid operator. Meanwhile demand is surging as people crank up heaters, with consumption setting a new winter peak record on Sunday.