RALEIGH, N.C. (WNCN) — Duke Energy again Sunday asked for North Carolina customers to conserve energy — after rolling blackouts planned for a half-hour at most kept many in the dark for hours over Christmas weekend.

More than 2,200 customers were still without power on Christmas Day in North Carolina after high winds and bitter cold hit the state Friday. Duke Energy also warned there could be more rolling blackouts Monday.

Nearly 550,00 customers were in the dark on Saturday mid-morning — mostly because of rolling blackouts. The number of customers from storm-related damage was down to about 40,000 just an hour before the rolling blackouts began.

Duke Energy said the blackouts would last just between 15-30 minutes in most cases.

But, at least one customer in Charlotte said her blackout on Christmas Eve lasted three hours.

Dozens of other people on Twitter also complained about the long outages — and no warning.

“I can’t believe Duke Energy cut off power to my Charlotte neighborhood at 7 am on Christmas Eve with no warning & are now saying these are planned outages,” Leslie Mac wrote on Twitter just before 8:30 a.m. Saturday “You didn’t plan well [and] you failed to even auto text your customers to allow us to prepare.”

The company said the rolling blackouts were “temporary outages that were taken to protect Duke Energy customers from more extended outages during extreme temps across much of the eastern U.S.”

But, many customers were upset when outages lasted for hours.

“Our power’s been out for 3+ hours and it’s 16 degrees outside. Apparently, they’re ‘rolling outages’ due to increased demand. No advance warning. Happy Christmas Eve,” a woman named Theresa wrote on Twitter.

On Sunday, Duke Energy spokesman Jeff Brooks said the outages were needed because some equipment was not working at top performance. He also said Duke Energy was unable to buy electricity from neighboring companies, who were at capacity because of cold weather beyond just North Carolina.

The rolling blackouts were only supposed to run until 9 a.m. on Saturday — but were still active as of 5:45 p.m., according to the company.

Brooks also said that it took several hours to restore electricity after the rolling outages.

He also said some outages were longer because of changing needs amid the cold weather.

“The way we determine the length of the outages is based on system needs at that moment and what capabilities we have to quickly reconfigure,” he said.

Brooks said all the company’s equipment was online Saturday, but some was operating at reduced availability.

He also said there was no other electricity from nearby that Duke Energy might normally tap into.

“We were faced with extreme temps that extended beyond the Carolinas that were also over most of the eastern United States,” Brooks said.

On Christmas Day, the company said customers should “continue implementing simple conservation measures until 10 a.m. Monday.”

The company warned rolling blackouts were possible again on Monday.

“As businesses open on Monday morning and people begin returning to the workplace during this time of sustained frigid temperatures, the company projects an increase in customer demand that could require rotating outages again on Monday.”