JOE KOHEN | The Associated Press
Five years ago, bystanders gathered in Times Square in Manhattan after a blackout in New York. The overall health and capacity of the nation’s transmission grid remain a problem.Five years after the worst blackout in North American history, the country’s largest utilities say the U.S. power system faces the prospect of even bigger and more damaging outages.

The specific flaws that led to 50 million people losing power in 2003 have largely been addressed, they say, but even bigger problems loom. Excess generating capacity in the system is shrinking, for example, and power-plant construction has slowed as costs to build and operate plants have soared.

At the same time, it is estimated that electricity use will increase 29 percent between 2006 to 2030 — much of it driven by residential growth, according to a government report issued in June.

“I’m really not a ‘Chicken Little’ player, but I worry that no one seems to be focusing in on this,” said Michael Morris, chairman, president and chief executive of American Electric Power, which runs the nation’s largest electricity transmission system.

Morris said massive outages this year in South Africa, which forced gold, diamond and platinum mines to stop production for five days, should serve as a warning to the United States.

Industry experts back Morris and say there is even more resistance to building new plants because of the debate over climate change and opposition to new transmission lines. The blocking of two coal-fired plants in Kansas is one example of the resistance.

“The level of excess capacity has shrunk … to a level barely within the planning toleration of the industry,” said Marc Chupka, with the Brattle Group, an energy consultant.

The blackout five years ago today shut off power to vast swaths of the Northeast and Midwest for as much as four days. Rolling blackouts continued in Ontario for a week. The outages caused as much as $10 billion in damages to the U.S. economy.

FirstEnergy Corp. of Akron, Ohio, which got the blame for the spread of the outages, has worked to shore up its transmission system. But the larger issues of the country’s total generating ability and the overall health and capacity of the transmission grid remain a problem, the experts say.

Rick Sergel, president of the North American Electric Reliability Corp., the agency that oversees the nation’s power grid, said, “We’re to the point where we need every possible resource: renewables, demand response and energy efficiency, nuclear, clean coal — you name it, we need it. And we especially need the transmission lines that will bring the power generated by these new resources to consumers.”

Construction of coal-fired generating plants has almost stopped, and new nuclear plants are years away, if they are approved at all, said Arshad Mansoor, vice president of power delivery and use for the Electric Power Research Institute. Better efficiency will go only so far, he said.

Morris, of American Electric Power, sees a potentially dire situation ahead, including the sort of power rationing that occurred in South Africa.