Electricity is coming back for those who lost power because of Sandy. At mid-day on the East Coast about six million are still in the dark, down from a high of eight and a half million. - 

51,000 men and women -- tree trimmers and liner workers from as far away as the West Coast -- are trying to restore power in the wake of the storm.

Todd Schneider with First Energy, the company that owns Jersey Central Power and Light, says there’s a lot of work to do, "There’s just tremendous destruction to our electrical system. The high winds took down poles, took down wires."

Total it up, and more than 900,000 New Jersey customers are in the dark. With so many people out of power, energy producers have been forced to slow production. The region’s electrical grid, PJM -- which serves 60 million people -- can’t hold much extra supply.

"We are the only commodity that cannot have large storage of our production. Within milliseconds of when we generate the power, it’s consumed by the consumer," says PJM’s CEO Terry Boston. 

According to Boston, producers can’t make as much energy as they usually do: "Systems start speeding up, motors turn too fast, can overheat. So we are very careful to balance the supply and demand."

Boston says the producers probably won’t get all of their customers back until next week.

Follow Dan Gorenstein at @dmgorenstein