British newspapers have said the suitor is Pacificorp, an electric utility based in Portland, Ore.
Utilicorp United, a utility based in Kansas City, Mo., has worked with three private services.
The Entergy Corporation, a huge utility based in New Orleans, was the winner with an $80 million bid.
The utility, based in Syracuse, put its unregulated power business up for sale last spring in an effort to concentrate on its regulated operations.
Pacificcorp, a utility based in Portland, Ore., said its earnings for the second quarter would be 30 percent below estimates.
The Concord station is the first of nine that the utility, based in San Francisco, will build this year, with seven open to the public.
There aren't really any synergies with an electric utility based in three states in the Midwest and the national structure we've got.
As in its interim report last November, the task force put most of the blame on FirstEnergy, a utility based in Ohio.
The utility, based in Berlin, Conn., had applied for a $228 million, 11.5 percent rate increase in December, citing low sales growth and increasing costs.
Pacificorp, a utility based in Portland, Ore., had been seeking to buy Energy Group since last spring when it made an offer of $5.8 billion.