BOSTON (AP) -- State energy regulators have fined three Massachusetts utilities nearly $25 million for "systematic and fundamental failures" in their response to two major storms in 2011.

The penalties were announced Tuesday by the Department of Public Utilities after a yearlong investigation.

Some customers were without power for a week after Tropical Storm Irene in August 2011 and a surprise October snowstorm.

By far the biggest penalty was assessed against National Grid, fined $18.7 million. The company said in a statement it was reviewing the decision.

NStar was fined $4.1 million and Western Massachusetts Electric Co. was fined $2 million. Both companies, divisions of Hartford, Conn.-based Northeast Utilities, planned to appeal.

Under a state law passed this year, the fines will be returned to consumers in the form of rate relief.