UPDATE 3-Calpine received unsolicited $11 bln bid from NRG

(Recasts to reflect Calpine confirmation)

By Michael Erman

NEW YORK, May 21 (Reuters) - Power company NRG Energy Inc (NRG.N: Quote, Profile, Research, Stock Buzz) has made an unsolicited bid to buy competitor Calpine Corp (CPN.N: Quote, Profile, Research, Stock Buzz) for roughly $11 billion in stock, Calpine said on Wednesday.

Calpine, which emerged from bankruptcy earlier this year, said it was reviewing the bid to determine if it was in the best interests of its shareholders.

The company said it received an unsolicited proposal from NRG on May 14 suggesting an all-stock deal. Under the terms of that proposal, Calpine shareholders would receive 0.534 shares of NRG stock for every Calpine share.

Hedge fund Harbinger Capital Partners, Calpine's largest shareholder, said earlier on Wednesday it believes the offer represents a good starting point and that Calpine's board should immediately negotiate with NRG over terms.

Harbinger owns more than 24 percent of Calpine's shares,

Calpine emerged from bankruptcy in January with more than $10.6 billion in debt.

A combination with Calpine would give NRG more presence in the Western U.S. power market, NRG's smallest market, and in the Southeast, with little overlap in the Northeast where NRG already owns 15 power plants totaling 7,000 megawatts.