Baltimore-based energy company Constellation’s plans to acquire a Houston, Texas-based natural gas producer in a $26.6 billion deal will boost the nation’s biggest energy firm right as

Constellation Energy Corporation ( CEG, Financials) said Friday that it will purchase Calpine Corporation ( CPN, Financials) for $26.6 billion in cash and shares, becoming the largest US renewable energy provider. The agreement combines Calpine's low-carbon natural gas and geothermal with Constellation's emissions-free nuclear.

Constellation Energy is nearing a roughly $30 billion deal to acquire power producer Calpine, people familiar with the matter said on Wednesday, a move that would significantly expand Constellation's generation assets at a time of rising U.