Constellation will buy Calpine with 50 million of its shares and $4.5 billion in cash. It will also assume about $12.7 billion in Calpine debt. The total value of the deal will be about $26.6 billion.

Constellation Energy agreed to buy Calpine for $16.4 billion, combining two of the country’s largest electricity generators at a time when their product is in high demand from tech companies.