The transaction's underwriters also have the option to buy an additional 1.56 million shares, worth another $80.6m.

NRG Yield, the yieldco spun out of NRG last summer, announced last month its intention to buy seven sub-projects within California's immense Alta Wind facility from Terra-Gen Power for $870m plus the assumption of $1.6bn of non-recourse project financings in place at the projects.

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