Sandbrook Capital has amassed $2.1 billion to invest in renewable-energy businesses, as the private-equity firm shifts its focus to the U.S. with its debut fund after making its first deals in Europe.

The Stamford, Conn.-based clean-energy investor wrapped up its Sandbrook Climate Infrastructure Fund I with $1.5 billion, or 50% more than its initial $1 billion goal. The firm also collected slightly over $600 million for related co-investment vehicles, said Kenneth Ryan, a Sandbrook partner. Roughly 35 investors backed the fund, he said.