The two companies agreed to buy all the shares in EverPower, the portfolio company of Terra Firma, with the acquisition subject to approval by the US government's committee on foreign investment in the United States (CFIUS). Transaction closing is expected by the second quarter of 2018, the companies stated.
The acquisition is Innogy's first in the US.
All parties have agreed to maintain confidentiality about the price of the transaction.
EverPower's portfolio consists of more than 20 projects across seven states, including the 240MW Big Sky project in Illinois, the 150MW Mustang Hills site in California, and the 139.4MW Twin Ridges wind farm in Pennsylvania.
It also has more than 500MW in advanced stages of development, with projects due to come online in 2020, according to Andrew Young, CEO of Innogy US Renewables.
Hans Bünting, COO Renewables of innogy SE, explains: "The US market is one of our key strategic growth areas for renewables. Establishing our subsidiary, Innogy Renewables US LLC, in 2016 was our first step to enter this market.
"The acquisition of EverPower's impressive pipeline is a logical step consistent with our commitment.
"We are very pleased to have made our first acquisition in the US. And this is just the beginning."
EverPower's Pittsburgh-based development team will also join Innogy, under the terms of the agreement.