The transaction will be completed in October 2021, once the Glen Kyllachy farm is fully operational, although the first export of electricity is targeted for July 2021.
The farm, designed to have a capacity of 48.5 megawatts, will be realised near Inverness without subsidies.
“This brings our commitments to subsidy-free wind farms to just over £100mln,” said Greencoat’s chair Tim Ingram.
“We are delighted to partner again with Innogy, who have the expertise and resources to deliver a high-quality operational wind farm.”
Shares were down 0.56% to 141.4p on Thursday afternoon.