The 396 megawatt project, located in the German North Sea, benefits from a guaranteed feed-in tariff until 2033 and has a 10-year operation and maintenance agreement with General Electric, Partners Group said in a statement.

Sources had told Reuters late on Monday that the deal was imminent and that it would give the farm an enterprise value of about 2 billion euros (£1.72 billion). Partners Group did not disclose the value of the transaction.

APG also declined to comment on the exact value of the transaction, but said it was one of their largest ever in renewable energy.

"This is a significant step for us and we expect to do more of these investments in the future", APG spokesman Michael Vos said.

APG already has stakes in Swedish and British offshore wind farms and other renewable energy projects around the globe.

"Renewable energy not only continues to be a transformative trend within the infrastructure asset class and an important component of Europe's future energy security, but it is also a key focus of Partners Group's infrastructure investment strategy," said David Daum, senior vice president at Partners Group.

Merkur, which can supply half a million households with electricity, was acquired in 2016 by a consortium led by Partners Group. Co-investors include investment manager InfraRed Capital Partners, Belgium's DEME Group, General Electric and the French Environment & Energy Management Agency (ADEME).

The consortium was advised by Bank of America Merrill Lynch on the sale, which includes APG buying a 64% stake in Merkur, while TRIG will acquire 36%.

TRIG, in a separate statement, said it would sell about 11% to minority co-investors managed by InfraRed once the deal is expected to be completed in the first half of 2020, leaving it with about a quarter.

(Reporting by Christoph Steitz and Bart Meijer; Editing by Michelle Martin)