The purchase of a 50-percent stake in Triton Knoll for an undisclosed sum follows state-owned Statkraft's strategic move to no longer invest in offshore wind power projects to free up cash to be able to pay a full dividend.

With 860 megawatts of generating capacity and total investments of up to 2 billion pounds, Triton Knoll is due to go live in 2021 and is expected to supply the equivalent of 800,000 British households with renewable electricity each year.

Innogy and Statkraft last month won a public tender for the project at an awarded price of 74.75 pounds per megawatt hour (MWh), making it cheaper than new nuclear generation for the first time.

"Some might consider it risky to shoulder the high investment sum alone," a Frankfurt-based trader said. Shares in Innogy, which have gained 6.5 percent since their listing last year, were up 0.6 percent.

Offshore wind parks typically involve several owners to share the high investments needed, usually starting at about 1 billion euros. Hans Buenting, Innogy's board member in charge of renewables, said the ownership structure would be reviewed in due course.

Innogy confirmed that a final investment decision for the project would be made in mid-2018.

(Reporting by Tom Sims and Christoph Steitz; Editing by Greg Mahlich and Victoria Bryan)