Infrastructure group Balfour Beatty has cashed in on its stake in a windfarm off the Kent coast as it looks to raise funds after a string of profit warnings.

The construction giant has sold 80% of the Thanet offshore transmission project for £40 million, two months after it acquired it from Swedish energy firm Vattenfall in a £164 million deal.

Infrastructure investment company Equitix has bought the project, which includes two 26km underwater cables, two 2.4km onshore cables, an offshore platform and an onshore substation at Richborough.

Vattenfall was forced to sell the high-voltage transmission system – which carries electricity from the windfarm to the National Grid – by the energy regulator Ofgem as part of a programme to save between £200m and £400m for consumers across the UK.

Balfour Beatty will still operate and maintain it under the 20-year licence granted by Ofgem and will keep a 20% stake, saying it considers the sector a “key market”.

Chief executive Leo Quinn said: “This disposal validates the directors’ valuation of the investments portfolio, which was updated last month, and clearly demonstrates the investment business’ ongoing ability to deliver significant value for the group.”

The 100-turbine wind farm, located about 12km off the coast of Foreness Point near Botany Bay, is still operated by Vattenfall and generates enough electricity for about 200,000 homes each year.

A Vattenfall spokesman said: “Vattenfall sold the transmission infrastructure associated with its Thanet Offshore Wind Farm late last year to Balfour Beatty.

“We note this latest transaction and also the fact Balfour Beatty will continue to operate the assets for the next 20 years.

“We look forward to a good working relationship with the owners as we focus on maximising carbon free generation from Thanet Offshore Wind Farm.”

Balfour Beatty, which employs 36,000 people, has offices in Beckenham.

It has offloaded several businesses in recent years to calm investors worried about its balance sheet.

Chief executive Mr Quinn took over in January after six profit warnings caused by overrunning projects and rising costs.