With an identified potential of about 15 gigawatts of projects and ACS' presence in Spain and Latin America, Vinci aims to bolster its energy contracting business and develop renewable projects, the company said.

"It's only beginning of the story...," Vinci's Chief Executive Xavier Huillard said during an analyst call, adding he was positively surprised by the quality and renewable energy potential in the pipeline.

"We are confident in the ability of this company to quickly be in the position to make one gigawatt a year", Huillard said but not specified how many the company would be able to produce longer term.

The deal price is based on an enterprise value of 4.2 billion euros as of the end of December, 0.7 billion euro equity value and additional contingent payments of 40 million euros per every gigawatt produced over a period of eight-and-a-half years, the French company said.

Vinci had made a non-binding offer in October, saying its proposal was based on an indicative enterprise value of around 5.2 billion euros.

Vinci and ACS will also form a 51%-49% joint venture to acquire mature renewable assets, the French company said.

The acquisition will be financed through Vinci's available cash and credit lines and will not have a significant impact on its balance sheet, the company said.

The deal, expected to close at the end of 2021, would add to Vinci's earnings from the first year after closing to the tune of mid- to high-single-digit range, it said.

($1 = 0.8522 euros)

(Reporting by Anait Miridzhanian, additional reporting by Pawel Goraj; editing by Jason Neely, Susan Fenton and Marguerita Choy)