The United States may become the largest market for renewable energy for E.ON, the world's largest utility by sales, within six years, the head of the company's green energy unit told Reuters in an interview.

Half of the company's generation capacity using renewable energy sources may be in the United States by 2015, as E.ON seeks to boost its total green generation capacity to 10 gigawatt within six years, said unit head Frank Mastiaux.

We plan to boost our (renewable energy) business with investments worth billions of euros, he said.

There is no comparable market to the United States, he said.

E.ON had kickstarted its renewable energy business in the world's largest economy in 2007 with the 1.4 billion euro ($1.97 billion) takeover of the U.S. business of Irish windpark operator Airtricity.

About a fifth of E.ON's investments in the period from 2007 to 2010, some 6 billion euros, are earmarked for renewable energy projects, plus an additional 2 billion euros in 2011.

The utility is focusing on wind energy for now in the United States and plans to build some 500 megawatt in capacity a year on average in the long term in the country, Mastiaux said.

E.ON currently has a capacity of some 1,200 megawatt overseas. E.ON plans to build windfarms itself and will not make more takeovers in the country, he said.

The company's 2015 target of 10 GW renewable capacity excludes water power.

(Additional reporting by Peter Dinkloh)

Renewable energy E.on Energy