MADRID, May 17 (Reuters) - Europe's largest utility Iberdrola will keep betting on offshore wind in the coming years, roughly tripling the value of its assets in the sector to 17 billion euros ($18 billion), Executive Chairman Ignacio Sanchez Galan told shareholders on Friday.

In the past couple of years, the Spanish firm has shifted its focus to upgrading and expanding power grids while taking a more selective approach to renewables that favours investments in offshore wind.

In the next three years, offshore wind projects will get more than 50% of the planned 15.5 billion euro investment in renewables, under a new plan presented in March.

The company currently has a project in Germany and two in Britain - including a partnership with Denmark's Orsted - in operation. Including the partnership, the projects account for around 6 billion euros in investments.

It is now building projects in the United States, Britain, France and Germany.

"Once finished, there will be 17 billion euro assets in this sector, which also have guaranteed income," Sanchez Galan said, since the production is already sold through long-term contract.

"Our commitment to offshore wind will continue," he said.

Iberdrola is currently bidding for new offshore wind farm auctions in Britain and the U.S., the chairman said.

"We have recently been awarded a new project in Japan and an offshore site for future construction in Australia," said Sanchez Galan, adding there was an "excellent outlook" for the technology.

($1 = 0.9224 euros) (Reporting by Pietro Lombardi; Editing by Kirsten Donovan and Mark Potter)