LISBON, Dec 21 (Reuters) - A unit of U.S. private equity fund KKR announced on Thursday a full takeover bid for Portuguese renewable energy company Greenvolt, which values the firm at 1.16 billion euros, and said it had already secured a controlling stake via agreements.

Gamma Lux said in a statement it was offering 8.3 euros per Greenvolt share, which is 11.5% above Wednesday's closing price of 7,45 euros and represents a premium of 32.1% compared to the weighted average price over the last six months.

It said that the offer became mandatory after the fund signed contracts to buy a total stake of 60.86% in Greenvolt from seven shareholders.

Greenvolt's equity is represented by more than 139 million shares.

This morning the shares were suspended from trading on Euronext Lisbon.

(Reporting by Sergio Goncalves, editing by Andrei Khalip)