UPDATE 2-NRG Yield to buy largest N America wind farm for $870 mln

* To assume project financing cost of $1.6 billion

* Deal to add 947 MW operating wind capacity

(Adds details, background, share move)

June 4 (Reuters) - Clean energy company NRG Yield Inc said it would buy California's Alta Wind Energy Center, the largest wind farm in North America, for $870 million from Terra-Gen Power LLC.

The deal will add 947 megawatt (MW) to the wind portfolio of NRG Yield and parent NRG Energy Inc, making it the fifth largest in the continent at 2,839 MW.

NRG Yield shares rose 2.2 percent to their life high of $47.95 on the New York Stock Exchange on Wednesday morning.

The U.S. Environmental Protection Agency on Monday announced a plan to slash carbon emissions from the power sector by 2030 to 30 percent below 2005 levels.

NRG Energy had said in December that it would close two coal-fired power plants in Maryland due to tightening air emission regulations.

NRG Yield, spun off from NRG Energy in December 2012, helps the parent acquire and operate renewable, conventional and thermal infrastructure assets.

The acquisition, including some land leases associated with the Alta Wind facility, is expected to add $220 million to NRG Yield's annual run-rate earnings before interest, taxes, depreciation and amortization, NRG Yield said on Wednesday.

Alta Wind, located in the Tehachapi Pass in California's Kern County, contracts long-term power purchase agreements with Edison International.

Terra-Gen Power is a renewable energy company backed by private-equity firms Global Infrastructure Partners and Arclight Capital Partners.

NRG Yield said it would assume project financing cost of $1.6 billion and expects the deal to close in the third quarter.

Bank of America Merrill Lynch acted as exclusive financial adviser to NRG Yield while Jones Day served as legal counsel.

NRG Energy shares were up slightly at $36.22.

(Reporting By Sneha Banerjee, Narottam Medhora and Ankush Sharma in Bangalore; Editing by Gopakumar Warrier, Simon Jennings and Joyjeet Das)