UPDATE 1-Duke Energy to build 200 mw wind farm in Wyo.

* Duke to build 200 mw wind farm in Wyoming

* Project expected to come online at end of 2010

SAN FRANCISCO, Aug 31 (Reuters) - U.S. electric utility Duke Energy (DUK.N) said on Monday it plans to build a 200-megawatt wind farm, its ninth in the United States.

The wind farm, which will be built in Wyoming, is expected to generate enough electricity to power the equivalent of 50,000 to 60,000 homes on an annual basis.

PacifiCorp, which operates as Rocky Mountain Power in Wyoming, will purchase all of the electricity generated by the project, Duke said.

The Wyoming project, which is forecast to come online at the end of next year, will be Duke's second-largest renewable energy facility. Duke, the third-largest U.S. electric power company, has committed to four new wind projects totaling more than 360 megawatts this year.

Construction for the wind farm is expected to begin in late 2009 or early 2010.

Duke said it will use at least 66 turbines from General Electric (GE.N) for the new wind farm.

(Reporting by Poornima Gupta; Editing Bernard Orr)