GE Renewable Energy has begun work to repower up to 706 older turbines at multiple wind farms in Iowa under a contract awarded in late September by billionaire Warren Buffett’s MidAmerican Energy Company.

Initial work centers on three facilities with a combined 283 GE turbines: Century (110), which entered commercial operations between 2005 and 2008; Intrepid (107), in service since 2004, and Victory (66), a 2006 complex.