MidAmerican Energy Co. has reached a conditional agreement with Vestas Wind Systems to purchase up to 1,000 wind turbines for its 2,000-megawatt Wind XI project in Iowa, the Denver Business Journal reported. It’s the largest order ever for a U.S. wind farm and believed to be one of the largest orders in the world, according to industry experts. Des Moines-based MidAmerican Energy, which announced the $3.6 billion project in April, highlighted the agreement with Vestas in a filing with the Iowa Utilities Board. If the board approves the project, the turbines will be delivered and commissioned from 2016 to 2019, Vestas said. With the investment in Wind XI, MidAmerican expects wind farms will provide 85 percent of the energy it delivers to its Iowa customers. When the Wind XI project is complete, MidAmerican says it will have invested more than $10 billion in wind farms.