Utility regulators in Iowa have issued an order approving MidAmerican Energy Company’s proposed 591MW “Wind XII” project that will be completed by the end of 2020.

Wind XII represents a $922m investment by MidAmerican, part of billionaire Warren Buffett’s Berkshire Hathaway conglomerate based in Omaha.

The Iowa Utilities Board is allowing the utility a return on the common equity portion of Wind XII that will be included in Iowa electric rate base at 11 percent.