Seattle: Warren Buffett has highlighted wind investments by MidAmerican Energy in his annual letter summarising the businesses of his conglomerate Berkshire Hathaway.. MidAmerican is already the largest owner of wind generation among regulated US utilities, and one of the top wind owners of any kind. It will have more than 2.9GW of installed wind capacity by the end of this year, Buffett writes in his eagerly read shareholder letter.