A wind energy expert says an upgraded power transmission system is needed if Maine is to achieve its goals for generating that renewable energy source. Larry Flowers of the National Wind Technology Center also told the 350 people attending a conference Tuesday on wind energy in Maine that transmission infrastructure is a problem all over the country as wind power develops. Gov. John Baldacci, who opened the daylong conference, said he wants Maine to be the first state to develop offshore wind power. He also agreed that a transmission upgrade is critical to wind power development. The conference drew about a dozen demonstrators. A leader, Steve Thurston of Roxbury, who said erecting all the windmills needed to meet Maine’s goals will have a devastating impact on the state’s mountains.