A Grand Forks wind power equipment plant that laid off half of its 600 workers a year ago is nearly back to full strength. Denmark-based LM Wind Power expects to have 570 employees at its North Dakota facility by the end of the year. The plant manufactures wind turbine blades. Company officials cite the extension of the federal wind production tax credit early this year for increasing demand. LM Wind Power, which also has a plant in Little Rock, Ark., grew from 350 employees in the U.S. in April to 700. It plans on growing to 1,200 workers in 2014.