Monroe-based Ventower Industries is running seven days a week, with two 10-hour shifts, four days a week and a third weekend shift, to meet the demand for its wind turbine towers. In business since August 2011, Ventower shipped its first wind tower sections a year ago. With 65 employees currently, it may add a fourth shift at night on the weekends. The company has been concentrating on the requirements of its largest customer, a major American maker of wind-energy equipment, for the construction of wind farms in the Midwest.