The 2.5 MW Liberty Wind Turbine is the largest wind turbine manufactured in the United States. The turbine was developed through a partnership with U.S. Department of Energy and its National Renewable Energy Laboratory for Clipper Windpower: Commercial sales for the new Liberty turbine started in June 2006 and now amount to more than 5,600 MW (2,240 units) of firm and contingent orders for deliveries in 2007 through 2011.