Multi-Rotor Wind Turbine

A multi-rotor wind turbine mounts several smaller rotors on a single support structure instead of one large rotor, an approach explored as a way to lower the cost of wind energy by challenging the usual assumption that bigger single rotors are always more efficient. Vestas built the best documented demonstrator, the 4R-V29, at the Riso campus of the Technical University of Denmark in April 2016, using four refurbished 225 kilowatt rotors, each 29.2 meters across, arranged as a bottom pair at 29.04 meters hub height and a top pair at 59.5 meters, angled 3 degrees outward from each other to keep their blade tips clear. Field measurements found the arrangement produced about 1.8 percent more power than a comparable single rotor turbine at below rated wind speeds, translating to roughly 1.5 percent more annual energy output, and its four separate wakes merged into a single wake structure faster, recovering between about 1.0 and 1.4 rotor diameters sooner than a single rotor turbine wake, a property that could allow turbines to be spaced closer together in a wind farm. The 4R-V29 operated for almost three years before Vestas decommissioned it in December 2018.