Materials commonly used in wind turbine blades are described below. It is used to transport wind turbine components. The variability of production from a single wind turbine can be high. The panemone is one of the least efficient types of wind turbine. These areas remain a highly active area of research in wind turbine aerodynamics. The aerodynamics of a wind turbine are not straightforward. In 2007, Areva purchased 51% of offshore wind turbine manufacturer Multibrid. Heligoland was the site of a trial of GROWIAN, a large wind turbine testing project. In January 2017, Areva sold its stake in the wind turbine manufacturer Adwen. The role of wind turbine cooperatives is not limited to single turbines. Other prototypes and wind turbine types were manufactured by NedWind. A wind turbine project was completed in 1999. This type of rig is commonly used in connection with offshore wind turbine installation. This factor affects the economics of wind turbine operation in cold climates. Power electronics are also at the heart of the variable speed wind turbine.