To boost the energy output of wind turbines, manufacturers are developing taller structures with longer blades. That’s because the wind at 100 meters blows more steadily and 4.5 percent faster than it does at 80 meters, with an energy gain of about 14 percent. Longer blades can rotate more slowly, yet produce more electrical power. Last year, close to 5 percent of new turbines in the United States were 100 meters high, and the trend is expected to continue worldwide.
But bigger size brings with it significant engineering challenges. The weight of the turbine rotor and hub alone generate static radial load and pitching moments. Wind forces add static and dynamic axial loads on both the bearings and rotor blades. The wind also generates pitching and yawing moments that cycle with the position of the blades as they rotate. The effects of these forces can multiply as a wind turbine gets larger.