This is an excerpt from the Second Quarter 2013 edition of the Wind Program R&D Newsletter.

The Wind Technology Testing Center (WTTC) in Boston, Massachusetts, recently acquired a significant piece of testing equipment needed to offer its industry partners a full state-of-the-art suite of wind turbine blade certification tests. As utility-scale wind turbines have grown in size over the last decade, their blades have become longer, heavier, and more costly to manufacture, install, and repair. Verifying the blade's strength and lifetime performance before it's installed on a turbine in the field is one of the critical elements to reducing the cost of wind energy. There are very few facilities in the world that have the capability to perform a full range of structural evaluations on turbine blades, including ultimate static strength, fatigue, vibration, and nondestructive tests.

Constructed with a combination of funding from the state of Massachusetts and the U.S. Department of Energy through the American Recovery and Reinvestment Act, the WTTC is one of the largest blade test facilities in the world, testing some of the longest blades made today for the multimegawatt wind turbines being deployed both on land and offshore. The blades can measure up to 90 meters (295 feet) in length.

The WTTC's new Ground-based Resonant Excitation (GREX) system enables the WTTC to conduct fatigue tests on the larger blades at higher test frequencies—and thus shorter testing times—than was previously possible using resonant masses attached to actuators on the blade. A highly accelerated fatigue test applies elevated dynamic loads in flapwise and lead-lag directions to simulate the equivalent loads experienced by a wind turbine blade in the field during its 20-year life expectancy. Since its installation in April, the GREX system has been successfully commissioned on one commercial blade fatigue test and is currently cycling on another multimegawatt wind turbine blade flap fatigue test.