Harvested by advanced technical systems honed over decades of research and development, wind energy has become a mainstream energy resource. However, continued innovation is needed to realize the potential of wind to serve the global demand for clean energy. Here, we outline three interdependent, cross-disciplinary grand challenges underpinning this research endeavor. The first is the need for a deeper understanding of the physics of atmospheric flow in the critical zone of plant operation. The second involves science and engineering of the largest dynamic, rotating machines in the world. The third encompasses optimization and control of fleets of wind plants working synergistically within the electricity grid. Addressing these challenges could enable wind power to provide as much as half of our global electricity needs and perhaps beyond.

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Three 9 m carbon fiber wind turbine blades have been designed through a research program initiated by Sandia National Laboratories. The individual designs feature such innovations as carbon spar caps, material-induced twist-bend coupling, and flatback airfoils, among others. All blades were constructed with conventional dry lay-up and VARTM infusion processes. Static tests of these blades were conducted at the National Wind Technology Center. The blades were subjected to flapwise loading to simulate the extreme wind loads expected for each design in a Class 2b wind site. The blades were loaded with a three-point whiffle-tree arrangement. Upon obtaining the predetermined test load, the blades were subsequently loaded to failure. Load, deflection, strain, and acoustic emissions were monitored throughout the experiments. All blades survived the specified test loads, with two designs exceeding it significantly. In addition, carbon strains of over 0.8% in both tension and compression were recorded in one of the tests. Finally, acoustic microphones were able to detect areas where damage was occurring, and indicated the beginnings of failure. This paper outlines the results of the structural tests that were conducted. Nomenclature VARTM = Vacuum Assisted Resin Transfer Method SNL = Sandia National Laboratories NWTC = National Wind Technology Center HP = High Pressure LP = Low Pressure

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In the past decade wind energy installations have increased exponentially driven by reducing cost from technology innovation and favorable governmental policy. Modern wind turbines are highly efficient, capturing close to the theoretical limit of energy available in the rotor diameter. Therefore, to continue to reduce the cost of wind energy through technology innovation a broadening of scope from individual wind turbines to the complex interaction within a wind farm is needed. Some estimates show that 10 -40% of wind energy is lost within a wind farm due to underperformance and turbine-turbine interaction. The US Department of Energy has recently announced an initiative to reshape the national research focus around this priority. DOE, in recognizing a testing facility gap, has commissioned Sandia National Laboratories with the design, construction and operation of a facility to perform research in turbine-turbine interaction and wind plant underperformance. Completed in 2013, the DOE/SNL Scaled Wind Farm Technology Facility has been constructed to perform early-stage high-risk cost-efficient testing and development in the areas of turbine-turbine interaction, wind plant underperformance, wind plant control, advanced rotors, and fundamental studies in aero-elasticity, aero-acoustics and aerodynamics. This paper will cover unique aspects of the construction of the facility to support these objectives, testing performed to create a validated model, and an overview of research projects that will use the facility.