A new design for gigantic wind turbines, with blades longer than two football fields, could help bring offshore 50-megawatt (MW) wind turbines to the world. Research being carried out in Sandia National Laboratories, which has locations in New Mexico and California, on the extreme-scale Segmented Ultralight Morphing Rotor (SUMR) is funded by the US Department of Energy's (DOE) Advanced Research Projects Agency-Energy program. The challenge: to design a low-cost offshore 50MW turbine requiring a rotor blade more than 200 metres (650 feet) long, two-and-a-half times longer than any existing wind blade. "Exascale turbines take advantage of economies of scale," said Todd Griffith, lead blade designer on the project and technical lead for Sandia's Offshore Wind Energy Program. Sandia's previous work on 13MW systems uses 100-metre blades (328 feet) on which the initial SUMR designs are based. While a 50MW horizontal wind turbine is well beyond the size of any current design, studies show that load alignment can dramatically reduce peak stresses and fatigue on the rotor blades. This reduces costs and allows construction of blades big enough for a 50MW system. Most current wind turbines produce power in the 1MW-to-2MW range, with blades about 50 metres (165 feet) long, while the largest commercially available turbine is rated at 8MW with blades 80 metres (262 feet) long. "The US has great offshore wind energy potential, but offshore installations are expensive, so larger turbines are needed to capture that energy at an affordable cost," Griffith said. Barriers remain before designers can scale up to a 50MW turbine – more than six times the power output of the largest current turbines, however.

Challenges to scaling up to exascale turbines

[caption id="attachment_36145" align="alignright" width="300"]CLICK TO ENLARGE Sandia’s 100m blade is the basis for the SUMR, a new low-cost offshore 50-MW wind turbine. At dangerous wind speeds, the blades are stowed and aligned with the wind direction, reducing the risk of damage. At lower wind speeds, the blades spread out more to maximise energy production. (Image: TrevorJohnston.com/Popular Science) CLICK TO ENLARGE Sandia’s 100m blade is the basis for the SUMR, a new low-cost offshore 50-MW wind turbine. At dangerous wind speeds, the blades are stowed and aligned with the wind direction, reducing the risk of damage. At lower wind speeds, the blades spread out more to maximise energy production. (Image: TrevorJohnston.com/Popular Science)[/caption] "Conventional upwind blades are expensive to manufacture, deploy and maintain beyond 10-15MW. They must be stiff, to avoid fatigue and eliminate the risk of tower strikes in strong gusts. Those stiff blades are heavy, and their mass, which is directly related to cost, becomes even more problematic at the extreme scale due to gravity loads and other changes," Griffith said. He said that the new blades could be more easily and cost-effectively manufactured in segments, avoiding the unprecedented-scale equipment needed for transport and assembly of blades built as single units. The exascale turbines would be sited downwind, unlike conventional turbines that are configured with the rotor blades upwind of the tower. SUMR's load-alignment is bio-inspired by the way palm trees move in storms. The lightweight, segmented trunk approximates a series of cylindrical shells that bend in the wind while retaining segment stiffness. This alignment radically reduces the mass required for blade stiffening by reducing the forces on the blades using the palm-tree inspired load-alignment approach. Segmented turbine blades have a significant advantage in parts of the world at risk for severe storms, such as hurricanes, where offshore turbines must withstand tremendous wind speeds over 200 mph. The blades align themselves to reduce cantilever forces on the blade through a trunnion hinge near the hub that responds to changes in wind speed. "At dangerous wind speeds, the blades are stowed and aligned with the wind direction, reducing the risk of damage. At lower wind speeds, the blades spread out more to maximise energy production." Griffith said. Moving toward exascale turbines could be an important way to meet the DOE's goal of providing 20 per cent of the United States' energy from wind by the year 2030, as detailed in its recent Wind Vision Report. See the Segmented Ultralight Morphing Rotor (SUMR) at work in the video below: https://videos.files.wordpress.com/dC69fRlF/updated-video-homepage1_dvd.mp4 The research team is led by the University of Virginia and includes Sandia and researchers from the University of Illinois, the University of Colorado, the Colorado School of Mines and the National Renewable Energy Laboratory. Corporate advisory partners include Dominion Resources, General Electric Co., Siemens AG and Vestas Wind Systems.