The design for a 50 metre blade is part of the pathway towards 200 metre exascale turbines planned under a programme funded by the Department of Energy (DoE) Advanced Research Projects Agency-Energy (ARPA-E), an agency that is bringing together America’s best and brightest scientists, engineers, and entrepreneurs.
Research by Sandia National Laboratories has resulted in a design for an extreme-scale Segmented Ultralight Morphing Rotor (SUMR). The challenge is to design a low-cost offshore 50 MW turbine requiring a rotor blade more than 650 feet (200 metres) long, two and a half times longer than any existing blade. 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.
At dangerous wind speeds, the blades would be stowed and aligned with the wind direction, reducing the risk of damage. At lower wind speeds, the blades would spread out more to maximize energy production. The thinking behind the SUMR’s load-alignment is inspired by the way palm trees behave in storms. The lightweight segmented trunk is rather like a series of cylindrical shells that bend in the wind while retaining rigidity. This radically reduces the mass required for blade-stiffening by reducing the forces on the blades.
Segmented turbine blades offer significant advantages in parts of the world subjected to severe storms where offshore turbines have to withstand tremendous wind speeds of 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.
The new blade design is based on Sandia’s previous work on 13 MW systems which uses 100 metre blades (328 feet). A 50 MW horizontal wind turbine is well beyond the size of any current design, but studies show that load alignment can dramatically reduce peak stresses and fatigue on the rotor blades. This in turn reduces costs and allows construction of blades big enough for a 50 MW system. Most current US wind turbines produce power in the range of 1-2 MW with blades about 165 feet (50 metres) long. The largest commercially available turbine is rated at 8 MW with blades 262 feet (80 metres) long.
“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. “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. Conventional upwind blades are expensive to manufacture, deploy and maintain beyond 10-15 MW. 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.”
Mr Griffith added 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.
Moving towards exascale turbines could be an important way in which to meet the DOE’s goal of providing 20 percent of the nation’s energy from wind by 2030, according to its recent Wind Vision Report.
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