Sandia study looks at massive 50MW turbines

Huge turbine blades could one day result in 50 megawatt (MW) offshore wind turbines, scientists a Sandia National Laboratories in the US believe. Scientists there are working on an extreme-scale segmented ultralight morphing rotor (SUMR) funded by the Department of Energy’s Advanced Research Projects Agency – Energy programme. The team is led by the University of Virginia and includes Sandia and researchers from the University of Illinois, University of Colorado, Colorado School of Mines and the National Renewable Energy Laboratory. Corporate advisory partners include Dominion Resources, General Electric, Siemens and Vestas Wind Systems. “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 Programme.

Sandia’s previous work on 13MW turbines used 100m blades on which the SUMR designs are based. Although 50MW turbines ae well beyond the size of any current designs, Sandia says 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 unit. Of course, barriers remain before designers can scale up to a 50MW turbine – which would be more than six times the power output of the largest turbines – in use today, and Sandia has not yet addressed the installation challenges such as turbine might represent.

“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,” Mr Griffith said. He said 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 maximize energy production,” Mr Griffith said, noting that moving toward exascale turbines could be an important way to meet the Department of Energy’s goal of providing 20 per cent of the nation’s energy from wind by 2030, as detailed in its recent Wind Vision Report.