Palm tree style wind turbine design can withstand hurricanes

Most current U.S. wind turbines produce power in the 1- to 2MW range, with blades about 165ft long, while the largest commercially available turbine is rated at 8MW, with blades 262ft long.

“Exascale turbines take advantage of economies of scale,” said Todd Griffith, lead blade designer on the project and technical lead, Sandia’s Offshore Wind Energy Programme.

Sandia’s previous work on 13MW systems uses 328ft blades 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.

Offshore installations are expensive, so larger turbines are needed to capture that energy at an affordable cost, explains Griffith.

“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,” continues Griffith.

He says 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 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 200mph. 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.” Griffith said.

Moving toward exascale turbines could be an important way to meet DOE’s goal of providing 20% of the nation’s energy from wind by 2030, as detailed in its recent Wind Vision Report.

The 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, Siemens and Vestas Wind Systems.