Wind Turbines Turn to Palm Tree-Like Design for Next-Gen Power

Until recently wind turbines have been relegated to land, with projects starting to emerge that harness the powerful offshore winds that come from the sea. The Department of Energy (DoE) is hoping to propel this use of wind energy forward in a big way, literally, with a new design for gigantic turbine blades that could make it feasible to deploy 50-megawatt (MW) offshore wind turbines.

The research comes out of the DoE’s Sandia National Laboratories, which has been working on exascale turbines -- two-and-a-half times larger than anything in use today -- thanks to funding from the department’s ARPA-E program.

A team led by Todd Griffith, technical lead for Sandia’s Offshore Wind Energy Program, is working on a low-cost offshore turbine with rotor blades more than 650-feet long that could produce an output of energy up to six times more than turbines in use today. These exascale turbines could help the DoE meet its goal of providing 20% of the energy in the US from wind by 2030.

Todd Griffith shows a cross-section of a 50-meter wind-turbine blade. The prototype could pave the way for 200-meter exascale turbines for harvesting offshore wind power.
(Source: Randy Montoya, Sandia Labs)

“Exascale turbines take advantage of economies of scale,” Griffith explained. “Conventional upwind blades are expensive to manufacture, deploy, and maintain beyond 10 MW to 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."

The new rotor design differs from conventional turbines in a couple of ways, Griffith said. Not only are the rotors on the turbine -- called Segmented Ultralight Morphing Rotors -- far larger than on typical turbines, but they also are used in a different way. The turbines are placed downwind of the tower rather than upwind in a shape that resembles a palm tree, and they bend like a palm tree’s leaves.

In this way, the rotor being designed by Griffith’s team can bend in the wind while still retaining segment stiffness, reducing the mass required for blade stiffening by reducing the forces on the blades using the palm-tree-inspired load-alignment approach, he said.

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Sandia previously experimented with this type of load alignment for a turbine rotor on a 13 MW system that uses a 100-meter blade, showing that it could reduce peak stresses and fatigue on the rotor blades. This work is informing the design of the larger blades in terms of making them functional and also helping reduce the cost of wind energy by capturing it at a greater scale, Griffith said.

Mass production also is a benefit of the blades, which would be even more cost-effective to manufacture than blades in use today, he said. The new blades could be manufactured in segments, which would eliminate the equipment needed to transport and assemble blades that are built as single units, Griffith said.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.