Photo Credit: National Renewable Energy Laboratory
A team of researchers is working to complete the design for a novel 50-megawatt offshore wind turbine, nearly six times more powerful than a record-setting 8.8-megawatt turbine recently deployed off the coast of Scotland. Testing will begin on prototype blades this summer in Colorado.
The massive turbine marks an about-face from conventional wind turbine design. The standard wind turbine installed today is a three-bladed machine positioned with the blades facing incoming winds.
The blades for the so-called Segmented Ultralight Morphing Rotor (SUMR) wind turbine would, conversely, face downwind. The “go-with-the-flow” design was inspired by palm trees, which have evolved to withstand hurricane gales.
Just as palm fronds bend and yield to the direction of the wind, the segmented blades for the SUMR turbine will fold together, aligned with the wind direction, in strong winds.
“We’re trying to have the turbine blades be more aligned along the load path, so we can get away with lower structural mass and have less fatigue and less damage,” said Eric Loth in an interview. Loth is chair of the department of mechanical and aerospace engineering at the University of Virginia and the SUMR project lead.
The research team believes the downwind design will make it possible to deploy extreme-scale offshore wind turbines in parts of the United States, such as the South Atlantic and Gulf of Mexico, where wind speeds can reach 200 mph during severe storms.
An ARPA-E grant-funded project
In November 2015, a research team lead by the University of Virginia was awarded a three-year, $3.56 million grant from the Advanced Research Projects Agency-Energy (ARPA-E) to design a 50-megawatt SUMR turbine. The team includes researchers from the University of Illinois, University of Colorado, Colorado School of Mines, National Renewable Energy Laboratory (NREL), and Sandia National Laboratories.
The research team meets regularly with an industry advisory board that includes representatives from major turbine makers such as GE, Siemens and Vestas.
The research team is aiming to design a 50-megawatt turbine that can reduce the levelized cost of offshore wind energy by as much as 50 percent by 2025. “We need to come up with turbines that are not necessarily more efficient but will cost less to build and maintain,” said Loth.
“You have to do something differently in the technology approach in order to go larger and larger,” Todd Griffith, an associate professor of mechanical engineering at the University of Texas at Dallas and member of the research team, said in an interview.
Shedding weight to reach scale
A primary goal of the project is to shed weight in the turbine blades. Added weight increases the “global loads” transferred from the blades to the turbine hub and, according to Griffith, is the main limitation to building ever-larger blades for conventional upwind offshore wind turbines.
“Weight reduction is a big driver in the design,” said Griffith, who began researching 100-meter blades a decade ago as a member of the offshore wind technical team at Sandia National Laboratories.
Conventional turbine blades are made mostly of fiberglass with some carbon fiber. You could incorporate more carbon fiber into the design to add strength, but it comes at a cost.
There are good reasons why fiberglass is the industry standard. It’s inexpensive and has good stiffness properties, said Loth.
Griffith is encouraged by ongoing research, funded by the U.S. Department of Energy, to reduce the cost of carbon fiber. “It’s something that may be perfectly tailored for our blades,” he said.
Segmented blades will ease installation
The research team is convinced that the standard upwind design with conventional blades won’t work for extreme-scale offshore wind turbines envisioned by the project.
“Conventional upwind blades are expensive to manufacture, deploy and maintain beyond 10 to 15 MW. They must be stiff, to avoid fatigue and eliminate the risk of tower strikes in strong gusts,” Griffith said in a statement announcing the ARPA-E grant.
Another concern is logistics. With turbine blades trending beyond 100 meters — the 12-megawatt Haliade-X turbine unveiled by GE last month will be outfitted with 107-meter-long blades — shipping the blades from the factory to the project site becomes challenging.
Blades for the 50-megawatt SUMR turbine are expected to be at least 200 meters long. A trunnion hinge near the hub would enable the blades to fully fold and stow in hurricane-force winds. And because each blade will be fabricated in five to seven segments and assembled at the project site, project developers will avoid having to figure out how to transport blades as long as two football fields.
The ultralight blades would be capable of morphing downwind, or as the researchers put it, “deforming into the direction of the flow.”
Prototype testing planned for late summer in Colorado
The research team will soon put their design concepts to the test in the real world. By late summer, testing will begin on prototype blades built at one-fifth scale to the 105-meter-long blades designed for a 13.2-megawatt SUMR turbine.
The two-bladed rotor, with 21-meter blades, will be installed on a 12-story turbine tower at NREL’s National Wind Technology Center located south of Boulder, Colorado.
An engineering and manufacturing firm based in northern Washington state that specializes in advanced composite materials and exotic metals, Janicki Industries, is building the blades, with delivery expected in early summer.
“We’re doing some things that haven’t been done before in terms of mimicking the loads and dynamics of the full-scale turbine,” said Todd Griffith. “We’re able to bring those characteristics down to the one-fifth scale where we can do the test very cost-effectively.”
Performance data from the prototype testing will be fed back into the team’s design models. The project team is scheduled to complete the design for a 50-megawatt SUMR turbine by next spring.