The University of Massachusetts Amherst

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Floating Turbines

A new way to develop offshore wind
  • picture of floating and fixed-bottom turbines off shore.

“In the U.S, about 60% of the available waters for developing wind energy are deep water sites, so it would require floating turbines.” – Matthew Lackner

Have you ever wondered why surfers prefer riding the waves on the Pacific coast of the United States rather than the Atlantic? Unlike the steep drop of the west coast continental shelf, the eastern seaboard slopes gradually into the sea, limiting the size of the waves. Though not great for surfing, that gradual slope presents an advantage to developing offshore wind energy.  

The gradual slope and smaller waves bode well for situating turbines that can be fixed to the ocean floor. But in some areas, near-coast conditions, such as shipping lanes, bird migratory paths, and pleasure boat use, can present barriers to fixed-turbine installation. Locating offshore wind farther out at sea poses a challenge, too, as fixed-bottom turbines are not a viable choice for deep waters. Matthew Lackner, Associate Professor of Mechanical Engineering and associate director of the UMass Amherst Wind Energy Center (WEC) is working on a solution. 

“In the U.S, about 60% of the available waters for developing wind energy are deep water sites, so it would require floating turbines,” says Lackner. 

Unlike a fixed-bottom turbine which has a foundation that’s attached to the ocean floor, a floating turbine sits atop a platform that is anchored to the sea bottom. It’s more dynamic than a fixed bottom system, and has advantages and disadvantages which must be understood to best develop and implement the technology, says Lackner. 

Designing for Deep Wate

“Instead of a fixed platform, you have a platform that can move in three dimensions and rotate in three dimensions” says Lackner. “It has six additional degrees of freedom. It’s harder to model and it potentially results in larger forces and moments on the structure, so it could impact reliability,” he says. 

Lackner and his team are using computer simulations and scaled model experiments to understand the technical challenges. It’s a complicated process that includes defining simulation conditions, identifying good turbine models, and testing safety factors to ensure the reliable operation of these very large turbines. 

As turbines have gotten bigger, so have the blades, says Lackner.  He asks, “What are the factors that limit the design and how do we approach this for further development? Acknowledging that the aerodynamics for floating turbines is complicated, can we design blades that are specifically optimized for floating turbines that go through more unsteady behavior compared to a fixed bottom turbine, to increase the efficiency of floating turbines?” 

The Pros 

Reduced installation costs. Floating turbines can be assembled in port and floated out to sea to be installed, potentially reducing costs. 

“Right now offshore turbines require huge vessels with these monster cranes to lift the components and place them, and they’re really expensive. So if you can mass produce and assemble turbines in port and then just float them out and connect the mooring lines to the anchors, that could be a much cheaper method for installation,” says Lackner. 

Wildlife protection. This method also reduces installation noise since it doesn’t require pile driving, mitigating disruption to wildlife and other negative effects to the marine ecosystem in the installation area. 

Public acceptance. Since floating turbines are implemented in waters farther from the coast they are out of view from people who live in these areas, says Lackner, mitigating some of the public acceptance issues that arise from developing offshore wind near coastal areas. 

The Cons 

Reliability. One of the research challenges to modeling floating turbines is the complicated nature of such a dynamic system. There is the potential for larger forces and movements on a floating structure than a fixed-bottom turbine, which could impact reliability. 

“Some of our recent work has shown that floating motion changes the power output of the turbine and the forces on the blades, so the design of the turbine may need to change,” Lackner said. 

The Future 

Lackner says that he sees floating turbines being implemented at commercial scales within the next decade. As the east coast becomes increasingly interested in this renewable energy, further research needs to be conducted to ensure proper development of floating offshore infrastructure. 

“With a floating turbine now, generally what you're doing is taking a regular offshore turbine and just plopping it on a floating platform and hoping for the best. I think integrated design is the next research area, where the platform, the turbine, the blades, and the controller are all designed in an integrated way to get an optimized floating system,” says Lackner.  “Five to ten years from now I would guess full commercial floating projects will get started, and I think by 2030-2040 the cost of floating wind can be competitive with the costs of offshore wind in general. It has some real advantages that, with economies of scale, will allow the costs to really come down.” 

The research that Lackner and his team conduct continues to be important to the implementation of offshore wind. Last year, Lackner and other WEC members published a white paper with the Massachusetts Research Partnership in Offshore Wind that outlines a strategy for multidisciplinary offshore wind research. By bringing in multiple disciplines to study floating turbines, the WEC helps to advance the development of this growing renewable technology that will be present in our oceans in the coming years. 

“We’re one of the few programs in the country that has such a broad and diverse set of experts all interested in wind. I think our success lies in our ability to approach these system-level topics and really find solutions that can’t be solved by a single person, but that require people from different disciplines working together.”

Shayla Costa '19

Banner Photo: Joshua Bauer/NREL