How do floating wind turbines work? With 5 companies winning the first US leases to build wind farms off California's coast, let's take a look
Published in Science & Technology News
Semisubmersible platforms have large floating hulls that spread out from the tower, also anchored to prevent drifting. Designers have been experimenting with multiple turbines on some of these hulls.
Tension leg platforms have smaller platforms with taut lines running straight to the floor below. These are lighter but more vulnerable to earthquakes or tsunamis because they rely more on the mooring lines and anchors for stability.
Each platform must support the weight of the turbine and remain stable while the turbine operates. It can do this in part because the hollow platform, often made of large steel or concrete structures, provides buoyancy to support the turbine. Since some can be fully assembled in port and towed out for installation, they might be far cheaper than fixed-bottom structures, which require specialty vessels for installation on site.
Floating platforms can support wind turbines that can produce 10 megawatts or more of power – that’s similar in size to other offshore wind turbines and several times larger than the capacity of a typical onshore wind turbine you might see in a field.
Some of the strongest wind resources are away from shore in locations with hundreds of feet of water below, such as off the U.S. West Coast, the Great Lakes, the Mediterranean Sea and the coast of Japan.
The U.S. lease areas auctioned off in early December cover about 583 square miles in two regions – one off central California’s Morro Bay and the other near the Oregon state line. The water off California gets deep quickly, so any wind farm that is even a few miles from shore will require floating turbines.
Once built, wind farms in those five areas could provide about 4.6 gigawatts of clean electricity, enough to power 1.5 million homes, according to government estimates. The winning companies suggested they could produce even more power.
But getting actual wind turbines on the water will take time. The winners of the lease auction will undergo a Justice Department anti-trust review and then a long planning, permitting and environmental review process that typically takes several years.
Globally, several full-scale demonstration projects with floating wind turbines are already operating in Europe and Asia. The Hywind Scotland project became the first commercial-scale offshore floating wind farm in 2017, with five 6-megawatt turbines supported by spar buoys designed by the Norwegian energy company Equinor.
Equinor Wind US had one of the winning bids off Central California. Another winning bidder was RWE Offshore Wind Holdings. RWE operates wind farms in Europe and has three floating wind turbine demonstration projects. The other companies involved – Copenhagen Infrastructure Partners, Invenergy and Ocean Winds – have Atlantic Coast leases or existing offshore wind farms.
While floating offshore wind farms are becoming a commercial technology, there are still technical challenges that need to be solved. The platform motion may cause higher forces on the blades and tower, and more complicated and unsteady aerodynamics. Also, as water depths get very deep, the cost of the mooring lines, anchors and electrical cabling may become very high, so cheaper but still reliable technologies will be needed.
But we can expect to see more offshore turbines supported by floating structures in the near future.
This article was updated with the first lease sale.
This article is republished from The Conversation, an independent nonprofit news site dedicated to sharing ideas from academic experts. It was written by: Matthew Lackner, UMass Amherst. News from experts, from an independent nonprofit. Try our free newsletters.
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Matthew Lackner receives funding from the U.S. Department of Energy.