Floating Wind Turbines Deep at Sea are Both Compelling and Costly

By Doug Peeples

SGN News Editor

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Researchers and wind energy advocates are setting their sights on the potential for harnessing the relatively consistent and powerful winds of the deepwater ocean—which could, despite some serious obstacles—provide the new Smart Grid with one of the most compelling renewable energy options available.

There are several advantages to deepwater wind over that generated on land or in shallow water—and probably as many disadvantages: The wind is stronger and more consistent, but exorbitant costs and mindboggling technical challenges are part of the equation, too. And transmission lines are needed to carry the wind power from the source to where it's needed. Undersea transmission lines are not uncommon and generally have approval and permitting processes similar to those for land-based systems, but probably more of them. In addition to meeting environmental and siting requirements — yes, even on the sea floor — tidal, meteorological, safety, failure, maintenance and other issues also must be addressed.

While undersea cable can be assembled on the sea floor, that option is impractical at depths over a few hundred feet. At that point, purpose-built barges and cranes are typically used. Costs vary depending on circumstances, but purpose-built equipment adds considerable expense to the already high cost of undersea transmission.

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Advocates: Payoff Worth the Cost

Yet ocean wind advocates are optimistic that their efforts will lead to technologies that will be able to add a significant amount of clean, renewable energy for the nation's electric grid.

The director of the Advanced Structures and Composites Center at the University of Maine, Habib J. Dagher, thinks the payoff would be worth the effort. "Our real opportunity for ocean energy is deepwater wind," Dagher was quoted as saying in a New York Times article.

With a little help from an $8 million DOE grant, Dagher is setting up a consortium of universities, government agencies, companies and nonprofits to take on the task of developing floating wind turbines. He anticipates having prototypes to test miles off the Maine coast in 2011.

Norway's Statoil, a large oil and gas company, beat everyone to the punch by launching a full-size floating turbine six miles off the Norwegian coast. It's the first full-scale floating turbine in the world.

The Statoil turbine is fastened to a ballasted cylinder and held in place with cables attached to the sea floor. it began generating electricity in September. However, the project—named Hywind—is more properly considered a research project than a generation project.

The prototypes Dagher wants to see off the coast of Maine will come from Principle Power, an American company, and Blue H USA, a Dutch subsidiary operating in the U.S. Blue H USA has asked for a permit to build a test platform, minus the turbine, more than 20 miles south of Martha's Vineyard to collect environmental and engineering information.

Deep sea floating turbines offer several tantalizing features. One is that they are out of sight over the horizon. A large wind farm proposed five miles off the coast of Cape Cod has been facing serious, vehement and well-funded and well-organized opposition from residents who insist the turbines would spoil their view. And two local Indian tribes contend the location of the proposed wind farm has cultural significance for their people.

While the Cape Wind project isn't dead in the water, what originally was an expensive proposition is becoming more so.

None of that would happen in the deep sea. The turbines would be far from shipping lanes, migratory bird and aircraft flight paths and fishing areas—all of which should make the permitting process easier. Also, the winds are much stronger and much more consistent over deep water. Advocates also say it makes much more sense to tap a resource close to coastal population centers than transmit it from distant wind farms on the Great Plains.

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Daunting Challenges

Sounds great, but the downside is daunting. A 5GW deepwater wind farm was estimated by Maine officials to require an investment of roughly $20 billion. The Hywind turbine had to be built at sea, and even those turbines that can be built on land or near shore are still going to be expensive. Consider installation, repair and even routine maintenance costs for a farm of turbines 10 miles offshore.

Also, as Dagher concedes, deepwater installations present an array of baffling technical issues. While the bulk of the structural floating platform technology comes from the offshore oil and gas industries, those platforms float and aren't stable. At this point, turbines are not designed to withstand constant jostling from high seas and storms. Couple those issues with the transmission line construction and maintenance  challenges noted above, and it doesn't take an Einstein to realize it is, to put it mildly, a very tough proposition.

"There's no technical reason why you can't take a platform, put a turbine on it and get it to work," said Jason Johkman, who analyzes offshore designs for the National Renewable Energy Laboratory in Golden, Colorado. But Jonkman, also quoted in the New York Times piece, said, "The only question is, can you do it at a reasonable cost?"

The bottom line? A host of mind-numbing technical challenges and equally mind-numbing costs versus a strong and relatively consistent source of renewable energy.

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