Charles H. Sloan-How Deep Ocean Wind Turbines Could Power the World

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Winter winds racing across the North Atlantic are so strong and steady, they could theoretically meet the world’s entire energy demand, new research shows. And with technology for floating wind turbines now being tested, the potential to tap some of that ample power source is growing.

On land, the atmosphere limits how much energy wind farms can generate. But over the ocean, wind speeds are 70 percent higher on average, and those winds are replenished from high up in the atmosphere.

“The question is, can we extract that power at a higher rate,” said Carnegie Institution for Science researcher Anna Possner, whose latest study calculates how much energy could be produced by arrays of giant floating turbines in the open ocean, far from land.

If the wind energy can be harvested more efficiently, that lowers the costs and encourages investment. And that could open new clean energy options in regions with high wind speeds, like the North Atlantic, and in areas that lack the wide coastal shelf necessary for building near-shore, fixed-base turbines, such as the U.S. West Coast and islands like Hawaii and Japan.

The new research, published in the Proceedings of the National Academy of Sciences, looked at whether wind turbines in the deep ocean would be subject to the same physical limitations as land-based turbines.

“Would multiple rows of turbines slow down the winds as much as on land? Our study shows something else is happening. The replenishment rate of kinetic energy is a lot higher,” Possner said.

The concentrated wind energy comes from the contrast between warmer temperatures over the far eastern Atlantic, where the Gulf Stream moves north along the U.S. coast, and cooler mid-ocean temperatures. The contrast stirs up storm activity that brings more wind energy down to the surface, said Carnegie climate and energy researcher Ken Caldeira, a co-author of the study.

Understanding the atmospheric conditions that help sustain the winds helps pinpoint just how much power potential is out there in the North Atlantic.

“On land, you need a 1,000-square-kilometer wind farm to produce a gigawatt of energy per year, about what an average large modern gas-powered plant produces. In our study area, the same size wind farm would produce 3 gigawatts,” Caldeira said. 

Floating Wind Turbines Could Tap This Power

Right now, the offshore wind industry is taking its first steps toward commercially producing energy in deep water, where turbine shafts can’t be built on the seafloor.

Statoil has been testing floating wind turbine technology for about nine years off the coast of Norway. This month, it plans to commission the first commercial wind farm, called Hywind, in the waters of the North Sea about 15 miles off the coast of Scotland.

Each of the five turbines towers 574 feet above the water, with blades 246 feet long. Together, they can produce 30 megawatts of power—enough energy for about 20,000 UK homes—carried by cable to Peterhead, Scotland. 

The turbines float on giant vertical stafts that end in massive underwater weights that stabilize the turbines. Each base is then anchored by cables to the sea floor, about 300 to 400 feet below the surface. Other designs for floating turbines include tri-point platforms and wide-base foundations floating near the surface, both tethered to the seafloor with cables.

Offshore Wind Costs Are Dropping

Energy from near-shore wind farms in Europe is already competitive with other sources, at $60-$65 per megawatt-hour, a price that would also be competitive in the Northeast U.S. power market, according to University of Delaware energy researcher Willett Kempton. Kempton has been involved in designing a future “supergrid” along the East Coast to efficiently move the concentrated energy from big offshore wind fields to cities.

Transmitting electrical power from turbines in deep ocean locations to the communities where it is needed is one of the biggest cost hurdles, along with the sheer logistics of building, operating and maintaining them, and there are still plenty of areas available to develop wind power closer to shore. But the cost of offshore wind power is dropping so fast that more remote locations could be feasible sooner than expected.

A recent Standard & Poors global ratings update notes that offshore wind installations are already creeping outward into deeper, more remote waters. That means increased risks from the elements, but the industry is expected to respond with engineering and design improvements and more support ships and equipment for maintenance and repair.

“In two years, it’s been more than a 50 percent price drop. We’re used to seeing maybe 10 percent per year,” Kempton said.

Such rapidly falling prices would make widespread deployment of offshore wind farms more attractive, and the new study maps the physical potential on a large scale, which can help shape development plans, Kempton said.

But for the short-term, he said, especially in the context of tackling climate change quickly, it’s wiser for the U.S. to pursue more conventional near-shore development. “We have a large continental shelf with consistent wind. We know how to build there, and the energy is just starting to come in at market cost. It’s time to hit the start button,” he said.

While the study of North Atlantic wind power is theoretical, and it’s important to consider the seasonal variation—there is much more energy potential in the winter—the overall results show deep ocean energy development is very promising, Caldeira said.

The findings will be useful as companies and countries consider the best ways to develop and deploy renewable energy on the massive global scale needed to meet ambitious carbon reduction goals, said John MacAskill, director of Offshore Wind Consultants Ltd. He likened it to studies showing a small patch of the Sahara could provide enough solar energy for all of Europe.

“This shows we’re not going to run out of the resource,” MacAskill said. “We just have to decide, where do we want to harvest it.”