Floating Wind Turbines to Be Tested

It's too costly to build turbines in deep water, where the winds are better. Two companies think floating windmills are the answer

PHOTO: Øyvind Hagen / StatoilHydro

22 June 2009—On the weekend of 6 June, boats hauled a 120-meter-tall steel tower into the Amoy Fjord off Stavanger, Norway. Pulled upright and filled with ballast water, the tower became the buoy for the world’s first full-scale floating wind turbine. The turbine, now placed 10 kilometers from the coast, is expected to start feeding power into the mainland grid by mid-July. Over the next two years, Norwegian energy company StatoilHydro will test how the 2.3-megawatt turbine holds up in 220-meter-deep water.

Much could go wrong. Corrosion, floating debris, sea ice, and marine growth are some of the concerns. More important, the buoy, which is tethered to the seabed with three cables, must keep the turbine from pitching and rolling too violently in ocean swells. If the buoys and cables fail, the blades could hit the water, or in the worst case, the entire turbine could overturn.

That could be disastrous for the more than US $62.5 million project. But the turbine’s developers at StatoilHydro don’t seem too worried. The buoy is based on a tried-and-tested design used for floating oil- and gas-drilling platforms. The ballast-filled steel cylinder extends 100 meters underwater, pulling the center of mass low to keep the turbine upright. The turbine can move sideways but can’t bob up and down much. ”We did a small-scale test in 2005 that gave us very promising results,” says Øistein Johannessen, StatoilHydro’s spokesperson for new energy. ”Both pitch movements and acceleration forces will be stronger [in the sea], but our initial hypothesis is that our motion controller will overcome these challenges.”

Blue H Technologies, in the Netherlands, is the only other company planning to generate power from floating turbines. It installed a prototype deep-water platform with an off-the-shelf 80-kilowatt turbine off Puglia, in southern Italy, in the summer of 2008. The company is now making its own turbines and expects to deploy an operational 2-MW unit next year. And it’s pushing for authorization for a 3.5-MW demonstration project off Martha’s Vineyard, an island off of the northeast U.S. coast. ”[We hope] to benefit from an interest in offshore wind energy from the current administration,” Neal Bastick, CEO of Blue H, says. ”The U.S. has no wind farms approved offshore, period, yet it has ideal conditions for offshore wind.”

But what advantage do floating turbines have over existing offshore turbines, whose bases are driven up to 30 meters beneath the seabed? Wind farms that are out of sight and far from busy coasts would face less public opposition, says Jason Jonkman, a wind technology researcher at the National Renewable Energy Laboratory (NREL) in Golden, Colo. Winds on open oceans are also stronger and steadier than in coastal areas, so turbines would be more productive. Floating turbines make the most economical sense for deep waters, because fixed turbines must be built taller and wider at the bases the deeper you go. ”Beyond 50 meters, it’s not cost effective to build a massive structure that’s pounded into the seabed,” Jonkman says.

Floating wind farms would be ideal for countries such as Norway, Italy, and Japan, which don’t have shallow coastal waters. And there’s a strong case to be made for the United States, where 810 of the more than 1000 gigawatts of offshore wind potential are in waters deeper than 30 meters, according to the World Energy Council.

At least over the next decade, most new offshore wind energy is going to come from fixed turbines. And the development will be nearly all in Europe. The European Wind Energy Association predicts the European Union will have installed 35 GW of wind power in shallow waters by 2020.

Yet a move to floating deepwater turbines is inevitable, according to NREL. That evolution could speed up if StatoilHydro and Blue H show that the economics of floating turbines work out better. StatoilHydro plans to make bigger 5-MW turbines in the long run, which could bring down energy costs. Today’s shallow-water turbines cost between $2.4 and $3 million per megawatt to install, according to the World Energy Council. But since floating turbines wouldn’t need seabed construction, large ships, or equipment out at sea, or require decommissioning a large installed structure, Blue H is ”bullishly sure we’ll be significantly less expensive,” says 'Blue H's Bastick.

About the Author

Prachi Patel is a contributing editor at IEEE Spectrum and a reporter for Spectrum Radio. In May 2009, she reported on a DVD concept that can store 1.6 terabytes on a single disk.

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