Could Floating Wind Turbines Solve Our Energy Crisis?

Wind is free, and there's plenty of it. Researchers around the world are racing to be the first to capture wind energy on the high seas.

By Daniel Hautmann??
TAGES-ANZEIGER/Worldcrunch

OSLO - It was two in the morning when ?Sway? went down. Hurricane Berit had whipped up winds to speeds of 165 km per hour over the Atlantic off Norway's coast. Even in the relatively sheltered fjord of Hjeltefjorden, near the mountains, Berit was in such a frenzy it tipped and sank Sway, the newly lauched prototype of a floating wind turbine.

Which is not to say that the floating wind turbine is a write-off - quite the opposite. The prototype will be back in the water soon, says manager Michal Forland, adding that Berit and its 6-meter high waves was too much for the 1:6 scale prototype: ?The hurricane would not have been able to affect the full-size turbine, which can handle waves of up to 40.6 meters.? Also, the prototype survived sinking. ?Its structure was not damaged; it?s just a question of replacing some of the electronic components,? says Forland.

Some of these components include instruments from the National Renewable Energy Laboratory (NREL) in Golden, Colorado. Caught between two oceans, the United States are very interested in the development of floating turbines. Among the NREL instruments on Sway were various sensors to measure just how such turbines move.

Around the world, the pressure is on as researchers and companies race to be the first to develop this highly promising technology. Capturing wind energy on the high seas is something that is becoming of increasing interest. NREL tests and calculations indicate that the potential for the U.S. alone is 900 gigawatts ? bigger than the sum total produced by all power plants in the country.

At the end of 2010, 98.5% of all the world?s wind turbines were on land. That is going to change, says John Olav Tande of the Norwegian SINTEF research foundation. ?The world?s oceans provide us with a practically unending potential, many times larger than global energy need,? says Tande.

The big problem with harnessing wind energy on the open seas is the depth of the water. Almost everywhere, it is so deep that floating platforms are the only option. For example, 61% of American offshore wind resources are over water depths of 100 meters or more. Japan?s coasts also represent a challenge, and in Europe parts of both the Mediterranean and the Atlantic off Norway are very deep as well ? up to 700 meters to the sea floor. Which per se is a good thing, says Jochen Bard of Germany?s Fraunhofer Institute for Wind Energy and Energy System Technology. ?The deeper the water, the stronger the wind over it.?

Learning from oil rigs

According to calculations, the usable potential of wind over water up to 200 meters deep is three times what it is in areas with a water up to 50 meters deep. That means that in Europe alone, 8,000 terawatt hours (TWh) could be harvested annually. (In comparison, in 2010, the amount of electricity used by the entire EU in one year amounted to 3,500 TWh.) Experts agree that floating platforms are the best way to capture these resources. But producing a floating turbine is a huge challenge because the machine has to dance with the waves and turn with the wind.

But there are any possibilities, some of which can be taken from the oil and gas industries, which have been erecting platforms in stormy seas for a very long time. These companies used to anchor their platforms to the sea floor ? but no longer, and today there are only floating platforms that are, especially in deep water, far cheaper to erect and just as solid. So it is logical that future wind turbines be erected in similar fashion.

?But it?s too early to talk about any kind of winning concept,? says Tande. Right now, the only thing we know for sure is that floating turbines offer a series of advantages, like being much faster to build than installations that have to be attached to the sea floor. Construction equipment and procedures are less complicated as well. Then there is the higher amount of wind harvested, which could compensate for the higher expense of the new technologies that have to be developed for the turbines to work.

A model for such turbines already exists ? Hywind, the world?s first full-scale floating wind turbine. The floating structure belongs to Norwegian energy company Statoil and has been up and running since September 2009. It proved during Berit that it can withstand hurricane force conditions. The installation sits 12 km off the southwest coast of Norway, where the Atlantic is 220 meters deep. Its spar buoy goes down 100 meters and is held in place by three cables fastened to the ocean floor.

The buoy is filled with water and stones, and weighs 3,000 tons. The tower thrusts 65 meters up out of the water, topped by a 2.3-megawatt Siemens rotor. Jochen Bard calls the project, which has already cost 50 million euros, a ?milestone.? It taught Siemens engineers that ?floating turbines can be built and run exactly like turbines on land assuming one has control over the movement caused by the floating,? says Per Egedal of Siemens Wind Power. ?What we need is cushioned control.?

The idea is to use movement and acceleration sensors in the tower to measure movement.The measurements can then instruct the drive to correct the rotation speed of the rotor as needed in real time and adjust the angles of the blades. According to Egedal, this is the technology needed for the era of floating wind turbines to begin.

Read the original article in German

Photo -??L.C N?ttaasen?

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June 3rd, 2012 - 19:06

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