💾 Archived View for gmi.noulin.net › mobileNews › 1441.gmi captured on 2023-12-28 at 20:19:13. Gemini links have been rewritten to link to archived content

View Raw

More Information

⬅️ Previous capture (2023-01-29)

➡️ Next capture (2024-05-10)

-=-=-=-=-=-=-

Floating challenge for offshore wind turbine

2009-09-08 04:04:58

By Jorn Madslien

Business reporter, BBC News, Stavanger, Norway

Heading offshore in the Rygercruise catamaran, it is a journey into uncharted

territory.

Not in terms of sea charts - the Norwegian energy giant StatoilHydro knows

these waters well, having spent the past 30 years drilling for oil and gas here

- but in terms of technology.

Statoil has constructed the world's first full-scale floating wind turbine a

couple of hours by catamaran from the oil town Stavanger, in the hope that one

day vast wind farms could be constructed far offshore in water depths of up to

700m.

Standing firm as the catamaran rolls in the waves, Sjur Bratland is optimistic

with regards to the technology's potential.

Yet, having spent the past two years listening to a whispering crowd of

nay-sayers, he wants proof. He wants to see for himself that the turbine can

cope with winter storms that whip the North Sea into a froth and winds that rip

roofs off houses.

And he wants to be sure that the supply industries can deliver the right

turbines, supply ships and so on.

Fortunately, Mr Bratland is in charge of the Hywind project, and he has been

given some 400m Norwegian kroner ($66m; 35m) to play with by Statoil, with the

government injecting a further 59m kroner.

Trouble shooting

As the turbine slowly emerges through the mist, the first impression is how

stable it is.

Hywind floating turbine Power: 2.3 megawatt

Above sea: 100m

Below sea: 100m

As the catamaran moves closer, the turbine stands as firm as if it was pinned

to the seabed, the way conventional offshore turbines are, its 65m tubular

carbon steel tower and slowly rotating 80m diameter blades, together stretching

100m above the sea.

The most interesting aspects of the turbine can be found in the depths of the

sea, where a 100m long steel cylinder weighing 3,000 tonnes thanks to its

ballast of water and rocks is anchored to the sea-bed with mooring lines that

can hold the structure at depths of up to 700m.

So-called slack anchors are used, allowing the structure to move with the seas.

In fact, in spite of its apparent sturdiness, the 138 tonne turbine is

constantly moving.

Everything below the water line is "known technology from the oil and gas

industry", where StatoilHydro has 30 years of experience from its extensive

offshore operations around the world, Mr Bratland explains.

"Actually, the really tricky thing is to apply this technology in a completely

new setting in a new industry," he says. "That has been a challenge."

Deap seas

The Hywind turbine will be tested over a two-year period, at the end of which

Mr Bratland hopes to have found proof that offshore wind farms can be built,

and that they are economically viable - perhaps even competitive with

conventional offshore wind.

Today's solutions are too costly as the margins are so much slimmer in this

area than in the oil and gas industry

Sjur Bratland, Hywind asset manager, StatoilHydro

Turbines pinned to the sea-bed are relatively cheap in water depths of up to

25m, when the basic monopole foundation can be used. At greater depths of up to

50m, the tubular turbine towers will need gravity bases and stronger steel

structures that push the price up.

Statoil's floating turbine requires the waters to be at least 120m deep, though

beyond that the sea is the limit - literally.

"But first, we'll need to look for smarter solutions that make it commercially

viable," says Mr Bratland.

Better and cheaper turbines

Above sea level, the offshore structure has been bolted together with a

conventional offshore turbine of the sort used for near-shore wind farms that

are bolted to the sea-bed.

Ease of entry for maintenance is a seemingly trivial yet major headache for Mr

Bratland.

Though the seas are relatively calm, the waves are nevertheless too large for a

safe mooring against the base of the structure to enable the BBC team to climb

the 17m steel ladders up to the service deck.

At a more fundamental level, turbine technology must be developed specifically

for far offshore conditions, he insists.

On land, turbines are getting taller all the time to accommodate ever larger

blades, explains Mr Bratland.

For the purposes of floating wind farms, such turbines are not light enough,

they are too tall and the rotor blades are too small, according to Mr

Bratland's early assessments, made even before the 2.3 megawatt turbine has

started delivering electricity through the sea-bed cable that connects it to

the Norwegian national grid.

He wants turbine manufacturers to produce lower turbines, to take advantage of

winds blowing strongly and steadily close to the surface of the sea. Closer to

land, the wind lifts to enter the beaches and climb over the cliffs.

Lower turbines should, together with clever design and material selection, help

reduce the turbines' weight, and thus their need for ballast, which in turn

should reduce sub-sea costs.

At the same time, Mr Bratland wants the power output of each turbine to be

raised to perhaps 6MW, and he wants it all to be cheaper than it is today.

This could be possible as there is tremendous potential for economies of scale,

both in terms of mass production, which reduces the cost of each turbine, and

in terms of the construction and management of vast wind farms offshore where

there are few limits on available acreages.

Moreover, onshore production of floating turbines that are then towed offshore

to be anchored in place should prove cheaper than the weather-restricted and

costly off-shore construction of sea-bed turbines.

Grid cables transporting the power to shore are neither expensive - in the

greater scheme of things - nor technologically complicated to roll out, so this

is a minor part of the project, according to Mr Bratland.

"Still, we have some way to go," says Mr Bratland.

"Today's solutions are too costly as the margins are so much slimmer in this

area than in the oil and gas industry."