MIT designs 'invisible,' floating wind turbines

PhysOrg ^ | 9/19/2006 | Nancy Stuaffer

[Uncledave]

MIT designs 'invisible,' floating wind turbines

An MIT researcher has a vision: Four hundred huge offshore wind turbines are providing onshore customers with enough electricity to power several hundred thousand homes, and nobody standing onshore can see them. The trick? The wind turbines are floating on platforms a hundred miles out to sea, where the winds are strong and steady.

Today's offshore wind turbines usually stand on towers driven deep into the ocean floor. But that arrangement works only in water depths of about 15 meters or less. Proposed installations are therefore typically close enough to shore to arouse strong public opposition.

Paul D. Sclavounos, a professor of mechanical engineering and naval architecture, has spent decades designing and analyzing large floating structures for deep-sea oil and gas exploration. Observing the wind-farm controversies, he thought, "Wait a minute. Why can't we simply take those windmills and put them on floaters and move them farther offshore, where there's plenty of space and lots of wind?"

In 2004, he and his MIT colleagues teamed up with wind-turbine experts from the National Renewable Energy Laboratory (NREL) to integrate a wind turbine with a floater. Their design calls for a tension leg platform (TLP), a system in which long steel cables, or "tethers," connect the corners of the platform to a concrete-block or other mooring system on the ocean floor. The platform and turbine are thus supported not by an expensive tower but by buoyancy. "And you don't pay anything to be buoyant," said Sclavounos.

According to their analyses, the floater-mounted turbines could work in water depths ranging from 30 to 200 meters. In the Northeast, for example, they could be 50 to 150 kilometers from shore. And the turbine atop each platform could be big--an economic advantage in the wind-farm business. The MIT-NREL design assumes a 5.0 megawatt (MW) experimental turbine now being developed by industry. (Onshore units are 1.5 MW, conventional offshore units, 3.6 MW.)

Ocean assembly of the floating turbines would be prohibitively expensive because of their size: the wind tower is fully 90 meters tall, the rotors about 140 meters in diameter. So the researchers designed them to be assembled onshore--probably at a shipyard--and towed out to sea by a tugboat. To keep each platform stable, cylinders inside it are ballasted with concrete and water. Once on site, the platform is hooked to previously installed tethers. Water is pumped out of the cylinders until the entire assembly lifts up in the water, pulling the tethers taut.

The tethers allow the floating platforms to move from side to side but not up and down--a remarkably stable arrangement. According to computer simulations, in hurricane conditions the floating platforms--each about 30 meters in diameter--would shift by one to two meters, and the bottom of the turbine blades would remain well above the peak of even the highest wave. The researchers are hoping to reduce the sideways motion still further by installing specially designed dampers similar to those used to steady the sway of skyscrapers during high winds and earthquakes.

Sclavounos estimates that building and installing his floating support system should cost a third as much as constructing the type of truss tower now planned for deep-water installations. Installing the tethers, the electrical system, and the cable to the shore is standard procedure. Because of the strong offshore winds, the floating turbines should produce up to twice as much electricity per year (per installed megawatt) as wind turbines now in operation. And because the wind turbines are not permanently attached to the ocean floor, they are a movable asset. If a company with 400 wind turbines serving the Boston area needs more power for New York City, it can unhook some of the floating turbines and tow them south.

Encouraged by positive responses from wind, electric power, and oil companies, Sclavounos hopes to install a half-scale prototype south of Cape Cod. "We'd have a little unit sitting out there andŠcould show that this thing can float and behave the way we're saying it will," he said. "That's clearly the way to get going."

This research was supported by the National Renewable Energy Laboratory.

Source: MIT, by Nancy Stauffer

[Boiler Plate]

Conversion from AC to DC and vice versa is fairly easy, however to transmit a hundred miles would require the use of extremely high voltages and most likely DC. The problem is that this would quite simply be a maintenance nightmare. Someone may come up with a way to do this economically but at present I would estimate at $100 a foot to install the power lines or about $50 million.

[Locomotive Breath]

http://ewh.ieee.org/soc/pels/pdf/pelsNL0306.pdf

page 17, figure 5 and 6

Fig. 5 - Doubly-fed induction generator
Fig. 6(a) - Synchronous generator with gearbox
Fig. 6 (b) - Multi-pole synchronous generator with field control
Figure 6(c) - Multi-pole permanent magnet synchronous generator

These are all AC machines. (The old-fashioned brush-type DC generator you're thinking of is too inefficient and high maintenance.) You'll note that, except for the doubly-fed synchronous, all systems take the ac and convert it to dc and then back to ac for connection to the utility. This is because the electrical output frequency of the generator depends on rpm while the utility is a constant 50 or 60 Hz. The two sets of crossing circles on the right represent a transformer that steps the voltage up for transmission from the remote site to the power grid.

[Locomotive Breath]

Well, that was just a guess on my part. The link to the offshore nuclear plants was very interesting but I don't see how it follows from what I said. Did you mean to reply to a different post?

[Red Badger]

No, I just thought you might interested in Offshore Floating Power ideas that go way back.............

[Locomotive Breath]

Got it. Thanks. I grew up and was in Norfolk at the time but don't remember this. I guess it went to FL to early to make much of a splash locally.

[Mogollon]

Also, they will kill hundreds of sea gulls, pelicans etc that happen to be flying past.

[Red Badger]

I think that it's overall, a good idea. NIMBY's can't complain, and even in the unlikely event of an accident, there's no one around to evacuate. Employees could don special suits to protect them..............

[Kenny Bunk]

How are they going to get the electricity onshore?

Big fat underwater cables connected to a substation in the the Hyannis front yard of a big fat guy I know.

[uglybiker]

Yeah, but where you don't have NIMBY's, you have BANANA's -- Build Absolutely Nothing Anywhere Near Anything.

Trust me. Somebody's gonna b**ch about it.

[Larry Lucido]

How are they going to get the electricity onshore?

Tugboats.

[Comstock1]

This is slightly off topic, but I recently encountered my first wind farm. I went through the Oklahoma panhandle at about two in the morning on my way from Amarillo to Denver about three weeks ago. Returning a couple days later I was shocked to discover that I had driven right through a very large wind farm that had dozens of these giant General Electric wind turbines.

I had never seen one before and I have to say it is quite impressive. There was very little wind that I could observe on the ground, but the turbines were turning at a fairly steady rate. The cattle grazing around them didn't seem to be disturbed at all.

[Red Badger]

The cattle grazing around them didn't seem to be disturbed at all.

Yeah, but the cows now give pre-churned butter and pre-mixed milkshakes........

[uglybiker]

And homogenized milk!

[fortunecookie]

Sure! And I get will get royalties for my idea when I was a teen to package yogurt and granola together. My friends laughed at my idea. I think McDonald's alone owes me millions! ;-)

(Don't ya hate it when a big group beats ya to it...)

[AFreeBird]

Alternators, just like in your car, produce AC power which is converted to DC to run your electrics and charge your battery.

So in this case, no conversion would be needed.

Alternator Secrets

[rellimpank]

---thanks a bunch--that's what I've been looking for ---

[rellimpank]

---AC power to go on line must be in phase and hold closely to 60hz--in fact, I suspect the most "precision" measurement the average person is exposed to is AC power from the plug in the house.

My curiosity was how varying wind speed is converted and the above excellent reference answered all my questions--

[Reeses]

How are they going to get the electricity onshore?

That would be a fun engineering test question.

They could make hydrogen gas and fly it in by air tanker. Hmmm, maybe the windmills could cause extra cloud formation and transport the energy via hydro power. That might be surprisingly efficient and would cool the Earth's surface, the man made clouds bouncing the sunlight out to space.

[antiRepublicrat]

(Don't ya hate it when a big group beats ya to it...)

I thought of anti-skip buffer memory in a portable CD player a couple years before they even started making portable CD players (without an anti-skip buffer, that didn't show for a couple more years).

I'd be a billionaire now.

[fortunecookie]

I thought of anti-skip buffer memory in a portable CD player a couple years before they even started making portable CD players (without an anti-skip buffer, that didn't show for a couple more years). I'd be a billionaire now.

Indeed. A very cool idea. I don't know that I'd be a billionaire with my granola/yogurt idea, but I'd probably bump into you at the Club, and ask how you were enjoying the brunch, featuring my granola yogurt in it's various flavors. ;-)