Energy

Extraordinary contra-rotating floating wind turbines to begin testing

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Contra-rotating vertical turbines could radically improve yield and reduce LCoE for floating offshore wind projects
World Wide Wind
Contra-rotating vertical turbines could radically improve yield and reduce LCoE for floating offshore wind projects
World Wide Wind
AF Gruppen and World Wide Wind have signed a deal to test the first prototype of the device
World Wide Wind
Anatomy of a contra-rotating floating VAWT
World Wide Wind
The team hopes to have an enormous commercial installation running before 2030
World Wide Wind
The towers could scale to unprecedented size and power
World Wide Wind
WWW claims its bottom-heavy, tilting, contra-rotating coaxial turbines solve offshore wind's scale limitations, and will grow to 400 m high, with a 40 MW capacity
World Wide Wind
The top turbine, mounted to a central blade, spins in one direction, while the bottom, and the tower's exterior, spins in the other, with the generator at the bottom
World Wide Wind
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A wildly innovative turbine that could halve the cost of offshore wind is set to go into testing in Norway. The 19-m (62-ft), 30-kW, contra-rotating vertical-axis turbine is a prototype of a design that could scale to unprecedented size and power.

Most wind turbines look like a propeller on a stick – which is fine, except once you take the concept out into the deep ocean, where the vast majority of the world's best wind power resources are, and scale it up, it's a design that makes less and less sense. All the heavy bits are right up the top, so it's difficult and expensive to build and maintain a floating version that doesn't want to tip over in the wind.

That's what makes World Wide Wind (WWW)'s contra-rotating VAWT such a fascinating alternative. All the heavy generator business is kept right at the bottom – indeed, under water and below the turbine's floating pontoon. That adds enough weight at the bottom to keep the whole thing from topping into the water, requiring only a set of mooring anchors.

Anatomy of a contra-rotating floating VAWT
World Wide Wind

The generator's rotor and stator are then connected to a pair of vertical-axis turbines, each running three blades at 45 degrees from the main tower shaft. The lower turbine is set to rotate in one direction, and the upper one, mounted on a pole that runs up the middle of the lower one, is set to rotate in the other direction.

The blades are simple and fixed, and harvest useful torque from the wind most of the way around, much like sailboats can.

"The only time it will not catch speed is when it's going directly upwind, or directly downwind," WWW CTO Hans Bernhoff told us in an interview last year. "As a vertical axis blade goes around, it more or less gets torque on 300 degrees of the 360."

The generator resistance can be managed by the microsecond to control the speed of the turbine.

Thus, whichever way the wind's blowing, the floating double VAWT passively tilts to an optimal angle, and the two turbines begin turning in opposite directions, effectively doubling the speed at which the "rotor" is turning in the "stator."

"You can think of that as a way to double your power generation, or as a way to reduce your generator cost by half," former WWW CEO Trond Lutdal told us. "So it's lower cost, it's much more scalable, and any maintenance happens at the bottom and not hundreds of feet up in the air."

The towers could scale to unprecedented size and power
World Wide Wind

The torque placed on the structure by the wind is effectively neutralized by the two opposing rotations. On top of this, the conical sweep of each rotor reduces blade tip speed, and produces less of a wake effect behind it, so in a practical wind farm situation, the company says they can be deployed closer together, generating more energy from a given area and reducing connection cabling.

Using some interesting materials choices, WWW says it sees a clear path to scale these machines up to a monstrous 400 m (1,312 ft) tall, at which point a single tower could harvest an enormous 40 MW – nearly twice what the world's largest wind turbines can do – and more importantly, it could massively drop the Levelized Cost of Energy (LCoE) for offshore wind to less than US$50/MWh – that's less than half the cost of what regular horizontal-axis towers are shooting for by 2027.

So they're a very exciting prospect, as well as a fascinating thing to look at, which is why we're happy to hear the team has signed an agreement to begin testing a small-scale prototype in partnership with AF Gruppen, one of Norway's largest industrial construction groups.

AF Gruppen and World Wide Wind have signed a deal to test the first prototype of the device
World Wide Wind

The 19-m prototype will be tested at AF's Envinronmental Base in Vats, nestled deep in the hills, on the banks of a fjord, off a fjord, off a fjord, off a fjord, on the heartbreakingly beautiful southeast Norwegian coast. Right among Slartibartfast's greatest and most fiddly work.

While there's no timetable laid out for this test, the company says its next prototype will be a much larger 1.5-MW pilot, scheduled to begin testing in early 2025 – and it hopes to launch a commercial 24-MW turbine before 2030, which would be the world's largest offshore turbine by a decent margin if it launched today.

“We are very proud to test our first prototype in cooperation with AF Gruppen,"says Bjørn Simonsen, new CEO of WWW, in a press release, "and look forward to the launch and subsequent test program, as well as exploring further opportunities for collaboration. We very much appreciate the support we have received from the AF team so far and are very grateful that they are letting us use their yard at Vats for the test."

Bring it on! If these massive machines do what they say on the tin, the world needs them yesterday.

Source: World Wide Wind

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9 comments
windykites
How will the generator be serviced, as it is underwater? The blades look much slimmer than the usual style, thus saving fibreglass.
BlueOak
Shouldn’t be all that difficult to have a hatch above sea level and a water tight access way down to the generator bits at the bottom for maintenance.
jzj
Why is the motor etc. positioned deep under water? If it was right above the pontoon, it wouldn't be destabilizing, and would be simple to maintain.
As for all the claims of efficiency, etc. -- well, let's just see how it works. I like the idea as simpler to install, but it doesn't seem inherently super-efficient. Obviously, wind turbines are all about clean swept area -- look at the fuss they go to in putting the blades ahead of the tower and not more simply place them behind the tower just to get a bit more unblocked swept area -- and this design has little clean swept area.
And unfortunately, I didn't catch the "Off a fjord..." reference.
oldpistachio
Wouldn't some of these features work, and make sense financially, on land also??? Starting the counter-rotating? Heaviest elements down low?

btw I thought that was a typo - I think it means a big fjord leads from the sea, then there's a smaller fjord, then a still smaller fjord branching off of that one etc.?
Baker Steve
What windykites says, and also what about acoustic noise upsetting the whales and whatnot?
Sumpvesen
The designers need to keep in mind that the vertical tube under water needs to have a diameter large enough to allow for the complete removal and replacement of the generator should this be necessary. In other words the generaor has to be able to be hoisted up and out through an access hatch located above water. Another option to consider is pacing the generator above sealevel with a ballast filled counterweight suspended deep bellow waterlevel. Jeg tror dette er en bedre ide.
anthony88
Does it generate enough power to charge a Fjord F-150 Lightning?
NMorris
@windykites, it should be easy enough to have a sealed unit gen set which simply gets detached and taken on shore for service, and plug a replacement on before you leave.
@jzj, put the gen set as far down as possible to be the counterweight most efficiently for the blades and tower above water level.
@oldpistachio, on land, the tilting wouldn't work as well as it does on the water. You would need a fully rotational hinge at ground level, which makes for high maintenance and risk.
@sumpvesen, why do you have to take the gen set up, why not a self sealing joint and take it off the bottom?
The.Lurkin.Jerk
Right direction on concept, but what we are shown in the nice illustrations needs complete rethink. This design is far too likely to have a blade strike the water, which will kill it in moments both from blade impact and imbalance. There is no reason to build straight towers either- the tower can and should have a roughly 45deg. bend near the top. 2 rotors is dubious and the lower rotor, after being formed to resist wave strikes, won't provide useful power. The blade config offers a small fraction of effective swept area compared to a conventional rotor. A conventional single downwind rotor, designed to swing up to spill wind, will give itself lift to counter the heeling that would result from strong wind. Any electric or mechanical equipment below waterline is unworkable, enough said there.
I'd be happy to help with a redesign; I have some experience in wind energy concept work.