Thinking big

Thursday, 26 November, 2015 - 11:00
The prototype of Siemens’ SWT-7.0-154 in Østerild, Denmark, was installed only a few months after the product launch at the EWEA Offshore trade show in Copenhagen. (Photo: Siemens)
The prototype of Siemens’ SWT-7.0-154 in Østerild, Denmark, was installed only a few months after the product launch at the EWEA Offshore trade show in Copenhagen. (Photo: Siemens)

The offshore market is ­currently a heady mix of top marks for ­performance and rotor diameters on the one hand and mergers on the other. The purpose of large rotor blades, more generator output and mergers is the same: slashing costs.

Areva Wind and Gamesa merging to become ­Adwen, and Vestas and ­Mitsubishi joining forces have triggered an ­initial process of consolidation.  Companies are aiming to reduce competition by garnering more market power and capital and improving their ability to weather periods of low order intake. In parallel, turbine suppliers are outdoing each other with considerable boosts in power output. The purpose of the new ­giants in the manufacturers‘ product ranges is to cut investors’ costs by achieving an offshore wind farm’s maximum capacity with ­fewer ­machines. This would mean less outlay for the ­components required, installation and subsequent operation.

With an 8 MW capacity and a rotor of 164 m in diameter, MHI Vestas Offshore Wind has gained the first breakthrough towards reaching 10 MW. For the V164, Vestas is sticking with its gear drive and relying on a medium-speed drivetrain. This is a definite technological trend regarding offshore. In this case two- or three-stage speed converters and a permanently excited generator are alternative options to direct drive. The idea behind these concepts is to reduce losses inside the gear drive by better efficiency in the partial load range and to minimize wear through moderate speeds. In the case of direct drives, the philosophy is that if there aren’t so many components inside not as much can go wrong.  For this technology, the cost benefits appear to be from the lack of a gear drive and the fact that fewer components reduce the need for maintenance. The biggest boost in capacity is currently from aerodynamically optimized rotor blades which are getting longer and longer. However, cost reductions of up to 40 % that the industry is hoping for can only be achieved by industrial processes and this is where volume matters most.

Vestas: grown to more than 1.7 GW

“Large-scale turbines affect cost greatly, since installing turbines and foundations is expensive. The new turbine was launched a little late on the market, but did perform well on the other hand”, comments Anders Bach Andersen, the V164-platform’s Product Manager at MHI Vestas. However, the launch was ­obviously not too late. Dong Energy has ­already ordered just under 700 MW and further investors regard it as their turbine of first choice. As a result, the pipeline has grown to more than 1.7 GW since the prototype’s erection early in 2014. The V164-8.0 prototype has now withstood 2,500 tests and managed tough ­endurance tests. “More test runs will be ­required before production gets underway and we intend to enhance availability ­further,” ­explains Bach Andersen.

The V164-8.0 prototype has now withstood 2,500 examinations and ­managed tough endurance tests.
(Photo: MHI Vestas)

In all, at a length of 20 and a width of 8 m, the 390 t nacelle ­closely resembles a comfortable ­detached house. The nacelle’s ­insides consist of the traditional structure with a massive rotor shaft. In order to ensure that only pure torque reaches the gear drive and the generator, a flexible coupling is inserted between the main shaft and gear drive. The compact three-stage planetary gear drive was designed by ZF Wind Power. Moreover, the turbine boasts other features. “For example, we can exchange the main bearing without having to take off the rotor,” explains Bach Andersen.

Adwen builds on Areva’s M5000

Adwen wants to follow suit with a prototype in the third quarter of 2016. The AD 8-810 will have a ­rotor diameter of 180 m and generate 8 MW of rated capacity as well. Despite the merger between Areva Wind and Gamesa, the new turbine will build on Areva’s tried and tested M5000. In this concept, the drive train and the coupling to the generator have been dropped, because the rotor was directly integrated into a large roller bearing. This helps rotor, gear drive and generator to form a single unit. Its centrepiece is a two-stage planetary gear drive featuring a gear ratio of 1:10. The permanent magnet generator already achieves its rated capacity at just under 150 revolutions. “Renk AG and Moventas will build the gear drives and ABB the generator of the new turbine,” says Head of Sales Paulo Pereira. Adwen has made minor changes to the concept. Previously, the entire nacelle had to be replaced if it was damaged. “Now the structure is divided up so that the main components can be replaced independently of one another,” explains Pereira. Overall, head mass including rotor is apparently 550 t, whereas it was just 356 t before. The turbine is ­being put through its paces on a new test rig at the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) in Bremerhaven where the new turbines are also to be built in future. The production of 80 turbines with 5 MW for the Wikinger project in the Baltic will start in November. Orders have also already come in for the new 8 MW generation. “The AD 8-180 is scheduled for three projects comprising 500 MW each in France”.




Like this AD 5-132, Adwen’s rotor, gear drive and generator also form a unit. However, unlike the 5 MW variant, key components for the 8 MW model can be replaced independently of one another.
(Photo: Adwen)


Senvion is staying faithful to traditional turbine technology. The Hamburg-based company ­continues to depend on a distributed drive train with components arranged in sequence in order to be able to respond flexibly to customer’s component wishes. The three-stage gear drive of the updated 6.2 MW with a rotor diameter of 152 m rotates at a slightly faster pace at a ratio of 1:116 and drives a doubly-fed asynchronous generator. The latter provides space-saving benefits in the nacelle, because synchronous generators with full-power converters are bigger in size. The generator also requires no rare earths. Unlike its forerunner at 6.15 MW and a rotor diameter of 126 m, Senvion is choosing longer blades and an updated drive train to combat the competition. “Compared to its forerunner, energy yield at wind speeds of 9.5 m/sec. is 20 % higher,” claims group spokeswoman Verena Puth. To date, Senvion has installed 101 turbines offshore and some 72 in the order books.  The manufacturer is hoping for growth through its new owner Centerbridge. The private U.S. investor took over from ­Suzlon in 2015. After all, the deal has raised the credit line with the banks from € 100 to 950 million.

Siemens is working on 10 MW

Siemens continues to have more than one string to its bow.  On the one hand, the 3.6 and 4 MW gear drive turbines are still much in demand. On the other, the technology group’s wind division relies on direct drive at 6 MW capacity and its lead in development and production. Siemens already has 83 turbines of this type with a rotor diameter of 154 m on the grid and some 322 further WTGs in the order books.  This will enable efficient industrial production processes to be set up in Brande in Denmark. This type demonstrates the fast pace of development today. Not all that long ago in October 2013, the SWT 6.0 was still the turbine with the largest rotor diameter worldwide. There will be no modifications to the blades for the time being. Instead, Siemens is ramping up an additional megawatt in capacity and plans to test the upgrade on 7 MW prototypes by 2018. “We focused on higher torque by using stronger magnets to boost capacity, which means a higher yield offshore of 10 %. The biggest advantage is that the production supply chain remains unchanged, because there are only few modifications,” says Michael Hannibal, CEO of the offshore wind division. Its weight of 360 t places the direct drive wind turbine well within the range of its competitors. Meanwhile Siemens is working on a new generation of 10 MW capacity.

Alstom is also opting for the direct drive. “Our analyses show that in comparison with gear drives, direct drive results in significantly fewer malfunctions. We therefore decided to choose offshore for ­direct drive,” says Marcus Rieck, ­Alstom ­Renewables’ Country Sales ­Director in Germany. “This resulted in the Haliade 150 at 6 MW capacity whose first prototype was installed in Le Carnet in the Pays de la Loire region in France in 2012. We have 238 turbines for French and 124 turbines for German projects in the pipeline, as well as 5 turbines for the first floating offshore wind farm in the US.” After selling its energy ­division to GE, as yet nothing has ­officially been heard about any major leaps in development. Instead, there were problems with the generator on one of the two prototypes in the form of a loose magnet and workshops were held with the manufacturers. ­“Production pro­cesses were examined by several partners and the packages equipped with magnets have a new design,” explains Rieck. The new factory in France can produce 100 turbines a year.

Torsten Thomas

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