Greater choice as turbines step up in size

The European offshore wind-turbine market continues to be dominated by a handful of manufacturers and models, with Siemens' 3.6MW turbines the clear leader.

The most common offshore turbine, the Siemens 3.6MW, is being challenged by 5-6MW models
The most common offshore turbine, the Siemens 3.6MW, is being challenged by 5-6MW models
Bigger and more powerful turbines from other makers, and from Siemens itself, are becoming available in increasing numbers, but statistics from the European Wind Energy Association (EWEA) reveal the overwhelming popularity of the Siemens workhorse.

In the 18 months from January 2012 to end of June 2013, 530 turbines were connected to the grid in European waters, with a total installed capacity of 2.21GW. Siemens provided 483 of those turbines, giving the German company a market share of 84.7% by turbine numbers and 78.1% by installed capacity. The only other significant players in this period were Repower with 50 turbines and the troubled Bard company with 37.

Several of today's mainstream offshore turbines were developed before the offshore market really existed. Prototypes of the Aerodyn-designed Multibrid M5000 (now Areva), Repower's 5MW turbine and Siemens' SWT-3.6-107 had all been installed during 2004. Repower and Siemens followed the common industry practice of using high-speed geared drivetrains, but Aerodyn adopted a more radical approach - a compact hybrid drivetrain with a fully integrated single-stage gearbox and low-speed permanent magnet generator (PMG).

What all three units have in common, however, is that they have been subjected to a number of upgrades and improvements, either through fitting a larger rotor, increasing the power rating, or both. Areva increased the rotor diameter of its M5000 from 116 to 135 metres, and introduced an enlarged nacelle. Repower boosted power rating from 5MW to 6.15MW, retaining the unit's 126-metre rotor diameter, although it is now developing one in the 150-metre-plus range. Siemens increased rotor diameter from 107 to 120 metres, and last year introduced an extensive model upgrade to a 4MW model with a 130-metre rotor diameter. This small-scale evolutionary scaling-up of an existing platform is a popular, succesful strategy that limits development risk and cost, while enabling innovation and allowing the companies to build on their turbines' track records.

Areva looks set to increase its market share next year with 120 5MW turbines in two German projects, and perhaps Repower, too with 48 6.15MW turbines due to be installed in German waters.

Large developments

The 6MW direct-drive turbines of French manufacturer Alstom - a newcomer to the offshore market - and the long-established Siemens, both feature a permanent magnet ring-type generator (PMG) mounted directly behind the upwind rotor. They both offer the choice of a "super-size" rotor in the 150-metres-plus range. The 73.5-metre LM-Alstom blade and 75-metre Siemens blade are among the industry's largest, yet they are relatively lightweight, slender designs that provide enhanced yields while minimising turbine loading.

Both companies claim the longer blades provide a 15-17% boost in annual energy production compared with 6MW turbines with 125-metre rotor..

The order book for Alstom's 6MW Haliade looks promising. It's the turbine of choice for the EDF Energies Nouvelles-led consortium that successfully bid for three of France's first offshore wind projects. Together they amount to 238 turbines with a total installed capacity of 1,428MW.

Technology trends

Direct drive is relatively new to the offshore sector, although the technology is well-proven onshore. On direct-drive turbines the rotor and generator turn at the same speed, eliminating the use of a gearbox and thus substantially reducing the number of potentially high-maintenance fast-rotating components.

The offshore market is also taking a close look at medium-speed drivetrain designs. Interest in this technology increased when prices for the rare-earth materials used for the powerful permanent magnets rocketed in the first half of 2011. Smaller, faster-turning medium-speed generators contain far less of those expensive materials, especially compared to direct-drive turbines. Another recognised reliability-enhancing benefit is that the trouble-prone high-speed gear stage is eliminated from the design.

Gamesa became a medium-speed pioneer when it installed its first 4.5MW onshore turbine in late 2008. This has now been further developed for onshore/offshore use into the 5MW G128 model, a prototype of which was commissioned to become Spain's first grid-connected offshore turbine in July. Plans for a bigger unit — in the 7-8MW range — are at an early stage.

Giant steps

Vestas has fallen a long way down the offshore ranks in recent years, its 3MW turbines long since supplanted by the 3.6MW Siemens as the industry's favourite. Now the Danish manufacturer is aiming to make up ground with its huge new offering, the V164-8.0MW turbine.

First announced in 2011 with a 7MW capacity, this medium-speed turbine features a record 164-metre rotor diameter and a drivetrain layout that bears considerable similarity to Gamesa's G128. Since upgraded to 8MW and with the design aimed at "maximising energy capture through an optimal rotor-to-generator ratio", a prototype should begin testing early in 2014.

In September Vestas announced it was joining forces with Mitsubishi Heavy Industries (MHI) in a 50:50 joint venture to develop the 8MW V164. MHI is investing EUR100 million in the project, with a further EUR 200 million dependent on the giant turbine hitting certain milestones. Vestas has made its order book for the upgraded V112-3.3MW offshore turbine and its existing offshore service contracts part of the venture.

How the joint venture affects the development and commercial future of MHI's own 7MW offshore turbine design, the SeaAngel, is not clear. Featuring an innovative hydraulic drivetrain, which enables the rotor to turn at variable speeds while the generator speed is fixed, and thus eliminating the cost, weight and complexity of a power electric converter, the SeaAngel is scheduled to start prototype testing in the next few months.

Samsung is also in the mega-turbine race with a 7MW unit featuring 83.5-metre blades for a record rotor diameter of 171.2 metres. Again, a prototype should start testing in the next few months.

Even bigger turbines are under consideration in some quarters. Dutch engineering consultancy Mecal presented a design concept earlier this year for a 12MW medium-speed turbine with a 200-metre rotor. Whether machines on such a massive scale will come to market in the foreseeable future is very hard to predict. A totally different technological development is Aerodyn's radical two-blade downwind turbine, of which Ming Yang of China is the first licensee. This turbine has been specifically designed for typhoon conditions as found in the South China Sea.

SIZE MATTERS ONLY THE BIGGEST CAN TAKE ON OFFSHORE

When Enercon started prototype installation of its 4.5MW E-112 direct-drive turbine in 2002, there were firm plans to enter the offshore market with force. A few years later, the German manufacturer dropped this plan and instead refocused the current 7.5MW E-126 successor turbine at the onshore market.

However, recent rumours suggest renewed offshore interest, a possible move that would be backed by Enercon's strong reputation for quality and high-performance combined with more than a decade of successful super-class track-record experience.

Deep pockets needed

Offshore projects continue to grow in size and complexity, becoming ever more expensive with an increased overall risk profile. Successful offshore market entry and participation requires a combination of sufficient company size, financial strength and access to the right technology. These combined capabilities are all essential preconditions for offering the necessary warranties covering all technical, financial and other long-term upkeep risks.

It seems realistic to assume that it will be the big names and large international companies that will increasingly dominate the future offshore wind industry. That Nordex as a medium-size wind industry player decided to abandon its ambitious plans for entering the offshore market supports this theory.

It is also likely that Siemens' current offshore market dominance will increasingly be challenged by other big names, particularly Areva, Alstom and MHI-Vestas.


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