Bremerhaven, Germany [Renewable Energy World Magazine] Manufacturing rotor blades for very large turbines is a highly complex procedure. Transporting and handling then brings another set of challenges. Eize de Vries reports on REpower’s joint venture that will exclusively manufacture rotor blades for the company’s on and offshore machines.
Only a few minutes’ walk from REpower’s Luneort-Bremerhaven offshore wind turbine assembly facility, PowerBlades GmbH has been operating a new manufacturing plant for large offshore rotor blades since the second half of 2008. A joint venture between German companies REpower Systems (51%) and rotor blade manufacturer SGL Rotec GmbH (former Lemwerder based Abeking & Rasmussen Rotec GmbH), the new rotor blade supplier was founded in 2007 with the aim of dedicated manufacturing of REpower-designed rotor blades – to serve this company’s rapidly expanding international onshore and offshore business.
Rotor blade specialists David Rowen and Lars Weigel, from REpower and SGL Rotec respectively, are in charge of the impressive €25 million Bremerhaven facilities where rotor blade serial production is gearing up as part of a carefully managed process.
SGL Rotec already has a decade-long design and manufacturing experience in the wind business. During that period the composite materials specialist built a wide variety of different rotor blades for a range of wind turbine suppliers, including some with lengths of over 50 metres. It now contributes this specialized know-how to the joint venture with REpower. So far, the two partners have developed several dedicated ‘RE-type’ rotor blades, and three of these new product types have already entered series production. Glass fibre-reinforced epoxy is applied as the standard ‘RE’ composite material. Carbon fibres are not part of the laminate. Rotor blade types for the 2 MW MM series are the 40 metre-long RE 40.0 fitted on the MM82, and the RE 45.2 for the MM92. The pitch-controlled variable speed MM92 is REpower’s main volume product and is characterized by its large 92.5 metre rotor diameter. A third, even larger, product is the latest RE 50.8 rotor blade for the 3.3 MW 3.XM, which has a rotor diameter of 104 metres.
By mid-January 2009 the main activities inside the 460 metre-long halls were the production of RE 45.2 and RE 50.8 rotor blades and the construction of new moulds. However, both sister blades are so big that it is difficult to differentiate between them at first glance. A second distinct feature of these ‘RE-type’ rotor blades – and in fact the majority of all 40m+ rotor blades manufactured today – is so-called pre-coning. The tips of these blades point away from the tower in a measure aimed at counteracting unavoidable blade deflection under load.
Building these state-of-the-art moulds, like blade manufacture itself, is a labour-intensive precision job, and includes piping, pumps and additional equipment required for the now common vacuum-assisted rotor blade manufacture. In this process manual resin application is replaced by a closed system in which a vacuum is drawn inside the mould, allowing the (epoxy) resin to spread across the fibreglass matrix. The end result is in many respects regarded as superior to hand lamination. A key advantage is that the laminate is largely transparent, while the percentage of air enclosures is much lower. Quality inspections aimed at detecting laminate failures are also much easier, and weight differences between individual blades are substantially smaller than when compared to hand lamination.
Deep-water terminal
The new PowerBlades production facilities in Bremerhaven-Luneort cover an area of more than 22,000 m2. Direct access to a new deep-water terminal is planned by 2011 and this new infrastructure development is regarded a major transport logistics and cost advantage for all four offshore wind companies currently concentrated at the Luneort Bremerhaven–Zentrum für Offshore-Windenergie industrial area.
The two other offshore wind companies include Weserwind (foundations) and Multibrid (turbines). All share the common and constant need to move large, bulky and sometimes also heavy wind farm systems and components. These special transports include more than 1000 tonne foundations, 200–300 tonne nacelles, and over 60 metre-long rotor blades.
‘This PowerBlades plant is custom-designed for the manufacture of large offshore rotor blades. Initially the company builds two different RE-type rotor blades in the size-range of 45–50.8 metres, but in future, blade output in Bremerhaven will fully consist of the RE 61.5. The plant layout has been optimized for the efficient and cost-effective future series manufacture of the 61.5 metre long rotor blades for REpower’s 5M and 6M turbines,’ explained David Rowen in one of the huge halls.
‘Apart from ensuring an optimized workflow, we put a lot of effort in the production technology itself. Another important issue is conducting production quality checks during all process stages. It is, for instance, essential that different glass sheet layers are put exactly in a correct position. Also the shear webs [structural reinforcements placed perpendicular to the shell structure], for example, have to be firmly connected to the inner part of the shells over their entire length. For this latter crucial aspect we developed a system of exactly placing these flexible 45 metre-long parts into the moulds within millimetres,’ Rowen added.
Integrated business process control
As part of comprehensive cost control and quality assurance (QA) strategy, PowerBlades implements an advanced integrated SAP business process system. This system provides daily detailed information on a wide range of key business variables like raw materials use, cost control, asset management, and maintenance expenses. Access to such a detailed overview allows it to serve as an optimization tool for all internal business processes. The company also operates a laboratory where specific samples are taken of the epoxy resin applied in each individual blade and samples of the ready laminate, among others. Chemical records of these samples and the pieces themselves are systematically stored and may prove particularly valuable in determining the cause(s) in the event of a blade failure.
‘In September 2008 we manufactured our first blade and 70 units were completed by the end of the year,’ says Rowen, adding: ‘Currently we are still in the process of gradually expanding series production volume, whereby a key emphasis is upon staff learning and overall process stabilizing. The key business priority for the moment is quality.’
Rowen plans to complete building a first RE 61.5 test blade around the end of 2009. This new rotor blade, like the 3.XM blade, will be a patented development containing a number of innovative yield performance boosting design features, see panel below. According to current planning, RE 61.5 rotor blade series manufacture will commence in 2010 and will gradually expand to 300 units a year by 2012. These RE 61.5 production numbers fully match with REpower’s own plans to boost annual 5M and 6M output to 100 units in 2012. Employee numbers in Bremerhaven will also expand further.
About 200 of PowerBlade’s employees came from unemployment. Rowen notes: ‘Staff recruitment for these mainly blue-collar jobs is fully locally sourced and each new employee therefore contributes directly towards Bremerhaven’s local economy.’ An interesting following statistic is that currently 16% of PowerBlades factory staff are female, a percentage that the company plans to increase to 25%.
‘Dedicated well-trained shop workers represent the most important asset for PowerBlades. This is directly related to the specific nature of our company being a specialized and labour-intensive composite materials processing plant,’ Rowen states. ‘In addition to relatively high labour costs associated with rotor blade manufacture, the materials costs are in fact significantly higher as a percentage of the rotor blade cost price. That in turn makes it necessary to also have good relationships with material suppliers.’ Rowen reveals that REpower is already planning a second manufacturing facility in Portugal, which is intended to become a near identical satellite of the still new Bremerhaven rotor blade plant. Indeed, some of the RE 45.2 moulds currently under construction will in time be moved to Portugal, where the market emphasis will be on supplying blades for the MM92.
Rotor Blade Innovation: ‘Spoiler and Stall Barriers’
6M rotor blades contain a patented, fully integrated spoiler near the cylindrical blade root, plus two so-called boundary layer barriers on the actual airfoil, an industry novelty. The feature – previously known as Evolution Option – has already been applied on the smaller 2 MW MM82 and MM92 models, says REpower CTO Matthias Schubert. ‘Today the spoiler and barrier combination is a standard technology feature on all REpower turbines fitted with third-party rotor blades. Their add-on spoiler is clearly visible on the blade root surface from ground level and as a dual function reduces drag as well as increasing lift performance. Most importantly, the technology optimization results in a yield increase in the range of 3% on our MM82 and MM92 volume models,’ Schubert says.
Three REpower 6M prototypes have just been erected at an onshore site near the Danish border. Schubert notes: ‘The combination of a 20% increase in rated capacity, plus the new optimized 6M rotor blade, will result in an annual yield increase of more than 10% compared to the current 5M model.’
The latest 3.XM model also features new inhouse developed airfoils. These 3.Xm rotor blades deliver the same performance without additional ‘external’ features like spoilers and barriers. ‘We have actually discovered the potential of these ‘add-ons’ while developing our own airfoils. As a result we introduced the latter innovation too in our 2 MW MM turbine platform. This in order to achieve the same yield performance with our own ‘RE-type’ rotor blades compared to third-party blades fitted with our add-ons’, Schubert concludes.
