What are the challenges involved in serial production of the new generation of huge offshore wind turbines? So far nobody really knows, as Vestas’ plans for a 7 MW turbine are on hold until 2014, and Siemens’ 6 MW SWT-6.0 and Alstom’s 6 MW Haliade 150 are both still in the testing phase. After winning the French tender for 1.43 GW, Alstom plans to roll out its monster turbine by scaling up its prototype manufacturing facility in St Nazaire, France using lessons learned from automotive manufacturing.

A visit to the turbine

The Haliade 150 sits at land’s edge in Le Carnet, in France’s Loire-Atlantique region, on a site that was planned as a nuclear facility in the 1970s but later abandoned. The Le Carnet site was chosen partly because it is geologically similar to the submarine environment where the turbine will eventually be installed; the coastal soil is essentially sand, said Frederic Hendrick, vice president for offshore wind. And the wind conditions at Le Carnet closely resemble those in the North Sea.

The Haliade tops a 75-metre tower, a 25-metre jacket foundation and monopiles driven 30 metres into the seabed. The foundation sits partially above ground, ‘onshore but installed as if it was at sea,’ explains Hendrick. The turbine was installed at the site in February 2012 and has begun its 18-month testing phase.

‘In offshore wind, size matters,’ says Hendrick. And offshore turbines don’t get bigger than the Haliade 150; its only current competitor, Siemens’ SWT-6.0, was designed to be super-lightweight, while the Haliade is massive.

Before you see it you know the turbine is big; you even know it’s very, very big. But you don’t really have a sense of just how big it is until you stand under it, with you and your car and the nearby trees and buildings all dwarfed by its sheer height and size, and feel the WHOOMP-WHOOMP-WHOOMP as its blades turn. The Haliade’s rotor is 150.8 metres in diameter, the blades are 73.5 metres long, and the turbine’s sweep is 17,500 m2. The turbine and its support structure boast a combined total weight of 1500 tonnes; the nacelle alone weighs 360 tonnes.

Hendrick believes in going big. ‘The size of the rotor is key,’ he says. ‘A bigger turbine leads to a better electricity price.’ Alstom claims that the Haliade can generate up to 40% more electricity per kg of material used in its construction than today’s offshore wind turbines, and that it will yield 15% more energy annually than other 6 MW turbines due to its larger rotor swept area and lighter blade, developed in conjunction with LM Wind Power. (Siemens claims that its SWT-6.0, with a 75-metre super-lightweight blade and a towerhead mass of slightly lower than 350 tonnes, will lower energy costs through ease and speed of installation.)

Onshore, the turbine accounts for 80% of total CAPEX for a wind project. Offshore, the turbine accounts for 35%, while the rest of the cost involves the connection to shore, installation, and O&M. During the design phase Alstom calculated the total cost of foundation, installation and maintenance against the cost of electricity, and arrived at 150.8 metres as the ideal rotor size for the Haliade.

‘If the wind speeds were lower, we could have gone for a 5 MW machine,’ says Hendrick. Wind speed at the Le Carnet site is around eight metres per second. ‘If they were higher, we would have gone for 7 MW – 8 MW.’

Design

Siemens places its mega-turbine components in the nacelle rather than in the tower. The company claims this facilitates pre-testing and pre-commissioning, potentially making installation quicker and easier, reducing power losses by transporting medium-voltage rather than low-voltage solutions, and making it possible to use lighter, cheaper copper cables.

Alstom, explains Hendrick, is moving in the opposite direction and putting components in the tower. He says having components in the tower is ‘better for commissioning’: before the Haliade’s tower was commissioned, 80% of the necessary connections were already made. He also says that when performing maintenance ‘you will be happy it’s all in the tower, at the bottom’. Commissioning accounts for just a few days in a turbine’s life, says Hendricks, while ‘O&M is the next 20 years’.

Almost all of the Haliade’s equipment is located on the first three levels of the tower. At the very top there is a helipad, from which maintenance personnel can gain access. Nearly all necessary maintenance can be performed from inside the machine; only bolt-tightening must be done outside. And there is a reinforced beam so that workers can lift the transformer down and bring it through the door. The transformer weighs two tonnes, and so does the crane installed to lift it.

The Plant

A short drive inland from Le Carnet, we meet Pascal Girault, plant manager at Alstom’s St Nazaire turbine manufacturing centre. Girault has a background in managing manufacturing plants for large automotive suppliers, and he brings experience in process automation for mass production. His previous positions included production centre manager, process & methods manufacturing manager, and plant director for companies making engine parts.

Alstom’s plant at St Nazaire is a temporary pre-series workshop; the company plans to expand into serial production in 2014, by which time it expects to build four separate manufacturing facilities for nacelles, generators, blades and towers in different French locations (the tower and blade facilities are planned for Cherbourg, and are expected to be operational in 2015). The nacelle factory is the only facility that is currently operational, and it currently manufactures the entire turbine. The company predicts that each factory will produce 100 units per year. An additional engineering and R&D centre is planned for the Pays de la Loire region.

Hendrick explains that ‘there was too much stress on internal resources to start four factories in one year; better to do it in two batches.’ Transport was a major issue in the company’s decision to build the factories in different locations: there is less constraint in manufacturing the blades and towers than in making the generators and nacelles because the latter are easier to transport longer distances to the site. Generators for the first two turbines – the test model installed at Le Carnet and a second one currently in production – were made in Nancy in the northeast of France, but while this solution, involving transport to St Nazaire by canal and sea, might be viable in the short term, Hendrick says that in the long term ‘it’s not a good idea’. A generator production facility is planned for the St Nazaire area, to be built by Alstom’s partner GE Power Conversion (formerly Converteam).

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Since many of the Haliade’s components will be located in the tower, the Cherbourg factory will assemble towers rather than fabricate them. ‘Where the metallic part of the tower will be made, we don’t know,’ Hendrick says, ‘but because of the internals in the tower, assembly is sensitive from a quality point of view.’

Alstom says that once it is scaled up to full production the St Nazaire facility will produce about 15 machines per year, with approximately 20 days spent on producing each machine. The temporary plant is expected to produce roughly 40 turbines before serial production begins at a permanent facility.

Employees work in two shifts. The 3000 m2 work space is divided into 15 stations manned by six people per station – no more, explains Girault, because of safety regulations. Currently 12 people work in the St Nazaire factory; by March 2013 a staff of 40-50 (half of which will be assembly workers, the other half engineers and technicians) is planned, and by 2014 the facility is expected to have a staff of 100.

Assembly

The Haliade’s nacelle is put together along an assembly line, in a dynamic construction process akin to the way automobiles are made. Girault explains that it takes 2.5 days to manufacture one nacelle.

Production takes place on a transport platform. A ‘multi-wheeler’ wagon moves the entire assemblage from one station to the next. The generator is moved with a hydraulic crane and is eventually bolted onto the nacelle.

Assembly begins with the turbine’s central block, which forms the interface between tower and nacelle. The central block contains the direction drive system, including a direction bearing. The central block also includes the helipad.

Next the intermediate block is fitted to the permanent magnet generator. The two blocks are then fitted together, ready to receive the rotor, and then the blades are fitted to the rotor.

At the end of the production process, parts are placed in a storage and logistics area before shipping. Blades, towers, nacelles and other parts sit to wait for installation close to the site.

A ‘self-improving system’

Girault terms his production process a ‘self-improving system’ and a ‘never-ending improvement loop’. His goal is a process akin to Toyota’s ‘lean system’ for auto manufacturing (also known as Toyotism). Lean manufacturing focuses on generating value for the end customer while requiring as little work as possible from the employees. Its principles are increasing efficiency, decreasing waste, and using empirical methods to decide what matters, rather than uncritically accepting pre-existing ideas. Lean manufacturing is widely viewed as building on earlier efficiency systems, such as Fordism, and taking them forward.

Girault believes in empirically testing his production process. Turbine assembly is broken down into discrete tasks which are timed, and then timed again to see if their duration can be reduced. The workers keep track of timing on a large wall chart which records how long it takes the assigned number of workers to do a particular job and is updated after each task is completed.

Girault conducts weekly audits on safety, quality, activity and logistics in order to streamline the process; employees are also encouraged to suggest areas for improvement and awards are given for workable ideas. For example, one employee suggestion that was adopted was integrating an ‘octopus’ tracking intelligence module, which monitors machines and processes, into the workshop; another suggestion was to fix mirrors to the underside of the generator in order to see whether there are workers near it.

Alstom’s engineering and R& D centre in Barcelona has designed detailed documentation for training purposes, which Girault hopes will make assembling a wind turbine ‘as easy as putting together furniture from Ikea’.

Rules and procedures applicable to serial production have been applied from the first unit produced in St Nazaire; Girault believes this will make subsequent commercial production easier to implement. In this way the current production facility is also a testing facility: it is constantly testing and refining the manufacturing process in which it is engaged.

Eventually Girault hopes that Alstom’s four French factories, planned to initially manufacture the 240 Haliade turbines to be installed from 2016 onwards as part of the French tender, will all benefit from the lessons learned at St Nazaire.

A big future

Hendrick believes that the Haliade 150 will be ‘the turbine for the coming decade’. He doesn’t believe that offshore turbines will get much larger because of limits linked to the size of installation vessels. And rotational speed is key: higher tip speeds can result in blade erosion in a saline offshore environment. Also, if rotational speed is reduced in order to get more power, ‘you’ll have enormous torque’, explains Hendrick. So will there be 15 MW-20 MW turbines? ‘I don’t believe it,’ he says. But the Energy Research Centre of the Netherlands’ 2011 Upwind: Design Limits and Solutions for Very Large Wind Turbines report found that 20 MW turbine designs should be achievable if some key innovations can be developed, and GE Global Research has already begun work on developing a generator for 10 MW-15 MW turbines. If turbines grow ever larger, innovation in manufacturing, assembly and transport will be increasingly necessary.

Tildy Bayar is Associate Editor of Renewable Energy World magazine.