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).