20 per cent of the total cost of wind turbines are accounted for by the tower and the related logistics costs for transport to the wind farm. For the Nordex Group, keeping these costs low is a further lever for reducing project costs for their customers. This is a major advantage, particularly in those markets where an auction system is used. For this reason, the Nordex Group uses concrete towers in addition to tubular steel and hybrid towers for parts of its product portfolio. What makes them special is that the manufacture of concrete tower segments is based on a mobile concept and is always located close to the wind farm, resulting in correspondingly low logistics costs. On-site production also means that the customer is able to meet any requirements for a local contribution to value added in a specific country. It also helps local economies to create direct and indirect employment.
The Nordex Group can now look back on 13 years of experience in the manufacture of concrete towers. In 2006, the first AW1500 turbine was installed on an 80 metre concrete tower in Spain. Recently a milestone was reached: the 1000th concrete tower for an AW125/3000 machine left the Brazilian factory in Lagoa do Barro do Piauí for the 595 MW “Lagoa dos Barros” wind farm. Thanks to the current order backlog for turbines in the AW platform, the Nordex Group will manufacture a further 1000 concrete towers by the end of 2020 alone.
Concrete towers offer additional advantages compared to tubular steel towers, precisely for hub heights of 100 metres and more. This is because the latter calls for very large diameters of the lower tubular steel segment in the case of large hub heights. The size of these steel segments means that overland transport is only possible to a limited extent and it is rarely practicable to manufacture them in the direct vicinity of the respective wind farm. A further advantage of concrete towers is that it is easier to ensure good concrete quality worldwide than it is to obtain the same quality for steel.
The concrete towers made by the Nordex Group consist of 20 metre-long prefabricated convex segments that can be assembled on site when the wind farm is under construction, and can be “stored” vertically on the wind farm until the nacelle is mounted. As the concrete tower facility is mobile, after completion of a wind farm, the structural forms and tools can be transported to the next project within the country.
Today, the Nordex Group can draw upon 11 such mobile manufacturing facilities worldwide, in Latin America, India, South Africa and Spain. More than 20 mobile “factories” have been set-up in the last few years. On average, some 250 staff are employed on-site with each mobile facility. The Nordex Group offers concrete-only towers for the AW3000 turbines with hub heights of 80, 100, 120 and 140 metres, as well as for the N155/4.5 of the Delta4000 series, with a hub height of 120 metres.