Hybrid structure aims to cut towering costs1 October 2009
The Dutch company Advanced Tower Systems has erected at a test site near Grevenbroich, Germany a pilot version of a novel hybrid wind turbine tower that cuts the unit’s cost by significantly decreasing the proportion of steel it contains.
The first wind turbine with an ATS hybrid tower and one of the largest such towers in the world has been completed at the Grevenbroich wind test site in North-Rhine Westphalia, western Germany. The concrete section was erected at the end of 2008, followed by installation of the Siemens steel tower segment. This pilot project was finally completed recently with the installation of the wind turbine nacelle – a
2.3 MW system made by Siemens – and the
93 m diameter rotor.
Netherlands tower specialist Advanced Tower Systems, a joint venture of Mecal BV, Hurks Groep BV and Juwi Holding AG established in May 2005, built the innovative tower which combines a lower segment consisting of long, narrow pre-cast ATS concrete components and an upper segment made of conventional steel elements. The wind turbine reaches a height of 180 metres with a hub height at 133 metres. The tower will be operated by the ATS Projekt Grevenbroich company, in which Juwi Netzwerk, Mecal Projects, Hurks subsidiary HB Bau GmbH and Siemens Project Ventures (SPV) are equal partners.
The wind turbine was inaugurated in May this year. ‘We are proud to be able to contribute our share to the pilot project. In terms of efficiency and implementation, the innovative concept is setting new standards’ says Gernot Ziegeldecker, managing director, Siemens Wind Power GmbH. ‘Renewable energies are a central topic for Siemens. Access to this tower technology provides Siemens with the innovation leadership’ said Dr Wolfgang Bischoff, md of Siemens Project Ventures.
The development of larger and higher wind turbines is a global trend in the fast-growing wind energy market. At the same time, wind farm owners aim to decrease their energy costs. This can be achieved by increasing the hub height. However, doing so implies an extra investment that has to be justified by the higher average wind speed.
Moreover larger wind turbines require larger tower dimensions. Conventional tubular steel towers are extremely hard to transport over land, especially if their diameter is over 4.3 m, and current steel prices make large steel towers very expensive. Advanced Tower Systems has developed the new tower concept as an economically and logistically attractive alternative to steel towers, suitable for wind turbines of 1.5 MW or more.
The patented hybrid tower design combines a pre-cast concrete segmented tower with tubular steel sections on top. The lower tower sections, which have a final diameter larger than the 4.3m road transport limit, are vertically divided into three or more thinner segments made of high-quality pre-cast concrete. These segments can be easily transported by ordinary trucks. The installation of the entire tower takes less than a week and can be done under most weather conditions.
The cost of ATS hybrid towers is comparable to those of other tower concepts. They turn out to be commercially attractive for large wind turbines, but also for ‘smaller’ turbines (1.5–2 MW, 75-100m), especially in those countries where the transportation of steel towers is problematic and where the concrete segments can be produced locally instead.
The concept is said to offer greater hub heights and therfore more energy production, transport flexibility, short installation time, lower cost, and the opportunity to source the concrete section anywhere in the world, thus providing local employment.
The finished product is said to be cheaper to maintain, offer a solid support structure for larger wind turbines and introduce no height or dimensional limitations compared to other types of tower. The end result, says ATS, is an improved Return on Investment.
‘The tower allows great hub heights and thus a higher energy yield to be achieved at comparatively low overall costs, and it is also easy to transport’ according to ATS managing director Frans Brughuis.
Compared to the commonly found hub height of 100 metres, the ATS system yields about 20% more energy. The higher expenditures incurred with the installation of the tower are recuperated within about four years according to ATS figures (Table 2). And maintenance costs are claimed to be very low. Over the long course of a project, this means significantly lower electricity generation costs which is particularly important at inland locations with lower wind speeds. The hybrid tower elements are designed so that no special transports are necessary and even rugged or difficult locations (for example, in forested areas) are easy to access.