WIND POWER

Hybrid structure aims to cuttowering costsThe 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.

Staff report

The first wind turbine with an ATShybrid towerand one of tbe largest suchtowers in the world has been completedat the Grevenbroich wind test site in

North-Rhine Westphalia, western Gemiany.The concrete section was erected at the end of2008. followed by installation ofthe Siemenssteel tower segment. This pilot project wasfinally completed recently with the installationof the wind turbine nacelle - a2.3 MW system made by Siemens - and the93 m diameter rotor.

Netherlands tower specialist Advanced TowerSystems, a joini venture of Mecal BV. MurksGroep BV and Juwi Holding AG established inMay 2005, built the innovative tower whichcombines a lower segment consisting of long,narrow pre-cast ATS concrete components andan upper segment made of conventional steelelements. The wind turbine reaches a height of180 metres with a hub height at 133 metres. Thetower will be operated by the ATS ProjektGrevenbroich company, in which JuwiNetzwerk, Mecal Projects. Hurks subsidiary HBBau GmbH and Siemens Project Ventures ( SPV)are equal partners.

The wind turbine was inaugurated in May thisyear. 'We are proud to be able to contribute ourshare to the pilot project. In terms of efficiencyand implementation, the innovative concept issettingnew standards" says GemotZiegeldecker.managing director. Siemens Wind PowerGmbH.'Renewable energies are a central topic forSiemens. Access to this tower technologyprovides Siemens with the innovationleadership" said Dr Wolfgang Bischoff. md ofSiemens Project Ventures.

The development of larger and higher windturbines isa global trend in the fast-growing windcnerg\ market- At the same time, wind farm

owners aim to decrease their energy costs. Thiscan be achieved by increasing the hub height.However, doing so implies an extra investmentthat has to bejustified by the higher average windspeed.

Moreover larger wind turbines require largertower ditîiensions. Conventional ttibutar steeltowers are extremely hard to transport over land,especially if their diameter is over 4.3 m, andcurrent steel prices ttiake large steel towers veryexpensive. Advanced Tower Systems hasdeveloped the new tower concept as aneconomically and logistically attractivealternative to steel towers, suitable for windturbines of t .5 MW or more.

ConstructionThe patented hybrid tower design combines apre-cast concrete segmented tower with tubularsteel sections on top. The lower tower sections,which have a final diameter larger than the 4.3tiiroad transport limit, are vertically divided intothree or more thinner segments made of high-quality pre-cast concrete. These segments can beeasily transported by ordinary tnicks. Theinstallation ofthe entire tower takes less than aweek and can be done under most weatherconditions.

The cost of ATS hybrid towers is comparableto those of other tower concepts. They tum outto be commercially attractive for large windturbines, but also for 'smaller" turbines (1.5-2MW. 75-lOOm), especially in those countrieswhere the transportation of steel towers isproblematic and where the concrete segmentscan be produced locally instead.

The concept is said to otTer greater hub heightsand iherfore more energy production, transportflexibility, short installation time, lower cost, andthe opportunity to source the concrete sectionanywhere in the world, thus providing localemployment.

The finished product is l̂ aici to be chenpcr to

maintain, offer a solid support structure for largerwind turbines and introduce no height ordimensional limitations compared to other typesof tower. The end result, says ATS, is animproved Return on Investment.

Performance'The tower allows great hub heights and thus ahigher energy yield to be achieved atcomparatively low overall costs, and it is alsoeasy to transpoti" according to ATS managingdirector Frans Brughuis,

Compared to the commonly found hub heightof 100 metres, the ATS system yields about 20%more energy. The higher expenditures incurredwith the installation ofthe tower are recuperatedwithin about four years according to ATS figures(Table 2). And maintenance costs are claimed tobe very low. Over the long course of a project,this means significantly lower electricitygeneration costs which is particularly importantat inland locations with lower wind speeds. Thehybrid tower elements are designed so that nospecial transports are necessary and even ruggedor difficult locations (for example, in forestedareas) are easy to access. tra

Table 1. Salient characteristicsBuilt and operated by: ATS Projekt Grevenbroicb GmbH

Hubbeigbt 133 metre

Total height 180 metre

Tower composition 76.S m of concrete (ATS)

and 55 m of steel (Siemens)

Nacelle Siemens SWP 2.3 MW

Rotor diameter 93 metre

Location Grevenbroich wind power test field,near Cologne, Germany

Table 2. Financial comparison - 100msteel tower with 120m hybrid towerProject: 2.3 MW onshore wind turbine

100 m tubular steel

6,4 m/s

€3.3 million

5288

486 500

Tower

Wind speed at bub height

Investment total project

Yield (MWh/yr)

Income (Euro/yr)

Payback time for additionalinvestment in 20 m extra bub beigbt

120 m hybrid

6.8 m/s

€3.525 m

6001

552 000

<4yrs

42 Modern Power Systems October 2009 www.modernpowersystems.com