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WindTech: Siemens' new 'easy transport' model

Siemens Wind Power has developed a new tower design that can be pre-manufactured and easily transported. The steel-shell prototype has been installed on a 2.3MW onshore turbine. The design focuses on hub heights above 100 metres, offering an alternative to state-of-the-art concrete and concrete-steel hybrid towers.

The polygonal tower is built of standardised smaller sections meaning the transport restrictions that apply to tubular steel towers could be eliminated. In theory the design allows for almost unrestricted tower heights, although the legal/practical tip height is regarded as 200 metres. Siemens is planning a 142.5-metre maximum hub height for the SWT-2.3-113, or a 199-metre tip height. For this configuration the tower base measures eight metres between the parallel sides.

The prototype's 90-metre hub height offers ample space inside for accommodating the transformer and additional equipment. The tower consists of 12 inward-facing, U-shaped sections of about one metre high at ground level. These sections are bolted onto the concrete foundation slab and connected vertically by friction force between adjoining flanges. Each added level has a narrower footprint and is assembled on the ground before being bolted to the previous level.

Moisture is prevented from seeping into the tower internals by a rubber lining pre-fitted all along the vertical contact areas and compressed during bolt tightening. Another distinct design feature is the access door, the frame of which has been reinforced on the inside by multiple thick steel layers, clamped together.

Siemens CTO Henrik Stiesdal said the design idea came from Danish supplier Ib Andresen Industri, which has previously manufactured smaller, welded-steel, shell-type towers for NEG Micon (now Vestas). "When Andresen approached us with this new concept based on advanced highly automated serial production, we considered it interesting and worth investigating," he added.

Stiesdal hailed three benefits of the system: the easy foolproof assembly process, the maintenance-free bolt-tension level, which remains sufficient throughout the 20-25 year design life, and the requirement for only one electric power tool during fitting and construction.

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