All photographs
© 1999 Soren Krohn

Manufacturing Wind Turbine Towers

Rolling Conical Tower Sections
Most modern wind turbine towers are conical tubular steel towers, as we learned on the page about wind turbine towers.
This image from a tower manufacturer's workshop shows how a steel plate is rolled into a conical subsection for a wind turbine tower. It is a bit tricky to achieve the conical shape, since the tension (pressure) of the steel rollers has to be different at the two sides in order to make the plate bend properly.
Towers are assembled from these smaller, conical subsections which are cut and rolled into the right shape, and then welded together.
Towers are usually manufactured in 20 to 30 m sections (65 to 100 ft.), the limiting factor being transportation on roads or rail. Typical modern tower weights are 40 metric tonnes for a 50 m (165 ft.) tower for a turbine with a 44 m rotor diameter (600 kW), and 80 metric tonnes for a 60 metre tower for a 72 m rotor diameter (2000 kW).

Designed by the Turbine Manufacturer
Towers for wind turbines are generally designed by each turbine manufacturer, since the entire wind turbine has to be type approved as a unit. (The reasons are explained in the page about structural dynamics). So even if some towers are manufactured by independent producers, they are always specific for each manufacturer.
Independent tower manufacturers are often also manufacturers of oil tanks or pressure vessels, since the machinery and safety inspection procedures are very similar.

Weight Matters
Tower weights (per installed power in kW) have declined by about 50% during the past five years due to more advanced design methods. Still, towers are a fairly heavy part of the wind turbine, so transportation costs are important. For larger markets it generally does not pay to transport towers more than 1000 km (600 miles) by road. In case the distance is larger (and the project is a large one), towers are usually manufactured locally.

Banana Peel Shaped Plates
In order to end up with a cone-shaped section, the plate used for rolling has to be curved along the longest edges, and the short edges are not parallel. Most tower manufacturers use programmable laser cutting tools in order to obtain the appropriate shape for the steel plate.