Nacelle Trailer (Low Loader)

Nacelle trailer (also called low loader) is one of the special vehicles currently used to carry WTG components from the factory to the wind farm.

His peculiarity is that it’s very low, only a few centimetres above the road: this is to allow transportation on public road, where bridges with a free height of 5 or less meters are common.

The weight of the nacelle is very near to the maximum that can be transported by road: in some cases, for instance with the Vestas V112, the drive train is carried separately from the rest of the nacelle and than it’s assembled on site.

There are even vehicle developed expressly for a wind turbines manufactures, such as the Nooteboom MEGA wind mill transporter developed for Vestas that allow savings as it is possible to load / unload without the use of a crane.

The average low loader has from 6 to 8 wheels, and the platform can be closed after the unload of the nacelle: fully extended the trailer is almost 30 meters, while closed is about 20 meters.

Carrying blades with a balloon

In very complicated wind farms blades and sometimes other components are carried by helicopters – an expensive solution, to be used only as “last option”.

What I’ve discovered today is that a balloon was used by CL CargoLifter to carry the blades in a small scale test made for Nordex at the former airport of Neuhardenberg using a 9 meters balloon on December 2007.

CL CargoLifter GmbH & Co. KG is company founded by former Cargolifter AG shareholders - Cargolifter AGfiled for bankruptcy in 2002, trying to develop an "Air Crane" to carry bulk load flying.

The balloon was filled with almost 300 cubic meters of hydrogen in nearly 90 minutes, and clinged at a winch. After the test, the balloon was quickly deflated, in only 5 minutes.

According to their study, a 40 meters diameter balloon is needed to lift a mounded rotor with 3 blades.

 

Wind turbines components transport problems

 

Transport related problems occupy a relevant percentage of time in my department.

It’s no big surprise, considering that the models that we are selling (V90, V100 and V112) have blades up to 55 meters.

Usually we have 3 different kinds of problems:

  • Bending radius
  • Vertical transition curves (for instance on top of hills)
  • Weight

Depending on the curve radius and the angle between the back and forward tangents, a widening may be needed. Unfortunately, due to the number of variables it’s really difficult to find a closed formula or to define this extra widening on an easy-to-use table.

For this reason, we use a software developed especially to solve this problems (AutoTURN, developed by Transoft solutions).

It is not the only available software: for instance below you can see one of this simulations, courtesy of Nooteboom and developed with their "in house" software for a 90 degrees V112 bend:

 

For the vertical transition curves the problem is more complicated, as there are even more variables (extension of the shock absorbers, number of wheels, height of the load and so on). For this reason we normally made a 3D model to work with, but this is a really time consuming work.

Below, and example of a problem I had to solve in 2010; it is a new curve that we built on an existing road because the existing curve radius (on the left) was too small. Due to the strong height difference from the beginning and the end of the new bend the trailer was touching below, and I've had to modify it after the construction. I've asked for an as-built of the situation, prepared a 3D model and defined point by point the new geometry.

 

The weight of the loaded truck is the third problem we face. Normally the nacelle is the heavier components, and the biggest problem is on the bridge we have to cross when we have to reach the construction site. If the bridge is relatively new usually it is possible to find the project or to know the load it is supposed to carry – the big problem comes with old bridge (sometimes even in stone) we meet around the world: in this case the only solution is to study it with the help on an external engineering.