Tower cranes: a real alternative to lattice boom cranes?

The constant search for higher rated power, taller towers and longer blades has pushed wind turbine manufacturers in an arms race to secure a position in an extremely competitive market.

Today in the onshore market there are machines with rated power close to 6MW, hub heights in a range of 150-165m and blades longer than 80 m. Several projects are currently under development considering these massive sizes.

Lately I have had the opportunity to analyse in depth a new solution which is emerging as an alternative to the traditional lattice boom cranes: the tower cranes.

I have analysed two scenarios, one with the standard lattice boom crane and an alternative scenario with the tower crane.

Standard scenario: lattice booms crane

Lattice boom cranes such as the Liebherr LG1750 have been the standard solution for the installation of the latest generation of turbines, with a tower height in a range up to 140+m.

This type of crane can be moved fully assembled between positions under certain assumptions (such as a very low road longitudinal slope and minimum road width of more than 6m).

If the crane has to be dismantled a substantial area for the boom assembly and disassembly process will be needed (in red in the image below).

Other characteristics that can have an impact on the project are:

  • A mountainous landscape: in this case the boom assembly area would be even more essential. This will have a substantial impact of civil works cost.
  • Very high installation rates (such as 3 or 4 turbines per week). The limited stock of lattice boom cranes suitable for this hub heights worldwide create a risk: either you book the cranes two years in advance (giving up the possibility of changing the schedule) or you wait - with the risk of losing the crane availability slot.

Alternative scenario: tower cranes

The idea of using tower cranes for wind turbines installation is not new in the onshore sector.

Said that, as far as I was aware of, the use of this typology of cranes has been negligible in the last few years.

Not so many references can be found in America or Europe. One example would be the installation of Gamesa’s G114 of 2,5MW 156m steel tower at the Borja Wind farm (Spain). The crane used was the Liebherr 1000 EC-B 125.

Common sense tells me that the experience turned out not to be very positive (otherwise I presume that the concept would have been replicated, while that does not seem to be the case).

More recently, new models from Krøll Cranes have been used in wind farms at the opposite side of the planet, in Thailand and Australia.

Big players like ALE are suggesting that this new concept is reliable.

One of the main references is the Theparak wind farm project in Thailand, where 60 V136-3.0 MW where installed using this crane.

Here we have a list of some of the projects installed in Thailand with tower cranes:

The main pros of the tower crane are:

  • Road width required: only 4.5 m (even as little as 3.5 m according some sources).
  • Cranes boom is only 70 m long.
  • Advanced crane bases allow savings in the critical path.
  • Lower minimum lifting radius compared to lattice boom areas.
  • Installation rates about 2 hours per component. An installation rate of 1 WTG every 4 days has been reached in the Thai projects.
  • Operational up to wind speeds of 15m/s.

On the other hand, cons would be:

  • Lack of experience of the operators with these new set of cranes and low offer worldwide.
  • Uncertainty on the actual installation rates due to insufficient track record.
  • Real installation costs are still unknown.

Depending on the characteristics of the project, Kroll cranes has available these models:

How would an hardstand layout adapted to both the tower crane and the new generation of turbines look like?

It seems that a tower crane could work using a standard hardstand without the boom area:

Some 3d models where created on real WTG locations to assess the actual impact on cost of this new configuration. Quantity reductions in topsoil stripping, excavation and fill material may lead to a cost reduction around 5000€ per hardstands (being conservative).

A nice image with a 3D model of the hardstand analysed is included below:

Even if potential savings in the civil works seem to be easy to achieve, a real total project cost reduction can be confirmed only considering the actual installation costs, which are not so clear at this moment.

Are tower cranes going to be a more mainstream solution in the future?

Only time will tell.

Blade mover – a flexible dual transport system

The two elements of the blade mover

One of the many problems posed by the huge wind turbine blades currently in the market is how to move them quickly and safely.

In some situations (like in the factories, or when blades are temporarily stored before installation) space can be extremely limited and there is the risk of damages. Additionally manipulating and moving the blades can be a time consuming activity.

To solve this problem a Danish company (SH Group) has developed an interesting solution, currently used by a blades manufacturer.

The “Blade Mover” uses two elements, one at the root of the blade (a trailer pulled by a vehicle) and the other at the tip, where a self-propelled vehicle with a diesel engine is driven by a technician using a remote control.

The vehicle at the tip is extremely manoeuvrable, allowing full control on the steering wheels – you can basically orientate the wheels in every direction you may need.

The tip element - an independent vehicle

The system has been develop to carry blades with a weight up to 80 Ton.

I also see from the pictures and the YouTube videos that it use custom frames. The frames are connected to the blade mover using a flexible sliding mechanism with safety pins.

The tip frame. All components can be modified to fit a specific blade

One additional benefit of this system is that it can work on uneven terrains absorbing height differences with a hydraulic mechanism.

The blade mover in action. The technician is using a remote control system.

 

Blades installation: more options than you might think

How are the blades of the wind turbines installed?

Although in general each wind turbine model has only one installation procedure, several technical alternatives have been developed through the years.

The quicker and easier method is probably to assembly the rotor on the ground. The three blades are connected to the hub and then lifted together in what is called “rotor installation” or more colloquially “the cross” (I guess because during the lift it vaguely remember a crucifix).

The main problem is that this solution need a lot of space. Additionally, as the blades are becoming bigger and bigger, it would be impossible to lift the weight of three blades at a height of more than 100 meters with the cranes currently available.

Another solution, very uncommon (actually I have never seen it in the real world) is the “bunny ears” method. Nacelle and two blades are lifted together, resembling (if you have a vivid imagination) the face of a bunny with two long ears.

The solution used more frequently nowadays is the single blade installation. The blades are lifted one by one and connected to the hub, usually horizontally although some turbine models are designed for an inclined or even vertical blade position.

Liftra, a company active in the wind industry, developed a tool called “blade dragon” that allow blade installation in every position.

The concept can be interesting in several situations – for instance if you want to disassembly a blade for repairing, you could use a smaller crane disassembly a blade in vertical position (that is, with the tip pointing downwards).

Liftra Blade Dragon inclined installation. Image Copright Liftra.

The single blade installation need a specific “blade lifting tool”. Such tools usually provided by the turbine manufacturer and are designed to fit a specific blade model.

Often there aren’t so many tools available (they are expensive, so their number is kept to a minimum) they can be a source of problems (for instance if the tool breaks or arrives late).

You will also need a second tool to turn the rotor, called "rotor turning tool" or "turning gear".

As the blades have to be installed horizontally, you will need to rotate the hub after the first blade is installed to have an empty socket in the right position, and repeat the procedure after the second blade is installed.

Those turning tools are hydro-mechanical. A power source is connected to a pump generating the pressure needed to rotate the gears.

The standard solution is to connect the tool to the disk brake used to stop the turbine in case of emergency. The brake disc wheel is toothed, allowing efficient coupling with the tool.

Liftra Blade Dragon vertical installation. Image Copyright Liftra

The single blade lift is generally more time consuming, as you will need 4 different lifts (one for the hub and three for the blades) compared to the rotor lift.

Liebherr crane configuration codes: what do they actually mean?

Have you ever wondered what is the logic behind the crane configuration codes used by Liebherr?

How could an unintelligible code such as “SL13DFB” being interpreted?

There is a logic behind the letters used – it has to be found in the German roots of the company.

The letters most frequently used in wind farm construction to define crane configurations are:

SL (“Schwer / Leicht”): This code means that the main boom of the crane is made of two different types of sections, “Heavy” (with a standard area) and “Light” (with a somewhat smaller area, used in the last segment of the boom). Between the “heavy” and the “light” sections s transition element is used

D (“Derrick”): The crane has a secondary boom, called “Derrick”.

F (“Feste Gitterspitze”): The crane use a jib (an auxiliary element assembled on the top of the main boom).

W (“Wippare Gitterspitze”): This is a different type of jib (a luffing fly jib). “WV” is the heavy version.

HS (“Hilfspitze”): This is one more jib configuration specifically designed for wind turbine assembly.

B (“Ballast”): The crane use a suspended counterweights system.

Types of cranes

Even if I’m not a specialist I would like to dedicate a post to a relevant element in a wind farm construction – the crane.

Crane procurement and wind turbines installation is normally organized by a specialized department, staffed with experts who knows what are the cranes available in the market and the implication of having a specific model instead of another on site.

In some countries, when the economy is thriving or if wind farms installations are booming, it can be really hard to find a free crane in the correct time slot - the few months when turbines are installed. In some case it might be necessary to import it from a different country.

Generally speaking, cranes can be categorized considering different technical characteristics:

  • Crawler vs wheels: cranes on wheel can use public roads and travel at a reasonable speed, while cranes with crawlers can go everywhere and they are often moved off road.
  • Standard vs narrow track: cranes on crawlers come in 2 version, with the crawlers at a “standard” distance (somewhere around 10 meters) and very near (below 6 meters). Obviously with a narrow track you will need less earthworks and the roads will be less expensive.
  • Telescopic vs lattice boom: 2 different solutions for the boom. “Hybrid” intermediate solutions are available

Cranes on wheels have a variable number of axles, usually somewhere between 6 and 9. As they are designed to be used on public roads the standard load per axle is 12 tons, even if partially rigged cranes can have a load per axle of 16 tons, 20 tons or even more.

The same crane can have different configurations, meaning that  the owner can purchase different tools and components to increase the maximum load and lifting height.

The configuration is indicated by hard to read manufacturers codes such as “T7YVENZF”. For instance, the code of the example means that the crane has a 100 meters telescopic boon, a Y- shaped guying system, an extension and a lattice jib.

Cranes can be moved from one wind turbine position to the following one fully rigged (not a frequent choice nowadays, given the increasing hub height of the turbines), partially dismantled or fully dismantled.

When a crane is dismantled the components are loaded on a truck and unloaded in the following wind turbine location. The number of trucks (and back and forth trips needed) depends on the crane model configuration but can be quite relevant: dozens of trips may be needed to move all components.

Alternative counterweights: an unusual use of the auxiliary crane

Use of the tailing crane as counterweight. Picture copyright Helling GmbH & Liebherr

If you are familiar with the huge cranes used in wind farm construction, you will know that a lot of time is consumed rigging and derigging the main crane.

Part of the effort is in the manipulation of the ballast (the counterweight needed to operate safely). The cranes use a modular ballast concept – different steel slabs are added or removed depending on the task to be performed.

These slabs are very heavy – the ones used by Liebherr for instance weight 10.000 Kg each and depending on the crane configuration and the type of lift you can have more than 20 slabs.

Several transport trucks back and forth trips are also needed to move these slabs around the wind farm.

It is important to know that usually the majority of the ballast is needed when the main boom is lowered to the ground (for instance to be dismantled) or it is lifted before the start of the erection works.

I have discovered that a German crane company (Helling GmbH) has developed an alternative technique. It seems that this solution has the blessing and approval of Liebherr, so maybe you want to consider it for your project.

Basically they used one of the hydraulic auxiliary crane as ballast.

In wind farm construction there always at least one “tailing” crane, helping the main crane rotating the wind turbine components in the correct position or assembling and disassembling the main crane itself.

They have had the idea to connect the auxiliary crane to the main crane (in this case, an LR 1600/2 erecting a Senvion turbine with hybrid tower).

The solution worked perfectly, and the 150 meter boom was lowered and lifted without problems.

Blade lifter: from dream to reality

This post is a follow up of my other post on the blade lifter.

When I’ve been discussing about this solution with the other guy in the business 3 or 4 years ago, they told me it was something utopic, a “nice to have, but still a dream”.

Well, apparently now the blade lifter arrived, and it’s here to stay - and with a more aggressive configuration.

We’ve used it in a project in central America together with GES, a company specialized in wind and solar project, who bought one.

I’ve also discovered that another transport company in Italy (SIA – they are specialized in WTGs components transport) bought one in August 2014.

Clearly, this unlock the power of the blade lifter in Europe: I’m sure that in some complicated situations, it will make sense to move it from a country to the other.

There is a very good post on the company web describing this solution – have a look.

They’ve also done a very professional video (embedded in this post).

Resuming the key features:

 

  • Produced by Scheuerle
  • Maximum angle 60°
  • Maximum capacity is 25 tons
  • Maximum slope: 23% (paved road) / 18% (dirt road)
  • Wireless wheel remote control

 

Enjoy the video!

Wind blade special transport: 45 degrees lifter for montainous roads

This is a blade special transport system that I’ve seen used by Enercon, for instance for Europe highest wind turbine in Europe, in Switzerland, but is not so common otherwise.

It is a hydraulic lifter, which allows lifting the wind blade up to approximately 45º.

Doing so it can guarantee important saving on the civil works, above all in mountainous areas where important earthworks have to be realized to reach the wind park.

It has to be used together with a 5 axle low loader, and its price is around 100.000€.

The biggest problem is that in many countries it couldn’t be used on the public roads, due to restriction the maximum height of the load (around 5 meters).

By the way I guess that special permit are granted in some countries (for instance I’ve seen several picture where this solution was used in public roads in Germany and Switzerland).

Nooteboom special trailers PDF and AutoCAD blocks

Royal Nooteboom Trailers is a Dutch company dedicated to special transport: flatbed trailers, low loaders and other amazing wind related vehicles.

They have developed several solutions for the transport of nacelles, tower sections and blades. Among their products, the MEGA wind mill transporter (for towers and nacelles) and the several families of blades trailers.

Nooteboom Teletrailers have an extendable load floor, single, double or triple extendible. They can go from 13,6 closed to 42 meters totally extended, or from16,6 closed to 48 meters totally extended,

Special tailored solutions can be developed for transport of blades over 50 meters.

They allow remote controlled, independent rear wheels steering, a really useful functionality to choose the best trajectory in complicated environments.

One of they last invention is the Tele-Step, specially designed for very long blades (50+ meters), with a peculiar turn table mechanism below the blade that permits movements otherwise impossible.

Another interesting product, the MEGA wind mill transporter, can load and unload the tower or nacelle without the help of a crane. It consists of 2 hydraulically adjustable lift-adapters that can be universally employed on various vehicle types. The lift-adapters are connected to the semi-trailers by means of a turntable, and the load can be rotated up to 80 degrees. The outstanding maneuverability is due to the fact that the swept path covered is determined by the size of the load only and not by the steering behavior of the vehicle. Pretty amazing.

It’s not easy to find technical drawings of their products online, so I’ve decided to share with the rest of the world several PDF / DWG from my private collection.

PDF

AutoCAD blocks

AutoTURN special transport simulation: pros and cons

Working in Vestas at dozen of wind farms worldwide I’ve had the opportunity to use frequently AutoTURN to simulate bends and other complicated maneuvers (for instance in towns or near existing structures) with special transports (mainly wind blades and tower section trailers).

Although it is not cheap (the price was almost 1800 € plus VAT: a lot of money, considering that it’s an AutoCAD plug in) I am satisfied with the software.

The main advantage is that you can check very quickly if you’re going to have a problem somewhere, even if you don’t have a topography (sometimes we work with a blurry Google Earth picture). It is very easy to use and intuitive at the beginning, and it includes the rear wheels remote control used nowadays.

Main drawbacks: there are only a few special vehicles for wind components transport in the library, so you have to make your own. I’ve replicated several Nooteboom trailers, as we often works with them, using the “personalized vehicle” feature.

Moreover it is not possible to simulate reverse gear. This is a big, big problem as several times we use it in real word situations. Workaround: I’ve modified a normal trailer (not a wind blade tow), and I use it when I desperately need reverse gear.

Third problem, many times it would be useful to simulate problems in 3D, as sometimes the tow get stuck somewhere in a vertical transition. There is an upgraded version who allows you to works in 3 dimensions, but it doesn’t include the vehicles we use in the wind industry, so it’s not useful. The only solution is to build a 3D model of the terrain as I explain in another post and see what happen below the truck. Unfortunately it takes many hours.