This year’s Bauma award for innovation in construction work went to rental firm Max Bögl for their use of a Liebherr 630EC-H70 tower crane in the erection of a wind turbine in Bischenberg, Germany. The award demonstrates that the lifting industry is starting to acknowledge the potential for tower cranes on wind farms. With wind energy in Europe one of the few sectors in the region that continues to grow, and wind farms increasingly being built in hard to reach locations, novel techniques like this are vital.
Gerd Tiedtke, Wolffkran’s product manager, says, "Typically, in wind turbine construction, crawler cranes are used. However, the transportation of these machines to the site is associated with high costs and an extreme logistical effort for the company assigned with the installation of the wind turbine."
Over the last few years, with the high capacity end of the crane industry finding much of its work from windfarms, 600t crawlers and 700-1,200t all terrains have been the crane of choice. In the wind end energy sector, however, economies of scale dominate: the higher the tower, the bigger the nacelle, the faster wind farm owners can expect to see a return on their investment. While turbines are getting bigger, the spaces in which to build them are getting smaller.
Tiedtke says, "Crawler cranes are based close to the ground and equipped with a long boom to get the height required to complete the construction. As the wind energy sector continues to grow turbines are increasingly being built in locations less accessible for these large machines, such as in forests and up in the mountains. Moving heavy machinery such as crawler cranes to these locations is a real challenge. In a forest for example you need to clear trees in order to make room for a 100-150m boom. Besides the resulting costs, there is also the ecological aspect to consider."
Wolffkran are one manufacturer who have been approached by those within the wind turbine construction industry seeking a method that is cheaper in terms of transport for locations that present logistical difficulties, the manufacturer is currently testing its solution and is close to performing its first job. In this emerging market there is however not a ubiquitous engineering method for these jobs, Wolffkran for example use a relatively smaller crane, Tiedtke explains: "Our concept is different. We use a luffing jib crane with a 50m boom on a 100m mast. In other words we are covering 100 m of height with the tower of the crane and another 50m with jib of the crane, which enables us to assemble wind turbines with hub heights of up to 140m."
"Besides the obvious advantages with regard to easier transportation and a smaller ecological footprint as opposed to traditional installations using crawler cranes, our concept also has the advantage of making do with a relatively short tower. Other tower crane concepts work with saddle jib cranes that need more tower elements to gain the necessary height. The foundation of the wind turbine can also be used to secure the crane and, therefore, if space is restricted, the tower crane is again at an advantage."
In today’s era of economic uncertainty, when spending on research and development can be restricted, Wolffkran had a lead over potential rivals as it was able to adapt a crane already in its product range.
"When it came to providing the customer with a suitable tower crane we were able to adapt a model already in our range: the Wolff 700 B. We redesigned the jib so that it can lift 95t at a 10m radius and 80t at 12m. We also shortened the counter jib to reduce the tail swing for the easiest possible installation of the actual turbine and propellers. Typically the Wolff 700 B for wind turbine installation will have a detachable external climber."
"We are always searching for new ways in which our cranes can be used and there is an increasing number of wind farms being built in Europe. We had a customer who actually came to us and asked us whether we could provide them with a crane to do this type of work. They approached us because of the costs involved in the regular crawler based installation. The investment is far less when using a tower crane."
Other companies have approached these projects differently. Max Bögl for example use a very different method to Wolffkran. Jürgen Kotzbauer, Max Bögl’s head of PR and marketing, explains: "Our self-climbing tower crane reaches a final hook height of over 150 m. This crane is ready for construction of the concrete tower and the final assembly of the steel tower and the turbine section. This specially patented assembly system enables problem free crane operations at wind speeds of up to 20 m/sec."
"The assembly of a turbine tower with a crawler crane requires a 160m cutting in any surronging woodland for the raising and lowering of the boom. With our self-climbing tower crane, this area and the actual position of the crane are omitted, so that the secured area in front of the wind tower can be reduced from approximately 3,600 sq m to approximately 1,400 sq m. The construction and dismantling of the crane is also much faster compared to a crawler crane."
"The Bischenberg project was our first wind farm, which we successfully installed with the self-climbing crane. From this project we have identified many customers and manufacturers of wind turbines where our tower crane method is advantageous."
It’s not just European firms that are beginning to use tower cranes in wind farm erection, Chinese company New Dafang Group has developed its own technique. The QLY9096 hydraulic wheeled tower crane is yet another take on the way in which towers can be used in the construction of wind turbines. The chassis of the wheeled tower crane uses an independent hydraulic suspension system and independent steering system. The tower body meanwhile is designed with a three-level telescoping system and the boom with three-level folding. This means that the crane can travel with boom lifted on slopes with gradient of 20%. The vehicle is 18m in length and 4.5m in width, which means that it can travel on 5m-wide road.
Predicting how this sector will develop is complex and each of those companies involved in developing this solution are aware of certain trends that could have a major impact on the take up of this method of construction. One of these is the increasing height of wind turbines, which has risen considerably and is expected to continue to rise, Tiedtke says: "The trend that appears to be developing with wind turbines is that they are getting higher and higher. If industry predictions are correct they could reach 200m within the next fice years. If we go to 200m the hinge point for the crawler is going to be too much, and will be beyond the machine’s performance, making things incredibly expensive. A solution must be found and this is where tower cranes come in."
"The cost of building wind turbines has also gone down which means that firms that do this type of work are under increased cost pressure and have to look for cheaper alternatives in the erection of wind turbines".
The point when the tower crane becomes the only option for company’s erecting a wind turbine currently seems quite far off, for the moment it makes sense for these firms to focus on those areas where the advantages are clear, as Jürgen Kotzbauer says:
"This is the future of wind turbine erection, but not for all projects. This solution is perfect for difficult terrain and in forest areas. For wind parks on flat surfaces the use of conventional systems are certainly still useful.
At Max Bögl we still use a range of solutions for different projects."
