Reaching the limit?13 January 2021
The wind turbines are getting bigger, leading to the deployment of higher capacity cranes for their installation. Are we reaching the limit as to the way the crane industry can serve this market? Sotiris Kanaris reports
“With targets set for the reduction of carbon dioxide emissions on a global scale, and the awareness of the limited availability of conventional sources, the demand for heavy lifting solutions related to onshore wind energy has increased,” says Arjen Vergunst, general manager wind operations at Sarens.
Sarens has been involved in wind energy projects around the world, supplying cranes for new installations as well as maintenance. “The majority of the jobs are new installations either on new wind farms or replacing older generations. With the improved technologies and the guarantees provided, the demand for maintenance has increased,” he adds.
These jobs have become more challenging over the years, as the wind turbine manufacturers have developed bigger, heavier and taller products. This has limited the number of crane models that can be used for this application.
“They [the wind turbine manufacturers] are also very aware of the limitations of the available capacity and the designs of the turbine components go up to the limitations of the equipment’s capacities. We also see now that components are being split and installed separately,” Vergunst says.
“In order to get the most output from the turbine, the turbines become higher, allowing bigger rotor diameters. Even with the same weight, but installed 20m–40m higher than a few years ago requires more crane capacity and is pushing the current available cranes to their limits.”
The companies installing the turbines are often put under “massive time pressure,” according to Vergunst. “From a crane perspective, there are basically two elements defining time.
Installation, the time it takes to lift the components; and relocation, the time it takes to move the crane from platform to platform. You can imagine with the increased weights and heights the crane configuration is heavier, more complex and involves more crane components.
Ultimately it is a combination of defining the crane and boom configuration that fits the needed capacity at height, meeting the time targets set by our clients, and the environmental restrictions we are facing both in rural areas as well as remote areas.”
Apart from time, he says there are other challenges associated with these jobs: “Obviously the turbines are installed in windy areas; with cranes utilised up to the maximum capacity, the impact of wind increases. Even if the crane would technically be able to do it, our installation partners are challenged to keep control over the component being lifted.
“In addition to the weather conditions, we often build the turbines in remote and rough areas. And of course the logistics due to geography of the project sites to get to and from the location. 40–50 truckloads have become more a rule than an exception.”
Wolfgang Beringer, marketing and communication at Liebherr- Werk Ehingen, adds that another challenge associated with wind turbine installations is that in many countries the best places for wind energy are used already. “So new locations have to be found in hilly landscape or also in forests. There the space for crane set-up is very restricted.”
Crane Of Choice
Beringer makes a comparison of the cranes currently used to the ones used ten years ago: “Ten years ago mainly large telescopic cranes were installing wind turbines on 80 to 90m towers with component weights of 60 to 80t.
Today, for the newest generation of wind turbines with over 140m hub height and weights over 100t, lattice boom cranes starting from 750t capacity are needed.”
The most popular Liebherr machines for this application are: the 750t LG 1750 lattice boom mobile crane, the 750t LR 1750 crawler crane with SX boom system as well as the 800t LR 1800-1.0 and 1,000t LR 11000 crawlers.
To the question what are the advantages of each crane type, Beringer says: “Crawler cranes offer very high lifting capacities and they can crawl with the load.
Mobile cranes are mobile on public roads and can be set up quickly. Only small space is required for set-up. But the lifting capacity is limited, so they are used for tower heights of maximum 100m. They are also used to assemble the lower tower sections of high towers. The upper sections as well as gondolas and wings are assembled by lattice boom cranes.”
Guntram Jakobs, product marketing manager for crawler cranes at Tadano Demag, sees a higher demand for crawler cranes for wind energy projects compared to five years ago.
The most popular Tadano Demag crawlers for these projects are: the 600t CC 2800-2, 650t CC 3800-1 with Boom Booster and 1,250t CC 6800-1.
Also popular is the PC 3800-1 pedestal crane, which Sarens has used for a number of projects, most recently to erect two wind turbines at the Bouwdokken wind farm close to the Dutch North Sea village of Vrouwenpolder.
Jakobs says the advantages of the pedestal crane compared to other types are that it needs less preparation for ground levelling and the easier transport from one job site to the next.
According to Tadano Demag, the crawler cranes need a large and perfectly straight surface with a gradient of 0 to 0.3° in order for an operator to be able to use their full rated lifting capacity, whereas the PC 3800-1 only needs four load-bearing surfaces for its outrigger supports. “And even these surfaces do not need to be perfectly aligned with each other. The reason for this is that the outrigger cylinders are able to compensate for small differences without a problem—up to 2.1° on a 12 x 12m support area.
This means that the pedestal crane requires significantly less ground preparation,” says the manufacturer.
Sarens’s Vergunst comments: “From Sarens’s perspective this is a crane with potential for the industry. However, since there are not many in the market, customers often chose for the known crane solutions and that is the challenge. We simply need to be given the confidence and opportunity by our clients in order to be able to show them what we can do with the PC 3800-1.”
All terrain cranes are also used in wind projects. “Generally speaking, larger all terrain cranes are still used to install smaller windmills. This is heavily depended on the region. Also larger all terrain cranes are now used for installation of tower sections or for rebuilding of smaller windmills; again this really depends on the region,” says Michael Klein, product marketing manager for all terrains at Tadano.
He cites the AC 500-8, AC 700-9 and AC 1000-9 models as the manufacturer’s most popular all terrain cranes for wind applications. “Our brand new AC 450-7 will also be used in wind industry, for example for rebuilding smaller windmills,” he adds.
Focus On Boom
Jakobs says the Demag CC 3800-1 is often used for wind turbine installations with the Boom Booster. Tadano Demag says the Boom Booster increases the main boom’s stiffness, boosting the crane’s lifting capacity by up to 65.3%. Boom Booster kits for CC 3800-1 cranes are available in lengths of 24 to 102m.
The welded steel structure consists of up to nine sections with a length of 12m, comes with the Demag fall protection system as standard, and is designed for being directly mounted on the crane. When equipped with the Boom Booster kit, the CC 3800-1 crane can reach a maximum hook height of 174.5m and lift loads of up to 92.5t. The Boom Booster kit enables it to handle lifts that would otherwise be the exclusive domain of cranes in the 750t class. These parameters make this multifunctional crane especially well-suited to erecting large wind turbines, which usually require lifting heights of more than 140m. Demag also offers a Boom Booster kit for the CC 8800-1.
The manufacturer says the Boom Booster increases the CC 8800-1 crane’s lifting capacity by up to 90%. Although the CC 8800-1 is not often used for wind energy projects, Sarens used it with Boom Booster to erect an Enercon E-126 wind turbine at the Windpark Noordoostpolder in the Netherlands.
Liebherr has also enhanced the technology of its machines, facilitating these applications. One example is the SX boom system, through which the manufacturer says it has achieved a higher hoist height and lifting capacity for its 750t LR 1750/2 and LG 1750 lattice boom cranes.
For the SX boom, lattice sections measuring 3.5m wide rather than 3m are fitted to the bottom section of the main boom on crane models LR 1750/2 and LG 1750. The SX2 and SX3 versions are additional extensions. With these, two or three lattice boom sections 6m wide and 14m long are fitted to the bottom section of the main boom. The improved lifting capacity values raise the 750t cranes to the next higher class with a lifting capacity of around 1,000t.
The German manufacturer has recently launched the SL8F2 boom system, developed in collaboration with American crane specialist Buckner Heavy Lift Cranes, which can hoist the completely assembled generator.
It all started in January 2018 when Buckner’s wind division director Kevin Long and his boss Doug Williams, together with Thomas Chandler from Mortensen, one of the largest energy companies in the USA, sat down round a conference table in Liebherr’s facility in Ehingen. At the time, Buckner already had the largest fleet of this model in the world comprising seven LR 11000 crawler cranes, primarily used to erect wind turbines.
The Liebherr 1,000t machine was able to manage the conventional wind turbines, but Long presented his idea of a jib with a lifting capacity of 220t, 40t more than in the past.
The final product offers an even higher capacity. The eighth version of the SL boom with the second version of the fixed F jib delivers a lifting capacity of 253t with a hook height of 114m, enough to hoist the 230t made up of the complete generator and load handling equipment up to the hub height of 108m.
Another advantage of SL8F2 boom system is that assembling the nacelle with the drivetrain and hub on the ground is easier and safer than at high altitude. Liebherr says it is particularly economical because the crane can operate without a derrick system. Buckner now has 17 models of the LR 11000 in action, five of which feature the new SL8F2 system. Liebherr has also developed the SLGS single-line guiding system for the installation of individual wind turbine blades using rotor blade yokes.
The system is attached to the main boom on the side facing the load. A rope is secured at the top of the boom head and tensioned using a rope winch below in the pivot section. A cable pulley with two connections to the outsides of the rotor blade yoke runs along the boom rope during the hoisting process. With its own power supply in the yoke, the two connections to the SGLS are tensioned so that the blade is stabilised in the wind and can also be moved into the correct angle for installation on the hub. Crane operators can retrofit the SLGS on all conventional wind power boom systems, including the new SX systems on LR 1750/2 and LG 1750 cranes, with the tensioning winch being installed instead of the luffing jib adjustment winch and the existing hydraulic system being used. Only the electrical system and software are added.
Beringer says the market has responded positively to the SLGS single-line guiding system: “We have several orders and many requests regarding the system.” Liebherr is continuing to develop technologies that facilitate wind turbine erection. “We are developing special wind systems for our brand new LR 1800-1.0. I also want to mention that we have prepared new lifting capacity tables involving higher maximum wind speeds for higher safety,” adds Beringer.
As wind turbine manufacturers continue to launch bigger onshore wind turbines, the question arises whether the crane sector is reaching the limit as to the way it can serve this wind energy market.
“In general you would think so, at the same time it’s also what everybody thought ten years or 15 years ago,” said Vergunst.
“Although it seems that based on the current capacity of the equipment that is able to handle the weights at such heights and able to “keep up” with the time constraint, we are getting to the limits. It is therefore a challenge for ourselves and our clients to think outside the box. Sarens has the capacity to come with smart solutions; design, develop and built cranes in-house (SGC cranes) if we need to.”
Jakobs says yes and no. “Yes because we are reaching physical limits by dynamic stability in combination with boom length and getting those long systems off the ground. No because bigger cranes can serve that but require much more space, and transport needs.”
“Wind power has driven the crane development for many years and will continue to do so in the future,” said Beringer. “But generally, the lifting capacities of lattice boom cranes are nearly unlimited, think of our 3,000t LR 13000 for example. Our job is to develop systems for most economical crane use.”