With large-scale growth predicted within the European wind power sector, cranes are set to become increasingly important to the growth of the renewable energy industry.

Cranes and other lifting equipment play a central role during the installation process of offshore wind farms. From the moment the components reach the dock to their preparation for installation, crawler and mobile cranes with capacities well into triple figures are used to move, store, stack and load the masts, turbines and blades. Once at sea, offshore cranes, some with capacities as high as 2,000t, take over and are used to combine the pre-assembled sub-assemblies to create the finished turbine.

The European Wind Energy Association (EWEA) describes itself as ‘the voice of the wind industry’. It has more than 500 members from over 50 countries, including manufacturers with a 90% share of the global wind power market, component suppliers, research institutes, national wind and renewables associations, developers, contractors, electricity providers, finance and insurance companies and consultants.

The EWEA predicts that wind power as a whole will flourish in the years to 2030. In its Pure Power report, which outlines wind energy development scenarios for 2010, 2020 and 2030, EWEA predicts installed capacity will grow from 56GW in 2007 to 300GW in 2030. Of this, the installed capacity of offshore wind energy will grow by more than 11,000% from 1.08GW to 120GW. Annual installation levels will grow to 19.6GW from 8.5GW by 2030, with the annual offshore installation level growing from 0.2GW to 9.6GW. This equates to the installation of more than 2,600 3.6MW turbines or 1,920 5MW models a year by 2030.

Financially, this will mean annual investments in wind power capacity of EUR19.4bn ($26.3bn), with a total investment in wind power of EUR187bn ($253.4bn) between 2021 and 2030. Environmentally, wind power will avoid 575 megatonnes of CO2, equivalent to taking 285 million cars off the road, and providing power equivalent to the needs of 195 million average EU households.

In a sign of the importance of offshore wind to Europe’s energy policy, EU member states have committed to building a new North Sea electricity grid. The European Council endorsed the European Commission’s (EC) Strategic Energy Review (SER) of November 2008, which contained the EC’s commitment to publish a blueprint for the new grid. The council described work on this as a ‘priority action’.

EWEA says there is enough wind blowing over the seas to supply all of Europe’s power, but without an offshore grid and increased interconnector capacity to transmit power to consumers, this vast potential will remain untapped. The EC’s proposal in the SER, it says, is seen by the wind industry as a vital move in order to support, in the council’s words, “the large-scale deployment of offshore wind power while preserving the reliability of the grid”. Building the North Sea grid will require more cranes, barges, and cable laying vessels.

Wind turbine manufacturer Vestas cites governments’ desire for a reliable source of renewable energy as a key driver for offshore projects. In particular, it says the UK government is “very focused” on the area, and has “presented a system that offers areas for construction as well as a reliable business case for the wind farm owner”.

RWE npower renewables, which operates the North Hoyle wind farm in the UK and is currently constructing the 90MW capacity Rhyl Flats project off the coast of north Wales, says wind turbine generation is a “proven technology, capable of generating significant amounts of renewable energy and being deployed rapidly in a variety of locations”.

“RWE Innogy, RWE npower renewables’ parent company, has committed to investing at least EUR1bn in renewables across Europe each year from 2008-2012 to reach its goal of having 4,500MW of renewable energy plant in operation or construction by 2012,” the company said in a statement. “Onshore and offshore wind power will be a key driver for this growth.”

To keep pace with these ambitions, some large-scale offshore wind farms are planned or are in the process of being installed: Greater Gabbard off the coast of Scotland will have a 500MW capacity; London Array in the outer Thames Estuary has a planned capacity of 1GW when fully complete; Horns Rev II in the Baltic Sea will have a 209MW capacity; North of Bligh BankI near Zeebrugge, Belgium will add 600MW of capacity; and Innogy Nordsee 1 in the southern North Sea will produce 960MW.

The loads

The weight of the loads needing to be lifted varies depending on the size of the turbine being installed. Vestas uses two sizes of turbine for its offshore installations: the V90 3MW and V80 2MW models. The V80 has a 37t rotor, 67t nacelle (the structure that houses all of the generating components such as the gearbox and drive train) and towers ranging from 120t to 225t, depending on hub height. The V80 rotor has a diameter of 80m sweeping an area of 5,027 sq m. The V90’s nacelle weighs in at 70t, the rotor is 41t and the towers are either 160t or 285t depending on the hub height. The rotor’s diameter is 90m, sweeping 6,362 sq m.

Offshore wind turbines can also reach capacities of 5MW, 6MW and even 7MW, meaning the size and weight of components will increase. 5MW turbine rotors have a diameter of around 126m, substantially more than on the 2MW and 3MW models.

American Superconductor Corporation is developing a 10MW direct drive superconductor wind turbine, which it says will weigh 120t compared to conventional direct drive generators rated to 10MW that come in at 300t. It has entered into a cooperative research and development agreement with the US Department of Energy’s National Renewable Energy Laboratory to work on the technology.

On land…

Crawler and mobile cranes provide the handling solution for components at the dock. Vestas employs mobiles in the range of 400t to 700t, such as Liebherr’s LTM 1300/LTM 1400 models, to load and disembark vessels in the port.

Upon their arrival, the components are placed onto transporters and transferred to storage sites where mobiles unload them once more. When installation is ready to commence, the components are transferred back to the dock for pre-assembly into larger sub-assemblies to take place before loading onto the installation barges.

Anders Søe-Jensen, president of Vestas Offshore A/S, says, “As much assembly work as possible is done at the quayside prior to shipping the parts towards the actual installation site, as it is naturally much more expensive to do this at sea. This means that, for instance, the tower is assembled, main components in the tower are added and the towers are prepared for connection to the foundations. The nacelle is fitted with the hub and in some cases two of the blades, which is called bunny ear configuration. Any blades that are not fitted to the hub at the quayside are stacked, so they are ready for transportation.”

This pre-assembly work calls into play crawler cranes in the region of 600t to 900t, such as the Demag CC 2800-1, with a smaller tailing crane, such as the Liebherr LR 1160.

A tandem lift is used to move mast sections into a vertical position where they are then stacked to reach their full height as part of the finished turbine, says Brian Hyde, technical services manager at crane rental firm Weldex.

Both Hyde and Søe-Jensen say the larger cranes can be equipped with a superlift assembly to aid in the final stages of pre-assembly work, including the stacking and moving onto the vessels.

Søe-Jensen says, “The overriding consideration is the ability of the crane to meet the requirements for lift capacity and radius. The layout of the site and the constraints the site may place on the operation also have a big influence, such as quay space, acceptable ground loading, loads, radii and will it be necessary to also load the installation vessel from the quay. So any pre-assembly operation will require careful engineering to ensure the correct cranes are specified for each part of the operation.”

…and at sea

Loading onto the installation vessel can either be carried out by the onshore cranes or those installed onboard vessels such as MV Resolution, MV Lisa A or MV Svanen.

Resolution, operated by UK marine plant equipment supplier MPI Offshore, has a maximum payload of 8,950t and can carry 10 3.5MW turbines. This load is handled by two Kenz cranes: a 300t main crane used to place foundations (a hammer can be dropped from the crane to tap the monopiles into place), the transition pieces and the turbines themselves; and a 50t auxiliary crane that is used to handle other supplies.

Svanen is a heavy lift vessel that was used by RWE npower renewables to lay the foundations at Rhyl Flats. With a hoisting capacity of 8,700t at 76m above the deck, the gantry crane is fitted with four hoisting blocks mounted in the lifting gear and suspended from two lifting beams. The wire rope equalising part can be clamped and the winches independently operated to allow fine positioning.

Lisa A is also being employed by RWE npower renewables at Rhyl Flats. It is one of two jack-up barges being used to install the 3.5MW turbines and is equipped with a Manitowoc 888 with ringer capable of lifting loads up to 600t.

Vestas uses vessels such as A2Sea’s Sea Jack and Sea Worker barges in its installation projects. Sea Jack is equipped with a Manitowoc M1200 Ringer crane that has a maximum capacity of 800t at 21m reach and 424t at 32m reach. Sea Worker employs a Favco Cranes PC300 offshore crane capable of lifting 270t at 22m radius or 84t at 54m radius.

Just as companies such as American Superconductor Corporation are developing higher rated turbines to generate more electricity from offshore wind farms, so crane manufacturers are upping the ante with supersize models capable of handling yet heavier loads at sea. Few come much bigger than Liebherr Nenzing’s MTC 78000, with lifting capabilities of up to 2,000t. It achieves a load moment of 78,000tm off a maximum lifting capacity of 1,600t at up to 35m radius while still being able to slew over 360°. At a maximum radius of 74m for the main hoist, the crane achieves a lifting capacity of almost 530t. In addition to the main hoist, the MTC 78000 offers two auxiliary hoists with lifting capacities of up to 500t and 50t respectively. The dead weight of the new crane is 1,420t, plus up to 300t for the base column. The first MTC 78000 is scheduled to be mounted in the coming weeks.

“This is the biggest crane that has been manufactured by Liebherr so far with a maximum lifting capacity of 1600t,” says Wolfgang Pfister, head of marketing at Liebherr Nenzing. “The crane will be mounted onto a heavy lift vessel. Two more units of this type have been sold to a German customer for the installation of offshore wind turbine elements in the North Sea.”

Dutch shipping group Vroon, MPI Offshore’s parent company, has placed an order for two new installation vessels for offshore wind energy projects, which will offer increased benefits over the Resolution. The vessels, also to be operated by MPI Offshore, will be equipped with cranes with 1,000t capacities at 25.5m radius and auxiliary 50t cranes, and can carry 6,000t of cargo. This improves on the Resolution’s 300t capacity main crane, also operating at a 25.5m radius,

Paul Gibson, MPI CEO, says,” We have had four years of operating experience with MV Resolution and our new vessels will incorporate many smaller and bigger improvements based on that. Now that offshore wind energy, in particular in the North Sea, is taking off to a much larger scale, we are there again in the forefront with our new enhanced vessels.”

For the cranes and their operators, there are a number of elements that have to be factored in when planning the installation of offshore wind farms. Tides, wave height, wind and seabed conditions all have to be accounted for, especially as wind farms are generally sited in areas where they can maximise their exposure to large volumes of gusting wind.

“It goes without saying that the installation and operation of wind farms offshore is much more challenging than onshore due to the fact that you have issues such as tides and sea bed conditions that you need to take into consideration,” says Søe-Jensen. “The unpredictability of the weather and wave height is a challenging factor as well, and one that affects the entire process.

“Once the installation is done and operation and maintenance crews take over the operation of the wind farm, the challenges of being dependent on the weather conditions continue. When onshore wind farms need maintenance you can walk up to them anytime you like, which is obviously not the case with offshore wind farms.”

Hyde adds wind and other prevailing weather conditions are only part of the issues in the planning and installation of offshore wind farms. Bird species are another.

Bird breeding seasons play an important role in timetabling and planning works, Hyde says, with the Royal Society for the Protection of Birds (RSPB) freely commenting on their desire to see the impact on wildlife taken into account when planning and placing offshore wind farms.

“There are three main issues related to wind farms; disturbance, habitat loss or damage and collision,” said a spokesman for the organisation.

“There’s also the construction noise associated with the installation and the development of the infrastructure to land the energy on the shore. They’re the main reasons why we would object to a planning proposal.

“But there are good examples, such as the London Array, which we see as the gold standard and the type of project we should all aspire to,” the spokesman continued. “The project’s environmental impact assessment identified a previously unknown internationally important population of wintering red-throated diver using the area. The developers worked with us on conditions that would limit the disturbance to the birds [the planned 271 turbines were restricted to 175]. They are continuing to monitor the impact of the project on birds and if they show no sign of adverse affects there is potential for the array to grow.”