Wind turbine installation: the long and windy road
Image credit: Nooteboom
Maximising returns from a wind turbine typically means locating it in an exposed place – on the top of a hill or increasingly out at sea. Developing equipment to access these locations has emerged as an industry in its own right.
“Wind power is leading the charge in the transition away from fossil fuels, and continues to blow away the competition on price, performance and reliability,” declares Steve Sawyer, secretary general of the Global Wind Energy Council. Dramatic falls in price have sparked rapid market growth. 2017 saw 52.6GW of additional wind power installations around the world, bringing the cumulative total capacity to 539.3GW. All this activity has created its own industry in construction and logistics services.
The fastest growing wind segment is offshore, with 18,814 MW of installed capacity in 17 markets around the world in 2017. This trend is set to continue, predicts Aleksi Minchev, marine and port operations specialist at UK-based global freight mangement firm WWL ALS.
The UK is a leader here, with just over 36 per cent of this offshore capacity.
The typical wind turbine comprises 8,000 parts that have to be transported to their final installation site. Turbine components are being delivered and assembled in increasingly remote places including high-altitude locations in the Rocky Mountains or extreme environments such as the deep waters of the North Sea.
Compounding these already tough logistical challenges is the increasing size and weight of turbines, particularly in offshore locations. The typical offshore 4.1MW turbine with a 90-metre hub height is set to be surpassed by 11MW colossi with hubs 125m above sea level and blades spanning 190m. Their blade tips will scythe the air, at a height two-thirds that of the Empire State building in New York.
Moving turbine components of this size by road, rail or even by ship is truly challenging and has not only encouraged wind turbine manufacturers to shift their production facilities to the ports, according to Minchev, but also sparked a number of innovations in shifting and lifting equipment.
Transport and lifting equipment
A single turbine can require up to eight hauls (one each to deliver the nacelle, hub, three blades and three tower sections. In order to ease the delivery and assembly of wind turbines offshore, turbine manufacturers are relocating to major navigable waterways or ports. Innovations and development of new or converted roll-on/roll-off vessels, longer blade trailers, self-propelled modular trailers (SPMTs) and blade adapters have made transport and transfers of components and equipment easier and faster.
As a result of such innovations, Guy Dorrell, spokesman at Spanish-based Siemens Gamesa Renewable Energy, says: “We have brought the installation time of a single offshore turbine down from around 2-3 days to inside 24 hours, despite the near doubling of generating capacity, with the necessary increase in scale of the component parts, over a four-year period.”
To satisfy the requirements of the increasing number of offshore installations, a fleet of specialised ocean-going cargo vessels has been launched in recent years. For example, Hamburg-based Hansa Lift has a vessel that can carry 90 blades 39m long and 35,000kg in weight on a single trip. In Europe alone there are now some 400 support vessels, 280 heavy-lift and construction vessels and a further 296 construction support and 162 cable installation vessels in operation, according to the Royal Institute of Naval Architects and the consultancy 4C Offshore. Currently, there are some 33 specialist vessels in the global wind turbine installation fleet.
John Oosthoek, market- and business intelligence manager at Royal IHC forecasts that over the next decade a specialist vessel will be launched each year, and to cope with deep waters and increasing scale of equipment, the new vessels will be bigger.
As offshore windfarms continue to spread across the world, from Europe and the US to Asia, supply and service vessels are increasingly in demand.
Similar to the car ferries that ply the English Channel or North Sea, turbine manufacturer Siemens employs dedicated roll-on/roll-off vessels to carry turbine components between its wind power factories in Hull, Cuxhaven, Port of Esbjerg and other North Sea and Baltic locations. These vessels have specially developed bows and extendable ramps controlled by hydraulic systems and are able to carry up to 12 wind turbine rotor blades. The advantage, as Minchev points out, is that: “Loading and discharging such vessels is more cost-effective by roll- on/roll- off vessels than the conventional lifting method.”
Self-propelled modular transporters
Heavy capacity hydraulic modular trailers or SPMTs with many axles are being increasingly used to drive components such as nacelles weighing over 350 tonnes on and off roll-on/roll-off vessels. SPMTs are more cost- effective in mobilising loads than conventional cranes. In order to cope with ever growing blade lengths, telescopically extendable wind blade trailers are being used. They can also be used in combination with barges to transport wind turbine components and other heavy cargoes such as transformers and generators along inland waterways to move components easily without the need for several separate crane movements. In short, the main purpose of these vessels and wheeled equipment is to reduce the number of crane operations needed to place components under the installation crane hook.
“One key innovation for the wind energy logistics sector has been rotor blade adapters,” states Minchev. These are usually radio-controlled gimbals mounted on platform trailers, so as to enable rotor blades to be picked up, positioned at an angle of up to 70°, pivoted as well as rotated around their own axis, which makes it easier to move such rotor blades around any obstacles. In areas with trees or buildings, hairpin turns or in the mountains, it makes easier to deliver such bulky loads to their destination, without the need for roads to be widened, trees felled or new routes to be created. The blade adapter allows blades between 57-65m long to be carried by road to onshore wind farms. This specialised piece of kit allows a truck loaded with a wind blade to negotiate tight road bends by raising the tip end.
Logistics and training software
Moving such large wind components overland can prove challenging for logistics operators and highway, rail and inland water authorities and is very costly for wind farm developers. The US Department of Energy reports that a 1,000-mile truck trip can cost more than $20,000. This is small compared with the $3.3m price of an average wind turbine, but with three blades per turbine and possibly up to 100 turbines the cost of transport alone amounts to a hefty sum.
For the offshore segment, logistics software can now be used to optimise operations. Shorelines offers design and maintenance tools built on its Shoresim simulation platform to identify the best course of action both during development of a wind farm and its subsequent operation. SIMSTALL simulates a full scope of offshore project construction, including port operations, logistics, installation, commissioning, and testing, while MAINTSYS analyses operations and maintenance and marine logistics.
Simulation software can also be used to improve safety and productivity. For example, CM Labs offers a training package on the operation of the Liebherr crawler crane, which is commonly used in wind turbine erection, so contractors can use it to instruct construction crews.
Traditionally, wind farm developers have used a variety of transport solutions to delivery components to site, including trains and lorries. However, in more difficult locations such as in mountainous areas or sites far offshore they are using heavy-lift helicopters to hoist components. There are several in use worldwide including the Russian Mi-26, Boeing’s CH-47 Chinook and the Airbus AS332 Super Puma.
The offshore wind sector has benefited greatly from the experience of the offshore oil and gas industry. Rather than reinvent the wheel, it has been able to borrow crucial equipment such as jack-up rigs, floating cranes, pole drivers and suction bucket or caisson foundations.
In shallow waters of up to 120m, self-powered jack-up rigs or vessels, equipped with large-capacity cranes and adjustable legs, act as a temporary fixed platform for assembly of turbine components on site. The hull is actually a watertight barge that floats on the surface. When the rig reaches the work site, the crew jacks the legs downward through the water and into the sea floor. Dorrell notes that these vessels, such as the Seajacks’ Kraken or Leviathan, have flexible deck space enabling them to carry components for multiple turbine installations in one voyage. Floating cranes
As turbines have got bigger and heavier and their foundations wider and installations shifted to ever deeper waters, contractors have favoured large floating cranes in preference to jack-up rigs. One of the largest is the 25,000t Asian Hercules III, which has a lifting capacity of up to 5,000t and a hook height of at least 120m, making it ideal for lifting monopile foundations and turbines into position. To ensure stability, water is pumped in and out of the vessel’s various bulkheads to prevent overturning.
Blue Hammer is currently being tested as an environmentally friendly pile-driving system for preparing offshore wind turbine foundations that is cheaper than conventional hammers. It was developed by Fistuca, a Dutch technology company spin-off from Eindhoven University of Technology. BLUE Piling Technology employs a large water column to drive a pile in the soil, instead of the steel ram used by hydraulic hammers, Fistuca explained. Gas combustion throws up this water column, which falls back on the pile under gravity, hence delivering two blows. This cycle is repeated until the pile reaches the desired depth. The noise of a conventional hammer is created by the rapid deceleration of a fast moving steel rod that hits the monopile.
Fistuca director Jasper Winkes explains: “The energy is transferred in a very short time span, typically 4-8ms. The result is a lot of vibrations that cause the pile to emit very high underwater noise. The BLUE Hammer delivers blows with a very heavy water column. The duration of the blow is 100-200ms and the increase and reduction in force are rather gradual, [so] the pile feels a blow that is more like a push than a short impact, resulting in reduced underwater noise levels.”
The Blue Hammer could remove the need for underwater noise mitigation as well as allow secondary steel to be pre-welded to the monopile before installation, potentially unlocking ‘transition piece free’ designs By reducing the time and number of operations offshore, this method should improve health and safety and result in significantly lower installation costs. Blue Hammer’s developers say the project will yield some €33-40 m lifetime savings for a 720MW offshore wind farm, which is equal to a levelised cost of energy (LCOE) reduction of 0.9-1.2 €/MWh.
Mono Bucket foundation
Suction bucket foundations are customarily used by offshore wind developers working in the North Sea, where waves may reach 20m or more. Universal Foundation’s Mono Bucket is installed using a patented control system to lower the pressure in the cavity between the foundation and the seabed, which generates water flow, lowering resistance around the edge of the foundation’s skirt and allowing the foundation to sink into the seabed. The installation system also controls vertical alignment, removing the need for a transition piece to adjust verticality. The structure comprises a multi-shell foundation with vertical stiffeners, a robust lid and a shaft for interfacing with turbines or other topside structures. Installation is noise-free and offers no risk to marine mammals, offshore installation crews or marine operators. When it comes to decommissioning, the foundation can be removed for reuse or recycling by reversing the suction process, applying water pressure into the foundation skirt so that it can be smoothly lifted from the seabed.
In conclusion, if the size of turbine components transported by road and rail is limited by regulations then wind energy manufacturers will need to break up their components into smaller modularised sections, easing the burden on logistical transport companies as well as the highway and water authorities. As for the growing offshore developments around the world these could be supplied and serviced from turbine manufacturing plants based around ports and shipped to their final destinations by the growing fleet of dedicated vessels.