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Offshore Wind Turbines Transporters Rise to the Challenge

Wind turbines are awkward creatures. Their heavy towers and nacelles, and long, fragile blades do not fit easily with conventional transportation methods. It’s technically possible to move anything from A to B, but transport then becomes a significant part of the overall expense. The pressure to lower the overall cost of wind power means that where turbines are built and how they move between factory, base port and field are more critical than ever.

With their huge size, the latest generation of 6- to 7-MW turbines only increases the challenge. To address this, manufacturers and developers are evolving tested technologies and innovating with new machinery, techniques and processes.

Turbines can travel in sections — blades, hub, nacelle, tower and generator — so keeping the weight of each load to a minimum. Blades are the most problematic component, and transportation is a fundamental part of their design. This means building in lifting and clamping points that will withstand the movement from horizontal to vertical or the loadings incurred when a ship is at maximum tilt in a storm. Racks and carriers specific to each blade model must handle these forces without damaging the blade.

In road transport, manufacturers have long worked closely with specialist manufacturers to make sure that there will be trailers available to fit the components of their latest turbines. Tower sections can be moved using special wheeled ‘dollies’ bolted to each end. These are usually specific to each tower type, though French company Nicolas’s telescopic adapter technology can transport both towers and nacelles by changing the clamps used.

“Every tower is different,” says David Collett, managing director of Collett and Sons. “The first trailers we bought became obsolete within two or three years and we have invested millions since then.”

Blades require extendable trailers with steerable axles, helping them negotiate tight turns. Collett provides a “swept path” GIS-based service that analyses exactly the route a component will travel. This means a developer will know which items of road furniture to remove, and also where a large component cannot pass at all. “The larger the blade, the more obstacles,” says Collett. “Not all software works so well. We have turned up to find access roads built in the wrong place.”

Coping with extreme challenges like Alpine hairpin bends has led to ingenious solutions. Scheuerle’s trailer-mounted blade adapter grips the root of the blade and, using hydraulic power, can lift it to an angle of 23°, lower it and turn it left or right. This means the blade can “float” over supporting walls, trees, buildings or other obstacles. In addition, it can be turned on its own longitudinal axis to reduce wind loading.

In America, Vestas employs custom railway wagons to ship its blades — including the 55-metre blades of the V112 — from its factory in Windsor, Colorado to the nearest port in Houston. Clamping the blade root to one wagon while the tip freely overhangs another means the train can safely negotiate the bends on the line.

The trend toward much larger rotor diameters in the latest generation of high output turbines challenges both logistics and turbine design. The “square-cube” rule dictates that energy output increases with the square of the rotor diameter, but loads increase with the cube. Though manufacturers are using new materials and structural designs to limit the increase in top head and tower mass, the new turbines generally have larger and heavier components to handle the higher bending moments and other loads.

With its rotor diameter of 126 meters, REpower’s 5/6M series is the largest currently operating offshore. Those in development are even bigger. For example, the rotor of Nordex’s proposed N150/6000 will measure 150 metres, while Vestas’ 7-MW V164 will have 80 meter long blades; both comfortably exceed the London Eye’s 135 meter diameter.

To move the huge 63 meter blades of its 7.5-MW E-126 turbine by road, Enercon came up with a simple solution. They simply fold them in half. “No part is longer than an E-82 blade,” says Henri Joppier, Enercon’s head of UK sales. “We deliver the nacelle in sections and it’s very easy to commission on-site. It’s a matter of design, at the end of the day.”

Enercon is the only manufacturer to do this, and even the cleverest trailers are reaching their limits with the largest one-piece blades. “Blades for the latest 6 MW turbines cannot practically travel by road,” says Collett.

So, with proximity to a deepwater port required to transport the latest turbines, on-site manufacturing is the rational way to reduce both logistical complexity and cost. Ideally, turbine and foundation manufacturers would load out from their back door onto the deployment vessel, but a central location for shipping to the main development sites is the next best option. Currently, sea freight is exempt from carbon tax and, though shipping costs (and congestion) rose up to 2008, they have since stabilised. If and when either of these factors changes, moving manufacturing closer to the deployment site will be even more attractive.

“We are trying to drive down the cost of offshore wind so we need to locate where we manufacture the various components carefully,” says Rob Sauven, managing director of Vestas Technology UK. “You want to move an 80 meter blade as few times as possible. Every time you handle it, the cost goes up.”

REpower’s Bremerhaven factory is ideally located for fields like RWE’s Nordsee Ost. With the developer’s operations base just around the corner at Bremerhaven container port, the 48 6M turbines REpower is supplying for the project will have a very short journey.

The proposed UK factories for Siemens in Hull and Vestas in Sheerness also promise cost-effective, on-site manufacturing: both have excellent access to the UK’s east coast where hundreds of turbines will be installed in the coming years.

Sheerness is appealing for many reasons: access to deepwater docks is one of them and a huge load-out space around the size of 70 football fields is another. V164 blade manufacturing and nacelle assembly is planned here, though this still depends on a firm order pipeline from developers.

“Logic says build it directly on the quayside,” says Anders Søe-Jensen, president of Vestas Offshore. “Getting the components in is not a problem but getting them out is, so you want to build it in the port from where it’s going to be loaded out.”

Though green technology is creeping into marine engineering with the likes of Damen Shipyards’ ASD 3212 diesel-electric-propelled “Green Tug,” transhipment between factory and project base relies almost exclusively on conventional vessels. Notable exceptions are Vestas’ two custom-built Bladerunner boats which move blades from the company’s R&D facility on the Isle of Wight to Southampton port for transhipment, and Enercon’s E-Ship 1 which, fittingly, harnesses wind power to help transport wind turbine components.

E-Ship 1 has four 27 meter-high Flettner rotors mounted on its deck. These are spun up using excess energy derived from the diesel engines’ exhaust gas, so making use of the force a spinning body in a moving airstream produces (the Magnus Effect) to help drive the ship. The same force is what causes the curved motion of a spinning football or cricket ball. This extra power reduces fuel consumption by up to 40 percent, and the ship’s adjustable cargo bay also lets it load many more wind turbine components than a conventional cargo vessel of the same size.

Transhipment also brings its own quayside challenges. For very heavy items such as nacelles, built-up towers and jackets, Collett uses self-propelled modular transporters (SPMTs) that have been used for many years in sectors like oil and gas, and petrochemicals.

“Moving blades up to 60 meters and nacelles between 200 and 400 tons is completely possible, but that’s strictly between the quayside and the storage area,” says Collett. “You work out the number of axles you need and bolt them together.”

Netherlands-based transportation specialist Wagenborg used SPMTs in various configurations to load out the REpower nacelles and rotors for the Alpha Ventus field last year. 20-axle lines of Scheuerle SPMTs transported complete rotors with diameters of between 116 and 118 meters, and weighing nearly 150 tons each, while the vast tripod foundations required a set of 22+8 axle SPMTs under each leg. To add to the challenge, the rotors had to slide right out over the dockside before the barge cranes were able to pick up the load.

The trip to the field is the next leg of the offshore turbine journey. Increased efficiency and lower costs are again the goal: offshore installation as a proportion of total CAPEX is predicted to fall from 23 percent to 18 percent by 2020, and innovative technology is paving the way.

For example, the GBF consortium’s gravity base foundation is deployed via a purpose-built barge. By adding or subtracting ballast, the barge can be sunk and raised in order to load a turbine, tow it to sea, sink it in position and then refloat in order to pick up the next one.

Suction bucket footings are also quick and cheap to install in soft seabed conditions. Mercon and ALE’s new EMI technology uses a standard barge equipped with a tilting frame in order to install monopiles or met masts with a multiple suction-bucket footing.

Driving down deployment costs also means finding the most efficient process for each offshore project — for example, whether to assemble the whole rotor onshore or to ship the blades and hubs individually and assemble them on-site. Lifting whole rotors means fewer offshore lifts and can be done in rougher weather, but racks of blades can be loaded more quickly at the quayside.

“You want the lowest cost solution for that particular set of components for that weather window,” explains Sauven. “Water depth, time of year, distance from port: each changes the equation and you need the flexibility to optimise for each site.”

Another choice is whether to ship turbine components out in smaller boats, giving better utilisation of the expensive on-site installation vessel. Specialist wind turbine installation vessels (WTIVs) can carry and install turbines and foundations themselves, but will be off-site when restocking back at the base port. With more demanding far offshore projects looming, the “mono-vessel” concept is gaining the upper hand.

“The available fleet of vessels require tugs and are much slower than the next generation new-builds, so there is no sense in using them to collect the components,” says Katie Faulkner, A2Sea’s sales support manager. “Because Sea Installer has a larger capacity and is self-propelled, she will be able to ‘cut out the middle man,’ and collect the components directly from the production line, take them straight out to the site and carry out the installation.”

The jack-ups currently used for turbine installation were mostly built for the oil and gas industry and adapted for wind, while the new WTIVs are bigger and more capable in every way, even compared to first generation installers like the MPI Discovery.

“These are absolute beasts in comparison to previous vessels,” says Max Paterson, sales and marketing coordinator at Seajacks, whose own WTIV will arrive this year. “Existing boats have blade racks overhanging the front, but Zaratan can stack them across the back of the deck.”

Today’s foundations can weigh over 700 tonnes, with nacelles tipping the scales at over 350 tons and towers in excess of 260 tons. Cranes must have the reach and radius to install these at more than 100 meters above sea level. Crane loads are going up from 300-600 tons to 800-1,200 tons or more, and employ a “wrap around the leg” design for optimum deck access.

New WTIVs have far more deck space with extra flexibility to cater for different projects, and can jack their heavier payloads in deeper water. DP2 capability comes as standard, transit speeds are higher, and accommodation allows for extra installation workers: all attributes intended to support far offshore deployment.

“At Thornton Bank, we were taking out one turbine per cycle,” says Richard Hatton, head of UK offshore sales at REpower. “This year we were taking out two sets. The new vessels will be able to take six or seven sets per cycle.”

RWE considers this area so important that it built its own boats and founded a dedicated company to manage all aspects of offshore logistics. Its two SeaBreeze class vessels are now working on the Nordsee Ost and Gwynt y Môr fields respectively. Contrary to fears of a shortage in only two or three years, there are now numerous WTIVs appearing on the market.

“Since we launched our plans, a lot of companies are building vessels. Every one is different, and in the next few years we will see which one is best,” says a spokesman for RWE Innogy.

Swire Blue Ocean’s Pacific Orca exemplifies the new generation. It will have a 1200 tonne crane, a transit speed of 13 knots and accommodation for 111 people. With a deck area in excess of 4,000 m2 and an 8,400-ton jackable weight, it will operate in up to 75 meters of water.

Fred Olsen Windcarrier’s two boats, Brave Tern and Bold Tern, will be delivered in the second half of this year. “They are built to cope with a 10 MW turbine and a 470 tonne hub weight,” says commercial manager Carl Erik Gurrik.

GeoSea’s Neptune will shortly start work on Thornton Bank while other new vessels due this year include Workfox’s Seafox 5, MPI’s Adventure and Discovery, another WTIV from Van Oord, and HGO InfraSea Solutions’ Innovation. The latter is the biggest yet, with a 1,500-ton crane and an 8,000-ton payload.

Deep water is the new frontier for turbine deployment. Going beyond 45 metres makes jacking impossible for almost all current vessels, and floating WTIVs would be the likely solution.

Dynamic stabilisation is an important technology here (and in all lifts involving floating vessels), reducing roll and so the dynamic crane loading, thus permitting relatively heavier lifts. Manufacturers like Liebherr are also working to improve the heave compensation systems already built into many marine cranes. “We lifted turbine components from floating vessels on the Beatrice Demonstrator in 45 meters of water,” says Hatton. “It’s faster because there’s no need to jack but it cuts down on the weather window. Better dynamic stabilisation is coming but it’s still a long way from being proven.”

Designers are now pushing vessel capability even further. For example, W3G Marine Ltd’s OWTIS (offshore wind turbine installation ship) concept offers a 1,500-ton crane. Gaoh’s twin-hull “offshore installation shuttle” would carry two complete turbines or foundations on a high gantry. Employing a combination of dynamic positioning along with both vessel and hoisting compensation systems would give it a claimed 80 [ercent operational window in the North Sea.

Offshore wind development is often compared with the early days of North Sea oil exploration. Here, the comparison has real resonance. Manufacturers, developers and the rest of the supply chain are working flat out to use the latest logistics technology to access Europe’s massive offshore wind resource — safely, swiftly and at the lowest possible cost

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