dcsimg Offshore wind turbines are setting new records - Ramboll Group
     
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Offshore wind turbines are setting new records

Offshore wind turbines move further out to sea to ensure stronger and more stable wind resources. This calls for innovative methods when designing new turbine foundations. Ramboll is ready with solutions for tomorrow's challenges. 
 

The boundaries for locating new offshore wind turbines are constantly changing. Building wind farms out at sea provides stronger and more stable wind resources, as well as a solution to avoid disturbing the local environment and the view shed from the shores.     

And the market for wind energy is growing rapidly. Plans are underway in Northern Europe, particularly in Germany and England, to build more than 100 offshore wind farms, with total construction costs of approximately EUR 150 billion. These turbine farms can help contribute to reaching the EU's objective for 2020 that 20% of all electrical power should come from renewable energy sources – and preferably from offshore wind turbines.

Whereas today's offshore turbines are typically built 10 to 20 km from land, it is expected that in five to ten years from now, wind turbines will be situated up to 80 km out to sea – at depths of 60 meters.  Prototypes of floating foundations that will be used for this purpose already exist for offshore wind turbines in Norway and Portugal. So in principle, it will be possible to build wind farms as far out to sea as you want.

 

Photo: Elsam

Ready for tomorrow's challenges

To prepare for tomorrow's technical challenges, a Ramboll employee is currently performing a PhD thesis as an industrial researcher in cooperation with the University of Aalborg investigating how the floating foundations react to strong winds, cyclones and storms.

"The construction costs for the floating foundations are still so large so that the technique is not yet profitable in most cases. But I am sure this will be a widely used solution at some point. We therefore believe that it is important to perfect our knowledge, so that we are also capable of mastering this technique. And one way to do this is to work with the prediction of movement and effects on the structures," says Søren Juel Petersen, Business Development Director in Ramboll.

Ramboll is world leader within the design of offshore foundations for wind turbines and has developed more than 2100 foundation designs for 37 offshore wind turbine farms around the world.  In other words, this is more than 65% of all wind turbine foundations installed in the world today.

Ramboll is currently designing the monopile foundations for the Gemini offshore wind farm, which will be one of the world's largest wind farms. Far out in the North Sea, 150 wind turbines will rise from water depths of up to 37 metres and supply more than 1.5 million Dutch citizens with renewable energy in 2016.

Oil – gas – approach

"As we move wind farms further out to sea, we face challenges related to design of larger structures that can withstand the larger waves, the stronger winds and the heavier loads. This means we need to use methods that increasingly resemble those in the oil and gas industries. This includes large structures known from the oil and gas industry that are proven to withstand the massive impact from the waves and forces from the wind," says Søren Juel Petersen.

Rather than building foundations for offshore wind turbines, on so-called monopiles, which consist of steel tubulars 5-6 meters in diameter,  the new types of structures are built as lattice structures, the so-called "jacket structures", bottom mounted on the seabed using three or four legs. The jackets resemble the foundations in oil and gas installations, which are built in much deeper water than has previously been the case for wind energy.

 

Photo: G. Boulougouris

Hotels at sea

There will be other new considerations when wind farms move to deeper water, far out at sea. Instead of using the traditional method of sailing the crew out to the wind turbines, it is now becoming more common to fly the crew to the living quarters that are being built in connection with the transformer platforms. The living quarters will function as a kind of hotel at sea; a concept already used by the oil and gas industry, with cabins, canteens, and recreational areas, where the crew can stay for up to two weeks at a time. From there the crew can then be flown or taken by boat to the individual wind turbines in the area.

"The hotels will remain for the lifetime of the entire project – which could easily be up to 25 years. They will be manned every day - all year round.  This will ensure that someone will always be available to maintain the platforms and turbines and be responsible for daily operations.  This is a very good solution with these offshore hotels, and it already makes sense when the offshore wind farms are 40 km from land.  And in 10-15 years, this will likely be standard practice for all offshore wind farms," suggests Søren Juel Petersen.

 

Photo: DONG Energy A/S

Two challenges for future offshore wind farms

1. We must drive down the cost

"The further out to sea that the turbines are placed, the more it will cost to maintain them. So the main issue will be to try to drive down the cost per produced kilowatt hour.  This can be done, for example, by using steel structures, requiring less maintenance, or by implementing projects under a smaller number of contracts - resulting in more complete solutions for better project optimisation. This would also allow closer involvement of the entire supply chain in the project."

Søren Juel Petersen, Business Development Director, Ramboll.

2 Transformer platforms must be profitable

"The costs associated with transformer platforms need to be brought down in the same way as most other wind turbine park components, so as to make them profitable in ever deeper waters. The most significant challenge is to establish a transformer platform concept that ensures the best and safest conditions for a risk-free installation of the platform, and in the case of the operator ensures the most reliable operating conditions during the lifetime of the platform. Here, it is important that the wind industry draws on past experience from existing off-shore facilities, and already during the design phase factors in whole life costs."

Peter Busch Nielsen, Deputy Director of Department Structures, Ramboll.

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Contact

Søren Juel Petersen
Søren Juel Petersen
Global Market Director
T+45 5161 8760
Esjp@ramboll.com
Klaus Jacob Jensen
Klaus Jacob Jensen
Director of Global Wind & Towers Division
T+45 5161 8617
Ekjj@ramboll.com