windenergie op zee

De NL installatieschepen Svanen en Jumbo weer in Rotterdam.

De klus is geklaard!
De Nederlandse installatieschepen Svanen en Jumbo hebben op 1 augustus alle fundaties geplaatst voor het Deense Windturbinepark Anholt.
Het schip De Svanen van Ballast-Nedam heeft in het Kattegat 111 stalen fundatie palen geslagen voor het nieuwste en grootste offshore windturbinepark “Anholt” in Denemarken. Het Nederlandse transportschip Jumbo Avelin heeft in een paar maanden tijd de gele tussenstukken boven op de stalen palen geplaatst waarop de windturbines kunnen worden gebouwd. Het Anholt Offshore Windturbinepark ligt tussen Djursland en het eiland Anholt in het Kattegat, zo’n 25 km vanuit de haven van Grenaa. Het grootste offshore windturbinepark van Denemarken met een capaciteit van 400 MW zal vier procent van het totale energieverbruik van Denemarken met CO2-vrije stroom te dekken. Het park moet eind 2013 in bedrijf zijn. Op 28 maart 2011, hebben de Deense pensioenfondsen “PensionDanmark en PKA (Pensionskassernes Administration)” 50 procent van Anholt Offshore Wind Farm overgenomen. Dit betekent dat ongeveer 840.000 Denen mede-eigenaar zijn van het offshore windturbinepark.


The last of the 111 transition pieces has now been installed on monopile no. 111 in Anholt Offshore Wind Farm. This means that all foundations for Anholt Offshore Wind Farm are in place, and DONG Energy is well on its way in the construction of Denmark’s largest offshore wind farm. The next step is the installation of 111 wind turbines.


A foundation consists of a monopile, a long cylindrical steel tube driven into the seabed, and a transition piece that connects the monopile and the wind turbine tower.


Wind is welcome – sometimes
After having completed the approximately 12-hour long sea journey from Aalborg, where they are produced, to the offshore wind farm, it takes about 7-8 hours to drive the up to 460-tonne monopiles into the seabed. The 170-tonne transition piece is then lifted into place and grouted on to the monopile. This exercise has now been performed for the 111th and last time by DONG Energy and MT Højgaard, the foundation supply and installation contractor.


“The wind and weather conditions in the Kattegat where the turbines are to be erected can be rough. This is of course a good thing when the turbines are spinning as it will result in large power production. However, during construction of the wind farm, we are not too fond of strong winds, and we’ve had to suspend installation of the foundations many times,” says Flemming Thomsen, Project Director, and he continues:


“That’s why I’m very pleased that we have managed to stay on schedule, and that we’ve now installed all 111 foundations. It’s an important milestone for the construction of Anholt Offshore Wind Farm and for the large team of employees and suppliers who have contributed to the project.”


5,000 boulders had to be moved
It has not always been easy to prepare the seabed for driving of the monopiles as the seabed holds a lot of challenges. Particularly in the northern part of the wind farm there are areas with very soft seabed, while there are many large boulders in the seabed in the southern part of the wind farm.  DONG Energy has moved a total of 5,000 boulders that have now been placed in 30 artificial reefs.


“Before we started the work, we scanned all the turbine positions. We have considered all possibilities, and we have the tools in place that are necessary to handle the challenges that the different seabed characteristics pose. Now that we have completed the foundations, we can focus on the next important tasks to come. We’re well underway with installation of cables between the foundations, and then we will start installing turbines on the foundations,” says Flemming Thomsen.


Svanen installed the monopiles
The installation vessel Svanen, which was originally built to construct large parts of the Great Belt bridge, has driven the foundations into the seabed. Svanen installed the first foundation on 31 December 2011 at 19.00, while the installation vessel Jumbo Javelin started installation of the transition pieces on 16 April, and this weekend it finished the last of the 111 foundations.


The 111 foundations have been manufactured in Aalborg by Bladt Industries and installed by MT Højgaard.


DONG Energy expects to start installing the turbines in the beginning of September.


In May this message was published:


One third of the monopile driving is complete
As of 1 April 2012, 37½ of the 111 monopiles that make up Anholt Offshore Wind Farm are installed, and as such one third of the driving is complete. As expected, there are great challenges associated with the seabed where both very soft areas and very hard areas are present.


The hydraulic hammer in operation.


The driving of monopile number 38 takes place in an area where the seabed is very hard, and when the pile was 6 metres from the desired depth the work had to be stopped due to a technical defect in the hydraulics. As the pile is standing stably and strong winds for the area was forecasted, it was decided that Svanen should stop the driving and make for port in Grenaa to repair the hydraulics.


When the wind goes down, Svanen will continue with the driving, but experience shows that it can be difficult to get the pile into motion again. Expectations are that it is only hard underground deposits and not rocks which have made the driving difficult; but if it turns out to be impossible to drive the pile further into the seabed, drilling equipment is standing by to drill the last 6 metres into the seabed.


Driving of monopile A14
On Friday 16 March 2012, the sun was shining as the monopile in position A14 was driven into the seabed. The driving itself took approx 40 minutes with several stops along the way to ensure that the pile was being placed within the limits.


Most of the almost eight hours the installation works took were spent handing over the monopile from the tug vessel to the installation vessel Svanen.


Before the pile was lifted out of the water, the plugs in the cable entries were removed.


Then the cable entry covers and the temporary rudder were removed and the pile could be up ended. During this process, the end covers were removed, and in the end the pile was placed on the exact location. In order to place the hydraulic hammer directly above the pile, Svanen was moved forward until the hammer was positioned directly above the monopile.


When the hammer was lowered on to the pile, the weight of the hammer alone made the monopile sink 6 metres into the seabed. After this, it took less than 30 minutes to complete the driving.


The driving itself took approx 30 minutes.


Preparations for installing the transition pieces
The vessel Jumbo Javelin, which will assemble the transition pieces, has just started mobilisation in Rotterdam and is expected to be calling at Aalborg Harbour in mid-April.

Animation of Jumbo Javelin.

At the same time, the water temperature is now above the 5 degrees Celsius required for the casting together of the monopile and the transition piece. In Aalborg, the installation procedures will be tested onshore before it all begins offshore.

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