Innovative monopile design and an award winning installation vessel pave the way for significant reductions in cost and installation time for offshore wind farms with increasingly larger foundations and heavier turbines at deeper water depths.

The installation of the last of 150 wind turbines at the Gemini Offshore Wind Park on 23 August 2016 and the official start of operation of Luchterduinen on 21 September 2015 have added new milestones to the records of Ramboll in offshore wind and to the excellent cooperation between Van Oord and Ramboll.

Preparing Van Oord’s award winning installation vessel for larger foundations and wind turbines

What makes Gemini and Luchterduinen so special is the fact that Ramboll not only delivered customized and innovative designs for the monopile foundations in time and to the full satisfaction of our clients; Ramboll also contributed significantly to the design of Van Oord’s offshore installation vessel Aeolus. This installation vessel was commissioned in August 2014 and performed admirably in these two first projects, without incidents and in record time ahead of schedule. Ramboll’s Wind and Towers Technology Director Alexander Mitzlaff states: “The well managed and trusting cooperation with Van Oord in the design and commissioning of Aeolus was one of the best experiences in my 37 years of offshore engineering work.”

In 2015, Aeolus won the prestigious KVNR Shipping Award of the Royal Association of Netherlands Shipowners. Mrs.Tineke Netelenbos, chair of the jury, explained the choice as follows: “The Aeolus of Van Oord is an excellent example of innovative power. The vessel has been fully equipped for the efficient installation of offshore wind parks. An exceptional aspect is that Van Oord has managed the construction of the vessel itself. This is a very impressive achievement. It is a spectacular vessel that represents a huge advance in the Dutch offshore industry and which may result in international spin-off”.

The initial design of Aeolus, especially the jacking system, provides room for upgrading of the vessel. Based on feasibility studies, Van Oord decided to invest in a significant modification of Aeolus with CIG and Ramboll being responsible for the design and engineering work. This will enable Van Oord to continue to install the increasingly larger foundations and heavier turbines at offshore wind farms.

Cost and time reducing foundation design approach at Luchterduinen

Also regarding the design of the monopile foundation structures, Gemini (150 x SWT-4.0-130, water depth up to 37 m) and Luchterduinen (42 x V112-3.0 MW MHI Vestas, water depth up to 24 m) are not just another two projects. What makes Luchterduinen so special is that the monopile does not have a transition piece as the tower is mounted directly on the one-piece monopile. All secondary structures (boat landing, access system, platform etc.) are attached to support points, which have been specially designed to withstand the accelerations during driving of the monopiles into the sea bed. This innovative design has resulted in a considerable reduction of costs as well as considerable reductions in the offshore installation time down to 12-14 hours per monopile.

Using monopiles in deep water at Gemini

With a total capacity of 600 MW Gemini represents one of the world’s largest offshore wind farms, located 85 km off the coast and at water depths of up to 37 m. For each of the 150 locations, Ramboll optimized the monopile designs with regard to the specific water depth and soil conditions.

Gemini is a milestone in offshore wind because this project demonstrates that monopile foundations can also be feasible in deeper water. In cooperation with Van Oord and Siemens, Ramboll developed a monopile design with a performance indicator of water depth, rated power and steel weight which no one before has thought to be achievable. This design contributed significantly to lowering the costs for the fabrication as well as for the offshore installation of the foundation structures and thus to lowering the levelized cost of energy (LCOE). Head of Department in Ramboll’s Wind & Towers division Klaus Andersen states: “The cooperation between Van Oord and Ramboll worked very well on the project, with highly skilled technical teams on both sides and a full dedication at both companies”.

Luchterduinen and Gemini demonstrate two important segments of the broad range of engineering and consultancy services Ramboll offer to the offshore wind industry. Worldwide, Ramboll has delivered the detailed designs of more than 65% of all offshore wind turbine foundation structures, a substantial number of substation designs and several relevant designs of floating wind turbines. Ramboll’s expertise in designing large jack-up installation vessels (in cooperation with partners CIG and Technolog) is combined with proven know-how in planning and supervision of offshore installations as well as asset management, the inspection/maintenance/repair complex, and decommissioning.