Mammoet Cuts Nissum Bredning Costs by Avoiding Dredging

Mammoet today (16 March) released details about the installation of four offshore wind turbines at Nissum Bredning, saying the turbines had been erected efficiently and cost-effectively by excluding dredging, which would have been imperative at this shallow-water site if a conventional approach had been employed.

Given the seabed conditions and shallow water depths of around three meters, Nissum Bredning cannot be accessed by installation vessels typically used at offshore wind projects without prior dredging.

Mammoet proposed a barge with an integrated ballasting system which allowed it to be lowered and grounded onto the seabed. This provided the necessary stability for the operation while eliminating the need for dredging. The solution effectively resembled an onshore installation and also simplified matters, as now the lift could be performed with a LR11350 crane, a land-based crane which among others is used for onshore wind power projects. Mammoet’s approach overcame the challenging near shore environment to safely install all four wind turbines. By excluding dredging from the process, the method saved time, costs and resources.”

The wind turbines are mounted onto gravity jacket foundations and grid-connected using a new cable and turbine concept with a 66kV voltage. The fourth and final Siemens Gamesa 7MW wind turbine was installed at the site in the Bay of Thyborøn in January, and the wind farm produced its first electricity on 17 February.

According to the latest post on Nissum Bredning project’s Facebook page, the Siemens team stated that they had never experienced so few errors during the commissioning of a new wind farm as with the four turbines at this new Danish nearshore wind farm.

The 28MW offshore wind farm, which is a testbed for Siemens’ technology, will get support by receiving a guaranteed feed-in tariff of DKK 0.7/kWh (EUR 0.09/kWh) for the initial 10 years for the first 50,000 full load hours of operation.