Mammoet cuts shallow water wind farm costs
Erecting a wind farm in shallow waters has provided a challenge because conventional methods could not be used. The water was too shallow for the dedicated offshore wind farm vessels and too deep for land based systems to be used.
This was the difficulty faced by the installation contractors working on the Nissum Bredning wind farm being established off the Danish coast. One solution would have been to dredge the area to allow deeper draft vessels to operate but this was an expensive solution.
Contractors Mammoet, who specialise in heavy lift operations, found a solution for the installation of the four offshore wind turbines at Nissum Bredning. The turbines have been erected efficiently and cost-effectively by excluding dredging, which would otherwise have been imperative at this shallow-water site if a conventional approach had been employed.
Mammoet proposed using a barge that was fitted 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 at the same time, eliminating the need for dredging and it created a firm base similar to that used for onshore operations. This base meant that the lifting operations could then be performed with an LR11350 crane which 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 are 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 in February.
According to the latest information from the Siemens team responsible for the installation of the wind farm they had never experienced so few errors during the commissioning of a new wind farm as with the four turbines at this new Danish near shore wind farm.
This 28MW offshore wind farm is a test bed for Siemens’ technology, and it will get support by receiving a guaranteed feed-in tariff of € 0.09 per kWh for the first 50,000 full load hours of operation.
By Dag Pike
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