SUMMARY
In a densely populated country such as The Netherlands it is almost
impossible to install large numbers of large windturbines on the mainland. That was the main reason to investigate the possibilities of siting
the windturbines offshore on the Dutch part of the North Sea Continental Shelf, with a further advantage of a higher windfactor.
The investigations comprised the questions of how and where to install large windturbines in large numbers, what the costs will be and how the production and installation should be organised.
Several types of structures for supporting the windturbines have been reviewed in steel and/or concrete, floating, resting on the seafloor or piled into the seabottom.
The North Sea usage for shipping, fishery, etc. has been compiled and the several activities have been considered for their possible conflicts with windturbine parks. It was found that three regions were available with as 1 ittle conflicting usage as possible.
Finally, the findings have been evaluated and some options were selected.
For very large numbers of windturbines (5000 are being considered) the cylindrical steel column structure was found the best option, taking maintenance of the structures into account. Depending on the soil characteristics in the regions considered the structure will be
piled into the seabottom or wil 1 be resting on the seafloor with the lower part being a sandfil led concrete caisson.
Special devices have to be developed in order to install the windturbines in a streaming production scheme of one or two per day!
The costs of offshore siting are rather high. For single production the
costs are estimated at 4 to 4.5 mill ion guilders (2 guilders~ 1 U.S. dollar). For streaming production the costs are expected to be reduced to 3 or
