The first German offshore wind facility is expected be put into operation sometime in 2009. A total of 12 giant wind turbines out at the North Sea will turn near the isle of Borkum, each one generating 5 megawatts of power, the largest worldwide. The electrical current they will produce will be conveyed over a distance of 45 km past Norderney to the mainland, at a depth of two to three meters buried in the seafloor.
In addition to many other technical challenges making the whole project controversial, a measurement problem regarding the cable needed to be resolved: How could the thermal conductivity of the seafloor be determined accurately enough to be able to predict the later influences of temperature on the buried cable?
The seafloor contains great quantities of pebble gravels which create many inhomogeneities and, naturally water which additionally interferes with any measurement due to convection. After several renowned test institutes had given up in the face of these obstacles , the commissioned engineering company turned to the measurement experts of the Physikalisch-Technische Bundesanstalt (PTB). And they were able to help.
Using a method they had recently developed themselves, they successfully measured the thermal conductivity of several seafloor samples at the required accuracy. The instrument had already proven its worth in in-situ measurements of river sediments of the Spreewald situated near the German town of Lübben. The measuring instrument is all-purpose. A manufacturer will soon be bringing it on the market under licence. First it will be presented from 26 to 28 May 2009 at the Sensor&Test trade fair in Nuremberg at the PTB booth.
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