10 November 2010

Offshore Wind Farms: Low Loss Solutions for Transferring Current

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Using wind energy where the wind blows strongest makes perfect sense as long as the energy can be readily transported to where it is needed.

he first offshore plants are already being erected, and many more are planned. But the farther they are away from the coast, the more urgent becomes the problem of transferring the current with as low a loss as possible. Over long distances, this is possible only with direct current.

To exactly determine the unavoidable losses also in this case, and to set up a metrological infrastructure for a future network of direct current transfer paths, a European cooperation project has been launched in which a great number of metrology institutes is involved. The starting signal for this project came from Braunschweig, from a close cooperation between the Technical University (TU) and the Physikalisch-Technische Bundesanstalt (PTB) which are now both intensively involved in the new project.

Already now the networks are getting narrow. The integrated European high-voltage network is used to complete capacity. Connecting other energy generators -- such as wind power stations, hydropower plants or solar power plants -- is hardly possible any more; new ways for the current must be found. As the construction of high-voltage power lines is often thwarted by protests from residents and does not come into consideration for offshore plants anyway, subterranean cables must be used. What is being planned is nothing less than a new transfer network all over Europe. If current is to be transferred via cables -- and over such large distances -- this is possible only with direct current, because in that case, the losses are lower.

The networks used so far, however, work with alternating current. This has been the case since the end of the 19th century, when the decision was taken to use alternating current instead of direct current for the large-area distribution of current. The decision was based on the fact that -- at that time -- a simple and effective current transfer with high voltage and, thus, without great losses, was possible only for alternating current. But this was long ago. And since in semiconductor electronics, new heavy-duty circuit breakers have been developed which allow even high powers to be converted efficiently from direct current to alternating current and vice versa, there is, in principle, nothing standing in the way of the new direct current network.


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