Ideally, energy from renewable sources should be used where it is generated, however, that is not always possible. Electricity produced at offshore wind farms, for instance, has to be transported to coastal areas. This usually requires the use of high-voltage direct-current transmission (HVDC), which offers the most efficient solution when cable lengths in excess of 80 kilometers are involved. HVDC systems use a converter station to transform alternating current (AC) generated by offshore wind farms into direct current, after which the direct current is converted back to alternating current on land. For example one of the offshore DC connection in the North Sea provides power with transmission losses less than four percent.
Electricity produced on land by solar power facilities and at wind and hydroelectric power plants also often needs to be transported over long distances to metropolitan areas. For example, new transmission lines with a total length of 3,800 kilometer are now being planned for the transport of power generated mainly by wind farms, from northern Germany to the country’s southern regions. DC is the current of choice for power transmission here as well. “These electricity highways will form the backbone of the energy network of the future,” says Jörg Dorn, Head of Product Development for HVDC converters at Siemens Energy.