Curtailment of wind energy due to electricity transmission bottlenecks is an increasing problem in Germany. The aluminium-conductor composite-reinforced high-temperature low-sag (ACCR HTLS) cables can transport up to twice the amount of electricity carried by conventional cables and can use existing pylons, thereby reducing problems connected with permitting and public objections to building new cable routes.
The study was carried out by RWTH Aachen university and 3M Deutschland, which manufactures ACCR HTLS cables.
It comes as the four German transmission system operators (TSOs) are working on a network development plan, to be ready in June.
"This is a very interesting option and we welcome any innovation that increases transport capacity - the less complicated it is, the better. But it's not that simple," said Annika Kiessler, a spokeswoman at TSO 50Hertz Transmission.
Put to the test
Last June 50Hertz began a pilot project to test the latest generation of ACCR cables, using a 200-metre route at Gustrow in eastern Germany that is not critical to system security but is embedded in the transmission network to create real test conditions. The pilot will investigate issues such as the best fittings to attach the cable to the masts in view of the high temperature the cables can reach.
"The manufacturers are happy to promote the cables but don't necessarily supply the corresponding fittings," noted Kiessler. Another aspect under investigation is how and to what extent other parts of the transmission network can take up the additional electricity when the transport capacity of one particular stretch of the network is substantially increased.
"Network expansion is the Achilles heel in the switch to renewable energy in Germany," noted Germany's wind energy association, Bundesverband Windenergie (BWE). Modernising cable routes using high-temperature cables can provide an economic alternative, said Hermann Albers, BWE president, which goes to show that new technologies must be taken more into account when planning network expansion.
A network study published by the German energy agency, Dena, in November 2010 had estimated that 3,600 kilometres of new cable connections would be required in Germany by 2020 to accommodate growing amounts of renewable electricity. "The ACCR cables study shows that the Dena study is not the ultimate wisdom," said Albers.