Breakthrough enables long-distance delivery of renewable energy
Smart grids are fundamental to allow increasing amount of renewable energy in the network. A much more flexible grid is also required in order to generate and transport solar energy from the Sahara to Sweden and connect more distributed generators. Researchers at KTH have contributed to the development of an eagerly awaited high voltage direct current (HVDC) circuit-breaker, which is essential to transmit renewable energy over long distances.
“In a smart electricity grid, it must be easy to redirect energy, depending on supply and demand, variation and local production. It must also be possible to close off parts of the grid for maintenance, without interrupting supply to consumers,” says Göran Engdahl, professor and researcher at the Swedish Centre for Smart Grids and Energy Storage (SweGRIDS) at KTH.
Sources of renewable energy, such as wind and solar power, vary to a much higher degree than traditional sources. The wind doesn't always blow, the sun can be obscured by clouds. At the same time, an increasing number of people are generating energy at home, or attempting to become self-sufficient. Thus, consumers also become producers, so called prosumers, creating an even greater need for flexibility in the grid. A smart grid must therefore be able to quickly accept, generate, transmit and switch between energy from different sources, both locally and from further afield.
Alternating current has traditionally been used for the transmission and distribution of electricity. Alternating current is easy to transform and there are only modest losses during transmission over short and medium distances. Moreover, it is easy to break the circuit, thanks to the fact that the current is zero 100 times per second. The losses in transmission over longer distances are great however.
“This is a waste of energy that has an impact on the environment and thus constitutes a financial cost to society,” says Göran Engdahl.
One solution is to use high voltage DC; a field in which KTH's collaborative partner ABB is a world leader. However, one problem with HVDC is that DC lacks passages through zero and is thus significantly harder to break. As a result, ABB has been working for a long time on ways to breaking HVDC, which is essential for large scale transmission of energy over long distances such as transporting solar energy from the Sahara to northern Europe.
This is where research at KTH comes into the picture. Göran Engdahl and his research colleagues at the Department of Electromagnetic Engineering have found a key to the problem. The answer is a high speed switching device, a critical component in an HVDC circuit-breaker.
“In order to break a direct current, the contacts must be separated extremely fast, which happens in the new switching device. The problem of transporting energy over long distances and in large quantities with the help of HVDC is thereby in principal solved.”
“Breaking the circuit is a hard nut to crack and it is exciting to be able to contribute to solving this problem.”
KTH's contribution to the development of the HVDC circuit-breaker is a spin-off from an EIT InnoEnergy project, in which the researchers are developing switching devices to enable the flexible, intelligent commutation of load currents in grids with locally-generated renewable energy. The project is partly funded by SweGRIDS, the Swedish Centre for Smart Grids and Energy Storage at KTH.
For further information, please contact Göran Engdahl, firstname.lastname@example.org , +46-8-790 7760.
Text and photo Marie Androv