DG grids: Why transmission innovation is turning to direct current

According to the International Energy Agency (IEA), renewables are expected to increase their share of global electricity generation from around 30 percent in 2023 to 46 percent by 2030, supplying nearly half of the world’s electricity. Keeping power grids reliable, affordable, and secure while managing that transformation is driving new forms of collaboration and innovation—including a new generation of direct current (DC) technologies.

In the late 19th century, Thomas Edison and George Westinghouse championed rival approaches to transmitting electricity in what became known as the "War of the Currents." AC ultimately became the dominant standard because it could be transmitted easily over long distances. Today, however, advances in power electronics are driving renewed interest in HVDC for applications where it can transport large amounts of electricity with lower losses.

One of the main purposes of HVDC systems is to transmit electricity over long distances. This allows renewable energy generation facilities, such as offshore wind farms, to supply load centers with clean power. In the case of Germany, it would enable the efficient distribution of large amounts of power from wind turbines on the North Sea to load centers such as Frankfurt, Stuttgart, and Munich. HVDC transmission systems can also be used to connect asynchronous AC grids, improving stability and reliability, and is the preferred system for underwater cables due to lower losses and higher efficiency.

While today’s power systems already combine AC and DC technologies, the role of HVDC transmission systems is expected to expand in applications where it delivers the greatest value. Unlike conventional AC grids, HVDC systems allow operators to actively control power flows, directing electricity where it is needed most. This provides distinct advantages for intercontinental power links, renewable energy integration, long-distance power transmission, and potentially for connecting large electricity consumers such as data centers. 

In HVDC systems, high-performance converter stations transform AC into DC for high-voltage transmission over distances of up to thousands of kilometers. Viking Link, for example, is the longest HVDC submarine interconnector in operation, spanning 765 kilometers between the UK and Denmark. At the receiving end, another converter station transforms the DC back into AC before it is distributed on the grid to the end consumer.

The projects also highlight the potential of combining Siemens Energy's DC circuit breaker technology with Mitsubishi Electric's expertise in power electronics. Together, the companies aim to deliver the first DC switching station of its kind in the European market. For Mitsubishi Electric, the collaboration also marks a significant expansion of its HVDC activities in Europe.

According to Foehr, today's grid technologies are simply too complex for any one company to develop alone. Public funding programs, research institutions and partnerships with other companies all have a role to play in driving innovation across the value chain.

"The partnership is also innovative in that it could help open up an industry that has been characterized by vendor specific, locked-in solutions from large players", says Foehr. A multi-vendor approach could also accelerate the development of common standards for future DC grids, where no equivalent of today's AC grid code yet exists. "We're just at the beginning of the journey," says Foehr. "The technology is there, it's starting to be built, and we're developing the standards together with other manufacturers and customers."

“This combined approach between Siemens Energy and Mitsubishi Electric marks a departure from conventional industry practice, where companies typically develop enclosed systems for the market,” says Foehr. “As power grids evolve, our work exemplifies how collaboration and complementary technological solutions are more than just the sum of their parts—and it’s partnerships like this that will get us to a more sustainable world.”

About the author: Tim Hornyak is a Canadian writer based in Tokyo, Japan, who has worked in journalism for more than 20 years. He has written extensively about technology, science, energy, culture, and business in Japan, as well as Japanese inventors, roboticists and Nobel Prize-winning scientists.

Combined video and picture credits: Christopher Jue