The wild Baltic Sea has produced its share of historic storms, and in the fall of 2023 it unleashed another titanic surge that pounded Germany’s north coast, causing 200 million euros’ worth of damage. But heavy weather is not enough to deter Germany in its quest to secure low-carbon energy; indeed, the same forces that drove that storm of the century in 2023 can be harnessed to produce electricity. The country is now boldly striking out into the Baltic, in the vicinity of Rügen, its largest island, where it has just begun to erect a series of large offshore wind farms. The mission is unfolding in light of the April 2024 Vilnius Declaration, in which the energy ministers of eight Baltic countries from Finland to Poland agreed to collaborate on aggressively developing the Baltic’s wind resources.
A key feature of that ongoing project is the transmission infrastructure that will deliver wind power safely to shore. GE Vernova, in a consortium with DryDocks World, will build a groundbreaking 2-gigawatt (GW) high-voltage direct current (HVDC) system on behalf of 50Hertz, a major German transmission operator — a project named Ostwind 4. When completed in 2031, Ostwind 4 will transfer renewable wind power to German industries and households through an HVDC link that is designed to be very reliable and stable. It’s all part of Germany’s big plan to ensure that 100% of the country’s electricity comes from renewables by 2045. “It’s always exciting to transmit renewable power from the sea to land,” says Thomas Bjork, chief technology officer for Grid Systems Integration (GSI) at GE Vernova. “We all want to leave a better world to our kids, right?”
The HVDC Tech Revolution
High-throughput transmission cables are becoming the must-have power sector accessory to get fresh renewable electricity to population centers, which are often far from where the sun is shining or the wind is blowing. HVDC is especially good at bridging long distances. In late 2023, the United Kingdom chose HVDC technology to transmit renewable power through its first high-capacity subsea link, which will run 196 kilometers (117 miles) between the east coasts of Scotland and England. This follows another megaproject, also in the North Sea, that saw a multi-country consortium choose HVDC to run 100 kilometers (60 miles) back to the shores of both Germany and the Netherlands. The technology not only boosts the volume of power that can be shipped but, crucially, cuts line losses in half, earning its moniker as a “power highway.” With the popularity of HVDC taking off, GE Vernova made the decision late last year to greatly expand its HVDC Competence Center in Berlin. The center will create 500 new jobs for highly skilled engineers, who will work to improve HVDC transmission technology further. This came on the heels of the announced expansion of the Grid Solutions business’s Stafford, U.K., site, which will add hundreds more jobs and further support renewables growth and overall electrification.
Bjork’s enthusiasm is very much grounded in the technical progress that keeps improving HVDC transmission, enabling greater volumes of power to be reliably transferred. Simply put, an HVDC cable in conjunction with a well-crafted converter system can take the AC power from a fleet of offshore wind turbines, transform it nearby in a large offshore substation into DC power, and then send this DC power down the cable with a voltage boost; once it arrives at a landed substation, it’s converted back to AC for public and industrial consumption. As HVDC technology continues to advance, however, it’s the converter systems created by GE Vernova that truly maximize their utility. Voltage-Sourced Converter technology, or VSC, allows for digital control and analytics that help keep systems running smoothly. While that is all amazing on its own, two new developments also make the Ostwind 4 project worth watching.
Offshore platforms, which house this VSC technology, have limited space. So switchgear, whose role is to identify electrical faults and switch off the power in the related area, has to be as compact as possible; for this reason, it is gas-insulated. The challenge, however, is not so much in the gear but in the gas itself. For more than half a century, a gas called SF6 has been necessary for the gear to function, and that’s a problem: It’s one of the most potent greenhouse gases, with a global warming potential 24,300 times higher than CO2. Therefore, GE Vernova has developed new equipment with its own alternative gas called g3 (pronounced “g cubed”). Applying g3 technology to the Ostwind 4 project will reduce the gas contribution to the global warming potential of high-voltage equipment by about 99% as compared with SF6.
The biggest change rolling out at Ostwind 4, however, is that the system will use not one but two HVDC cables, plus a third medium-voltage cable for the return current, thus moving the architecture from a “symmetrical monopole” to a “bipole” configuration. On a simple level, Bjork says “this means that if someone drops an anchor on one cable, you’ve still got one more that can transmit half the energy.” But the features of the bipole approach have broader implications. The bipole system can transmit more power than a monopole can. Better still, reliability of power flows — already a concern in grid stability, given the rise of fluctuating renewable power — is greatly enhanced by the redundancy of a two-cable design. Indeed, more than 50% of German electricity is now driven by renewables, the bulk of it from wind and solar. As Bjork points out, “there’s a bit of a contradiction here, when you begin to transmit a lot more power.” On one hand, developers want to increase the power levels in their HVDC links, but utilities are then faced with the challenge of keeping the grid stable if a fault occurs and they experience a loss of power from this more powerful link. Dealing with losing 1 GW is a lot easier than dealing with the loss of 2 GW.
HVDC and the Dream of Power Diplomacy
What if the HVDC revolution creates so many power highways that they can eventually start to connect to one another? Well, guess what. That’s the next idea coming. HVDC technology today can connect disparate AC networks of different frequencies, but going forward, programs such as InterOPERA are aiming to create standards that allow HVDC links to be integrated together, ultimately forming what some call an HVDC “supergrid.” Bjork says the infrastructure being built today in the North Sea and Baltic region could one day be leveraged into an even more exciting, efficient network if the technology advances. In such an array, nations could connect to one another’s offshore generation and transmission, sending surplus power to wherever it’s needed.
Bjork says standardization of HVDC is also front of mind for developers, utilities, and OEMs. Standardization is a requirement if we are to meet the market demand for this technology. He explains that there’s a convergence happening right now among offshore wind developers to embrace this very same 2-GW bipole system for future projects, and Bjork says that’s terrific, because it will help reduce rising costs, provide benefits of repetitive construction, and help capture lessons learned to lower the overall risk on future projects.
But the big prize Bjork is thinking about is speed of construction, to enable a faster scale-up of renewables. “There are so many projects up and about,” he says. “There are bottlenecks with cable production. There are bottlenecks in producing platforms. When we come to a point that we can actually do this in a standardized way, we could, for sure, shorten the delivery times. And that’s where we’re all heading.” If Bjork is right, soon every region on earth that’s building renewables will want to connect them with HVDC to reap these same benefits.
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