High-voltage direct current (HVDC) technology is quietly revolutionizing how electricity moves across continents, making it possible to transmit renewable energy from remote deserts and offshore wind farms to distant cities with far less waste than traditional AC power lines. After losing a century-long battle to alternating current (AC), DC is staging a comeback, powered by advances in power electronics that have made it cheaper, more efficient, and essential for a grid increasingly dominated by wind and solar energy.

Why Did Direct Current Lose to AC in the First Place?

The story of power transmission is one of technological triumph and historical accident. In the late 1880s, Thomas Edison championed direct current while Nikola Tesla and George Westinghouse backed alternating current. Edison even publicly electrocuted animals to convince the public that AC was dangerous. But the real problem wasn't safety; it was the transformer. This simple device, made of coils wound around an iron core, can easily step AC voltage up or down, which is essential for transmitting power efficiently over long distances. DC had no equivalent at the time, so AC won what became known as the War of the Currents.

That dominance lasted for over a century. But starting in the late 1920s, Swedish engineer Uno Lamm, later known as the father of HVDC, began improving a device called the mercury arc valve, which could convert high-voltage AC into DC and back. The first commercial HVDC link opened in 1954 between mainland Sweden and the island of Gotland. The United States followed in 1970 with the Pacific DC Intertie, an 846-mile overhead line moving hydropower from the Pacific Northwest south to Los Angeles. Each technological advance, from mercury arc valves to thyristor valves to modern voltage source converters built on high-power transistors, made converter stations smaller, more efficient, and more controllable.

What Makes HVDC Critical for Today's Energy Transition?

Three key properties of modern HVDC make it indispensable for a grid increasingly powered by wind and solar energy. First, transmission loss is dramatically lower. Modern HVDC lines lose roughly 3 percent of electricity per 1,000 kilometers compared to roughly 7 percent for comparable AC lines over the same distance, cutting losses in half. Second, HVDC can span much longer distances efficiently, which matters because the best wind resources are often in remote plains or far offshore, while the best solar resources are typically found in deserts, far from the cities that need the power. Third, HVDC can stitch together grids running at different frequencies or out of phase with each other, something AC interconnection cannot do without much more expensive equipment.

How Is HVDC Being Deployed Around the World?

Three major projects demonstrate how HVDC is growing in reach and influence across continents. In the United States, Pattern Energy began testing the SunZia wind farm in April 2026, the largest in the western hemisphere, paired with a 550-mile, plus-or-minus 525 kilovolt HVDC transmission line, the largest voltage source converter HVDC installation in the country. The line carries about 3 gigawatts west to Arizona, with roughly a third used locally and the remaining 2,131 megawatts continuing to Southern California. In June 2026, Pattern Energy announced that SunZia had reached full operational capacity.

In Europe, the LionLink project, a nearly 2-gigawatt HVDC interconnector planned for the early 2030s, will carry North Sea wind power to the United Kingdom and the Netherlands while linking the U.K.'s National Grid to the Synchronous Grid of Continental Europe. LionLink is just one piece of a much larger buildout; the European Commission is targeting 64 gigawatts of cross-border HVDC by 2030. Under the Hamburg Declaration, signed in January 2026 by the U.K. and nine other European countries, signatories committed to delivering 100 gigawatts of North Sea wind through joint cross-border projects, part of a longer-standing goal of 300 gigawatts of North Sea offshore wind by 2050.

China's ambitions are even more expansive. In 2019, China's State Grid energized the Changji-Guquan line, a 1.1-million-volt direct current power line dubbed the "Power Silk Road," still the longest and most powerful HVDC line in the world. It carries 12,000 megawatts of electricity, equivalent to 12 power plants, enough to power 50 million Chinese homes. The line begins in Xinjiang, a remote desert region in northwestern China, where a converter station transforms wind and solar power into a million-volt river of direct current that flows east for roughly 3,300 kilometers through six provinces, over the Yangtze River, and into a second converter station in Anhui province, where it is converted back to AC and fed into the grid powering China's densely populated east.

What Is China's Vision for a Global Energy Network?

The Changji-Guquan line embodies one of China's grandest ambitions. In 2016, Liu Zhenya, then Chairman of China's State Grid Corporation, presented his vision for a Global Energy Interconnection: a planet-wide network of clean-energy superhighways linking over 100 countries and 80 percent of the global population with 180,000 kilometers of ultra-high-voltage power lines. Since then, the idea of a global, interconnected clean-energy network propped up by ultra-high-voltage DC lines has garnered a mix of interest, doubt, and concern, but it also represents a striking turnaround in how the world thinks about power transmission.

How to Understand HVDC's Role in Your Power Grid

• Transmission Efficiency: HVDC lines lose roughly half the electricity that AC lines lose over the same distance, making them ideal for moving power from remote renewable energy sources to distant cities.
• Distance Capability: HVDC can efficiently transmit power over thousands of kilometers, enabling countries to tap wind and solar resources in remote regions and deserts that would be impractical with AC infrastructure.
• Grid Flexibility: HVDC can connect grids running at different frequencies or out of phase with each other, allowing countries to share renewable energy across borders and integrate offshore wind farms with multiple onshore grids simultaneously.
• Infrastructure Sharing: A single HVDC network can serve multiple countries and regions, reducing the need for separate point-to-point transmission lines and creating a more flexible, interconnected energy system.

The shift from AC to HVDC represents more than just a technological upgrade; it is a fundamental rethinking of how electricity moves across the planet. As renewable energy sources become dominant, the efficiency gains and long-distance capabilities of HVDC make it the natural choice for a grid that must move power from where the sun shines and wind blows to where people actually live and work. The projects now under construction in the United States, Europe, and China suggest that this transition is not a distant possibility but an unfolding reality that will reshape global energy infrastructure for decades to come.