Offshore wind power hits DC transmission milestone

Asia's first offshore wind power project to utilize flexible direct current transmission technology has reached a historic milestone, transmitting more than 10 billion kilowatt-hours of clean electricity to the grid in August, its operator China Three Gorges Corp said.

The milestone demonstrates that the CTG Jiangsu Rudong 800-megawatt offshore wind power project has successfully provided practical validation for the large-scale application of high-capacity, long-distance flexible DC transmission technology in China's offshore wind sector.

Located in the Huangshayang sea area off Rudong county, Nantong, Jiangsu province, the facility is the world's largest-capacity and highest-voltage (400 kilovolt) offshore wind flexible DC transmission project of its kind.

As offshore wind development pushes into deeper and more distant waters, traditional alternating current transmission is increasingly constrained by distance and capacity limitations. Consequently, flexible DC transmission has emerged as a superior technological alternative for the industry.

However, as the world's first 400 kV offshore wind flexible DC transmission project, the Rudong facility initially lacked mature operational precedents.

Industry experts noted that the milestone comes at a critical juncture as China's offshore wind sector rapidly shifts its development focus from near-shore waters to deep-sea and far-offshore regions, where wind resources are significantly more abundant and stable.

As wind farms move further out to sea, traditional AC cables suffer from severe power losses over long distances, making flexible DC transmission an indispensable technological lifeline for the industry's next phase of expansion, said Lin Boqiang, head of the China Institute for Studies in Energy Policy at Xiamen University.

Lin said the project has accelerated the maturation of the domestic supply chain for high-end marine engineering equipment.

The commercial application of critical, home-grown components — such as ultra-high-voltage flexible DC converter valves and specialized submarine cables — effectively breaks technical bottlenecks that previously hindered deep-sea wind power commercialization, he said.

Since achieving full-capacity grid connection in 2021, the project has operated safely and stably for over 1,600 days, maintaining an impressive equipment availability rate of 99.5 percent, said CTG.

The 10 billion kWh of clean energy generated so far is sufficient to meet the annual electricity demand of approximately 4 million households. This output is equivalent to saving 3 million metric tons of standard coal and reducing carbon dioxide emissions by 7.4 million tons, significantly contributing to the nation's green transition, it said.

Operating in a harsh marine environment characterized by high humidity, high salinity and frequent typhoons, the engineering team had to overcome a series of unprecedented challenges, including managing novel equipment, integrating complex systems and handling difficult emergency responses.

The team successfully achieved technical breakthroughs in ensuring the stable operation of the 400 kV flexible DC system, conducting long-distance submarine cable monitoring and maintenance, and regulating high-load working conditions. These efforts have ensured the safe, stable and highly efficient operation of the far-offshore wind farm.

"Compared with traditional AC transmission methods, the project has reduced transmission line losses by approximately 1.2 percentage points, resulting in cumulative transmission cost savings of more than 735 million yuan ($109 million)," said Wang Xuefeng, deputy general manager of the Nantong company under CTG's Jiangsu branch.

Looking ahead, as the technology matures and localized manufacturing costs continue to decline, flexible DC transmission will become the standard configuration for China's upcoming gigawatt-scale deep-sea wind power clusters.

This will ultimately ensure the stable, low-loss and efficient integration of massive amounts of marine renewable energy into the national grid.

zhengxin@chinadaily.com.cn