Inside Heart of the Sea Wind: China's Largest Offshore Converter Station
What Just Left Port
In late May 2026, a semi submersible vessel eased out of Nantong in Jiangsu province carrying a 25000 tonne structure known officially as Hai Feng Zhi Xin, translated into English as Heart of the Sea Wind.
According to a detailed account from Xinhua, the platform measures 85.5 metres in length, 82.5 metres in width and 44 metres in height, covering a deck area roughly equal to a standard football pitch and standing about as tall as a fifteen story building. It was built by Shanghai Zhenhua Heavy Industries, widely known by its acronym ZPMC, and it travelled more than a thousand nautical miles to a wind farm site off Yangjiang City on China's southern coast, where it was installed using a precision float over method that engineers say required accuracy measured in millimetres, as reported by CGTN.
ZPMC describes the platform, in a statement carried by Power Technology, as the world's largest offshore converter station, built to support the Three Gorges Yangjiang Qingzhou V and Qingzhou VII wind farms, which together carry a combined installed capacity of two gigawatts.
A closely related project reported by ECNS, the Sanshandao offshore wind transmission scheme run by China Southern Power Grid, uses an identical class of converter technology at the same voltage and capacity to move power from the Yangjiang waters toward the Guangdong Hong Kong Macao Greater Bay Area, underlining just how central this single piece of equipment has become to the region's energy strategy.
The Problem a Converter Station Actually Solves
To understand why a single offshore structure earns this much attention, it helps to understand a limitation that has quietly capped offshore wind ambitions for years.
Every turbine blade spinning at sea generates electricity in alternating current, the same form of power that flows through household wiring. Sending that power to shore through undersea cables works fine over short distances, but alternating current loses a meaningful share of its energy the farther it travels through a cable, a problem that grows quickly once wind farms move beyond roughly one hundred kilometres from the coast.
The fix is to convert that alternating current into direct current before it makes the long underwater journey. Direct current suffers far smaller losses over long distances, which is why continental power grids increasingly rely on it for cross country transmission.
An offshore converter station is essentially the machine that performs this conversion at the source, out in open water, before electricity begins its trip back to land. As ZPMC put it in a statement distributed through EQS webdisclosure, converting offshore alternating current into direct current reduces transmission losses over long subsea cables and unlocks access to wind resources sitting more than one hundred kilometres from shore, allowing development to push into deeper and more remote waters that were previously uneconomical to connect.
The Technology Behind the Steel
What makes Heart of the Sea Wind unusual is not just its size but the specific type of direct current technology packed inside it. The platform uses what engineers call flexible direct current, more formally voltage source converter based high voltage direct current, or VSC HVDC.
Unlike older line commutated converter systems that require a strong existing grid connection to function properly, voltage source converters can operate more independently, respond faster to fluctuations in wind output, and connect more easily into weaker or more remote sections of a power grid.
An engineer with Guangdong Power Grid Co, quoted in the ECNS report on the related Sanshandao project, described the approach as an integrated offshore to onshore direct current transmission model built specifically to meet the demands of large scale offshore wind development, addressing the technical difficulty of moving that much power over such long distances at scale.
According to the ZPMC statement, the project set six distinct industry records at once. Alongside its status as the largest single unit converter station by transmission capacity, it also runs the highest voltage flexible direct current system yet deployed for offshore wind, marks the first project to combine alternating current and direct current transmission within a single integrated system, represents the first centralized flexible direct current transmission project of its kind, and is the first application of plus or minus 525 kilovolt direct current subsea cables for long distance offshore renewable transmission.
Inside the platform, the station collects electricity generated by 163 individual wind turbines, steps up the voltage and performs the alternating current to direct current conversion before the power begins its subsea journey, a process described in the Xinhua report on the project's engineering design.
Numbers That Explain the Scale
| Specification | Figure |
|---|---|
| Weight | Approximately 25000 tonnes |
| Dimensions | 85.5 metres long, 82.5 metres wide, 44 metres tall |
| Transmission capacity | 2000 megawatts, single unit |
| Voltage | Plus or minus 500 kilovolts, with 525 kilovolt subsea cables |
| Annual output supported | Approximately 6 billion kilowatt hours |
| Distance from shore | Over 70 kilometres, in waters with no nearby onshore support facilities |
| Turbines connected | 163 wind turbines across the Qingzhou V and VII farms |
Once fully commissioned, the station is expected to deliver approximately six billion kilowatt hours of clean electricity every year, according to figures reported by Interesting Engineering. That volume is roughly comparable to the annual electricity consumption of well over a million typical households, flowing directly into Guangdong, one of China's most energy intensive provinces and a manufacturing and export hub whose demand for reliable, lower carbon power has grown steadily alongside its industrial base.
Why Guangdong and Why Now
The location is not incidental. Guangdong sits at the centre of China's push to decarbonize its southern coastal industrial belt without slowing the region's economic output, and offshore wind has become one of the few renewable sources capable of delivering power at the scale that province requires.
China's own 15th Five Year Plan, covering 2026 through 2030, sets a national target of 100 gigawatts of installed offshore wind capacity, a goal reported by Xinhua that reflects how quickly near shore locations suitable for wind development have become saturated, pushing the industry into deeper and more distant waters where converter stations of this kind become not just useful but essential.
The project also fits into a broader pattern of milestones China's offshore wind sector has reached within a matter of months. In February 2026, the world's first 20 megawatt offshore wind turbine, built entirely from domestically manufactured components, was connected to the grid in Fujian province.
Shortly afterward, the world's largest floating offshore wind platform by single unit capacity finished installation in the same waters off Yangjiang, using independently developed polyester fibre mooring lines rated to withstand roughly 1300 tonnes of tensile force. Taken together with Heart of the Sea Wind, these projects mark what Xinhua's coverage frames as a deliberate national effort toward self reliance in offshore wind engineering, reducing dependence on foreign turbine and transmission technology that dominated the sector for much of its first two decades.
What Comes Next
Installation of the converter station was completed in early June 2026 using the float over method engineers had spent months preparing for, and it now stands ready to begin channelling power from the Qingzhou wind farms toward the mainland grid.
The related Sanshandao transmission scheme, which shares the same voltage class and capacity rating, is expected to extend that power further still, routing electricity through a subsea cable running about 115 kilometres and an onshore line stretching approximately 180 kilometres to reach the load centres of the Greater Bay Area, according to the ECNS report on the project.
The bigger story sitting behind the steel and cabling is one of infrastructure catching up with ambition. Wind resources far out at sea are generally stronger and steadier than those closer to shore, but for years the technology needed to bring that power back to land at an acceptable cost simply did not exist at scale.
Heart of the Sea Wind does not solve every constraint facing deep sea wind development, but it demonstrates that the core transmission bottleneck, the one separating strong offshore wind from a usable electricity supply, is now a solvable engineering problem rather than a theoretical one, and that has implications well beyond the coast of Guangdong for any country eyeing its own deep water wind resources.
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