Their goal is blunt: turn a muddy tidal flat into a stable power hub, move vast amounts of solar electricity inland, and do it with record-breaking infrastructure that pushes offshore renewables into new territory.
A record-breaking “energy highway” for offshore solar
The Tianwan coastal project, in Jiangsu province on China’s east coast, has become a flagship for next‑generation solar power. Developed by state-owned giant China National Nuclear Corporation (CNNC), it combines an enormous offshore-style photovoltaic farm with a 220 kV transmission line stretching 19.45 km.
The 19.45-kilometre, 220 kV line is the longest of its kind ever built specifically to evacuate power from an offshore solar project.
The line sits on 64 new steel pylons and links the tidal-flat solar arrays to the onshore grid at full capacity. State Grid’s Lianyungang Power Supply Company, which built the link, describes it as an “energy highway” for a simple reason: without it, gigawatts of clean electricity would be stuck in the mud.
Construction of the transmission line began in February 2025, just months after work on the solar site itself kicked off in May 2024. Chinese authorities pushed the schedule hard, and the pace of deployment shows how fast the country can now turn energy mega‑projects from blueprint to live asset.
Tianwan: a solar farm where the sea meets the land
Tianwan’s location is not a classic offshore wind farm out at sea, nor a regular solar park on solid ground. The project sits on tidal flats – broad coastal zones that flood and drain twice a day. The land is soft, waterlogged and constantly reshaped by tides.
These muddy shallows are poor candidates for housing, farming or industry. For Beijing, that makes them ideal real estate for renewables. They are sun‑drenched, relatively close to industrial clusters on land and, until now, largely unused for productive activity.
The Tianwan photovoltaic project carries an installed capacity of 2 million kilowatts, roughly 2 GW in Chinese planning language. In operation, it should deliver around 2.2 billion kilowatt-hours of electricity each year, equivalent to the annual consumption of hundreds of thousands of Chinese households, depending on usage patterns.
Annual output from Tianwan is expected to avoid burning about 680,000 tonnes of standard coal and prevent roughly 1.77 million tonnes of CO₂ emissions per year.
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For a country that still relies heavily on coal, those savings matter. They also help local authorities meet increasingly strict energy and emissions targets imposed from Beijing.
Building high voltage infrastructure on moving ground
Foundation engineering under tidal pressure
The biggest technical headache did not come from the high voltage equipment itself, but from the unstable ground underneath it. Tidal flats offer little bearing capacity. Soil is spongy, water‑saturated and constantly stressed by waves, currents and changing water levels.
Traditional concrete foundations would have required heavy cofferdams, long curing times and extensive earthworks. On a shifting, wet platform, that approach would be slow, risky and more damaging to coastal ecosystems.
Engineers instead used fully sealed helical piles – essentially giant steel screws twisted deep into the subsoil. Each pile works like a corkscrew anchoring the pylon to denser layers below the soft surface.
- Helical piles cut construction time versus poured concrete bases.
- They improve stability under cyclic tidal loading.
- They reduce the volume of excavated material and on-site concrete.
- They limit disturbance in ecologically sensitive tidal zones.
By optimising the line route and using these screw‑in foundations, the team cut the project’s physical footprint and reduced the risk that storms or long‑term erosion could threaten the masts.
A tightrope act between sea, land and grid
Every component of the line had to cope with harsh coastal conditions: corrosion from salt spray, dynamic wind loads and access challenges during bad weather. Construction windows were often limited to specific tidal states, forcing crews to work in short, tightly planned bursts.
Grid planners also had to integrate the new solar output into an already dense industrial region. A 220 kV rating reflects that need. It sits above distribution-level voltages, allowing bulk power transfer from the coast into higher-voltage backbone lines without major congestion.
Without a robust high voltage link, even a multi‑gigawatt solar project risks curtailment – power left unused because the grid cannot take it.
Tianwan’s line tackles that bottleneck directly. It gives operators a stable evacuation path, reducing the chance that strong midday solar output will be wasted, especially during periods of low demand.
How Tianwan fits China’s coastal energy strategy
Tianwan is not a one‑off showpiece. It sits inside a broader Chinese push to turn coastlines into giant clean‑energy platforms that combine wind, solar and, in some cases, storage and hydrogen production.
Offshore solar complements offshore wind, which already dominates many Chinese coastal regions. Solar output tends to peak in clear daytime conditions, while wind often rises in the evening or during different weather systems. Mixing the two can smooth overall generation profiles, which eases pressure on the grid.
By building large projects close to ports, refineries and industrial parks, planners try to shorten the distance between generation and consumption. That limits transmission losses and can defer the need for new long‑distance lines from remote inland plants.
An industrial chain that runs from sand to substation
Tianwan also showcases China’s grip on the global solar supply chain. From purified polysilicon to wafers, cells and finished modules, Chinese companies dominate production capacity. International Energy Agency data suggests the country accounts for over 80% of global module manufacturing, with shares above 90% in some intermediate steps like wafers.
| Stage | Approximate Chinese share | Key point |
| Polysilicon | ~95% | Control of refining capacity |
| Wafers | >90–95% | Highly standardised, ultra‑large factories |
| Solar cells | >90% | Mass production lowers global costs |
| Modules | 80–85% | Dominant share of exported panels |
What Tianwan adds is proof that this manufacturing muscle now pairs with engineering know‑how in grid integration. China is not just exporting panels; it is building complex systems at home that stitch those panels into a high-capacity network, even in environments many countries still consider too tricky to develop.
What a 220 kV coastal line really does
For non‑specialists, voltage ratings can sound abstract. In simple terms, higher voltage allows more power to move along a line with lower losses. Think of it as turning up the “pressure” so the same wire can carry more electricity over long distances.
At 220 kV, Tianwan’s line functions as a regional backbone. It can move hundreds of megawatts from the coast into Jiangsu’s grid without forcing operators to constantly reroute power. That stability matters when solar output swings with passing clouds or seasonal sun angles.
Transmission losses over 19.45 km at this voltage remain relatively low, which helps the project meet its promised coal and CO₂ savings. Lower losses also mean fewer extra plants are needed elsewhere to make up for wasted energy.
Risks, trade-offs and what comes next
Projects like Tianwan still face real challenges. Tidal flats are delicate ecosystems. Construction and operation can affect bird habitats, marine life and sediment flows. Chinese developers now talk more about “ecological red lines”, but enforcement varies by region.
There is also the question of resilience. As sea levels rise and storms intensify, coastal infrastructure must bear greater stress. Helical foundations and corrosion-resistant materials help, yet long-term testing will show whether this generation of projects can last for decades without major rebuilds.
On the positive side, the Tianwan model could be adapted elsewhere. Countries with large tidal zones – from the UK’s estuaries to parts of Southeast Asia – could pair offshore wind with “tidal flat solar” and medium-length transmission links. The combination would free up land inland for housing and farming while keeping heavy industry supplied with increasingly low‑carbon power.
For investors and policymakers, Tianwan sends a clear signal: the bottleneck in renewables is shifting. The big questions no longer stop at “how many panels can we buy?” but extend to “where do we put them, and how do we move the power reliably to where it is needed?” China’s latest record-setting line on a muddy edge of Jiangsu is one very visible answer.