On a stretch of shifting seabed facing the industrial city of Lianyungang, China has linked a giant offshore solar project to the grid using a 19.45‑kilometre high‑voltage line, turning a difficult patch of coast into a power hub.
A record-breaking energy ‘motorway’ off the Jiangsu coast
The Tianwan coastal photovoltaic project, led by state-owned China National Nuclear Corporation (CNNC), sits on tidal flats where land and sea trade places every few hours.
In that harsh setting, China has built what it describes as an “energy motorway”: a 220 kV transmission line stretching 19.45 kilometres, supported by 64 newly erected steel pylons.
Laid across unstable tidal mudflats, Tianwan’s 19.45 km, 220 kV line now holds the world record for an offshore solar evacuation route.
The line started construction in February 2025 and is designed to carry the full output of the Tianwan offshore solar park, preventing the plant from becoming an isolated “power island” with nowhere to send its electricity.
Gao Bo, head of the project management centre at State Grid’s Lianyungang power supply arm, has compared the new line to an expressway: without it, traffic would snarl on local back roads; with it, clean electricity can flow freely to the regional grid.
China’s biggest offshore solar project so far
Tianwan is not a floating solar farm in deep water. It is built on shallow coastal flats that sit exposed at low tide and submerge at high tide.
The project carries around 2 million kilowatts of installed photovoltaic capacity and can deliver roughly 250 MW to the grid at any given moment.
According to official documents, once fully commissioned, the plant is expected to generate about 2.2 billion kilowatt-hours of electricity per year.
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The annual output of Tianwan should replace about 680,000 tonnes of standard coal and prevent around 1.77 million tonnes of CO₂ emissions every year.
That climate benefit roughly matches the yearly exhaust from several hundred thousand typical passenger cars, depending on mileage and fuel efficiency.
Turning useless mudflats into power assets
China’s planners see a specific advantage in these coastal zones.
Tidal flats are often unsuitable for housing or crops. The ground is soggy, salty and constantly stressed by waves and tides.
Yet they sit close to large industrial belts along the eastern seaboard, where electricity demand remains intense and often peaks during daylight hours when solar panels perform best.
The Tianwan scheme follows a simple logic: cover large, mostly unused coastal surfaces with solar modules, then ship the output straight into nearby industrial load centres via short, high-capacity lines instead of building long corridors across populated land.
Engineering on a moving, waterlogged foundation
The geology at Tianwan brings unusual complications.
Tidal mudflats have low bearing capacity. The sediment is loose, saturated with water and constantly worked by tidal forces, waves and wind.
Traditional concrete foundations for pylons would have required extensive excavation, long curing times and heavy machinery, all in a zone that floods twice a day.
Helical piles screwed into the seabed
To manage those constraints, Chinese engineers deployed helical piles at an unprecedented scale for this type of infrastructure.
These piles resemble enormous metal screws that anchor pylons deep into the subsurface when turned into the ground, rather than simply hammered in or set within bulky concrete bases.
By “screwing” pylons into the tidal flats instead of pouring huge concrete pads, builders increased stability, cut installation time and limited ecological disturbance.
This technique brought several operational benefits:
- Faster installation windows between tides
- Lower risk of foundation failure due to soil liquefaction
- Reduced need for heavy, stationary equipment on soft terrain
- Smaller physical footprint per pylon in a sensitive coastal ecosystem
Route optimisation also mattered. Designers worked to minimise the total length of line and the number of pylons while maintaining safety clearances, which again reduced disturbance to tidal habitats and cut material use.
Numbers that reshape regional energy flows
Once the project runs at full capacity, Tianwan’s 2.2 billion kWh per year will cover a significant share of local demand.
In a typical industrial city, that much output can supply hundreds of thousands of households, or offset a substantial slice of consumption in nearby factories.
For China’s energy system, projects like Tianwan serve as coastal relays: they absorb sunlight in areas where land competition is low and feed power directly into dense, coastal grids with minimal transmission loss.
This approach reduces pressure on inland farmland and urban land, where rooftop solar and ground-mounted plants increasingly compete with other uses.
Where Tianwan sits inside China’s solar strategy
China has already built vast deserts full of solar arrays in its western regions, but those are often far from major cities.
Coastal and offshore solar schemes in provinces such as Jiangsu and Shandong add another layer: they shorten the distance between generation and consumption, reducing congestion on east‑west power corridors.
Tianwan signals a shift from just manufacturing solar hardware to assembling complete, integrated renewable systems in complex real-world locations.
The project also complements offshore wind, which already lines parts of China’s coast. Solar and wind output tend to peak at different times and under different weather conditions, making joint use of shared transmission hubs more efficient.
China’s dominant grip on the solar supply chain
Tianwan also illustrates a deeper reality: China’s near-total control of global photovoltaic manufacturing capacity.
From the raw polysilicon feedstock to finished panels, Chinese firms occupy the leading slot at almost every step.
| Stage | Chinese share (2025‑2026) | Key points |
| Polysilicon | ~95% | Dominant in refining and chemical processing |
| Wafers | >90‑95% | Highly standardised, mass-scale production |
| Cells | >90% | Huge, automated factory lines |
| Modules | 80‑85% | Panels shipped worldwide, including to Europe and the US |
| Total PV manufacturing capacity | >80% | Hundreds of gigawatts added annually inside China |
That manufacturing muscle lets projects like Tianwan access equipment quickly and at relatively low cost, from panels to inverters and cables.
It also means that when Beijing chooses to push a new segment – such as tidal‑flat solar – it can mobilise entire industrial chains in a short timeframe, from specialised foundations to customised high‑voltage gear.
Why a 220 kV line matters for reliability
For many readers, “220 kV” is just a number. In power engineering, it marks a threshold where lines stop serving local distribution and start operating as part of the high‑voltage backbone.
Running Tianwan through a 220 kV corridor gives grid operators options: they can re-route flows, integrate the plant into regional balancing schemes and cut losses over distance compared with lower-voltage alternatives.
This configuration also makes it easier to pair Tianwan later with storage assets, such as large battery parks or even green hydrogen facilities, without redesigning the main link to the grid.
Potential scenarios around Tianwan
Several medium-term developments are already being discussed by analysts and local planners:
- Adding battery storage to smooth output during passing clouds and tidal shadowing effects from structures
- Combining solar from Tianwan with nearby offshore wind farms to share high-voltage infrastructure
- Supplying dedicated industrial users, such as chemical plants or data centres, through green power purchase agreements
- Using the site as a testbed for new panel designs better adapted to salty, humid conditions
If even part of these scenarios materialise, the 19.45‑kilometre line becomes more than a record; it turns into a platform for a cluster of coastal clean‑energy activities.
Risks, challenges and lessons for other countries
Building on tidal flats carries clear environmental and technical risks.
Ecologists worry about impacts on bird feeding grounds, fish nurseries and sediment flows. Regulators and engineers must weigh those concerns against the benefits of displacing coal‑fired generation.
Heavily corrosive marine air can attack metal structures and electrical equipment, raising maintenance costs and demanding careful material selection and coatings.
For other countries considering similar projects – from Southeast Asia’s deltas to tidal coasts in Europe – Tianwan offers a real‑scale case study:
- Helical pile foundations can work on soft, intertidal ground at scale.
- Short, high-voltage connections limit transmission losses and ease integration.
- Dense local industry helps absorb variable solar output without overbuilding storage.
The geopolitical dimension also deserves attention. Heavy reliance on Chinese components can lower costs yet raises resilience and dependency questions for Western buyers that might want to replicate Tianwan‑style projects at home.
As more of these coastal solar schemes appear, debates over supply chain security, marine protection and access to grid capacity are likely to intensify far beyond China’s shores.
