Jiang Du is a Structural Engineer for Empire Engineering, based in Beijing. Jiang has been analysing shifting Monopile sizes around China and Europe. Here are his observations:
Last year, I commented on the heaviest offshore wind jacket that was 2,500 tons. Today I came across a project and was surprised to find that a new record has been set:
| Item | Weight | Manufacturer |
| Offshore wind jacket | 2,700 tons | SK Oceanplant |
| Project Name | Height | WTG |
| Taiwan Fengmiao 1 | 97 m | VestasV236-15.0MW |
Source: https://www.china-mcc.com/news_show-20195.html
This record jacket is being installed in Taiwan by SK Group.
This year also saw a change in the world’s largest offshore wind monopile foundation in terms of diameter and weight, with diameter increasing from 10.5 meters 3-4 years ago to 11.5 meters, and the weight rising from 2,400+ tons to 2,700+ tons. This series of massive monopiles for Inch Cape will put the UK’s offshore wind farm back on top, snatching the title of the world’s heaviest and largest-diameter monopile from China, although the manufacturers are still Chinese companies.
Dajin and CWHI, two Chinese companies that supply monopiles to the Inch Cape offshore wind farm, recently shipped their first batch almost simultaneously. Although the weight of the first batch has not yet reached the maximum of 2,700 tons, the diameter has already reached 11.5 meters.
In addition to diameter and weight, another important parameter for a monopile is the pile length. Published data from Inch Cape shows that their piles reach 110 meters in length. But it still does not exceed the Chinese record holder in Cangnan, Zhejiang province, which reached 115 meters.
Has China reached its peak monopile size?
If restrictions on offshore foundation types were relaxed, the longest offshore wind foundation pile could reach 133.5 meters – a record that is also currently held by Cangnan.
It’s clear how proud the media were when covering these offshore wind piles. However, reports from the years following 2022 suggest that the fabrication of 2,400-ton monopiles in China has largely ceased, with the only recent exception being the XXXL monopile for the Inch Cape project. Logically speaking, given China’s reputation as an “infrastructure powerhouse,” one would expect it to push for even larger, longer, and heavier designs in China. Yet progress seems to have stalled, with Scotland now holding the record.
Is bigger better?
From a foundation engineer’s point of view, however, increasing the size of the foundation is not always what we want.
Larger monopiles reflect improvements in manufacturing, transportation, and installation capabilities, but do not necessarily indicate a corresponding advancement in design capability.
Offshore wind foundations need to be designed specifically for each site. When a 2,500-ton foundation suffices to meet design requirements, but it is designed as 3,000 tons, this reflects a lack of optimisation in the design. In other words, the role of the foundation engineer is to quantify the design – a process technically referred to as the “quantitative evaluation of foundation solutions.”
Even for a 2,500-ton monopile foundation, the possible combinations of diameter, length, and wall thickness are virtually unlimited. While software can generate hundreds of viable solutions, only an experienced foundation engineer knows which design parameters are critical.
Comparing Europe and China
Looking at European and Chinese projects, it becomes evident that European monopiles tend to be“stockier”than their Chinese counterparts in that they have larger diameters and shorter lengths. This is particularly noticeable in the Inch Cape project, where the diameter and weight are the world’s largest, but the length is relatively moderate. This observation relates to the highly specialised field of geotechnical engineering, or more precisely, pile–soil interaction.
Comparing the project water depths of China and Europe makes the situation even harder to understand. The Cangnan project in Zhejiang, mentioned above, has a water depth of 19–26 meters, whereas the Inch Cape project in Scotland reaches a maximum depth of 60 meters. Yet, the pile at Cangnan is 5 meters longer than that at Inch Cape.
How can we explain this?
In addition to the differing preferences for TP-less monopiles in China and TP-based designs in Europe, this phenomenon can also be attributed to geotechnical considerations.
Cangnan is, from an engineer’s perspective, defined by exceptionally soft and deep surface mucky clay layers. Building an offshore wind farm here requires an unusually long“stabilising pile”to anchor the upper structures.
In contrast, European seabed soils are generally much stiffer. Apart from that, engineers employ the“PISA”method to accurately determine the horizontal/rotational stiffness that a stocky pile can provide in European sites. An appropriate increase in pile diameter can reduce the required embedment length, thereby leading to a more optimised monopile design.
In fact, I am inclined to believe that in recent years, the“PISA”method has also been adopted in the design of monopiles in China.
Around 2020, related research and publications began to emerge, and software providers, like Bentley, actively promoted the methodology which gives reason to believe that the lack of new weight records in monopile is not without explanation.
In addition, with the improvement of jacket foundation design capabilities, jackets used in water depths of around 50 meters can now weigh about 1,600 tons. When we consider the weight of the four embedded piles, the total weight of the jacket foundation could even be lighter than that of a monopile designed for a site with similar water depth.
Where to from here?
In Europe, a monopile can support a 15 MW offshore wind turbine at a water depth of 60 meters. In China, monopiles in 50-meter water depths – even for supporting smaller capacity turbines – have yet to appear. Likewise, monopiles supporting 15 MW turbines, even in shallow waters, have not yet been realised in China.
What turbine capacity could a monopile support in a Chinese offshore wind farm, and at what water depth? This is an interesting question that warrants close attention going forward.
Reach out to Jiang on LinkedIn or read more about Empire Engineering’s offshore wind expertise.
