Norwegians Developing Monopile Foundation For 100-Metre Depths
The title of this post, is the same as that of this article on offshoreWIND.biz.
Monopile foundations are a common fixed foundation for offshore wind farms.
The article starts with this paragraph.
Norway’s Entrion Wind and Techano AS have signed a Memorandum of Understanding (MoU) through which Techano AS will join the ongoing development and test project planned to take place in Kristiansand, Norway for the patent-pending fully restrained platform (FRP) offshore wind foundation technology said to extend the operating depth of the monopile technology to up to 100 metres.
It does seem that the Norwegians are intending to take this type of foundation to new heights. Or is it new depths?
A picture in the article shows a tall monopole held in position by three wires securely anchored in the sea-bed. It reminds me slightly of the sort of flag-poles, that we used to build in Scout camps in the 1960s, using Scout staves, ropes and tent pegs.
But seriously in the 1970s, I did the calculations for a company called Balaena Structures, who were trying to develop a reusable oil and gas platform.
- The company had been started by two Engineering professors from Cambridge University.
- The platforms were formed of a long steel cylinder, which would have been built horizontally in the sort of ship-yards, that were used to build supertankers.
- They were to be floated out horizontally and then turned upright.
- Weight and the gumboot principle would have kept them, in place.
The design also included a square platform on the top end. Originally, they were planning to put the platform on top after erection, but I showed that, it would be possible to erect cylinder and platform, by just allowing water to enter the cylinder.
The project had a somewhat unfulfilling end, in that they never sold the idea to an operator and the company closed.
But I still believe something similar has a future in the offshore energy industry.
It could be a foundation for a wind turbine or possibly as I indicated in The Balaena Lives, it could be used to clear up oil field accidents like Deepwater Horizon.
Could This Be A Design For A Hundred Metre Plus Monopole Foundation?
Construction and installation would be as follows.
- A long cylinder is built in a ship-yard, where supertankers are built.
- One end, which will be the sea-bed end after installation, is closed and has a skirt a couple of metres tall.
- The other end is profiled to take the transition piece that is used as a mount for the wind turbine.
- A float would be added to the top end for tow-out. This will help the cylinder to float and erect.
- Water would be added into the cylinder and, if the dimensions are correct, it will turn through ninety degrees and float vertically.
- It would be towed to a dock, where a large crane on the dock would remove the float and install the turbine.
- The turbine and its foundation would then be towed into place and by adding more water lowered to the sea-bed.
- The float would be reused for the next turbine.
Note.
- The float is needed to nudge the cylinder to turn vertically.
- If the Cambridge professors were right, the skirt and the weight of water would hold it in place.
- Traditional moorings could be added if required.
- No heavy lifts are performed at sea.
- The concept would surely work for a floating turbine as well.
But then what do I know?
I was just a twenty-five year old engineer, mathematician and computer programmer, who did a few calculations and a dynamic simulation fifty years ago.
Are Floating Wind Farms The Future?
Boris Johnson obviously thinks so, as he said this about floating wind farms at the on-line Tory conference today.
We will invest £160m in ports and factories across the country, to manufacture the next generation of turbines.
And we will not only build fixed arrays in the sea; we will build windmills that float on the sea – enough to deliver one gigawatt of energy by 2030, 15 times floating windmills, fifteen times as much as the rest of the world put together.
Far out in the deepest waters we will harvest the gusts, and by upgrading infrastructure in such places as Teesside and Humber and Scotland and Wales we will increase an offshore wind capacity that is already the biggest in the world.
Just because Boris said it, there is a large amount of comment on the Internet, describing everything he said and floating wind turbines as utter crap.
Wikipedia
The Wikipedia entry for floating wind turbines is particularly informative and gives details on their history, economics and deployment.
This is a paragraph from the Wikipedia entry.
Hywind Scotland has 5 floating turbines with a total capacity of 30 MW, and operated since 2017. Japan has 4 floating turbines with a combined 16 MW capacity.
Wikipedia also has an entry for Hywind Scotland, which starts with this sentence.
Hywind Scotland is the world’s first commercial wind farm using floating wind turbines, situated 29 kilometres (18 mi) off Peterhead, Scotland. The farm has five 6 MW Hywind floating turbines with a total capacity of 30 MW. It is operated by Hywind (Scotland) Limited, a joint venture of Equinor (75%) and Masdar (25%)
Wikipedia, also says this about the performance of Hywind Scotland.
In its first two years of operation the facility has averaged a capacity factor in excess of 50%.
That is good performance for a wind farm.
Hywind
There is more about Hywind on this page of the Equinor web site, which is entitled How Hywind Works.
This is the opening paragraph.
Hywind is a floating wind turbine design based on a single floating cylindrical spar buoy moored by cables or chains to the sea bed. Its substructure is ballasted so that the entire construction floats upright. Hywind combines familiar technologies from the offshore and wind power industries into a new design.
I’ve also found this promotional video on the Equinor web site.
Note that Statoil; the Norwegian government’s state-owned oil company, was renamed Equinor in 2018.
Balaena Structures
In the early 1970s, I did a lot of work for a company called Time Sharing Ltd.
At one point, I ended up doing work for a company in Cambridge started by a couple of engineering professors at the University, which was called Balaena Structures.
They had designed a reusable oil platform, that was built horizontally and then floated out and turned vertically. They couldn’t work out how to do this and I built a mathematical model, which showed how it could be done.
This is said about how the Hywind turbines are fabricated.
Onshore assembly reduces time and risk of offshore operations. The substructures for Hywind Scotland were transported in a horizontal position to the onshore assembly site at Stord on the west coast of Norway. There, the giant spar-structures were filled with close to 8000 tonnes of seawater to make them stay upright. Finally, they were filled with around 5500 tonnes of solid ballast while pumping out approximately 5000 tonnes of seawater to maintain draft.
It sounds like Statoil and Equinor have followed the line of thinking, that I pursued with the Cambridge team.
My simulations of oil platforms, involved much larger structures and they had some other unique features, which I’m not going to put here, as someone might give me a nice sum for the information.
Sadly, in the end Balaena Structures failed.
I actually proposed using a Balaena as a wind power platform in Could a Balaena-Like Structure Be Used As a Wind Power Platform?, which I wrote in 2011.
I believe that their designs could have transformed the offshore oil industry and could have been used to control the Deepwater Horizon accident. I talked about this in The Balaena Lives, which again is from 2011.
Conclusion
It is my view, that floating wind farms are the future.
But then I’ve done the mathematics of these structures!
Did Boris’s advisors, as I doubt he knows the mathematics of oblique cylinders and how to solve simultaneous differential equations, do the mathematics or just read the brochures?
I will predict, that today’s structures will look primitive to some of those developed before 2030.
The Anonymous Widower 