The cost of offshore wind is falling dramatically. In just two years from 2015 to 2017, the price to be paid for new projects fell by over 50%.
There are many reasons that Ørsted and other developers have been able to drive down costs at this dramatic rate, and one is size. Projects are getting bigger and so are wind turbines. With the latest models now standing taller than the Gherkin building in London, it’s clear that significant innovation has occurred over the past few years to make these huge structures a reality. And of course you can’t build a house – or a wind turbine – without the right foundations.
Foundations are also a major cost when building a project, accounting for around a third of the total capital expenditure. So, innovation in this area – designing, fabricating and installing foundations more efficiently and at lower cost – has a crucial role to play as we continue working to drive down the price of offshore wind.
Typically, most existing offshore wind farms have used monopile foundations and there have already been big changes as monopile design has moved away from the oil and gas inherited design methodologies from the 1950s. Those designs still are effective for long, slender piles with a diameter to length ratio of 1:50, and diameters typically smaller than 2 metres. However, since our monopiles are essentially designed to sustain the high horizontal loads from the wind, the required diameters are getting larger than 7 metres, with diameter to length ratio closer to 1:4.
The performance measurement of over 1,000 installed wind turbine foundations allowed us to confirm that the previously used methodologies resulted in conservative over-design of the monopiles, i.e. the piles were longer than required. It was clear that we needed to “sharpen the pencil” by creating customised design methodologies specifically targeting offshore wind turbine foundations. By doing this we have been able to improve efficiency and reduce costs.
Partnering with leading academic institutions like the University of Oxford and Imperial College London has also helped to continually improve foundation design. Recently, we completed the PISA (Pile Soil Analysis) project giving us new static design methodologies that allow us to have a leaner and optimised monopile foundation design.
And we’ve signed a further five-year agreement with the University of Oxford focussed on cyclic loading, which is the repeated loading that comes from the action of wind and waves on the structure. This is a hugely important element in foundation design, and improvements could not only lead to significant cost reduction as we support even bigger turbines in even deeper waters, but also enable us to safely extend the lifetime of the turbines.
Another challenge is reducing noise when installing foundations. We can put mitigation measures in place, but these are expensive and we’re always looking to innovate to remove the issue entirely.
One of the possible solutions is the use of the suction bucket foundation concept. In this case, the foundations are installed by applying suction to allow the penetration into the seabed in a virtually noiseless operation. Ørsted was the first company to use this technology for offshore wind turbines and this solution makes development for sites with water depths over 45 metres feasible, further opening the possibility of sustainable and cost-effective energy production.
Monopiles and jackets are not the solution for every site either, and floating wind turbines both capture the imagination and have the potential to be an excellent solution for sites where the water depth is greater than 60 metres – or virtually any depth imaginable.
All this is just a snapshot of what’s happening in this area of offshore wind development and there’s already been remarkable innovation in foundation design over such a short space of time. We can be proud of the UK’s role in developing, maturing and deploying the latest technology. And of course, we can’t rest up either with turbines getting bigger and bigger all the time! What’s clear though is that innovation in foundations is helping to make the utility-size offshore wind farms of the future a reality.