Evolution of Offshore Foundations – Offshore WIND

By Dario Mulazzani, DAVI Product & Market Specialist Wind Energy & Heavy-Duty Division.

Located in such a dynamic and extremely powerfulelement as the sea, foundations represent one of the main elementsof any offshore wind farm, accounting for over one-fourth of the total equipmentcost. As they mustsupport the wind turbines, absorbing all the forces and loads and providing asafe and stable base, defining the right typologyof foundation can have a huge impact both on the economicand technical sides.

Offshore wind farms cantypically be placed in a few selected locations only. There are two mainconditions limiting the range of use of this type of installations:

The development of newtechnologies, manufacturing and construction procedures, the increase in thesize of wind farms and turbines together with higher societys awareness ofvisual and environmental impacts, have led to the displacement of theseinstallations further from the coastline than ever before.

Depending on thedepth of the seabed, as well as the surrounding conditions, different foundationsolutions can be used:

There is however a typologythat stands out above the others, both infrequency and range of use: the monopiles, being selected in more than 60% of the worldwide offshore windinstallations. Monopiles are deployed in the majority of depths andenvironments due to main characteristics, as follows:

Inorder to adapt to the needs of new more efficient and demanding wind farms,monopiles design has evolved over the years. Its main dimensions, diameter,thickness and length have steadily increased to be able to support higherand heavier more powerful turbines installed at greater depths.

It has been observed that both the length and the diameter of the piles have evolved proportionally to the power of the turbines, maintaining constant ratios which can be summarized as follows:

For instance, for a 6-7MW turbine (being the most mature capacity to date), monopiles are typically inthe 90-100m length range with diameters and thickness at bottom sections of 9mand 90-100mm respectively for an overall weight often exceeding 1500 ton.

Asmentioned, offshore installation allows for the deployment of larger turbines(both in terms of capacity and physical size), mostly due to constraintsrelated to onshore transportation of the relevant heavy and expansiveequipment: this is desirable as a wind farm comprised of larger turbines willnecessarily require lower investment and maintenance cost per installedcapacity, maximizing the project profitability.

It is hence likely thatoffshore wind turbines capacity will keep increasing with some manufacturersalready bringing to the market 12-14MW turbines (such as the GE Haliade-X,currently being tested onshore). Although the aforementioned ratios are expectedto decrease due to physical limitations, the so called XXL monopiles will weighup to 3000 tons with diameters and thickness at bottom sections rangingfrom 12-14m and 120-140mm respectively.

Other foundation typologies are expected to follow a similar increasing trend.

The manufacturing challenges

All types ofoff-shore foundations are comprised of large plates jointed together and rolledinto cans and cones; such workpieces are then assembled and welded into largestructures which, in the case of Monopile Foundations, can reach up to 120min length. With plates thickness often exceeding 140mm and increasinglylarge diameters (>12m) it becomes critical to minimize the amount ofcircumferential welding required to grow the overall length, often leading tothe selection of increasingly large plates (up to 4.5m in width, withweights often exceeding 150 tons each).

Thus, fabricatorsengaged in the manufacturing of such heavy-duty off-shore foundations will needto face and overcome two main manufacturing constraints, as follows:

For all these reasons, the fabrication of offshore foundations is certainly the most challenging and time-consuming rolling operation.

Stayahead of the Market with DAVI!

Fabricators are hence in need of a technology partner able to deliver high performance and reliable rolling solutions, capable of sustaining the demanding serial production characteristics of this Industry by increasing rolling accuracy, output and operators safety while decreasing downtimes, floor-to-floor processing time and manpower requirements.

Since 2007,when DAVI Wind Energy Division was created, DAVI has been leading theMarket thanks to its cutting-edge technology developed working alongthe most accredited project developers and towers and foundationsmanufacturers.

For instance, tobetter serve the Off-shore Wind Energy Sector, dedicated heavy-duty feeding andhandling equipment are continuously being developed and updated toensure that Fabricators entering the DAVI World are provided with the mostadvanced hardware allowing them to maintain competitiveness in a fastchanging and dynamic environment, requiring more and more challengingworkpieces to be manufactured every year.

To date DAVI isalready the technology partner selected by most major players, with over 300installations dedicated to the Wind Energy Industry worldwide andapproximately 60% of the overall Wind Energy rolling machines marketshare.

Dont miss out, stay ahead with DAVI!

Note:The opinions, beliefs, and viewpoints expressed in this article do not necessarily reflect the opinions of Offshore WIND.

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Evolution of Offshore Foundations - Offshore WIND