By Dario Mulazzani, DAVI Product & Market Specialist Wind Energy & Heavy-Duty Division .
Located in such a dynamic and extremely powerful element as the sea, foundations represent one of the main elements of any offshore wind farm, accounting for over one-fourth of the total equipment cost . As they must support the wind turbines, absorbing all the forces and loads and providing a safe and stable base, defining the right typology of foundation can have a huge impact both on the economic and technical sides.
Offshore wind farms can typically be placed in a few selected locations only. There are two main conditions limiting the range of use of this type of installations:
The development of new technologies, manufacturing and construction procedures, the increase in the size of wind farms and turbines together with higher society’s awareness of visual and environmental impacts, have led to the displacement of these installations further from the coastline than ever before.
Depending on the depth of the seabed, as well as the surrounding conditions, different foundation solutions can be used:
There is however a typology that stands out above the others, both in frequency and range of use: the monopiles , being selected in more than 60% of the worldwide offshore wind installations. Monopiles are deployed in the majority of depths and environments due to main characteristics, as follows:
In order 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 higher and 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 6-7 MW turbine (being the most mature capacity to date), monopiles are typically in the 90-100m length range with diameters and thickness at bottom sections of 9m and 90-100mm respectively for an overall weight often exceeding 1500 ton.
As mentioned, offshore installation allows for the deployment of larger turbines (both in terms of capacity and physical size), mostly due to constraints related to onshore transportation of the relevant heavy and expansive equipment: this is desirable as a wind farm comprised of larger turbines will necessarily require lower investment and maintenance cost per installed capacity, maximizing the project profitability.
It is hence likely that offshore wind turbines capacity will keep increasing with some manufacturers already bringing to the market 12-14MW turbines (such as the GE Haliade-X, currently being tested onshore). Although the aforementioned ratios are expected to decrease due to physical limitations, the so called XXL monopiles will weigh up to 3000 tons with diameters and thickness at bottom sections ranging from 12-14m and 120-140mm respectively.
Other foundation typologies are expected to follow a similar increasing trend.
The manufacturing challenges
All types of off-shore foundations are comprised of large plates jointed together and rolled into cans and cones; such workpieces are then assembled and welded into large structures which, in the case of Monopile Foundations, can reach up to 120m in length. With plates thickness often exceeding 140mm and increasingly large diameters (> 12m ) it becomes critical to minimize the amount of circumferential welding required to grow the overall length, often leading to the selection of increasingly large plates (up to 4.5m in width, with weights often exceeding 150 tons each).
Thus, fabricators engaged in the manufacturing of such heavy-duty off-shore foundations will need to 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.
Stay ahead 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 operator’s 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 the Market thanks to its cutting-edge technology developed working along the most accredited project developers and towers and foundations manufacturers.
For instance, to better serve the Off-shore Wind Energy Sector, dedicated heavy-duty feeding and handling equipment are continuously being developed and updated to ensure that Fabricators entering the DAVI World are provided with the most advanced hardware allowing them to maintain competitiveness in a fast changing and dynamic environment , requiring more and more challenging workpieces to be manufactured every year.
To date DAVI is already the technology partner selected by most major players, with over 300 installations dedicated to the Wind Energy Industry worldwide and approximately 60% of the overall Wind Energy rolling machines market share .
Don’t 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.