Siemens Gamesa Renewable Energy and Aalborg University are leading a five-year project that aims to significantly reduce the cost of energy from offshore wind by developing and industrialising new components
The last decade has seen a large number of projects that aim to reduce the cost of offshore wind. Many have been successful, and the levelised cost of energy from offshore wind has fallen by 65%.
Most of these technology development efforts have focused on one particular piece of equipment – new, larger turbines, control systems for windfarms or using drones, for instance – but the i4Offshore project that Siemens Gamesa and Aalborg University head up is different. By the end of it the project partners hope to have paved the way for the introduction of several new components: state-of-the-art offshore turbines, innovative array cable concepts and more cost-effective jacket foundations and suction buckets for those foundations.
The goal, as Siemens Gamesa Renewable Energy head of offshore balance of plant innovation Jesper Møller told OWJ, is to demonstrate and test technology that can eliminate bottlenecks and further reduce the cost of energy from offshore wind. It aims to deliver a solution that provides consumers with electricity that is less expensive than any fossil fuel and any form of renewable energy, including hydropower and solar. All in all, i4Offshore is one of the largest and most comprehensive offshore wind projects of its type.
The project is officially entitled ‘Integrated Implementation of Industrial Innovations for Offshore Wind Cost Reduction’ and is the subject of a grant from the European Union’s Horizon 2020 research and innovation programme of nearly €20M (US$22M). Goals include demonstrating significant cost reduction across the entire value chain – from manufacturing to assembly to installation and operations and maintenance.
At the heart of this wide-ranging effort is a plan to demonstrate at a commercial offshore windfarm:
“The project is actually much more than just a demonstration,” Mr Møller told OWJ in a late-April interview. “It combines new technology with lean manufacturing, new ways to transport components and innovative strategies for installation and maintenance and O&M.
“We are particularly focusing on bottlenecks in the supply chain, but cost reduction is the paramount concern. We aim to make use of new types of modularised jacket components that will allow for leaner, faster, more reliable and more efficient transportation, installation and O&M. We also hope to make decommissioning much easier and reduce the environmental footprint of offshore wind, using a type of suction bucket that can be installed almost noiselessly.”
Another advantage of the suction bucket foundation is that at the end of the turbine’s operational life it is easier to remove, along with the jacket and transition piece, which can then be re-used or recycled.
Elements of the technology due to be demonstrated in the i4Offshore project were first used by Siemens Gamesa on the Nissum Bredning offshore wind project, an innovative 28 MW project in the waters off north-western Denmark that saw the first use of a series-produced SWT-7.0-154 direct drive offshore turbine, a 66-kV transmission system, jacket foundations with concrete transition pieces and a cable-in-pipe solution.
The cable-in-pipe solution now being taken forward in the i4Offshore project is revolutionary because it would allow offshore windfarms to use less expensive cables of the type manufactured for use onshore. There are a lot more manufacturers of this kind of cable, so costs would be lower as a result of greater competition and because manufacturing processes would be less expensive.
Another advantage of cable-in-pipe is it does not require using a large, specialised and expensive cable-lay vessel. In the Nissum Bredning project what was, essentially, an off-the-shelf onshore cable was installed, housed in a high-density polyethylene pipe.
A further advantage is that because the cable would not need to be armoured, there is no steel involved in its construction and no electrical losses. Mr Møller and his colleagues believe that the many potential advantages of the cable-in-pipe solution could make it 30% less expensive than conventional offshore array cables.
The novel hybrid foundation concept to be demonstrated in the i4Offshore project uses a concrete rather than a conventional steel transition piece. One obvious advantage of a concrete transition piece is cost and the large number of manufacturers who could produce a component of this type. Another advantage is that the weight of a concrete transition piece would add to the overall stability of the foundation, pushing down on the suction bucket-type foundations that the partners in the project are planning to use with it. This means smaller, lighter buckets that use less steel can be used.
One of the focus areas for the jacket itself is that it should be easy and economical to mass produce. The aim is to break down its design into ‘nodes’ that can easily be manufactured – ideally using low-cost techniques such as robot welding.
Mr Møller explained that conventional jacket foundations of the type currently used in the offshore wind industry are expensive to manufacture, in part because the process is labour-intensive and because specialised welding is required. At the moment, the i4Offshore team is leaning towards using a four-legged jacket foundation, but that is not set in stone.
Suction buckets have been used with jackets before, but a new low cost solution is being sought in i4Offshore
Innovation will also enable the suction buckets for the jacket foundations to be mass produced and for costs to be reduced. The aim is to use coil steel rather than the more expensive steel plate currently used in this type of structure.
As highlighted previously by OWJ, Siemens Gamesa, Aalborg University, Fred Olsen Windcarrier and Offshoreenergy.dk are already working together on a related project funded by the Energy Technology Development and Demonstration Programme (EUDP) to demonstrate the advantages of industrialising an enhanced suction bucket foundation for offshore windfarms.
The aim is to mature and industrialise the suction bucket concept, which has been used on a small scale to date, towards commercial-scale applications. The companies believe an industrialised suction bucket concept could be used to ‘slash’ installation costs for foundations.
The concept merges the noise-free installation advantages of suction buckets with industrialised fabrication techniques using coil steel, a fabrication technique originally developed by Siemens Gamesa and the Danish steel specialist Ib Andresen Industries for application in onshore towers. Applying innovative fabrication methods such as this to suction bucket technology will enable steel thicknesses to be reduced to less than 20 mm, compared to today’s typical thickness of 30-40 mm. Coil steel costs less than conventional steel plate and availability is higher.
Altogether, 15 organisations are participating in the i4Offshore project apart from Siemens Gamesa and Aalborg University. They include Universal Foundation, Bladt Industries, Per Aarsleff, Salzgitter, Windar Renovables, Dr Techn Olav Olsen, NKT Cables GmbH & Co KG, SINTEF Ocean, Bureau Veritas Marine & Offshore, Maersk Broker, Deugro Danmark, Fred Olsen Windcarrier and the Technical University of Denmark.
The components being advanced in the i4Offshore project will be brought together for demonstration on a Danish offshore windfarm, probably one developed by Vattenfall, which has signed a letter of intent to participate. If all goes according to plan, the demonstration should take place in late 2022 or early 2023.