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Offshore Wind Journal

Pan-European projects advance the cause of floaters

Mon 13 May 2019 by David Foxwell

Pan-European projects advance the cause of floaters
Equinor’s Hywind project led the way in floating offshore wind but much work needs to be done to commercialise other concepts

A number of collaborative projects got underway early in 2019 that aim to take floating offshore wind concepts from the proof of concept stage closer to commercial readiness

Interest in floating offshore wind is growing quickly. Numerous floating wind concepts have been proposed but most – with the exception of Equinor’s Hywind Scotland project – are at the precommercial stage.

If floating wind is to become a reality, much work needs to be done to understand the effects of wind and waves on foundations and on the turbines installed on them, particularly given the sometimes extreme environmental forces they will be exposed to in deep water. With this knowledge gap in mind, research organisations around Europe are working with manufacturers to gather the data they need to make floating windfarms possible.

Among a growing raft of projects is a Danish one that recently got under way that aims to provide tools to manufacturers and developers that will enable them to commercialise designs and make it less expensive and easier to produce floating foundations.

The Technical University of Denmark (DTU) is leading the FloatStep project, which will culminate in a series of model tests designed to assess the effect of winds and waves on floating wind turbines and foundations.

Also involved in the project are DHI, turbine manufacturer Siemens Gamesa Renewable Energy, Stiesdal Offshore Technologies, the company behind the TetraSpar foundation, Stromning, a Danish company that specialises in research and development and in computational fluid dynamics and the University of Western Australia, which will provide offshore hydrodynamics expertise.

The aim of the project is to optimise the design of the floating wind turbine foundations and ensure they are suited for use in what the DTU described as “very deep water.” At the same time, the consortia wants to make it less expensive and easier to produce floating platforms, and service and maintain them once in service.

Over the next four years, the researchers leading the project will use their knowledge to improve the tools and methods used to design the floating foundations the offshore wind turbines are installed on. Doing so will see the project partners develop and test new and improved calculation models that can be used for all types of floaters.

The models will be validated against analyses of full-scale measurements undertaken in a related project in Norway that Stiesdal Offshore Technologies is participating in. Model tests in DHI’s wave tank will be used to emulate the conditions a foundation would be exposed to in the Atlantic. As highlighted previously by OWJ, the TetraSpar foundation developed by Stiesdal Offshore Technologies will be tested with a full-scale 3.6 MW turbine in the North Sea, off the coast of Norway, in 2020.

“Normally, you design the structure of an offshore wind turbine, and then look at how to make it,” said Stiesdal Offshore Technologies chief executive Henrik Stiesdal. “We based our design on using components that can be standardised and quickly and economically constructed. This makes such a foundation much less expensive. The foundation is also a simple robust structure, which helps to reduce costs compared to what we have seen so far.”

Stiesdal Offshore Technologies’ foundation is suitable for use in water more than 100 m deep. “But the further out to sea you go, the more factors come into play,” said DTU Wind Energy professor Henrik Bredmose. “Everything becomes more extreme. The further out you go, the stronger the wind and the more extreme the waves. We are therefore developing models to calculate how strong waves affect the floater and the mooring that holds it in place.”

Strong winds and wave loading also expose floating offshore wind turbines to high levels of vibration, so the design of the foundation and turbine tower must be carefully balanced to ensure that oscillations do not arise that could adversely affect the performance of the turbine.

Extreme waves also generate great pressure on the structure of a foundation and can also create oscillations in the foundation and turbine, so the research team led by DTU will use computational fluid dynamics to model the flow around a floater and predict the effects of wave action.

Another issue the Danish team plans to address is fatigue in the mooring systems for floaters. Waves arriving at the foundation in groups can create oscillation in a mooring system that can lead to fatigue in anchor cables. Their effects will be modelled by the researchers and compared with data obtained using scale model testing at DHI and full-scale measurements from Norway.

Cost-competitive technology

Another project that got under way earlier in 2019 sees the European Marine Energy Centre (EMEC) lead a consortium from Ireland, the UK, France, the Netherlands and Germany that aims to demonstrate floating wind’s cost-competitiveness.

The €31M (US$35M) project has been approved and, subject to consenting, a full-scale floating wind turbine will be deployed for testing off the west coast of Ireland at a Sustainable Energy Authority of Ireland (SEAI) test site near Belmullet, County Mayo, by 2022. Apart from EMEC, the project also includes SEAI, Saipem and other European organisations.

Funding has been secured from Interreg North West Europe to accelerate the uptake of floating offshore wind. The project will demonstrate the survivability and cost-competitiveness of floating offshore wind technology. It will also support the development of an active supply chain in the region.

Known as Accelerating market uptake of Floating Offshore Wind Technology (AFLOWT) the project will see EMEC apply a wealth of knowledge and expertise from related sectors to test and demonstrate floating offshore wind.

Saipem will be supported by project partners with research and development insights coming from Cable Life Cycle Assurance in France, Maritime Research Institute Netherlands, Fraunhofer Institute for Wind Energy Systems in Germany, University College Cork and Electricity Supply Board Engineering & Major Projects in Ireland.

The floating turbine will be tested for a year at SEAI’s Atlantic Marine Energy Test Site off the west coast of Ireland. Deployment is currently planned for 2022.

Single-point mooring could significantly reduce costs

Concepts such as PivotBuoy hold great potential but testing is needed to validate them

An innovative single-point mooring system that could significantly reduce the cost of floating offshore wind is to receive €4.0M (US$4.5M) of EU Commission Horizon 2020 funding.

X1 Wind’s PivotBuoy is to be tested by a consortium of nine partners, led by X1 Wind, who will deploy a prototype at a test site at the Oceanic Platform of the Canary Islands (PLOCAN). X1 Wind believes the technology could reduce platform weight by as much as 80% compared with other floating foundations and could reduce costs by 50%.

The project aims to validate the benefits of the PivotBuoy system and other innovations to reduce installation, operation and maintenance costs, paving the path to achieve €50/MWh (US$56/MWh) in commercial-scale floating windfarms.

The system combines advantages of single point mooring systems with those of tension-leg platforms and a more efficient downwind structural design, enabling a significant weight reduction compared to spar and semi-submersible systems.

The consortium will integrate a part-scale prototype of the PivotBuoy into a downwind floating wind platform designed by X1 Wind at PLOCAN’s test site. The system will be installed by 2020, where other innovations related to assembly and installation will be validated.

The project consortium combines experienced industry partners and R&D organisations from the offshore wind, naval and oil and gas sectors, and is formed by nine partners from six different countries: X1 Wind, ESM, WavEC, PLOCAN, EDP, INTECSEA, DTU, DNV GL and DEGIMA. The project will start on 1 April and will last for 36 months.

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