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How do floating turbines work?

Floating wind power – the next frontier for renewables?

 

The blades of the Kincardine wind farm rotate 15km off the coast of Aberdeen, their monumental structures mounted on five triangular platforms, each weighing 3,000 tons.

Floating on North Sea waters 60-80 meters deep, they are collectively capable of generating 200,000MW of clean electricity a year – enough to power 50,000 Scottish homes.

This is the largest floating offshore wind (FOW) farm in the world and a graphic snapshot of what can be seen on the horizon of the energy industry.

As the leading economies ramp up their commitments to decarbonize and transition to cleaner power, the global offshore wind industry is expected to record a CAGR of 12.3% between 2021 and 2026. Revenue generation is forecast to reach $56.8bn – an increase of $25bn.

Europe is the largest market for offshore wind with a 57% share and the North Sea has long been the cradle of the industry. “This is because of the windy conditions, of course, but also, significantly, because of its relatively shallow waters,” explains Jean-Marie Grosset, Energy and Construction Underwriter at AGCS.

“This has allowed ‘bottom-fixed’ turbines to be installed on the seabed at depths of about 30 meters around the coasts of the UK, Denmark, Germany, and Belgium. Development of the industry was also supported by the accessible manufacturing footprints those countries have nearby.”

But 80% of the world’s offshore wind blows over waters deeper than 50 meters and often farther away from shore, where installing bottom-fixed turbines is either impossible or economically unfeasible.

This has limited the extent of offshore wind deployment in the past, but promising developments in FOW technologies mean all that might be about to change.

An industry on the commercial cusp

Unlike bottom-fixed platforms, which are constructed offshore, FOW platforms are largely assembled in a dry dock, then towed out to the site of their installation, where they are anchored with mooring lines.

Prototypes and pilot projects in FOW have grappled with the practical problems associated with their massive scale, aerodynamics and instability. But in recent years a number of technologies have come to the fore that engineers believe can overcome these.

FOW remains more expensive than fixed offshore wind, and while technical and logistical challenges still exist for large-scale deployment, as well as the need for funding from investors and governments, costs are expected to fall as FOW scales up. The industry is poised for industrialization.

And the potential is huge. The 74.05MW of FOW power that is currently installed in Asia and Europe is estimated to increase to 127.87MW of deployed technology by January 2022. Europe has the highest potential for FOW, at 4,000GW, followed by the US at 2,450GW and Japan at 500GW.

FOW allows power to be generated in areas of deeper water with higher, more consistent wind speeds, and the list of countries keen to assess its feasibility outside Europe includes South Korea, Japan, Taiwan, and the US, where the Department of Energy is investing more than $100mn into researching, developing and demonstrating FOW technology, with a particular eye on California.

Not surprisingly, many global energy players are investing in FOW’s potential.

“With floating offshore wind, the major energy companies are able to mobilize and leverage existing skills in areas such as offshore platforms and pipelines,” says Grosset. “It also feeds into their strategic plans for transitioning to cleaner energy.”

A less risky undertaking

Constructing a turbine on land, rather than offshore, has advantages. As well as being safer, it reduces the extent of specialist heavy lifting required and sophisticated vessels used for that purpose.

It also opens up the possibility of new and more cost-effective means of operating, as wind turbines are mobile and could, in theory, be dismantled and towed back to port for maintenance.

Another advantage is that FOW is less likely to meet with resistance from coastal communities, as the wind farms are installed further out to sea, reducing concerns about noise and visual pollution.

However, the fishing industry has raised some concerns about the level of intrusion it might have on their operations and marine life.

New technology, new hazards

Installing innovations offshore inevitably introduces new risks, but the full extent of these is not yet known because the technologies are still immature.

However, mooring, cabling and weather extremes are potential areas of concern with FOW. Mooring lines are particularly vulnerable to failure due to fatigue, corrosion, impact or harsh marine conditions.

“We had a claim, quite a substantial loss, where a chain that was used to lift a mooring line broke and fell into the ocean,” says Grosset. “As developments are made further out to sea, around the world, we will see challenges in accommodating harsher conditions.”

“The structures themselves can sustain those conditions but any kind of maintenance – even relatively minor – will become more critical in that environment. This could result in more significant business interruption or delayed startup if the facility is not yet operational.”

Stefan Atug, Engineering Global Practice Group Leader at AGCS, adds that changing weather patterns will increase this risk. “The units themselves can withstand windstorms, but the mooring and cabling systems are less tested.

Most claims in bottom-fixed offshore wind have been connected to cabling, and we expect this will also be the case with FOW. The losses we’ve seen with cabling, especially during construction, tended to be impact losses where they were bent too much, for example, or cut by an anchor. I anticipate the inter-array cabling, which connects one unit to another, will be more challenged on a floating wind farm.”

As with conventional offshore wind turbines, the risks associated with humidity, oxidation, corrosion, hazardous weather, and salt water are ever present.

Mitigating the winds of change

“The main risks with floating turbines arise from the fact that so many of their parts are designed to move,” says Atug, “and whatever moves has a lifetime limit because it incurs more wear and tear.”

Then there are issues of scale, adds Joachim Eichhorn, Energy & Construction Underwriter at AGCS. “If you’re looking at longer distances, the longer the cable, the higher the probability of a loss.

The same applies to the design and manufacturing – there will be quality control issues to consider in the context of greater distances and harsher conditions.”

With so many moving parts and little-known risks, contingency planning is paramount. “The industry relies on a lot of specific competencies,” says Grosset. “Choosing the most competent designer, builder and operator and the most expert service providers is critical.”

Atug adds quality control is key and that owners or operators should ensure designers, manufacturers and other contractors share responsibility for this, not only during the testing period, but for an agreed period of time after a plant is operational.

Floating offshore wind: four possible solutions

Four different technologies have emerged to make floating offshore wind generation possible. The first three are loosely moored to the seabed, while the tension leg platform is more firmly attached to the seabed and more stable.

1) Barge (water depth +30m)
2) Semi-submersible (water depth +40m)
3) Single point anchorage, or SPAR (water depth +100m)
4) Tension leg platform (water depth +50m

Collaboration is the way ahead

Before FOW can be deployed on a commercial scale, there are technical issues to resolve that will require innovative solutions from developers, manufacturers and the supply chain.

According to the Floating Wind Joint Industry Project (FWJIP), an R&D initiative between the Carbon Trust and 17 international offshore wind developers, these challenges are common to several floating wind projects and suitable for industry-led collaborative R&D.

They include heavy lift maintenance and the logistics of this for wind farms further away from ports, tow-to-port maintenance, and moorings in challenging environments. Water depth, whether it’s very deep or very shallow, can be problematic, as can seismic environments and certain seabed conditions.

“It is expected that many of these challenges can be overcome using existing solutions from other sectors,” the FWJIP report states, “but there is a need for further investigation to establish the true level of risk presented and undertake research that can reduce risk throughout the project life cycle.”

Eichhorn says: “There are comparable, transferable skills and technologies in the offshore oil and gas sector that can be drawn upon to de-risk the development of FOW.”

“Pressure will grow in the coming years to produce energy away from the land. Renewables, whether it’s onshore wind or solar, use a lot of land, and this can conflict with agricultural or housing needs.

“However, given FOW turbines are arguably less intrusive on the environment than those that are fixed, we don’t anticipate significant increase in environmental-related litigation – there might even be less – but the industry and technology are so new this remains to be seen. We don’t foresee increased risk from cybercrime, compared to existing offshore wind plants.”

As the industry emerges from the realm of R&D, prototyping and feasibility studies, there are now calls for policymakers to commit to it with a supportive regulatory framework, investment in infrastructure, and funding and investment solutions that will support commercial roll-out.

Only then, say industry experts, can the seemingly limitless potential of FOW become cost-effective to harness and fully integrated into the energy market.

This article is shared by courtesy of Allianz – www.agcs.allianz.com

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