Superclass offshore wind turbines pose new installation challenges

Offshore wind turbines are reaching dizzying new heights and capacities. Will the rest of the industry be able to keep up?

Foundations ready to be installed at the 1.5GW Hollandse Kust Zuid project, which will feature 140 Siemens Gamesa 11MW turbines (pic:Vattenfall/Jorrit Lousberg)
Foundations ready to be installed at the 1.5GW Hollandse Kust Zuid project, which will feature 140 Siemens Gamesa 11MW turbines (pic:Vattenfall/Jorrit Lousberg)

This is a feature from Windpower Monthly's October 2021 issue. Click here to read the full edition

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The past couple of years have seen the announcement of ever-taller turbine models, with major manufacturers upping the game in terms of power output, height and rotor diameter. Launch has followed launch in a race to the top.

Siemens Gamesa Renewable Energy (SGRE) was the first out of the blocks in spring 2020, with its 14MW SG 14-222, featuring a rotor diameter of 222 metres, recently upgraded to 236 metres. This followed not long after the launch of its 10MW turbine in January 2019, and an 11MW version in March 2020. The OEM claims its new model will increase annual energy production (AEP) by 25% compared with its predecessor.

GE announced a 14MW uprate of its Haliade-X in December 2020, following the 12MW and 13MW turbines in the same series. The largest specification boasts a rotor diameter of 220 metres and a capacity factor of 60-64%. The turbines will be at the UK’s 1200MW Dogger Bank C Dogger Bank C (1200MW) Offshoreoff Yorkshire, UK, Europe Click to see full details wind farm, the first two phases of which will use the 13MW model.

In February 2021, Vestas made its V236-15.0MW turbine public. With a rotor diameter of 236 metres and a wind-swept area of 43,743m2, the Danish manufacturer says it will have 65% higher annual energy production than its next largest offshore wind turbine, the V174-9.5MW. Its first commercial deployment is expected to be for utility-developer EnBW in its subsidy-free 960MW He Dreiht He Dreiht (960MW) Offshorenorth-west of Borkum, Germany, Europe Click to see full details project in the German North Sea.

Vestas did not hold the record for long. Just a few months later, Chinese turbine maker MingYang Smart Energy launched what is currently the world’s highest-rated offshore turbine at 16MW, featuring the largest-ever wind industry rotor diameter at 242 metres, and the longest blades at around 118 metres long. The company says the MySE16-242 produces 45% more energy than the previous MySE 11.0-203.

Why bigger is better

It is the increased efficiency — and therefore lower cost — that is the main benefit of these bigger turbines, according to Feng Zhao, head of strategy and market intelligence at the Global Wind Energy Council (GWEC).

“Bigger turbines will reduce capital costs significantly due to fewer foundations and cables, and those larger rotors will help boost AEP. Also, thanks to fewer turbines, there will be savings in terms of project construction and Opex,” he says.

The more turbines grow in size, the greater potential there is to reduce the levelised cost of energy (LCoE) and increase AEP, which will make offshore wind a vital resource for supporting country-level net-zero commitments, Zhao adds.  

Auction systems now used by many governments for tendering offshore wind result in very aggressive bids by developers, which in turn has put the onus on OEMs to develop increasingly efficient turbines, according to Peter Brun, global offshore wind segment lead at consultancy DNV.

“The average capacity factor of an offshore wind turbine is around 50%, but with these new turbines, capacity factors will go up to 64%. This means they will spin more times and therefore capture the wind more effectively, and also work better when the wind is low,” he says.

The more cost-effective offshore wind becomes, the more it can contribute to the world’s pressing net zero ambitions. Despite projected compound annual growth rates of 29% in 2020-25, and 13% in 2026-30, installed offshore-wind capacity will need to grow even faster to meet carbon-emission reduction targets, according to a report published by GWEC in September.

The existing 35GW wind fleet is less than 2% of what is needed to reach net-zero by 2050, GWEC says, and the 270GW expected by 2030 will be just 11% of what is required.

Vessel shortage

One of the main challenges facing the new generation of super-sized offshore turbines is installation, particularly finding vessels able to transport and lift components that can weigh more than 250 tonnes, further from shore and in deeper waters.

There are only 11 vessels globally that are able to support the installation of turbines greater than 10MW, according to GWEC’s offshore wind vessel database.

Analysts at IHS Markit have warned that increases in turbine size are already outpacing the infrastructure needed to install them. According to an IHS Markit report published in May, there are currently no offshore wind turbine installation vessels (WTIV) able to install the 15MW-plus turbines that will be hitting the market in the next three years, although some vessel suppliers have disputed this.

Van Oord has ordered a vessel that will be able to install 20MW turbines and lift 3,000 tonnes

“The increase in size of offshore wind turbines has been rapid over the last decade, and it’s been extremely difficult for vessel owners to keep up. A vessel is normally designed to have a lifespan of 25 years,” says Catherine MacFarlane, construction vessel base manager at IHS Markit.

“We track a fleet of 16 WTIVs, excluding the mainland China fleet. All of these vessels are ten years old or less, and yet all of them will require hugely expensive crane upgrades, if possible, in order to be technically able to install next-generation turbines,” she says.

The short lifespan of the existing fleet has made vessel owners and their investors wary of investing too soon in new-builds until there is more certainty in the market about the capabilities required for installation of next generation turbines, says MacFarlane.

Arnstein Eknes, director of special ships at DNV’s maritime business, agrees that, with a new WTIV costing several hundred million dollars, rapid advances in turbine size have made investors and ship owners cautious. Vessels will need cranes with bigger capacity to lift the components of extra-large turbines, with foundations, nacelles and blades all increasing in size.

“Many vessels that were built five years ago are too small to lift the new turbines. If you build the ship with a plan to use it for 10-15 years, but you need to upgrade it after 5-8 years to make the cranes bigger, that’s a cost,” Eknes says. “We’re hoping that further growth [in turbine sizes] won’t be too fast, because then there’s more time to recover the cost of renewing the equipment.”

Need for policy framework

Investing in WTIVs is “a chicken and egg” scenario, according to DNV ’s Brun. Politicians need to translate their offshore wind ambitions into firm legislation that businesses can use to show to the bank to support investment decisions, he says.

McFarlane also sees scope for governments to solve this problem. “Short to medium term, firm government commitments through national targets, auctions and dedicated offshore-wind support schemes will increase the willingness of companies to finance the construction of new WTIVs,” she says.

Six vessels that can deal with 14MW-plus turbines are under construction and expected to enter service by 2023. But IHS Markit projects that the global industry will need to invest a minimum of $1.2 billion to $2 billion to build at least four additional vessels to meet global demand from 2026. IHS Markit’s supply-demand analysis excludes Chinese WTIVs as these do not operate outside of its own waters.

A further seven companies had announced plans to build up to 16 new vessels with capacity to install next-generation turbines at the time of IHS Markit’s research, but these were not firm contracts, and final investments had yet to be secured.

Risk of delays

Including the detailed engineering stage, it takes around three years on average for a WTIV destined for the global market to be built, IHS Markit says. If sufficient WTIVs are not ready in time, there could be a serious impact on the project’s construction schedule — and when it can start delivering power.

“We have seen situations unfold previously where another WTIV has been drafted in, at a cost to the contractor, and acts as a front-runner vessel if the arrival of the original vessel is delayed,” MacFarlane says.

Delays could also impact on carbon- reduction targets set by governments to meet the Paris Agreement, she adds.

Equipment used on future WTIVs will need design alterations to cope with the extra-large turbines, particularly the maximum hook height of the crane onboard the vessel, and the maximum lift capacity of the crane, according to MacFarlane.

The current thinking in the industry is that ships need a hook height of 150 metres or more, and a minimum lifting capacity of 1,500 tonnes to install 14MW-plus turbines, she says. Another consideration is the deck space and payload of the vessel — for farshore projects, the number of turbine sets able to be carried onboard the vessel, and therefore the number of round trips to port, becomes a key consideration.

Lifting technologies

The higher the turbines are raised, the windier it is, Eknes points out. While this is an advantage for generating energy, it presents a challenge for installation — lifting to such heights requires extra stability, and seasonal timing.

Several initiatives are underway to address this issue. One is the Tetrahedron high-lift crane, which the Rotterdam-based developers say will be able to cope with 12-20MW-plus nacelle and blade installation thanks to efficient force flow through its “3D-triangle” shape. The concept, aimed at both existing and new jack-up vessels, has been awarded a design verification certificate by DNV and won Windpower Monthly’s Turbines of the Year 2020 Innovation category.

Vestas’ venture capital arm has also got in on the act with an investment in segmented crane technology being developed by S&L Access Systems. The Salamander Quick Lift Crane Technology uses a base frame with a jack-up press for crane segments. According to the technology developer, segments can be added to enable heavy lifts on hub heights well above 200 metres, with the crane being erected in parallel with the installation of the wind turbine. Currently the company is working on a prototype aimed at the onshore market but sees “substantial potential” for offshore wind installations.

“The whole industry is trying to work out how to control the lift, how to increase the reach of the lift, and the weight of the lift, so they can deal with the turbines that are coming in two to three years from now. That’s very much the key bottleneck. To transport something on the ship is not a problem, you just build bigger ships. But to lift with precision 200 metres above the sea surface, that is a challenge,” Eknes says.

Dutch WTIV operator Van Oord says it is confident that it can manage projects with the bigger turbines, such as the Sofia offshore wind farm, one of the four projects on Dogger Bank. This will be using Siemens Gamesa’s 14MW turbines. “We are anticipating the ongoing scaling up of projects by modifications to our equipment, and in our replacements and investments for expansion,” says a spokesman.

Van Oord recently announced it has ordered a vessel capable of installing 20MW turbines and operating on methanol. It is expected to enter service in 2024.

Geographical restrictions

Another issue as offshore wind expands globally is that two thirds of the current WTIV fleet are located off mainland China, and these vessels do not operate in other markets. Most of the rest are concentrated in the North Sea, resulting in significant time and expense to travel to installation sites elsewhere. Countries outside China and northern Europe will need new vessels for other regional markets, IHS Markit points out.

In particular, countries with local-content rules might struggle with WTIV supply. The US wants to install 30GW of offshore wind by 2030, but WTIVs must be compliant with the Jones Act, which requires that all vessels carrying goods between two points in the US are built, owned, crewed and flagged in the US. The first, and so far only confirmed US-built and flagged WTIV (see box, right) is not set to enter service until 2023, according to the firm’s analysis. “In some geographies, governments may consider lifting certain restrictions to make the global WTIV market more liquid,” MacFarlane says.

Cable-laying vessels

Energy transmission from offshore wind farms also needs planning far in advance, with two to four years being typical, according to DNV. There are plenty of vessels available that can carry out intra-field installation of offshore cabling infrastructure, it is mostly a matter of planning and ordering the vessels in time, says Eknes. However, large export cables that carry the energy to shore are big and expensive, with a limited number of vessels that can undertake this type of work.

More vessels that can install large export cables will also be needed (pic: Jan de Nul Group)

“New cable layers need to come to the market — that is also quite a big investment for ship owners and cable manufacturers, so again, it’s a matter of planning and predictability,” he says.

Despite these logistical challenges, the offshore wind industry is bullish about the continued growth in turbine size. It is not yet possible to tell how big the turbines will eventually end up, according to Belen Jacome Giler, commercial product manager at SGRE. “We have been asking ourselves that same question for 30 years, since we installed the first offshore turbine. The development of new technologies, which we did not know about at the time, have enabled us to go larger and thus harvest more wind, increasing the AEP potential of our customers’ sites,” he says.

However, other elements must be considered to ensure the business case of OEMs and developers are robust, he notes.

“It is not a job for one company alone — it is a whole industry challenge. As long as we have a healthy industry that enables the realisation of these beautiful machines, we will be able to overcome the associated costs and maximise the benefits,” he adds.

GWEC expects machines up to 20MW to be developed by 2030. “We’re talking about potentially a 20MW turbine with a rotor diameter of 275 metres, or even greater by 2030. This could be possible based on the current rating,” says Zhao. “MingYang’s new 16MW model will push the US and European OEMs to continue the technology innovation and push them to release bigger models even quicker than expected.”

Charybdis – America's first offshore wind turbine installation vessel

Named after a sea monster in Greek mythology, Charybdis will not only be the US's first WTIV, but will also be able to install 12MW-plus turbines. US utility Dominion Energy is leading the consortium behind the project, which also involves Danish offshore wind developer Ørsted and US energy company Eversource.

The $500 million vessel is being constructed in Brownsville, Texas, at global shipbuilder Keppel Amfel's shipyard, using domestically sourced steel. It expects to employ up to 1,000 US workers during construction and will use an American crew.

The Jones Act-qualified WTIV, which is expected to be sea ready by late 2023, will be used to build the 704MW Revolution Wind Revolution Wind (704MW) OffshoreRhode Island, USA, North America Click to see full details and 924MW Sunrise Wind Sunrise Wind (924MW) Offshoreoff New York, USA, North America Click to see full details projects, both under joint development by Ørsted and Eversource.

The Charybdis will also support construction of Dominion Energy's 2640MW Coastal Virginia Offshore Wind (CVOW) Coastal Virginia Offshore Wind (CVOW) (2640MW) Offshoreoff Virginia Beach, Virginia, USA, North America Click to see full details project off the coast of Virginia Beach, which is due to be completed in 2026.
It is hoped that construction of the vessel will catalyse the development of a new domestic supply chain for the growing US offshore wind industry.

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