The very first offshore wind farm, just off the coast of Vindeby in Denmark, was commissioned in the far off days of 1991. Its 11 turbines together produced a mere 5MWh annually. In the past decade or so, the average power capacity of an offshore wind turbine has risen from 3MW in 2010 to 6.5MW in 2022, and we’re already starting to see offshore turbines in development that will be able to produce over 15MW on their own.

This growth in power production is due to a number of factors – improved engineering, better materials and so on – but the largest contributor is the size at which these turbines are now constructed. The turbines at Vindeby had a blade length of 17m and a total height of 54m. By contrast, Vestas’ V236- 15.0 MW – 64 of which are set to be installed at the He Dreight offshore wind project in Germany in 2025 – has a blade length of 115.5m and a total height of up to 280m.

While onshore turbines have to factor in certain restrictions that limit their size – public opinion, for one, which frequently opposes local wind farm development – offshore turbines are largely free of these concerns. At the same time, wind levels are generally higher out at sea, due to the lack of friction over the water. On land, mountains, trees and buildings all serve to break up the wind flow. As a result, the biggest turbines are sent out to sea – due to their size, they can harness the high wind levels and produce more electricity than their onshore counterparts.

Of course, you’ve first got to get the turbines shipped out and installed at sea, and as offshore turbines continue to grow, this is starting to pose a problem. Most offshore turbines are installed using wind turbine installation vessels (WTIVs), and back

in 2020, there were only 16 WTIVs serving the entire world. Now that turbine sizes are growing, however, many of these vessels will need to be upgraded or operators will have to invest in new ones, if they are going to be able to install the super-sized turbines that will become the norm by the end of the decade.

A matter of size

According to research published by Rystad Energy in February 2022, the demand for offshore wind turbines will outpace the supply of WTIVs capable of handling these new, larger turbines by 2024. Between 2010 and 2021, turbines with 8MW capacity or higher accounted for just 3% of global installations, but that figure is expected to rise to 53% by 2030. To meet this demand, the need for WTIVs that can handle turbines of this size – and also carry out heavy maintenance and repairs of the installed base of turbines – will rise from 11 vessel years in 2021 to almost 60–65 by 2030, not accounting for the demand in China.

With all this in mind, it’s no surprise that the industry is starting to express concern, as this issue could cause a bottleneck for upcoming offshore wind projects. “There is not enough capacity to meet the targets within the target date set at the moment. There is still time for new builds to be added to achieve this. Otherwise, projects would face delays,” says Martin Lysne, senior analyst for rigs and vessels at Rystad Energy. To date, there haven’t been many purpose-built vessels constructed for the explicit purpose of wind turbine installation, because there has been an existing fleet of heavy lift vessels already in place. However, as these turbines grow larger, they will require very tall cranes in order to be installed, and there currently aren’t any vessels with cranes at the height that will be required in the next few years.

This hesitancy over constructing more WTIVs largely stems from a lack of knowledge over what turbine sizes will look like in the next few years – turbine installation operators have been hesitant to commission ships that are obsolete by the time they finish production. As a result, WTIV numbers have remained largely stagnant.

Now, however, a much clearer pipeline is coming into focus due to governments setting firm targets and increased efficiency in leasing processes, which has resulted in more grants for wind farms. As a result, some new-build vessels have recently begun construction – 11 will be built by 2025, all of which will be capable of carrying turbines with over 14MW capacity, according to IHS Market.

However, if more vessels aren’t commissioned to meet upcoming demand, the offshore wind industry will have to deal with project delays across the board. This will have a knock-on effect, increasing the time required for governing bodies to reach their wind power targets. A recent Rystad Energy report expects global offshore wind capacity to grow by more than five-fold between 2021–2030. Europe intends to install around 100GW of new offshore wind capacity by 2030, while the US is aiming for 30GW in the same period, but they’ll need the WTIVs to meet those targets.

“There are new builds, but they’re not enough new builds – so, we need more,” says Lysne. That’s where things start to get challenging, as it’s difficult to put an exact number to the issue. Certainly, if countries intend to hit their green energy targets by 2030, many more WTIVs will be required. However, if these targets are drawn out a little further, in the years after 2030, then fewer vessels will be needed. How important, then, is it to the stakeholders involved to hit those targets?

“Here at Rystad, people say we’re not as optimistic as others out there,” says Lysne. “But we look through each and every project, and then we determine [whether] this will be able to get done or not. Our target for the US by 2030 is 21GW, while many others are saying 30GW – because that’s the goal. We’re saying we don’t think this is feasible – [the US] will be able to reach the targets, [but] it will take some more time.”

Prepare for the future

The industry is, in some areas, starting to plan ahead for the growth of offshore turbines. The first 10MW turbine was only installed off the coast of Europe in December 2021 – in the form of a Vestas’ V164-10.0 MW turbine at 1.1GW Seagreen, Scotland’s largest and the world’s deepest fixed-bottom offshore wind farm. However, WTIV operators are already building cranes that will be ready to handle 20MW turbines – of course, there are currently no projects lined up at that size.

These larger vessels will also be more efficient at installing smaller turbines, as they will be able to carry more components back and forth than previous models due to their larger deck space. “So, although they will be bigger and more expensive, I think they will be more efficient at installing the current generation [of wind turbines] and future-proofing themselves for the next generation,” says Lysne. Other parts of the industry are preparing for the future by upgrading their fleets. Fred. Olsen Windcarrier and Cadeler have both been busy, working to double the crane size of their vessels from a carrying capacity of 800t to 1,600t. Cadeler also has new builds under construction. Of course, you can only upgrade a vessel up to a certain point – the width of the ship will influence how much weight the legs of the crane can bear.

With the changes made to these vessels, they will be able to stay in use for longer, as enlarging the base number of WTIVs will help to develop the operations and management market. When the size of wind turbines eventually outstrips these vessels and they no longer have the crane capacity to lift a whole nacelle, these ships will still be able to be repurposed for blade replacement and decommissioning work at the end of a turbine’s lifecycle.

Similarly, even if WTIVs are no longer able to function in some markets, there will still be space for them in others. Asia, Lysne notes, has been lagging behind Europe and the US in terms of turbine sizes for a while now, because its wind farms are located in shallower waters closer to the shore. This trend is beginning to change, but there will still be some demand for lower-size turbines in Asia in years to come. There has already been some movement with WTIVs initially built for work in Europe transitioning over to projects in Asia.

It’s also worth noting that the development of the floating wind sector will ultimately lessen the reliance on WTIVs. In the past, floating wind has been held back by its high cost, but those costs are gradually coming down. Floating wind turbines don’t require WTIVs – they can be installed dockside and then towed out to sea. Floating wind energy offers a number of benefits over traditional offshore turbines – they can be placed even further out at sea where there are higher levels of wind, as they don’t need to be built into the seafloor.

However, should floating wind turbines become the predominant form of offshore wind power, what would that mean for WTIV operators? “If you look to 2035–40, and beyond that, then we start to really look at the potential of floating wind being a big concern from a WTIV perspective. We are positive about floating wind, but it is a risk factor to keep in mind when constructing a WTIV,” Lysne says. “But I think you would still see that we have enough projects to make the investment worthwhile until then.”

The Jones Act

Of course, there are other challenges that are holding back the development of new-build WTIVs. In the US, the Jones Act is a century-old federal law that requires goods shipped between US ports to be transported on ships that are built in the US, mostly owned by US entities, and operated by US citizens or permanent residents. In theory, this prevents vessels built outside the US from operating on US wind farm projects.

Compounding this issue is the fact that it’s far more expensive to build WTIVs in the US. One big new build by Dominion Energy is costing around $500m, yet in Asia, a vessel of around the same size, or even slightly larger, is being built for offshore wind installation company Eneti at a total cost of $330m.

For many companies, this additional expense will turn them away from constructing their own ships, and instead look for ways to circumvent the Jones Act. Some European operators, like Maersk, are now building WTIVs targeting the US market – the vessels will simply operate out of non-US bases, such as ports in Canada, and use Jones-Act-compliant feeder vessels to deliver the crew and components.

“Given the current climate, and the fact that several projects will now use a feeder vessel strategy in the US, it’s going to be difficult to justify the more expensive US-built, Jones Act WTIV,” says Lysne. “The US Maritime Administration (MARAD) has just announced a ship financing package for wind vessels. Policy changes like this could make more Jones Act WTIVs more likely.” However, this workaround process adds another layer of complexity, as it requires the feeder vessels to bring components out to the WTIVs at sea. Lifting and transporting these objects from moving vessels create new points of failure, and is all but unproven at the kind of scale that the new large turbines will require.

While there is still some space for optimism, if the world is truly serious about meeting its 2030 targets, much more needs to be done to address the lack of WTIVs in the coming years. If there’s one thing that’s certain, it’s that offshore turbines are going to keep on growing in size, and that needs to be matched by the industry’s ambition. If not, and we see more projects put in place than the global WTIV fleet is able to handle, the bottleneck that this will cause will be a major headache for the industry for years to come.

This article first appeared in World Wind Technology magazine.