Operating profiles makes offshore wind ships natural choice for hybrid approach


In OWJ’s webinar ‘Green vessels for a green industry: the offshore wind sector’s race to decarbonise its assets,’ which took place on 10 June 2020, delegates heard the offshore wind industry has quickly become a leader in efforts to address emissions from ships.

They also heard adopting technology to reduce emissions does not just make sense from an environmental point of view: it makes great economic sense too.

Introducing the webinar, DNV GL business/segment director, special ships, Arnstein Eknes said of decarbonisation in the offshore wind industry, “The future is already here,” and like other webinar participants he highlighted the adoption of hybrid propulsion as a natural first step towards reduced emissions.

Highlighting the trend towards decarbonisation in the energy sector as a whole, and offshore wind’s ever-growing role in the energy transition, Mr Eknes said demand for a wide range of offshore wind vessels was likely to grow quickly, including installation vessels, cable-layers, service operation vessels (SOVs) and crew transfer vessels (CTVs). All of these vessels need to decarbonise and make use of environmentally friendly technology, he said, but would go about it in different ways.

Mr Eknes said different vessels would adopt different emissions reduction technology, not least because their power requirements vary widely but, for most, hybrid propulsion was an obvious start point.

He used the example of the subsea/walk-to-work vessel VOS Stone, working on the Arkona offshore windfarm in Germany, to highlight how a vessel’s operational profile varies. While committed to the project, the vessel spent only about 20% of its time underway. It was moored for approximately 30% of the time, at anchor 4% of the time and had ‘restricted manoeuvrability’ as much as 41% of the time. What is more, when sailing, the speed at which the vessel operated varied widely.

Another example he used was that of the service operation vessel Esvagt Njord on the Dudgeon offshore windfarm. The ship was underway, sailing for approximately half of the time, was stationary for about a third of the time and was moored about 11% of its time.

“For many of these vessels, flexibility in their power systems is essential,” he said, highlighting the rapid uptake in battery power in the sector. “By installing battery systems in a hybrid configuration, offshore wind vessels can reduce fuel consumption and emissions and reduce operating costs,” he explained, noting that the transition to battery power would mean shore power should “become the industry standard.

“The technology is available today,” he said, “but from a commercial point of view it is very important to have a holistic view of who should invest for this to work and trigger the undoubted benefits.

“Power demand for large vessels can be significant and a proper understanding of charging philosophy and pricing is required for it to become attractive. Also, the initial cost for first movers will be higher before more standardised solutions are available, providing scale effect on price.”

Mr Eknes said he also expects hydrogen – green hydrogen – to become an important fuel in the offshore wind industry, particularly given offshore wind’s ability to produce green hydrogen at scale.

“The first step should be to embrace energy saving where possible,” he told the webinar. “We know that hybridisation will work with vessels that have large variations in power demand and battery uptake on new projects demonstrates this clearly.

“To operate in an energy-efficient manner reduces costs, and charterers are seeking low or zero-emissions supply chains,” he said. An obvious example of the kind of industry leaders driving developments such as these is Ørsted, which recently unveiled an ambitious plan to become carbon neutral, along with its supply chain.

“For some segments of the market fully electric service vessels will be feasible, assuming the charging infrastructure is available. Alternatively, low or zero-carbon fuels such as hydrogen, in the form of ammonia or liquid organic hydrogen carriers are the most likely the next step for this industry.

“Bridging technology can facilitate the transition from traditional fuels, via fuels with lower-carbon footprints, to carbon-neutral fuels,” he concluded.

Arnstein Eknes (DNV GL): “hybrid propulsion is an obvious place to start”

Arnstein Eknes (DNV GL): “hybrid propulsion is an obvious place to start”

ABB global product and portfolio manager John Olav Lindtjørn told delegates ABB sees three main trends in vessels of all types, but particularly in the offshore wind sector. These are: electrification, digitalisation and connectivity.

Mr Lindtjørn said electric power has many advantages, not just the fact it is ‘greener’. “[The] electric power plant is simpler,” he said. “And it helps to make vessels more economical to operate.”

He cited the example of a new cable-layer, NKT Victoria, which has 60% lower fuel consumption than comparable conventional vessels, thanks to its Onboard DC grid and its ability to use a shore connection when in port spooling cable.

He also highlighted the fast pace of development with multi-megawatt fuel cell systems. “Multi-megawatt fuel cells are becoming a reality,” he said, noting that ABB is working with clients on potential applications of fuel cells right now.

Mr Lindtjørn said the operational profile of offshore wind ships such as SOVs and crew transfer vessels lends itself well to applying solutions such as energy storage systems.

He suggested it might one day be possible for SOVs to charge their batteries or even bunker with clean fuel like hydrogen while offshore. Vessels working on windfarms close to shore could easily recharge their batteries from shore, he said. “For windfarms further from shore, fixed bunkering points could help facilitate early adoption of clean fuels such as hydrogen for a fuel cell-powered vessel,” he explained.

“For smaller vessels operating on batteries, the most important challenge would be to have cost-efficient charging infrastructure. As the cost of batteries declines and as their energy density improves, the business case for batteries will become more attractive, especially where operational profiles require more onboard energy storage,” Mr Lindtjørn said.

Global Marine Group engineering manager Andy Newman also highlighted the environmental and economic benefits that flow from adopting new technology that can decarbonise offshore wind vessels. He highlighted the large number of CTVs operating worldwide and the aggregate effect that making them more environmentally friendly would have. His company has taken a step in that direction with a hybrid CTV that will be ready for service later in 2020.

“It is important to bear in mind that the price of fuel for conventional vessels with diesel engines fluctuates a great deal,” Mr Newman said. Storing fuel on a vessel is not straightforward and that fuel is not available ‘on demand.’ As you use that fuel, a vessel’s trim changes, which must be considered operationally, and diesel machinery has lots of moving parts that need regular maintenance and can break down. “As a result, technology that can decarbonise vessel operations has very clear commercial benefits too,” Mr Newman said.

As highlighted above, Global Marine Group’s CWind business unit has already taken the first steps towards decarbonisation, in the form a hybrid CTV it is building.

The CWind hybrid vessel, which will have a surface-effect ship (SES) hullform, will have a number of advantages, he said. These include fuel savings of in excess of 12% compared to a conventional vessel of the same capacity; the ability to conduct transfers to turbines and other offshore structures at greater heights – potentially 20-30% higher; and shore-site voyage time will be reduced by 30% because the SES unit is faster than a conventional unit.

“By having a viable hybrid option now, we are taking an important step towards developing an all-electric propulsion system. We are opening up offshore charging opportunities and making ourselves hydrogen-ready,” he said, noting that fuel cells can “replace some of the diesels” without adopting an “all or nothing” approach.

Vattenfall Network Solutions business development manager Carolina Escudero told the webinar that growing numbers of windfarm operators are committed to decarbonising their supply chains. She also noted that many of the vessel decarbonisation solutions highlighted in the webinar would require shore-to-ship power. This will require investment from ports and the involvement of other actors in the chain, from windfarm owners to vessel owners.

“All of the stakeholders need to be involved in this process,” she said, “and more effort needs to be made to achieve standardisation and avoid solutions that are too bespoke and not suitable for a range of vessels.”

As she told OWJ in an interview on the subject of electrification shortly before the webinar took place, Vattenfall believes an electric future is possible for the CTV sector and, in the longer run other vessels, but multiple stakeholders need to be engaged to make it happen.

“At the moment, not much capacity is available, and as a result, connections are not cheap. Ports might not want to upgrade their electrical infrastructure without support, and vessel operators can only progress hybrid and electric vessel projects if they can charge vessels in port,” she explained.

“There are a lot of questions around electrification, not least who pays for new onshore infrastructure, but change is coming, and we believe the key to advancing electrification is partnerships.

“We expect a range of solutions to appear in the near future,” Ms Escudero explained. “Offshore wind is a particularly exciting sector for vessels and propulsion at the moment. The projects funded by the Offshore Wind Accelerator in the UK will all likely require a level of ship-to-shore power to enable their emissions reduction ambitions.

“Electrification of powertrains on larger vessels is challenging with the technology we have available at the moment, but we have seen an increase in all-electric powertrains combined with conventional options in readiness for a future increase in battery power density that would enable them to go completely fossil-free,” Ms Escudero explained.

“No matter the size of the vessel, I expect use of shore-to-ship power to increase and become widespread. This increase will follow as a direct result of the push from large wind developers to decarbonise their operations. The reason I expect this to increase is that the technology required to provide ship-to-shore power is proven. It only needs capital investment from ports.”

Responding to her point, Mr Lindtjørn described the example of the ferry sector, where infrastructure to support vessels regularly using the same route has been tailored to the needs of electric ships, a model that might be applied in offshore wind.