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Add hydrogen to unlock the potential of floating offshore wind

29/6/2022

6 min read

Sea support vessel steering away from floating offshore wind turbine with other floating turbines in distance Photo: ERM
The ERM Dolphyn design for a floating offshore wind system features an electrolyser installed for hydrogen to be fed into a trunk line through array pipelines

Photo: ERM

Investment in shared offshore hydrogen transmission infrastructure could unlock the potential of deep offshore wind energy, explains David Wickham, Hydrogen Consultant with ERM.

In order to reach net zero targets by 2050, the UK will require significant increases in installed renewable energy production capacity and long-term storage to meet inter-seasonal heating demand. Fortunately, the UK is well-positioned with a plethora of offshore wind resources. However, the majority are located in deepwater regions well away from the shore, with an estimated 790 GW in water depths of 50–100 metres and 1,030 GW in water depths exceeding 100 metres.

 

Due to these depths, floating offshore wind is one of very few economically feasible ways to harness this energy resource and is therefore set to play a vital role in the decarbonisation of the UK economy. As these wind farms will be located far away from shore, implementing appropriate infrastructure to take the energy from production source to demand will be critical to generating sufficient green energy in a net zero future.

 

Here we explore the use of appropriate hydrogen infrastructure and how its technical and economic characteristics can help unlock floating offshore wind.

 

Three main configurations 
There are three main configurations for converting floating offshore wind to hydrogen.

 

Centralised onshore electrolysis – where each wind turbine is connected to a central floating substation via electrical array cables. The power is then fed back to shore via a high voltage direct current (HVDC) cable, where it is fed into an onshore substation and an electrolyser (see Fig 1).

 

Schematic explaining centralised onshore electrolysis 
Fig 1: Centralised onshore electrolysis configuration schematic 
Source: ERM

 

Centralised offshore electrolysis – where each turbine is connected to a central floating substation via electrical array cables. The electricity from the substation is then fed into an offshore electrolysis facility, where it is converted to hydrogen and piped to shore (see Fig 2). 


Schematic explaining centralised offshore electrolysis 
Fig 2: Centralised offshore electrolysis configuration schematic 
Source: ERM

 

Decentralised offshore electrolysis – where each wind turbine has an electrolyser installed on its floating platform. The electricity generated from the turbine is directly converted to hydrogen and fed into a trunk line through an array of pipelines (see Fig 3). 


Schematic explaining decentralised offshore electrolysis configuration 
Fig 3: Decentralised offshore electrolysis configuration schematic 
Source: ERM

 

Based on ERM’s analysis, decentralised offshore electrolysis is considered to be most advantageous and has led to the design of ERM Dolphyn technology which shares this topology. ERM Dolphyn combines electrolysis, desalination and hydrogen production on a floating wind platform, with the green hydrogen transported to shore via a pipeline.

 

The 200 MW Salamander floating wind project, developed by Simple Blue energy in partnership with Subsea 7, signed a memorandum of understanding last year with ERM for the potential use of the Dolphyn hydrogen technology. The project is working closely with Scottish Gas Networks (SGN) to potentially integrate the system into future hydrogen infrastructure or as a blend with existing gas infrastructure.

 

Under the UK government’s new energy strategy, there is the ambition to deliver 50 GW of offshore wind capacity by 2030, of which 5 GW will come from floating offshore wind in deeper seas.

 

Cost-effective configuration 
When compared to other possible offshore wind-to-hydrogen arrangements for a single wind farm, there are numerous benefits. Firstly, it is the most cost-effective configuration, at all distances from shore as shown in Fig 4. Secondly, it is modular, allowing for shared infrastructure and provides more flexibility in the event of an outage due to technical issues on a turbine or maintenance schedules. Lastly, as can be seen from Figs 1–3, because the electrolyser is located on the wind turbine floating platform, floating sub-stations are not required.

 

Graph showing levelised cost of hydrogen for three floating offshore wind-to-hydrogen configurations 
Fig 4: Levelised cost of hydrogen (LCOH) of the three floating offshore wind-to-hydrogen configurations for a range of distances from shore  
Source: M. Peel et al, A match made at sea: Hydrogen and floating wind, unpublished

 

Having compared decentralised offshore electrolysis to other floating wind-to-hydrogen concepts, it is also important to compare it against floating wind-to-electricity solutions.

 

Recent research in this field indicates that floating wind-to-hydrogen is expected to fall within the same levelised cost of energy (LCOE) as floating wind-to-electricity, as shown in Fig 5. This comparability in LCOE can be explained by three factors:

  • The higher capex and installation costs of HVDC cables when compared to hydrogen pipelines.
  • The lower carrying capacity of a single HVDC cable vs hydrogen pipelines.
  • Electricity losses over longer distances through HVDC cables.

 

Furthermore, there are other benefits to hydrogen pipelines compared to electricity cables, including providing an alternative renewable energy vector to areas of the UK with high electricity grid constraints (eg the South Wales region) and reduction in cable congestion on the sea bed, which allows the sharing of transmission infrastructure.

 

Graph showing LCOE for floating wind versus electricity 
Fig 5: LCOE – floating wind vs electricity               
Sources: various*

 

Main advantage  
One of the main advantages of decentralised offshore electrolysis for floating offshore wind is the potential to utilise hydrogen pipelines for shared offshore transmission infrastructure.

 

Hydrogen pipelines allow for oversizing to create a trunk line leading out to the shore and connecting to a single wind farm. As mentioned, decentralised hydrogen electrolysis is modular, therefore, additional wind farms can be deployed and connected to the trunk line – something that is not possible with electricity infrastructure.

 

Taking this approach to deploying offshore wind can result in greater economies of scale being achieved due to the relatively small increase in costs of hydrogen pipelines as their capacity is increased, allowing for a further reduction in LCOE and truly unlocking floating wind’s potential.

 

Furthermore, this configuration is analogous to what is seen in the oil and gas sector. This is exemplified in the installed oil and gas infrastructure in the North Sea region, see Fig 6.

 

Map of North Sea oil and gas infrastructure 
Fig 6: Oil and gas infrastructure in the North Sea (the dots represent oil rigs and the lines represent pipelines)         
Source: OSPAR

 

Notably, there are only five pipelines leading into the St Fergus terminal. This highlights the vast amount of energy being transported into Scotland and supplied to the rest of the UK through shared infrastructure, enabling the low cost of fossil fuels. Hydrogen transmission infrastructure would have the additional benefit of allowing the UK to build on the extensive expertise of its oil and gas sector, reducing costs and playing a part in a just transition by enabling oil and gas workers to retrain for employment opportunities in the renewables sector.

 

Key takeaways 
In conclusion, the UK has a significant amount of wind energy located far away from shore. In order to harness that resource, it is vital to develop optimal transmission infrastructure and to create economic green energy.

 

Hydrogen pipelines are well suited due to their significant economies of scale, with increased capacity allowing oversizing of trunk pipelines to allow a modular roll-out of offshore wind farms.

 

In order to achieve this, it is vital to start the conversation now on collaboration and sharing offshore transmission infrastructure to allow the effective planning and design of efficient energy systems.

 

Last, but certainly not least, floating offshore allows the UK to build on its vast knowledge from the oil and gas sector, decreasing costs and allowing for a just transition.

 

In summary, hydrogen looks set to play a vital part in the UK’s decarbonisation. With a plethora of offshore wind resources located far away from shore, the technical and economic characteristics of decentralised floating offshore electrolysis can provide wide-scale, economically beneficial green hydrogen that demonstrates the potential of being in a similar, if not lower, LCOE region as floating offshore wind-to-electricity.

 

There are clear benefits to starting the conversation now of collaboration on sharing offshore transmission infrastructure to allow for effective planning and design of efficient energy systems, harnessing the vast knowledge of the oil and gas energy sector, decreasing costs further and helping to pave the way to a just transition.

 

 

*For Fig 5 sources, see:  

  • a) A study looking at the LCOE for a range of floating wind turbine concepts. The wind farm consists of a hundred 5 MW turbines situated 100 km away from shore.
  • b) A detailed technical and economic model which is applied to two scenarios: Hywind – five 6 MW turbines, supported on a spar-type foundation, located 25 km away from shore; and Kincardine – five 9.5 MW turbines, located 15 km from shore.
  • c) A techno-economic model for a reference wind farm in 2030 with a hundred 10 MW turbines, 10–100 km from shore.
  • d) Analysis by M Peel et al (unpublished) of the LCOH of various configurations for floating wind-to-hydrogen, for a 600 MW wind farm located 90 km from shore by 2030.
  • e) Analysis conducted by ORE Catapult, looking at the synergies between offshore wind and hydrogen production, for a range of LCOH in 2030 for decentralised floating offshore wind with various electrolyser technologies.