Multipurpose artificial islands - Offshore Service Facilities

Multipurpose artificial islands

Island Concepts

Wim Klomp

7 April 2021

Multipurpose artificial islands | 7 April 2021

Content

1. Functionality of energy islands

2. Concepts for offshore islands

3. Evaluation of concepts

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Multifunctional island (25 – 100 ha)

◼ HVDC substation & cable entries

◼ P2G for electricity conversion

◼ Operation & maintenance base for windfarms

◼ Data centres

◼ Search and Rescue base

◼ Aquaculture

◼ …..

Functionality of energy island

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Small HVDC island (6 – 20 ha)

◼ HVDC substation

◼ Cable entries and connections

◼ Quay for Installation and access


Area demand for different functions

◼ Substation (HVDC)

Area is needed for HVDC substation, AC switch yard, cable entries from windfarms and cables to mainland and other countries

(interconnections), operations building, workshops and accommodation. Present assumption is that substations for 2 GW are

efficient and these are being developed for platform as well as for island concept. Typical area demand for 2GW “island

concept” is 8 ha land. Access to the island is arranged via a sheltered port basin (shared with others) and a berth of 100 m, with

terminal area of some 1 ha.

◼ Power to Gas

For efficient use of all power from offshore wind farms it is believed that generated power needs to be used for generation of

Hydrogen or other gases to be able to store the energy and transport it more efficiently via power cables. Technology for large

scale conversion is to be developed. For hydrogen production, seawater is used as resource and area is needed for

desalination, hydrogen generation and hydrogen storage. An area of 11 ha is estimated for transformation of 2GW capacity. Use

of a available quay (occasionally) is assumed.

◼ Energy storage

Several systems storage systems are currently being developed, for example Pumped Hydro storage to Thermal storage and

Compressed Air Energy Storage (CAES). Required surface area and subsoils volumes are very different. A surface area of

some 10 to 15 ha will give possibilities and flexibility for energy storage systems.

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Area demand for different functions

◼ Operation & maintenance base for Wind farms

Accommodation for maintenance crew, storage for spare parts, workshops for repairs/testing. Port basin and safe mooring for crew vessels and maintenance jack-ups. A helipad needs to be included to move personnel to the island.

A land area of some 3 ha per 2 GW windfarms and a berth (150 m) and port area of some 1 ha per 2 GW wind farms. In case island is also used as basis for construction of new windfarms a larger area is to be expected.

◼ Data centres

An offshore energy island would also be a good location for data centres. Data centres required electricity and cooling water, which is both available on the island. Data cables can be part of an international network of data connections.

Land area needed for a datacentre is expected to be small, 1 ha per data centre.

◼ Other uses

Other uses can be support for aquaculture (drying area for weeds and/or processing facilities), search and rescue services, military/coast guard base. Most have only a small area demand on land and in the basin.

For artificial islands located further from the coast (say 250 to 300 km from shore) a offshore supply base to support construction of wind farms could be beneficial. This does require a significant area on land (10 ha for 1 GW/year installation) and in the port basin (5 ha for 1 GW/year installation).

Especially for multipurpose use of the island, some additional area is required for roads, utilities and or recreational. An increase of the net area of some 10 - 20% is recommended.

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Multifunctional island (10 GW)

Functionality on energy island

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Small HVDC island (2 - 4 GW)

HVDC (4 GW) 16 ha

Power to Gas (6 GW) 33 ha

Energy storage 10 ha

O&M wind farms (10 GW) 15 ha

Accommodation/utilities 5 ha

Other uses 10 ha

Roads/corridors 6 ha

Port basin/quay 25 ha

Total 120 ha

HVDC (2 GW) 8 ha

P2X (2 GW) 11 ha

Road/utilities 1 ha

Quay or Port basin 1 to 5 ha

Total 10 - 25 ha


Island concepts

Revetment type

◼ Sand base / pancake

◼ Traditional revetment of rock and

armour units

◼ Crest height typically 12 to 15 m

◼ Sand fill above high water level

Caisson type

◼ Gravel berm underneath caisson

◼ Caisson with wave wall


◼ Drainage canal behind caisson

◼ Sand fill above high water level

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Caisson type

Revetment type


Island concepts

Laguna type

◼ Sand berm / pancake

◼ ‘sustainable’ reef breakwater of sand and rock, gentle slopes


◼ Small island with ‘light’ revetment and floating pontoons in sheltered conditions

◼ Large footprint, but more variability in environmental ecotopes

◼ Flexible, especially for functions which can be placed on floating pontoons

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Laguna type


Evaluation of concepts

Revetment type Caisson type Laguna type

Costs + + 0

Ecology 0/+ 0 +

CO2 - footprint 0 -/0 +

Flexibility / extension 0 -/0 +

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• Laguna type is relatively expensive, especially for smaller islands• Caissons may be more favourable in deeper water, higher wave conditions and smaller

islands• Laguna type less CO2-footprint due to less concrete volume.• Laguna type can be more easily expanded in area. This can be done either by floating units or

increasing the size of ring construction. Caisson type is less flexible as the toe construction would have to be removed.


Discussion

Energy transition in the North Sea should be developed with a vision for long-term use and

possibly extension areas and future function changes. Also the ecological aspects and

work & living conditions on the island should be taken into account. The oil & gas platforms

in the North Sea should therefore not been taken as example.

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VindØ Consortium, Denmarkhttps://www.flickr.com/photos/22437367@N00/944354


Poll question

What do you estimate an island (in the North Sea, about 50 ha; in 25 m water

depth, without applications on it) will cost to build?

a) around 100 million euro

b) less than 500 million euro

c) around 1 billion euro

d) more than 2 billion euro

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Multipurpose artificial islands - Offshore Service Facilities

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