Energy transmission infrastructure in the marine environment

• Pages: 71-109

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8. ENERGY TRANSMISSION INFRASTRUCTURE IN

THE MARINE ENVIRONMENT

This section of the document is concerned with impacts relating to the installation, operation,

and decommissioning of energy transmission infrastructure in the marine environment, and

its connection to the onshore grid across intertidal areas. The principle components of this

infrastructure are subsea cables and pipelines. Impacts from offshore electricity substations

and LNG terminals as well as the transport of oil and gas by shipping, and associated

infrastructure such as port facilities, as well as offshore production platforms are not covered

in this document. Information is available on the potential environmental effects associated

with these activities and infrastructure, and it should be noted that these can be significant

e.g. major oil spills and impact on marine Natura 2000 habitats and species. There is also

relevant guidance available from a number of sources including the European Commission,

Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR),

Convention on the protection of the marine environment of the Baltic Sea Area (HELCOM)

and the International Maritime Organisation( IMO, on potential mitigation measures

35.

The environmental impact of marine energy transmission in Europe associated with the

offshore oil and gas industry has been the subject of extensive study for more than 50 years.

Over that period lessons learnt, new technologies, and improved understanding of impacts

have resulted in a significant body of information on how to avoid and/or mitigate potential

impacts. This information is not only relevant to the oil and gas industry but also to the newer

marine energy technologies such as offshore wind, marine current turbines and potential

future infrastructure associated with Carbon Capture and Storage (CCS). Opportunities and

approaches to mitigating effects, based on good practice experiences from across the EU

and beyond are introduced in this section and the reader is also directed to other sources of

information on this subject.

8.1. An overview of current energy infrastructure in EU marine waters

The unequal global distribution of energy sources such as oil, gas, coal and even some

renewables, compared to locations where energy demand is greatest means that there is

considerable transport of energy, in all its forms, around the world. A significant amount of

the infrastructure which has been built to transmit the necessary materials is in the marine

environment. In Europe this is not only located in the relatively shallow waters of the

Continental Shelf, the Baltic, the Irish Sea and the North Sea but also in the deeper waters of

the Mediterranean, the Norwegian Trench and the Atlantic to the north and west of the British

Isles.

Cables and pipelines provide the main infrastructure, and there are also potential new uses

for existing pipelines such as deployment as part of CCS operations.

8.1.1. Oil and gas

35 http://ec.europa.eu/environment/nature/natura2000/management/docs/Wind_farms.pdf;

http://ec.europa.eu/news/energy/101013_en.htm ; http://qsr2010.ospar.org/en/ch07_01.html

http://www.ospar.org/content/content.asp?menu=00210305000000_000000_000000

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Oil and gas has been the mainstay of the offshore energy industry in European waters for

nearly 50 years starting with the discovery of the Brent and Forties field in the North Sea in

the 1960s. Pipelines of different sizes and construction materials provide the essential

infrastructure to transport fluids involved in oil and gas production (Table 2). Ancillary

equipment which forms part of the infrastructure includes concrete mattresses which secure

flow lines to the seabed, and crossings which may be constructed using mattresses, grout

filled bags and cast concrete structures with protective rock dumps. An estimated 35,000-

45,000 concrete mattresses have been deployed on and around oil and gas subsea

infrastructure in the UK sector of the North Sea for example, and more than 45,000km of

pipeline and cabling (Oil & Gas UK, 2013).

Table 2. High level categorisation of pipelines in operation in the North Sea (Figure 1 from Oil

& Gas UK, 2013)

Pipeline

Description

Typical

Dimensions

Applications

Primary Materials

of Construction

Additional

Coatings

Trunklines

Up to 44 inches

diameter, up to

840 kilometres

long

Major export

infrastructure for

oil and gas

Carbon steel

Anti-corrosion

coating plus

concrete weight

coating

Rigid flowlines

Up to 16 inches

diameter, less

than 50

kilometres long

Infield flowlines

and tie-in spools

Carbon steel or

high specification

alloy

Polymer anti-

corrosion coating

Flexible flowline

Up to 16 inches

diameter, up to

10 kilometres

long

Infield flowlines

and tie-in-spools

Carcass of high

specification

alloys and

polymer layers;

alloy-end-fittings

Polymer external

coatings

Umbilical

Between 2 and 8

inches diameter,

up to 50

kilometres long

Chemical,

hydraulic and

communication

distribution

Thermoplastic

polymer or high

alloy steel tubes;

wire armoured

protection

Polymer external

coatings

Power Cables

Between 2 and 4-

inches diameter;

up to 300km. long

Power

distribution

between and

within fields

Copper cores with

wire armoured

protection

Polymer external

coatings

Oil and gas pipelines are present in all the regional seas of Europe. In the Mediterranean

three pipelines transport gas directly from North Africa to Spain and Italy. Pipelines and

cables associated with major oil and gas developments in the northern North Sea, gas

developments in the southern North Sea as well as production wells in the Irish Sea, Celtic

Sea, Bay of Biscay and Gulf of Cadiz also form part of the transmission infrastructure

(OSPAR, 2010).

Undersea cables associated with offshore oil and gas are another component. Four different

types are used for Alternating Current transmission; single or three conductor oil-insulated

cables and single or three-conductor PolyEthylene (PEX) insulated cables. These have not

only increased in number as the sector has developed over the last 50 years but also in their

technical complexity to the point where some offshore installations, such as Floating

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Production Storage and Offloading facilities (FPSOs) can be powered from shore based

facilities via submarine cables.

8.1.2. Offshore wind, wave and tidal current power

In the last two decades, the growth of the renewable energy industry in Europe has included

an expansion into the marine environment. Initially small numbers of wind turbines were built

close to the shore in the North Sea and Baltic Sea with generation capacities of less than

1MW. Turbine size and the scale of projects have increased and changes in the technology

and economics of offshore wind has enabled construction to take place in deeper waters,

sometimes more than 20km from the shore. Most of the current offshore wind farm capacity

in Europe is in the North Sea (Figures 10, Table 3)

36 . The largest of these, the London Array

in the outer Thames estuary (175 turbines with a combined capacity of 630MW), is currently

the largest offshore wind farm in the world.

Figure 10:

Table 3. Installed Offshore wind capacity in Europe in by the end of 2016 (Wind Europe, 2016)

COUNTRY

BE

DE

DK

ES

FI

IE

NL

NO

SE

UK

TOTAL

No. of

Farms

6

18

13

1

2

1

6

1

5

28

81

No. of

turbines

connected

182

947

517

1

11

7

365

1

86

1,47

2

3,589

Capacity

Installed

712

MW

4,10

8

MW

1,2

71

M

W

5

MW

32

MW

25

MW

1,11

8

MW

2

MW

202

MW

5,15

6

MW

12,631

MW

The infrastructure associated with energy transmission from offshore wind farms includes

subsea transmission cables with landfall and transition pits. As the number and size of these

facilities has grown there has been a corresponding increase in the density of cable networks

close to the shore as well as in the export and inter-array/in-field cabling. The Horns Rev 2

offshore windfarm has 70km of inter-array cabling for example

37 (Figure 3) and more than

200km of inter-array cabling has been laid for the London Array offshore windfarm. Both

36 https://windeurope.org/wp-content/uploads/files/about-wind/statistics/WindEurope-Annual-Offshore-Statistics-2016.pdf

37 http://www.4coffshore.com/windfarms/horns-rev-2-denmark-dk10.html

Installed capacity - Cumulative share

by country (MW)

The UK has the largest amount of

installed offshore wind capacity in

Europe representing 40.8% of all

installations. Germany follows with

32.5%. Despite no additional capacity

in 2016, Denmark remains the third

largest market with 10.1% and the

Netherlands (8.8%) displaces Belgium

(5.6%) to have the fourth largest

share in Europe