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Routing Subsea Cables
for Scottish Offshore Renewable Search Areas

Ingrid Iredale

(MSc Dissertation)


Introduction Methods Results Discussion and References

Introduction

Strong economic and political support, combined with a sophisticated technology industry has made the UK a World leader in offshore renewable energy (Kern et. al., 2014, and Jay, 2011). Scotland, in particular, has considerable potential, with 25% of Europe's wind and tidal resources, and 10% of the wave resources (Scottish Government, 2013). Scotland is committed to gaining 100% of its energy from renewable sources by 2020. One barrier to attaining this is the lack of a coordinated electricity grid system. The current network requires upgrading: new subsea cables need to be built to transmit the electricity to shore; and onshore electricity substations and the onward cables need to be improved before they can cope with the additional power from more variable natural sources. New subsea cables should avoid abrasive surfaces and objects protruding from the seabed. They should also avoid sensitive benthic habitats. This MSc dissertation suggests environmentally-friendly subsea cable routes for offshore renewables.

Methods

A multicriteria decision analysis matrix (Malczewski, 1999) was used to apply weights to ecological variables and create a cost surface model using ArcGIS. UK Biodiversity Action Plan Habitats and man-made obstructions were buffered and made into partial or full masks along with Marine Protected Areas, to be incorporated into the cost surface. From this, cost distance rasters were created and used to define cost paths.

Results

Table 1. Weights calculated with a pairwise comparison matrix, and applied to EUNIS predicted habitats

Habitat Code Habitat Description Weights
A3.1 Atlantic and Mediterranean high energy infralittoral rock 0.021577176
A3.2 Atlantic and Mediterranean moderate energy infralittoral rock 0.033068758
A3.31 Silted kelp on low energy infralittoral rock with full salinity 0.067349292
A4.11 or A4.13 Very tide-swept faunal communities on circalittoral rock or Mixed faunal turf communities of circalittoral rock 0.048866411
A4.12 Sponge communities on deep circalittoral rock 0.090953842
A4.27 Faunal communities on deep moderate energy circalittoral rock 0.123206361
A4.2 Atlantic and Mediterranean moderate energy circalittoral rock 0.090953842
A4.31 Brachiopod and ascidian communities of circalittoral rock 0.123206361
A4.33 Faunal communities on deep low energy circalittoral rock 0.164757068
A5.13 Infralittoral coarse sediment 0.00996192
A5.14 Circalittoral coarse sediment 0.00996192
A5.15 Deep circalittoral coarse sediment 0.00996192
A5.23 or A5.24 Infralittoral fine sand or Infralittoral muddy sand 0.021675235
A5.25 or A5.26 Circalittoral fine sand or Circalittoral muddy sand 0.021675235
A5.27 Deep circalittoral sand 0.021675235
A5.33 or A5.34 Infralittoral sandy mud or Infralittoral fine mud 0.033040741
A5.35 or A5.36 Circalittoral sandy mud or Circalittoral fine mud 0.033040741
A5.37 Deep circalittoral mud 0.033040741
A5.43 Infralittoral mixed sediments 0.014009068
A5.44 Circalittoral mixed sediments 0.014009068
A5.45 Deep circalittoral mixed sediments 0.014009068



Figure 1. Cost Distance Map with Suggested Subsea Cable Routes. Information contained in this model has been derived from several sources: Scottish Natural Heritage, 2012; Crown Copyright/SeaZone Solutions Ltd, 2014; Crown Copyright/Marine Scotland, 2014; the National Grid, 2013; and the EUSeaMap Consortium webGIS data (jncc.defra.gov.uk/page-5040), which is made available under the pilot project for European Marine Observation Data Network (EMODnet), funded by the European Commission's Directorate- General for Maritime Affairs and Fisheries (DG Mare). All rights reserved. Not to be used for navigation.

Discussion

These cost paths are impractical when taken precisely, due to the number of kinks and bends in them. The paths do not always follow the best possible route, as there are many connecting substations factored into the model, and the paths travel along the least expensive route alongside them. Path number 5 is the best example of this plotting error. It might also be preferential to avoid passing a cable through an SAC (route 14). However, when considered generally, the analysis is more useful. Several practical routes are suggested, and there could also be a connection point from the Isle of Mull.

A follow-on study could examine this subject further, developing the model to investigate the relationship between distance and the cost surface. An interactive user-interface to select weights and make the process more transparent, would also be useful.

References

Jay S (2011). Mobilising for marine wind energy in the UK. Energy Policy, 39: 4125-4133

Kern F, Smith A, Shaw C, Raven R and Verhees B (2014). From laggard to leader: Explaining offshore wind developments in the UK. Energy Policy, 69: 635-646

Malczewski J (1999). GIS and multicriteria decision analysis. John Wiley and Sons Limited, Canada

The Scottish Government (2013). Planning Scotland’s Seas: Scotland's National Marine Plan (Consultation Draft). www.scotland.gov.uk/Publications/2013/07/9185