Pentland and Waters Round 1 Array Layouts

R. O’Hara Murray July 2014 : Revision 1.0

An output of the TeraWatt project.

1 Introduction

The licensing documentation, mainly scoping documents and Environmental Statements (ES), currently held by Marine (MS) for the planned developments in the Pentland Firth and Orkney Waters (PFOW) has been reviewed. Limited information was available regarding the final array layouts. This is due to uncertainties in what the final technologies used will be and that the projects are still being planned. The approach taken by developers for their envi- ronmental impact assessments, leading to their environmental statements required for licensing, is to consider an envelope (often termed Rochdale envelope) of possibilities. The limited information available in the licensing documentation has enabled generic array layouts to be constructed for the purposes of hydrodynamic modelling within the TeraWatt project. Figure 1 shows the final PFOW array layouts. Note that no devices have been placed within the EMEC test sites.

Figure 1: The final array layouts within the PFOW, with the name of the leased properties.

July 2014 2 TeraWatt Project Figure 2: The proposed Inner Sound horizontal axis tidal farm array layout.

2 Generic Tidal Array Layouts

The information within the MeyGen ES was primary used. The ES uses an example array layout for the proposed 86 devices, forming the phase 1 development. The spacing used in the ES was 45 m cross stream and 160 m downstream, with the rows of turbines being staggered. It was unclear as to whether the cross stream spacing in the ES was hub to hub or blade tip to blade tip. The lease site is for 200 MW. Therefore, by assuming the whole lease site is filled with 200 x 1 MW turbines, it was found that a hub to hub spacing of 50 m enabled the area to be filled (Figure 2). The generic tidal array layout for 1 MW horizontal axis devices was chosen to have a spacing 50 m cross stream and 160 m downstream, with the rows staggered. All but one of the planned tidal developments propose using 1 MW tidal devices. The exception is the Brough Ness de- velopment which is most likely to use the Marine Current Turbines (MCT) 2 MW device. The generic device spacing was simply doubled for this development (100 x 320 m staggered spacing), see Figure 3. The generic spacing of 50 x 160 m (cross stream x downstream) enabled the number of proposed devices to easily be fitted within the other development sites. The generic array layout was adopted but only for a small section of the leased areas. Figure 4 shows Cantick Head as an example.

July 2014 3 TeraWatt Project Figure 3: The proposed Brough Ness horizontal axis MCT SeaGen tidal farm array layout.

Figure 4: The proposed Cantick Head horizontal axis tidal farm array layout.

July 2014 4 TeraWatt Project Figure 5: The proposed West Orkney South Pelamis P2 wave farm array layout.

3 Generic Wave Array Layouts

Four out of the Six wave development sites within the PFOW plan to use the 750 kW Pelamis II wave attenuator device. The scoping report for the West Orkney South development site indicated that the Pelamis devices will most likely be deployed in arrays of 22 devices, in two staggered rows, with a space of 10 times the device length between arrays (1800 m). The most efficient way to fill the proposed West Orkney South development area with arrays of this size was to use a 400 x 400 m (centre to centre) spacing of devices (Figure 5). This array layout was not possible within the Marwick Head development site, so an array of 66 devices with a 350 x 400 m (cross stream x downstream) staggered spacing across 4 rows was developed (Figure 6). The Costa Head development plans to use use the 2.5 MW AWS III flexible membrane wave absorber. In order to fit 80 of these devices (200 MW) within the development area, a 550 x 600 m (cross stream x downstream) staggered array was used (Figure 7). The Brough Head development site plans to use the 1 MW Oyster III device. The example array provided in the Brough Head coastal processes impact assessment report suggested that the devices should have a spacing of between 25 - 65 m. A spacing of 45 m was chosen for this study. The devices are 26 m wide which gave a centre to centre spacing of 71 m. The licensing documentation revealed that the devices should be in 10 - 15 m water depth. Therefore, for this study the devices were distributed in approximately 5 arrays of 40 devices (200 MW total) along the 12.5 m depth contour (Figure 8). The bathymetry data provided by The on a 20 m grid was used.

July 2014 5 TeraWatt Project Figure 6: The proposed Marwick Head Pelamis P2 wave farm array layout.

Figure 7: The proposed Costa Head AWS III wave farm array layout.

July 2014 6 TeraWatt Project Figure 8: The proposed Brough Head Oyster III wave farm array layout.

4 Outputs suitable for model input

Matlab was used to create the regularly spaced arrays within the leased areas. A WGS 1984 Universal Transverse Mercator (UTM) 30o N projected coordinate system was used. The loca- tion of individual devices were saved in ASCII comma separated variable files with file names of the form ‘Layout Lease name UTM30N.txt’. Figures of each array were saved with file names of the form ‘Layout Lease name.png’. These data can be found on the TeraWatt FTP server un- der the ‘Array Layouts’ directory. The Excel spreadsheet ‘Developments.xlsx’ contains a table of the PFOW developments with some summarised information on the array layouts. Details regarding the devices, such as turbine rotor diameter, are also listed here.

July 2014 7 TeraWatt Project