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Site Selection

Factors   Tidal Speeds   Geographical Position   Size   Errors  


Factors

Four factors were considered when selecting the sites to combine into a supply strategy:
  1. Tidal speeds
  2. Geographical position
  3. Size
  4. Errors introduced
Once a set of sites was selected, the power output for a single MCT unit at each site was phased together on one graph and analysed. The total power was calculated and the range of variation observed. This process was repeated for different combinations of sites (by trial and error) until the fluctuation in the total output was minimised.

Seven sites were selected:
  1. Pentland Firth, South of Skerries
  2. Pentland Firth, South of South Ronaldsay
  3. Pentland Firth, Inner Sound
  4. West Scotland, Kyle of Rhea
  5. West Scotland, Southwest of Orsay, Islay
  6. Kintyre, South of Mull
  7. Galloway, South of Mull

Figure: Selected Sites


Figure: Phased output from single 1000kW MCT Units installed at the sites selected

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Tidal Speeds

Where possible, locations were selected with mean peak tidal speeds that are greater than the rated speed required, so that the turbines operating potential is maximised. The basecase 1MW turbine selected for the project required a rated speed of 2.4 metres per second.

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Geographical position

The sites position determines the time of HW and LW and in turn when the peak speeds occur (the times of HW and LW change with longitude). To ensure power can always be generated so a baseload can be supplied, the peak speeds of the sites selected must be evenly distributed across the 12.4-hour cycle (as shown in the figure below).


Figure: Ideal distribution of tidal stream speed from multiple sites

Achieving such a perfect distribution of sites (and speeds) was more difficult in practice due to the geographical spread of the locations around Scotland, which experience the speeds required. The times of HW and LW for the selected sites displayed in the figure below shows the distribution. The sites at the Kyle of Rhea and the Pentland Firth, Inner Sound are very important sites as the largest gap occurs between the times of HW at these sites.


Figure: Tide times for multiple sites

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Size

The size of the site i.e. the available area that was considered available to install the MCT units (taking into account the constraints detailed in the Site Analysis section of the project) was also very important when selecting the sites, as this determined the potential capacity of the site and the size of the baseload that could be supplied.

For example, selecting 3 large sites and 1 small site, would limit the overall output to the available capacity that could be installed at the small site. Alternatively, this combination may produce a shortfall in overall output when the small site is generating maximum the power and the other sites are not, and therefore increase the required amount of electricity to be generated from storage.

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Errors

Errors reduced when selecting the sites where possible. Due to the errors introduced by the assumptions made when selecting the site area described in the Site Analysis section, areas immediately adjacent to each other were not selected. For example, South of South Ronaldsay and North of the Skerries in the Pentland Firth.

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