The intention is to deploy many tidal stream turbines at suitable sites in array configurations. In this instance not only is the station keeping of the individual device important but that the buffer zone between adjacent devices is maintained. This is what is known as limiting excursion.
The mooring design goal is to minimise excursion. The concluded design must be able to keep the device within a small horizontal motion envelope while occupying a minimal seabed footprint.
Array Options Considered
Several configuration types were considered for this design. Three options were deemed feasible and warranted further investigation:
Option 1: Shallow Buoy - Single Line (Base Case) - (left)
Option 2: Shallow Buoy - Multiple Lines - (center)
Option 3: Deep Buoy - Multiple Lines (Spar Buoy) - (right)
Calculations were carried out to determine the concentrations at which arrays of devices could be deployed. A base calculation of one square kilometre was employed. This is an arbitrary figure. While it is unlikely that any channel will be of this dimension, most suitable sites being narrow channels, it is a convenient indication in developing the design to determine which array configuration is the most efficient.
The concentration of devices is only one factor in determining the most effective design configuration. The amount of materials involved will also have a bearing on the determination of the final design.
The major considerations are mooring line lengths, anchorage type and the cost of electrical cabling. Electrical connection to onshore by deploying submarine power cables will be a significant factor to be considered when costing such a project. Anchorages also have the potential to skew the project viability so careful preliminary planning into site selection will be key.
Capital expenditure on mooring equipment & deployment operations will be extremely important to the economic viability of the project.