Wave Farm Infrastructure
Some infrastructure is required to support the installation of Pelamis machines offshore.
Project Boundary Markers
Project boundary markers, as stipulated by the governing navigational authority, will need to be installed prior to Pelamis associated equipment in order to delineate the area to be avoided by marine traffic. Usually cardinal marker buoys are the standard method to mark out the boundaries of offshore renewable projects.
Each machine requires its own individual mooring spread consisting of the main moorings and a yaw restraint line. The main moorings consist of a number of anchors connected to a central point. The yaw restrain line is a simple single anchor and mooring line configuration. The majority of components in the mooring system are standard, off-the-shelf equipment commonly used in the oil & gas and shipping industries.
There is scope for neighbouring mooring spreads to share anchor points, depending on the anchoring techniques employed at the site. The Pelamis mooring spread has been designed to minimise its footprint area, allowing the highest concentration of MW capacity to seabed space and reducing infrastructure costs (on a typical site approximately 15MW of generating capacity could be installed within 1km2).
Subsea Power Cables
A power export cable is required to take the power from site to shore. The export cable is laid by contracted cable installers in the manner and route identified in the development and specification stage (note larger projects may require more than one power export cable). From each array of Pelamis machines a dynamic downfeeder cable connects to the export cable, with the machines in the array connected together via dynamic inter-connector cables. The dynamic cables are installed after the mooring spreads are complete and are then connected to the export cable. This split allows the export cable to be installed ahead of the other offshore infrastructure, in turn allowing work on the onshore sub-station to be conducted in parallel with the offshore work. Once connected, the subsea cable network can be commissioned and tested for integrity from the substation, prior to machine installation.
The machine is connected to its anchoring and electrical infrastructure through a patented latching system located at the end of a mooring yoke. This system allows the machine to be quickly, easily and safely connected and disconnected from its subsea infrastructure. This connection/disconnection of the Pelamis machine is a routine operation conducted as part of a normal operations and maintenance programme, and is discussed in more detail under ‘Operations & Maintenance’.
Pelamis Wave Power has conducted all installation engineering necessary for site construction work completed to date and has now used a wide range of installation vessels.
The modularisation in the design of the offshore infrastructure provides flexibility in the specification for the required installation vessels, which in turn provides flexibility in the programming of the work and lower installation costs, depending upon vessel availability and current market rates.
This design feature also adds flexibility for vessels and operations for decommissioning of a Pelamis installation, something which Pelamis Wave Power has also demonstrated successfully.