The wave and tidal sector is moving from single device demonstration sites to multi-device arrays. One of the challenges the industry faces is the design of a cost effective and efficient electrical network to collect and transmit power from these devices to the shore. For some projects, such as MeyGen in the Pentland Firth, the solution is to connect each turbine to the shore individually. However, for projects further from shore or with complex landfall conditions, a marine electrical array will need to be designed and built. This report was commissioned by the Offshore Renewable Energy (ORE) Catapult under the umbrella of the Marine Farm Accelerator to investigate an optimum architecture for such arrays. Based on previous work on the subject, the report looks at a number of options for marine array electrical architectures. Taking into account feedback from manufacturers and developers, four options for multiple device connection were identified. These were:
- Direct Connection;
- Surface Piercing Hub;
- Floating Hub; and
- Subsea Radial Network.
Each of these connection options was analysed and an estimation was made of the relative Capex and Opex costs. In addition, the technology required to realise each option was also investigated and specific areas of development identified. Direct connection of individual devices using horizontal direct drilling is a method that is already in use but costs of using this method build up rapidly as the marine farm moves further from the shore. For marine farms at any distance from the shore, surface piercing hubs represent the least risk in terms of available technology but may be expensive to build and may have consenting issues. Savings can be made in the use of floating hubs but these will require the adaptation of existing technologies. The least expensive option would appear to be subsea radial arrays. However, these will require the development of new subsea plant using existing components and will present challenges in terms of deployment and cable management. It is clear that technology development opportunities exist that will allow the future cost of constructing a marine electrical infrastructure to be reduced.
In the future, the marine farm developer will have a crucial role in deciding on an optimum design of marine farm architecture. They will have to make the difficult decisions on issues such as device type and connection options. They will have to take into account not only the capital cost but also the inherent difficulties with servicing marine energy devices. These decisions and the experience gained from early projects will ultimately shape the development of the most efficient marine energy electrical architecture. This report attempts to provide some information on the unique set of challenges that marine energy devices place on any electrical system.
To view the other reports in this series, follow the links below.