Abstract
The Wave Hub is an exciting opportunity to ensure the UK continues to play a leading role in Wave Energy. This design concept of the Wave Hub was thoroughly researched in the Technical Feasibility Study (TFS) with the underwater system or "wet hub" emerging as the preferred way forward. A simplified description would be 'socket' connecting Wave Hub Converters (WECs) to the national grid.
In this Wave Hub Development Phase, much more detailed work has been carried out to flesh out the design details. This work includes reflecting the results of various studies and investigations executed in parallel with the design. The design development has now progressed to a point where it is necessary to confirm design decisions and freeze the main elements in order to be able to complete the tender information.
The engineering design work carried out in the Wave Hub Development Phase has confirmed the technical feasibility of the 'wet hub' option. Suitable components have been identified which are generally either qualified, or under qualification, to oil and gas industry offshore standards or proven in service, thus minimising the cost and time needed for component development.
Further information has been elicited from WEC developers on their requirements and preferences. Extensive discussions have been held with an extended range of potential suppliers. It is probable that a complete offshore system, suitably qualified and proven, can only be supplied from one source.
Some final results and interpretative reports are awaited from a few of the parallel studies as well as guidance from the consenting processes but it is not expected that any of these will have a major effect on the engineering design as described here.
A design has been developed for a 20MW capacity system in a similar configuration to their TFS design. The system now operates at 24kV with transformation from 11kV (or possibly 6.6kV) for WEC connection. This is suitable for a connection at 33kV at Hayle, which matches commercial requirements and the capital available. The Termination and Distribution Unit (TDU) is entirely passive and no maintenance is expected during the project lifetime. The Power Conditioning Units (PCUs) are designed so that they may be retrieved for maintenance.
The feasibility of trenchless construction of a cable duct under the dunes has been confirmed. It is now proposed that the main sub sea transmission cable be pulled ashore and through the duct, thus eliminating the jointing chamber on the beach.
The substation has been expanded in size to cater for a 24/33/0.4kV transformer and a possible power quality improvement unit to facilitate connection of the carious WEC generators if the latter should prove necessary.
The budget cost for the 20MW capacity scheme at £17.3 million exceeds the TFS estimate. This cost increase arises from a number of factors, the most important of which are the uncertainties over costs from the main power cable and the installation. Both these factors are affected by an unstable market at present.
The operational and maintenance costs are estimated at £166,000 per year excluding management and overhead.
Other key issues affecting the through life cycle of the system like the Operation and Maintenance, Designers' Risk Assessment and the Decommissioning Plan are described within this document and appendices.
This report provides a synopsis of the final design as of May 2006.
The critical design decisions have been taken as follows:
- Total connection capacity of 20MW
- Provide four connection points of 5MW capacity each
- There will be no provision for later expansion of system to a capacity of 30MW
Meetings are planned with selected Developers at which more information may be elicited. These meetings will also be an opportunity to provide them with more Wave Hub design information. Any major changes requested by Developers at this stage is likely to cause delay and should be avoided.
The preferred design option has been developed following extensive discussions with a number of contractors and suppliers of subsea and onshore plant. There was however, reluctance by some to divulge details of plant or methodology which would have assisted in the design development. The preferred design option is therefore, the best gleaned and interpreted from the information given. It is neither a definitive option nor necessarily the best option. It is proposed that tenderers be given the option to propose alternative options in their tenders.