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Preliminary economic assessment and analysis of grid connection schemes for ocean energy arrays

Date: October 14, 2013 at 13:57 GMT

Abstract: This paper addresses a preliminary assessment of several alternatives for grid connection of arrays of tidal and wave energy devices and provides general guidance for the lay-out definition and the choice of electrical connection configuration. The work has been undertaken as a part of ‘EquiMar’ a project funded under the European Community's Seventh Framework Programme FP7/2007-2013 under grant agreement n° FP721338.

A general outline of the requirements of electrical connection and an insight of the main different alternatives for grid connection is first presented. It is shown how distance to shore, depth and installed power affect the choice of the type of transmission (HVAC or HVDC) and how the engineering of the connection infrastructure for large scale arrays is still a challenging subject, especially for complex elements like electrical substations. Subsequently a methodology for electrical efficiency calculation and global economic assessment is proposed and applied to different case studies, taking into account different sizes and distances to shore. 

The main losses are concentrated, for relatively large lengths, on the electrical cables, and their estimation is based on a distributed parameters line model. Additional losses due to offshore and onshore substations are considered based on referenced values by suppliers.

Results from the efficiency calculation will provide criteria for the selection of the appropriate transmission voltage and will be based on performance matrix and curves claimed by device developers. 

Finally, a global economic assessment methodology is proposed and applied to some of the cases utilising simplified costing functions of the items that compose the design and installation of a grid connection infrastructure.

Results are provided for different operational durations of the project and for different discount factors. Even though the methodology applied is general and does not deal with the detail that a realistic deployment project would require, it is believed that it will be useful for preliminary assessment and guidance to the design of ocean energy arrays. 

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