Abstract
This report provides comprehensive and general guidelines for the definition, design and selection of electrical connection configuration of marine energy converters.
Functional requirements for electrical connection are firstly outlined based on the different device designs and configurations and the main effects influencing connection configuration are subsequently described. Furthermore, general guidance on power quality requirements is given through a brief description of the principal criteria specified by most of the national grid codes and regulations. The example of the wind energy sector is considered to be crucial in the early stage development of marine energy farms, even though the current scale of offshore installations should not represent a major issue in terms of satisfying power quality specifications. It is assumed that future concepts will host on-board power converter and transformer to allow for efficient connection. The kind of conversion and control will be dependent on the generator type.
A range of options for different electrical connection configuration schemes is presented. Rated power and distance to shore are considered as fundamental variables to determine a suitable configuration. Depending on these inputs and on the device type, some elements might not be necessary but it is expected that future multi-megawatt arrays will require voltage elevation and reactive power control (or power conversion in case of DC transmission) to be performed offshore by means of purposely designed substations. The choice between AC and DC transmission will mainly depend on transmission length and power being the latter one probably economically suitable for very large installations placed at several tenths of kilometres from the coast.
Assessment of electrical configuration options should also focus on the technical and economical feasibility of the proposed solutions, particularly concerning the difficulty of offshore installation and maintenance operations. The example of the testing sites currently under development is useful but not really applicable to future large scale infrastructures. The structural design of offshore substations will probably be a major challenge for large scale wave and tidal farms and economies of scale will have to be sought to make purposely designed cables and connectors economically competitive.