Review of offshore cable reliability metrics

Reliable cable systems are essential for offshore wind operation. Industry trends have led to a large number of offshore cable connections being installed recently, with 11027 MW of offshore wind connected at the end of 2015 compared to just 2955 MW in 2010 [1]. Despite the increase in connections, the publically available reliability data in this area is almost non-existent. With several connections in planning of both similar and increasing lengths it is essential to better understand these metrics.

A review of published reliability data was undertaken in order to populate a database which is presented in this paper. This data focusses on a number of connection types including both AC and DC connections across a number of cable ratings and configurations. From this database it is confirmed that reliability figures currently being used across the literature generally conform to those currently being experienced in the offshore wind industry. However it is established that failure rates taken from some reports are not accurate as the technology and environments these are calculated from are typically different from those used in offshore wind farm connections. This information is collated and converted into reliability metrics in order for comparisons to be made.

Analysis of the cost of an outage experienced by a windfarm is also carried out in this paper. The results of which establish that the revenue lost from a cable failure could potentially be substantial. The findings in this paper would also suggest a greater risk of failure in the early life of a windfarm and as such a greater potential cost associated with this risk.

It is important to have a better understanding of offshore renewable energy cable connections as the reliability of a cable has a significant impact on the Levelised Cost of Energy. With a greater understanding of the metrics investors can make more informed decisions with respect to the technology that is installed as well as the importance of the installation process itself, due diligence on subsequent OFTO asset purchases and the maintenance plans that have been outlined for the connection.