Reliability analysis of wave energy converters

Abstract

The energy demand worldwide is increasing, and such demand should be satisfied with renewable resources to diminish the carbon footprint. There are a few ways to produce clean energy such as wind, solar and marine energy; however, some technologies are more developed than others and more expensive than others. Wave energy is a type of technology that allows the generation of energy from waves' motion; its theoretical potential is enormous, and it is essential to exploit that resource to satisfy the increasing global energy demand. However, wave energy converters (WECs) have not achieved the desired maturity level commercially and on the design. Its high cost and current stage of development require significant analysis to improve the design and reduce costs. Reliability analysis of WECs is vital to compare different types of converters and identify the most critical components with the highest failure rate. Following a WECs classification, generic WECs have been developed, surrogating failure rates from other industry databases (e.g., oil & gas and wind industry) and adapting them into the WECs environment. Then, the overall system failure rate has been calculated. After all the analysis and comparison between the WECs’ sub-assemblies, hydraulic PTO has been identified as the type of PTO with the highest failure rate mainly because it has a higher number of components, while direct drive is the sub-assembly with the lowest failure rate. Overall, the structure sub-assembly failure rate is significantly lower when the WEC is installed on the shoreline because materials, such as concrete, are used and are not exposed to extreme conditions as if it was located offshore. Moreover, those converters do not require mooring systems and their structure is less complex, decreasing the overall failure rate. Later, based on the criticality analysis and failure modes, it was identified that the hydraulic systems have components with a higher criticality value – if the component fails, the generation of electricity stops, and urgent maintenance is required. On the other side, a simpler PTO such as a direct drive has a lower number of components with high criticality values, suggesting that such PTO has a lower failure rate and less critical components.