Increasing the Reliability of WECs: a Key Operational Cost-cutting Opportunity

As the demand for renewable energy sources continues to grow, wave energy converters (WECs) are becoming increasingly popular as a means of generating electricity from ocean waves. WECs need to work in areas where waves are very strong, implying that commissioning and maintaining the device could be challenging and costly. Therefore, increasing the reliability and safety of WEC systems would present a significant operational cost-cutting opportunity.

The first step towards reliability is failure analysis

A reliable WEC must be designed, built and operated as intended for the duration of its expected use in a way that minimises the risk of failure. Failure analysis is an essential tool for achieving this goal, as it can pinpoint potential failure modes that need close monitoring. As such, it can identify likely failure mechanisms and failure-related causes that demand immediate attention.

For instance, the basic failure analysis example shown below indicates twenty-three failure modes spread throughout the multiple component failures of a generic WEC. This basic failure analysis is an essential initial step for identifying the primary causes of failure in a generic WEC. These include material-related factors (such as wear, fatigue and corrosion), operational-related factors (such as blockage and contamination, which can result from insufficient inspection and ineffective maintenance), manufacturing-related factors (such as overheating, misalignment, seal failures, leakage, faulty signals), and environmental-related or unknown factors (such as marine growth and unknowns). The next step is to associate costs or risks with each WEC’s subsystem component failure analysis.

Scientific illustration
Example of the WEC failure analysis at the subsystem level obtained from an FMECA database for a generic WEC. The failure analysis can help in gathering information of most failure types (failure modes) and failure mechanisms (the way that a failure occurs), which may be related to possible failure causes, such as design flaws, manufacturing, operations and materials.

Critical analysis determines the degree of failure consequences

The degree of the failure’s consequences at the component level can be examined if criticality analysis is added to the initial failure analysis. An example of this concept is illustrated below, using a modified Failure Mode, Effects and Criticality Analysis (FMECA) approach taken in the Techno-Economic & Environmental Impact Evaluation work package (WP4) of the IMPACT project. It uses the failure rate to determine an occurrence rank, the maintenance costs to determine the severity rank, and the local or global failure impact to determine effect rank.

A recent blog post titled “Wave Energy Converters—What Fails and Why?” used this blog post to outline the major critical components of a conventional WEC that need to be prioritised when attempting to take potential corrective action, such as changing materials, designs or maintenance strategies depending on the failure cause categories mentioned earlier.

Scientific illustration
Example of a criticality calculation based on a modified FMECA approach. It uses the failure rate to determine an occurrence rank, the maintenance costs to determine the severity rank, and the local or global failure impact to determine effect rank.

Reducing FMECA’s subjectivity

Due to lack of sufficient experience regarding long-term WEC operations in the water, the FMECA involves a significant degree of subjectivity, for example, when calculating the ranking scores of occurrence, severity and failure impacts. At a specific location, the life-cycle Operation and Maintenance (O&M) of the WEC could include important metrics that the usual FMECA may overlook. These measures include lost energy revenues and downtime, which is the period when a device’s energy output is halted due to a component failure or maintenance activity. Downtime may last longer than anticipated due to location inaccessibility, a shortage of technicians or a lack of spare parts to repair a defective component. All these factors have a large cost impact on the WEC’s economic performance when evaluating the criticality of components and mitigating measures.

Integrating O&M and FMECA

The criticality rating of a component’s failure modes can be established objectively using an integrated O&M and FMECA technique. In this strategy, a determining factor is the O&M-related cost priority number. The more critical a component is, the higher its cost priority number is.

An effective WEC maintenance strategy that concentrates on critical components can also be developed by integrating O&M with FMECA. This can improve the revenue and reliability of the system while also reducing the risk of downtime and costly repairs. This method calls for rigorous data collection and calculation.

In 2023, UCC plans to carry out a study looking into this topic. This technique will be used to calculate the cost criticality numbers of two different kinds of WECs for two potential sites. The results will be published in an open-access journal.

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About Mitra Kamidelivand

Mitra Kamidelivand is a research fellow in University College Cork, MaREI, a partner in the IMPACT project.