A Methodology for Equitable Performance Assessment and Presentation of Wave Energy Converters Based on Sea Trials

This paper provides a methodology for the analysis and presentation of data obtained from sea trials of wave energy converters (WEC). The equitable aspect of this methodology lies in its wide application, as any WEC at any scale or stage of development can be considered as long as the tests are performed in real sea conditions and that the results contain statistical information concerning the stated performance of the WEC for every sea state. This will allow the estimation of the annual energy production (AEP) of the WEC at any location of interest. The representation of the performance will be more viable when more performance data has been gathered and consequently its statistical appreciation will become more reliable. However, the performance analysis can be applied from the early stage of the tests as it can provide a good overview on the achieved results and it could already identify characteristics of the tested WEC. The harsh environmental conditions in which sea trials are performed involve a large range of engineering development and device monitoring challenges. The off‐shore environment is by nature uncontrollable and only predictable to a certain extent, requiring the WEC and all its components to be designed for extreme conditions. This unfortunately induces large costs for the device development and some WEC components do not always perform optimally. Moreover, having the WEC tested in every possible sea state might take very long, as some might occur only very sporadically. This often leads to testing campaigns that are not as extensive as desired. Therefore, the performance analysis should be robust enough to allow for not fully complete sea trials and sub optimal performance data. In other words, this methodology is focused at retrieving the maximum amount of useful information out of incomplete data sets. This methodology presents a way to assess the performance of a WEC, being tested in real sea conditions, by evaluating its performance (in a first approach) separately for different wave conditions. These “different wave conditions“ are defined as zones and the range of their corresponding wave parameters are defined in accordance with the availability of data and resolution of the scatter diagram [4] [2]. For each of these zones, the performance of the WEC will be stated together with a statistical parameter describing the reliability of the stated performance. Based on the performance of each zone, an overall appreciation of the performance can then be created. As for the specific wave parameters of each zone a performance is mentioned, this can be applied to scatter diagrams of other locations of interest. Furthermore, as the non‐dimensional performance will be used, it represents also different scales of the machinery. The methodology also allows to perform a parametric study, as the performance data can be chosen accordingly. The uncertainty of the performance for a zone is based on the selected performance data that are chosen to represent the sea conditions. A minimum amount of data points will have to be considered for every range of zones, in order to ensure it repetitiveness/reproducibility, and a limit will be set regarding the maximum range of a sea state. Although the representation of the environmental conditions in which the tests occur will be reduced to the bi‐variate Hm0‐Te scatter diagram, the influence of other environmental parameters are still expected to be present in the representation of the performance by the inclusion of different data points for every sea state. The extent to which other environmental parameters or even device dependent parameters influence the performance of the WEC can also be investigated using this methodology.